Life-Related Hazards of Materials Applied to Mg–S Batteries

Abstract

Nowadays, rechargeable batteries utilizing an S cathode together with an Mg anode are under substantial interest and development. The review is made from the point of view of materials engaged during the development of the Mg–S batteries, their sulfur cathodes, magnesium anodes, electrolyte systems, current collectors, and separators. Simultaneously, various hazards related to the use of such materials are discussed. It was found that the most numerous groups of hazards are posed by the material groups of cathodes and electrolytes. Such hazards vary widely in type and degree of danger and are related to human bodies, aquatic life, flammability of materials, or the release of flammable or toxic gases by the latter.

1. Introduction

Nowadays, it is observed the strong development of various reversible electrical energy storages (batteries) based on Li electrodes, which are applied in commonly utilized electronic devices, automotive control and drive systems, and net applications [1,2,3,4,5]. The role of a safe charge and discharge processes for various batteries at high energy densities was emphasized in [6,7]. Such a high energy density in cells/batteries can be obtained using Li-metal anodes due to their specific capacities and low potentials [8,9]. The cycling process in cells utilizing lithium electrodes is accompanied by the formation of metallic lithium needle-like dendrites. The latter limited the electrochemical performance of cells over time and increased the fire hazard due to short circuits [10,11].

As an alternative to the Li–S batteries, Mg–S batteries are cheaper, exhibit a higher energy density, and are safer compared to the Li–S ones that have been developed [12,13,14]. The development of effective Mg–S batteries was bounded by a lack of inexpensive and non-nucleophilic electrolytes [15,16].

Parambath et al. [17] noticed that Mg–S cells have a high overpotential between charge/discharge cycles, rapid capacity fading, low cycling efficiency, and slow kinetics. Such problems are strongly affected by the dissolution of polysulfides (PSs) in the electrolyte and their subsequent shuttling to the Mg anode side.

Similarly, to the Li–S cell [18], the Mg–S one comprises an anode, a cathode with binder, an electrolyte, a separator, and a current collector [15,16,19], and sometimes a protective layer on the anode, as suggested in [17]. The scheme of the Mg–S cell is shown in Figure 1 (based on [20]).

Wang and Buchmeiser [16] reported that the number of studies on rechargeable Mg–S cells (Figure 2c) has recently significantly increased (Figure 2a). A timeline of various findings relating to the Mg–S cells in the time range from 2011 to 2019 is shown in Figure 2d. Figure 2b comprises an overview of the topics addressed in papers relating to Mg–S cells. From such a survey, it is clearly visible that studies on novel electrolyte systems, modifying sulfur cathode materials, and mechanistic studies were significantly preferred. By contrast, only a few studies concerned the other components of an Mg–S cell, such as the anode and the separator.

Wang and Buchmeiser [16] described how during discharging, oxidation of the Mg anode results in the generation of Mg²⁺ ions and a pair of electrons. Mg²⁺ ions travel to the S cathode via the electrolytes and separators, whereas the electron pair travels from the anode to the cathode via an electrical circuit loading the cell. In the cathode zone, S changes in a stepwise manner into long-chain polysulfides (PSs), short-chain ones, and, in the end, into Mg–S. During charging, Mg²⁺ ions are reduced and deposited onto the anode surface. The Mg–PSs re-react with some oxygen to form the initial sulfur state.

Although the design of the Mg–S cell was and is often modelled on that of the Li–S cell, the chemical reactions occurring in both types of cells differ from each other. The different reaction pathways affected by the preferential stabilization of S₂^2– and S₄^2– in the presence of Mg²⁺ and Li⁺ are shown in Figure 3 [28].

Zou et al. [28] explained that the precipitation of S₈ and MgS₂ from PS solutions confirmed a low concentration of dissolved PSs in the Mg²⁺-containing solutions. The lower PS concentration in the presence of Mg²⁺ than that of Li⁺ resulted from the high electrostatic force between Mg²⁺ and S_x²⁻, due to the greater charge density of Mg²⁺ than that of Li⁺, which supports the solid precipitation. The early MgS₂ precipitation and low PS concentration provided a sluggish “solid–solid” dominant reaction pathway and weakened the use of both solid S₈ and Mg–S.

The differences in the chemical reactions taking place in the Li–S cell and in the Mg–S cell have a great influence on the characteristics of such cells. Two subsequent galvanostatic discharge/charge profiles of Mg–S and Li–S two-electrode cells are shown in Figure 4. Such profiles point out that the Mg–S cell has limited discharge capacity, large polarizations, and rapid capacity decay [28].

Wang et al. [29] also reported that the major practical problems of Mg–S cells related to the soluble Mg–PS intermediates and their inter-electrodes shuttling inducing high overpotentials, low S utilization, and poor Coulombic efficiency.

A separate problem related to the use of Li-ion and Li–S cells, and soon, also for the Mg–S ones, is their durability. This applies to situations when such cells are or will be used in nets powered by wind farms, photovoltaic devices, and others, where grids may experience large fluctuations in the available electric energy or electric voltage due to local overloads or environmental conditions such as weather conditions, accidents, and others. Then, such batteries become, periodically, the only sources of energy for the grid, or they are used to compensate for unfavorable temporary disturbances. The optimal selection of cells with a long life and good cyclability can determine not only the comfort, but sometimes also the health or even life of people, especially when it is associated with the need to provide power to medical devices operated in hard-to-reach areas.

Ford et al. [30] noticed that Li–S cells exhibited the well-known tendency to self-discharge. From a practical standpoint, the battery shelf-life is very important. Unfortunately, the Mg–S cells also suffer from severe self-discharge. For a common Mg–S electrolyte, they determined a multi-step self-discharge pathway. Covalent S₈ diffused to the metal Mg anode and was transmuted into ionic Mg–PS in a non-faradaic reaction. Mg–PSs in solution were meta-stable, prone to prolonged reaction, and precipitated as solid Mg–PS species during both storage and operation.

The most often investigated form of Mg–S cell is the coin cell one (Table 1).

Although the coin Mg–S cell configuration is normally used in the laboratory for research, as has been presented further, commercial cells are commonly met in the form of cylinder cell or pouch cell configuration. The typical rechargeable battery configurations, including the coin one, the cylindrical one, the prismatic one, and the pouch one, are presented in Figure 5 [31].

Although the considerations presented in [32] particularly concern pros and cons of Li-ion cells, the features of the analyzed configurations may be very similar when such configurations are applied to Li–S cells and Mg–S cells.

The cylindrical cells exhibit high specific energy and mechanical stability and are adapted to automated manufacturing. Such a cell design allows added safety features impossible with other formats. It has high cyclability, long life, and low cost, but less than ideal packaging density. They are often applied to portable devices.

The prismatic cells are placed in an Al or SS case to enhance stability. Jelly-rolled or stacked, the cell is space-efficient but more expensive to manufacture than the cylindrical cell. Prismatic cells are utilized in electric powertrains and energy storage systems.

The pouch cell utilizes a laminated form placed in a bag. It is lightsome and relatively cheap, but under exposure to humidity and high temperatures exhibits a shorter life. There is a necessity to add a light stack pressure to prevent delamination and thus prolong the cell life. For Li-ion cells, a swelling of 8–10 percent over 500 cycles can occur. Large cells operate best with light loading and moderate charge times. The pouch cells are used for similar applications as the prismatic ones.

According to [33], Li-ion battery packs require a mandatory protection circuit to assure safety under all circumstances.

Governed by IEC 62133, the safety of a Li-ion cell or packs needs to be provided with the following safeguards:

• A Built-in PTC (positive temperature coefficient) for protecting against current surges;
• A CID (circuit interrupt device) for opening the circuit at a cell pressure of 1000 kPa;
• A safety vent for liberating gases on undue pressure buildup at 3000 kPa;
• A separator for inhibiting ion flow by a melting process when exceeding a certain temperature threshold.

The application of such safeguards for Mg–S cells also increases the safety of such cells, but in some cases can be an overprotective action and needs further research and optimization, particularly relating to the costs of their realization.

Wagner et al. [34] investigated the pouch cell prototype built within the framework of the Mag–S project, funded by the German Federal Ministry of Education and Research and in cooperation with Custom Cells Itzehoe (CCI) GmbH in Germany.

Montenegro et al. [35] described a prototype magnesium rechargeable battery (MRB) of the Mg–S-type comprising cells, each with an Mg foil anode, an S cathode, a magnesium tetrakis (hexafluoroisopropyloxy) borate electrolyte, a plastic separator, and Al composite pouch cell packaging. They found that the pouch cell housing and electricity requirements for battery manufacture posed potential threats to the environment. The Al pouch cell packaging was found to strongly contribute to global warming, abiotic depletion, human toxicity, acidification, and photochemical oxidation.

According to Bautista et al. [36], the same authors proposed the following two modified pouch cell models: MgS-Evo1 and MgS-Evo2. The first configuration allowed a pouch cell mass share reduction from 45 wt.% to 3 wt.%. The second model allowed decreased separator thickness and, correspondingly, a mass share decrease from 10% to 2 wt.% and a much lower footprint.

Bieker et al. [37] reported that, unlike hard-case cell housings, pouch cells do not allow too much excess of liquid electrolyte without losing shape and stability.

Among the different cell formats (cylindrical, prismatic-hard case, and pouch), pouch cells best allow maximizing the specific energy because of the low weight of cell packaging. For the manufacturing of single prototype cells, stacking of electrodes and separators can be carried out with less effort than winding an electrode-separator stack for cylindrical cells [38]. Moreover, the cell volume changes can be evaluated and eventually better controlled or compensated [39,40,41]. In addition, several stages are feasible, starting from one-layered [42,43] versions with manageable active material amounts and going up to a few [40,44,45,46] and multilayered pouch cells [40,47,48,49]. The higher the stack, the more electrode area and, consequently, more sulfur-carbon composite is required [50].

The cylindrical type for Mg–S cells was proposed in [51].

According to [52], the Mg–S battery may be safer than the Li–S battery because Mg plating usually proceeds without dendrite formation.

The safety of the Mg–S battery is mainly related to the vapor pressure of the electrolyte. The over-pressure building up to 70–150 kPa during the heating of the cell up to 20–45 K over the electrolyte boiling point can trigger the battery explosion. The exothermic reaction between MgS and H₂O induced a sudden temperature jump in the battery.

The distinct performance, safety, and cost behaviors of various ether types of electrolytes resulted from the different CH₂CH₂O chain lengths.

A modified DME with a higher boiling point can be ideal for the Mg–S cell.

The Hazard Communication Standard (HCS) determines any chemical substance classified as a physical hazard, a health hazard, a simple asphyxiant, combustible dust, pyrophoric gas, or hazard not otherwise classified as a hazardous chemical. The HCS also defined the physical and health hazards, and the classes and categories of such hazards, Hazard Communication. The evolution of Mg–S batteries is accompanied by various hazards related to the use or manufacturing of the components of these batteries. The aim of the study was to identify such hazards and battery components that cause the most of these hazards. It turns out that such hazards belong to three groups. The first one comprises the possible occurrence of fire, flammable gas or explosion, and corrosion in contact with the atmosphere or water. The second one relates to the toxic or allergic effects on skin, eyes, the gastrointestinal and respiratory tracts, to the generation of genetic defects, damage to fertility or unborn children, organs, and carcinogenicity. The last one relates to aquatic life.

2. Anode Materials

2.1. Metallic Mg Anodes

Various Mg–S batteries use Mg metallic anodes, which have a strong effect on their electrochemical performance due to its interactions with an electrolyte [10,53,54,55,56,57,58,59,60,61].

The phenomenon of the blocking deposits (in layer form) on the Mg anode resulting from electrolyte disintegration or reaction with traces of H₂O and O₂ averts the diffusion of Mg²⁺ ions. Thanks to this, reversible Mg deposition and dissolution are limited [54,60,61]. Among others, polar aprotic solvents such as carbonates and nitriles often form an impenetrable film on the metallic surface. This decreases the available types of the electrolyte [11,61,62].

An anode made of metallic Mg in the form of discs [21,63], plates [22], ribbons [64], or foils [21,23,24,65,66] has a low surface area [16]. Table 1 presents some Mg–S batteries using Mg anodes in the form of foil [22,25,28,52,67,68,69,70,71,72], disc [13,21,30,73], foil disc [24,74], ribbons [64], and others. The largest group is those using Mg foil anodes.

Table 2 contains some information related to the hazards of metallic Mg [75]. According to [75,76], Mg in contact with water releases flammable gas. It may cause skin and temporary eye irritation. When ingested, it may cause irritation of the gastrointestinal tract. When inhaled, it may cause irritation to the respiratory system. According to [76,77], it is also self-heating and may catch fire.

2.2. Alternative Anodes

Carbonate-based solvents are much more resistant to corrosion and anodic oxidation compared to ether-based ones [78]. On the other hand, when the Mg metal reacts with carbonate solvents an impermeable film on top of the Mg anode is usually generated, strongly limiting Mg deposition during charging [60,79,80]. To compensate for this unwanted tendency, the use of a conductive and preventive auxiliary layer on Mg anodes is necessary [79,81,82,83]. Such a layer, usually the PVD (physical vapor deposited) one, may block the corrosion process of the metal surface caused by tracers of O₂ or H₂O, S, and the electrolyte [84]. Such a protective layer should be uniform and of a thickness below 10 nanometers to provide high ionic conductivity with no increase in cell impedance [84]. Therefore, an atomic Al₂O₃ layer deposited on Mg can be suitable for Mg anodes [84,85,86].

Table 2 shows information about the hazards related to the use of Al₂O₃ [87]. It seriously irritates eyes and damages organs via prolonged or repeated exposure. It is able to irritate the respiratory tract.

Various hazards related to the use of materials for anodes in Mg–S cells are presented in Figure 6. The largest number of the hazards identified belonged to the hazard group related to the possible occurrence of fire, flammable gas, or an explosion. Three single hazards were identified that referred to the hazard groups related to the toxic or allergic effects on eyes, the respiratory tracts, and the generation of damages to organs, respectively.

Only a few materials are used for the anodes in Mg–S batteries, which pose only a few hazards associated with their use.

3. Separators

Various separators usually isolate a cathode and an anode in the liquid electrolyte cells, allowing a free ion transport [88,89]. The Mg–S batteries mainly utilized separators based on glass fiber sheets [12,22,23,65,66,67,68,73,90,91,92] and microporous polymer membranes [13,64,93,94,95,96,97]. Glass fiber separators possess better thermal dimensional stability, porosity, permeability, and ionic conductivity than the other ones, but they are more expensive and need more electrolyte [88,89].

Table 1 presents some Mg–S batteries utilizing separator materials such as PTFE [25], PE film [21], borosilicate glass fiber sheet [71,90], glass fiber [22,26,28,30,52,67,68,72,74], Celgard microporous membrane [13,30,93], CNF-coated glass fiber [24], glass microfiber filter [70,73], ENTEK PE membrane [94], glass wool [98], and others. It is seen that the glass fiber separator is the most often used in Mg–S batteries.

There has been no information found about hazards related directly to the glass fiber separators. However, some of these related to the use of glass fibers have been available.

According to [99], glass fiber, when ingested, is able to cause disturbances in the gastrointestinal tract. Breathing in glass fiber dust or particulates is able to irritate the nose, throat, and respiratory tract. The contact of the skin or eyes with glass fiber dust or particulates can temporarily irritate skin or eyes. Long-term exposure to a glass fiber environment may cause temporary negative effects.

According to [100], woven fiberglass fabric exhibits a mechanically irritating ability. Breathing such dust and fibers can temporarily irritate the mouth, nose, and throat. Their contact with skin can result in itching and transitory irritation. Their contact with eyes can initiate a temporary mechanical irritation. Ingestion of them can initiate a temporary mechanical irritation of the stomach and intestines. Prolonged breathing or skin conditions that are mechanically irritated can increase the probability of worsening health from contact with this material.

Due to the low solubility and irreversibility of MgS and Mg₃S₈, the surface of separators can be modified to increase the Mg–S cell performance [24,27].

Yu and Arumugam [24] reported an activated carbon nanofiber (CNF)-coated glass fiber separator, prepared using vacuum filtration.

There has been no information found about hazards related directly to the activated carbon nanofiber (CNF)-coated glass fiber separators. However, some information related to the use of carbon nanofibers has been available.

According to [101], carbon nanofibers are found as a non-hazardous substance or mixture. Moreover, according to [102], carbon (graphite) nanofibers are found as a non-hazardous substance or mixture. However, according to [103], graphitized carbon nanofibers are flammable as both liquid and vapor. They are detrimental in contact with skin or if inhaled. They can seriously irritate the eyes and are able to damage fertility or an unborn child (Table 2).

The use of a catalyst to reactivate neutral MgS and Mg₃S₈ also allows for improving the cyclability. For example, TiS₂ has a catalytic effect on the activation of low-order Mg–PSs [104,105,106]. Moreover, Xu et al. [27] reported a TiS₂-coated separator obtained via vacuum filtration.

According to [107], TiS₂ releases flammable gas when in contact with water. It irritates the skin and seriously irritates the eyes. It can also irritate the respiratory tract (Table 2).

Wang et al. [29] utilized a functional Mo₆S₈ modified separator with a high adsorption capability of PSs and acted simultaneously as a mediator, accelerating the PS conversion kinetics.

Various hazards related to the use of materials for separators in Mg–S cells are presented in Figure 7. The four pairs of the identified hazards belonged to the hazard group related to the possible occurrence of fire, flammable gas, or an explosion, and the hazard group related to toxic or allergic effects on skin, eyes, and the respiratory tracts, respectively. A single hazard was identified and referred to the hazard group related to the generation of damages to fertility or an unborn child.

Similarly, in the case of anode materials, only a few materials are utilized as separators in batteries, which pose only a few hazards related to their use. However, such hazards are more numerous and much more varied compared with the case of the anode materials.

4. Cathodes

Mg–S batteries utilized intercalation cathodes [108,109,110,111,112], e.g., transition metal sulfides such as TiS₂ and Mo₆S₈, [14,63,113,114], as well as transition metal oxides such as V₂O₅ [115,116] or MnO₂ [117,118], MoO₃ [119] conversion cathodes such as sulfur and oxygen, organic cathodes such as 2,5-dimethoxy-1,4-benzoquinone [120,121,122,123,124] and carbon-based cathodes such as fullerenes [125] have been investigated and discussed so far [54,111,120,126,127,128]. Wang and Buchmeiser [16] reviewed mainly sulfur-based conversion cathodes. The other types of cathode materials have been discussed in other reviews [53,55,112,116,120,128,129,130].

Table 1 presents some Mg–S batteries used as cathodes of the S/C type [15,25,26,67], S/CMK type [21,52,71,72,90], S/ACC type [22,30,70,74], S/CNTS type [15,24,73], S/MOFs type [68], MgPS/G-CNTs type [131], S/NG type [13], S/rGO type [93], S/MC type [64,94], S/CB type [98] and S/KB/PTFE type [28]. It is clearly seen that the S/C type, the S/CMK one, and the S/ACC one are the most often reported types of cathodes applied in Mg–S batteries.

There was no information found about hazards relative to the use of the Mo₆S₈.

Some clusters with an Mo₆S₈ unit have been reported to decompose to MoS₂, molybdenum metal, or both, by thermal treatment under various atmospheres [132,133,134].

Chen et al. [135] notified the low toxicity of MoS₂-very-thin-film.

However, according to [136], MoS₂ powder causes serious eye irritation and may cause respiratory irritation.

Manganese oxides (MnO₂) as pseudocapacitive electrode materials showed environmental friendliness [137,138,139].

Some hazard expressions related to MnO₂ are shown in Table 2.

Ji et al. [140] notified the non-toxicity of MnO_x (i.e., MnO, MnO₂, Mn₂O₃, and Mn₃O₄).

According to [141], MnO₂ is detrimental when swallowed or inhaled. Despite its incombustibility, it intensifies the combustion of other substances.

Table 2 presents some hazard expressions related to V₂O₅ [142]. It is detrimental when swallowed or inhaled. It can irritate respiratory tract. It probably elicits genetic defects and damage to an unborn child. It also induces damage to organs via long-term or repeated endangering. It is poisonous to aquatic life.

Whittingham [143] suggested a low toxicity of a cathode made of V₂O₅.

According to [144], MoO₃ is toxic if swallowed. It seriously irritates the eyes and can irritate the respiratory tract. It probably, causes cancer and is detrimental to aquatic life, with long-lasting effects.

Table 2 presents some hazards related to the use of 2,5-dimethoxy-(1,4) benzoquinone [145]. According to [146], it is irritating to the eyes and skin on contact. Inhalation causes irritation of the lungs and respiratory system.

Fullerenes can also cause hazards [147] as presented in Table 2. According to [148], they cause serious eye irritation and may cause respiratory irritation. Moreover, [149] reported that fullerenes may cause eye irritation and dermal irritation. Their inhalation may lead to lung irritation and may irritate the gastrointestinal tract. High concentrations of dust may be irritating to the eyes and skin.

Active Cathodes Materials

Contrary to intercalation cathodes, in the S-based one belonging to the conversion cathode groups (O₂-, CuF₂-, AgCl-, and S-based), the cyclability of battery results in the reduction and oxidization of elemental sulfur [7]. The unwanted phenomenon of O₂-based cathode materials is the irreversible formation of the electrochemically inactive discharge product MgO [150]. The discharge products of CuF₂- and AgCl-based cathodes also exhibit low solubility [150].

According to [151,152], oxygen may cause or intensify fire and is a known oxidizer. Usually transported under pressure, it may explode if heated (Table 2).

Hazards related to the use of CuF₂ [153] are shown in Table 2. It causes severe skin burns and eye damage and may cause respiratory irritation [154]. According to [153], contact with acids liberates very toxic gases containing hydrogen fluoride and copper oxides.

Table 2 contains also some hazards related to the use of AgCl [155]. According to [156], it causes respiratory tract irritation. It can irritate the eyes, skin, and digestive tract. It also can induce cyanosis. According to [157], it can induce corrosion in contact with metals, and exhibits a high level of toxicity to the aquatic life with long-lasting effects.

Yoo et al. [54] stated that sulfur is appreciated due its non-toxicity and a high theoretical energy density (1675 mAh g⁻¹). Table 2 presents sample information about hazards related to the use of sulfur. According to [158], it exhibits flammable features and can irritate the skin. As reported in [159], it is able to be detrimental when swallowed or inhaled.

Du et al. [65] reported that the cathode materials in Mg–S batteries utilize carbonaceous materials with elemental sulfur (α- or β-S₈). The use of various porous carbon additives for the accommodation of S₈ in the cathode allows enhancing the loading of active materials and limiting the diffusion of PSs [93]. The utilized carbon materials comprise carbon black [25,160], activated carbon clothes (ACC) [22,66,74,85,92], and metal organic frameworks (MOFs) [68].

Two reports about the toxicity of Super P carbon were found in the literature.

Chaudhuri et al. [161] found a carbon black (Super P) as a particle of low toxicity (PSLT). However, carbon black can reveal its direct genotoxicity or even reproductive toxicity. High concentrations of carbon black results in the inflammation and oxidative stress in the lungs, sometimes followed by mutations.

As reported in [162], Super P carbon may induce irritation of the eyes and skin.

As reported in [163], elemental C exhibited a very low toxicity. A health hazard can occur when humans are exposed to carbon black, not elemental C. Chronic inhalation endangering to carbon black can temporarily or permanently damage lungs and heart. Pneumoconiosis was observed in employees producing carbon black. Inflammation of the hair follicles and oral mucosal lesions occurred during skin endangering. Carbon black was not found as carcinogenic to humans. The high toxicity can be exhibited by some simple C compounds such as carbon monoxide (CO) or cyanide (CN). The environmental effect of C was found to be neutral.

Tamames-Tabar et al. [164] studied the toxic effects of the porous metal-organic frameworks (MOFs) comprising Fe, Zn, Zr carboxylates or imidazolates. The MOF NPs exhibited low cytotoxicity. The lower toxicity was observed in the Fe carboxylate NPs and the higher toxicity in the Zn imidazolate ones.

Ruyra et al. [165] studied the toxic effect of uncovered MOFs on zebrafish embryos. They found that such an effect was affected by the material setup and the leaching manner of metal ions.

During studies on rat pheochromocytoma cells, Ren et al. [166] found that the toxic effect of IRMOF-3, a rigid cubic zinc-based MOF, was affected by time exposure and strength.

Studying the behavior of hepatic cells (HepG2 and Hep3B) and lung cells (A549 and Calu-3), Grall et al. [167] found a weak toxic effect of mesoporous MOFs based on Fe, Al, or Cr.

Wagner et al. [168] evaluated the toxic effects of MIL-160, a microporous hydrophilic Al-based MOF comprising a five-membered ring and an oxygen heteroatom, and ZIF-8, a hydrophobic framework of zeolitic imidazolate, on human bronchial epithelial (BEAS-2B) cells.

There was no information found about the hazards related directly to the use of activated carbon clothes (ACC). However, Table 2 contains some information about the hazards related to activated carbon. According to [169], activated carbon may cause eye irritation. Its dust may also cause respiratory irritation. According to [170], its powder is self-heating in large quantities and may catch fire. In the latter case CO and CO₂ may be liberated.

The application of elemental S in cathodes can induce the unwanted so-called “shuttle effect” [73,74,171]. This phenomenon can be avoided when sulfur is encapsulated in carbon-based materials, such as microporous [95,172], mesoporous [173], or hollow carbonaceous materials [174,175,176]. Mg–S batteries cathodes utilize porous carbon materials, such as CMK-3 [12,21,177], nitrogen-doped graphene [13], carbon nanotubes (CNTs) [65], carbon nanofibers [24,178], and reduced graphene oxide (rGO) [93].

Table 2 contains some hazards related to the use of CMK-3. According to [179], ordered mesoporous carbon CMK-3 is suspected of causing cancer. Under fire conditions, carbon oxides are formed. Similarly, mesoporous carbon [180] is suspected to cause cancer.

There was no information found in the literature about hazards related to the use of nitrogen-doped graphene.

However, Wang and Jiang [181] studied the toxic effects of graphene oxide (GO) and N-doped graphene quantum dots (N-GQDs) on red blood cells (RBCs). The adsorption of GO extracted the lipid bilayer, causing hemolysis and aberrant forms of cells. By contrast, N-GQDs violate the structure and conformation of lipid, inducing only aberrant cells.

According to [182], graphene nanoplatelets can create a combustible dust-air mixture. They can irritate eyes, skin, and respiratory tract irritation.

As reported in [183], conductive graphene sheets can irritate skin, mucous membranes, and eyes.

According to [184], the toxic effects of the graphene-family nanomaterials (GFNs) in animals or cell models was affected by the lateral size, surfacial structure, functionalization, charge, purity, formation of aggregates, and corona effect. The GFN toxic effect took the form of physical destruction, oxidative stress, unwanted DNA changes, inflammation, apoptosis, autophagy, and necrosis. In the mentioned mechanisms, (toll-like receptors-) TLR-, transforming growth factor β- (TGF-β-), and tumor necrosis factor-alpha (TNF-α) dependent-pathways formed the signaling pathway network that was highly dependent on the oxidative stress.

Table 2 presents some hazards related to the use of carbon nanotubes and carbon nanofibers. According to [185], CNTs cause serious eye irritation and may induce respiratory irritation.

According to [186], carbon nanofibers seriously irritate the eyes and can irritate the respiratory tract. However, according to [101], they exhibit no known hazards.

As reported in [187], reduced graphene oxide (rGO) may cause irritation to the respiratory tract, skin irritation, and eye irritation. However, according to [188], and [189], it exhibits no known hazards.

Using the CMK-3 as cathode material facilitates preparation of strongly organized interwoven composites [177]. The formation of MgS, MgS₄, and various Mg_XS₈ (x = 1, 2, 3, 8) structures in the cathode have been reported during Mg–S battery cyclability [26,27,177].

There was no information found about hazards related to the use of Mg₃S₈, MgS₄, or MgS₈.

According to [190], a high amount of MgS is self-heating and potentially fire-catching. It causes severe skin burns and damages the eyes. It is detrimental if swallowed, poisonous in contact with skin, and very poisonous to aquatic life.

Besides the mesoporous CMK-3/S cathode, a porous graphdiyne can be applied as a cathode material.

Du et al. [73] obtained an S-comprising cathode based on S graphdiyne (SGDY). Graphdiyne (GDY) was a carbon allotrope with layers of benzene rings and butadiyne linkages.

There was no information found about hazards related to the use of sulfur-doped graphdiyne.

Zheng et al. [191] compared some properties of graphene oxide (GO) and GDY oxide (GDYO). Contacts of GO NPs with a human hepatocyte membrane led to its ruffle, methuosis, and apoptosis. Adhesion of GO to cells results in their stress and the creation of reactive oxygen species. In contrast, GDYO did not adhere to the cell membrane. Both GDYO and GO were able to induce vivo mutagenesis but no erythrocyte-killing effect. Additionally, both of them proved to be antioxidants and bioequivalent in binding to single-stranded DNA and doxorubicin.

Wang et al. [94] used a microporous carbon as the carbon host for the adsorption of small S_2–4 inside its structure and of S₈ molecules on the outside wall of the carbon and prepared a sulfur at microporous carbon composite (S@MC) as the electrochemical active material for cathode. Cui et al. [192] proposed the positive electrode utilizing S, a metal sulfide, and a ternary Cu composite. The metal sulfides included FeS₂, SnS₂, MoS₂, Co₃S₄, and Ni₂S₃. Such materials can effectively block the shuttle effect on the Mg–S battery.

According to [193], microporous carbon exhibits no known hazards.

Table 2 presents some hazards related to the use of FeS₂, SnS₂, MoS₂, CoS₂ and Ni₂S₃. There was no information found about hazards relative to Co₃S₄.

According to [194], FeS₂ can induce an allergic skin reaction, and allergic or asthmatic symptoms, or breathing problems after inhalation. It is also very poisonous to aquatic life, with prolonged effects.

As reported in [195], SnS₂ irritates skin and seriously irritates eyes. It can also irritate the respiratory tract.

According to [196], MoS₂ causes skin irritation, serious eye irritation, and may cause respiratory irritation. Similarly, as reported in [136], MoS₂ powder seriously irritates the eyes and can irritate the respiratory tract.

As reported in [197], CoS₂ can induce an allergic skin reaction, and is very poisonous to aquatic life with prolonged effects.

According to [198], Ni₂S₃ can induce an allergic skin reaction and genetic defects. It also can induce cancer when inhaled. It damages organs via prolonged or repeated exposure and is very poisonous to aquatic life with prolonged effects.

Most Mg–S batteries possess cathode materials utilizing elemental S or S hosted by microporous or mesoporous carbon materials. The shuttle effect, similarly to Li–S batteries, strongly affects the efficiency of Mg–S batteries. To weaken this effect, sulfur can be covalently bound to a conductive carbon matrix, as applied in various Li–S batteries [199,200,201,202,203,204,205]. Moreover, preventive layers on the active material in the cathodes can also block the dissolution and loss of S from the cathode material [206].

Various hazards related to the use of materials for cathodes in Mg–S cells are shown in Figure 8. The highest number of the hazards identified belonged to the hazard group related to the toxic or allergic effects on the eyes. Only a single hazard was identified and referred to the hazard group related to the generation of damages to fertility or an unborn child. Moreover, only two pairs of the hazards identified belonged to the hazard groups related to the generation of genetic defects and organ damage, respectively. No hazard was identified related to the corrosion.

It is clearly visible that the materials of cathodes in Mg–S batteries belong to the group posing a lot of hazards related to the use of such materials, much more than those related to materials for anodes or separators in Mg batteries. Such hazards vary widely in type and degree of danger.

5. Current Collectors

In Mg–S cells, the current collector material strongly affects their electrochemical behavior, especially when they use halogen-comprising corrosive electrolytes [207]. The available metal-based current collectors are in the form of the following: Al foil [13,21,23,65], stainless-steel (SS) foil [12,66,92,95,96], carbon-coated aluminum foil [91], copper [64,65,94,95,97], and the anticorrosion alloy Inconel 625 [90,93,95].

Table 1 presents Mg–S batteries using Inconel 625 [22,74,90,93], stainless steel (SS) [28,30,67,68,69,71], Cu [15,64,67,73,94,98], and the others as a material for the current collector. The above-mentioned materials are most commonly used for current collectors, while the Al, Ni, Mo, and CNF are more seldom reported.

Table 2 presents some hazards related to the use of Al foil, stainless steel, graphite, copper, and Inconel 625 alloy.

According to [208], Al foil has a low hazard for trained personnel and in solid form is not hazardous. Moreover, as reported in [209], it is not a hazardous material. However, according [210], it is a flammable solid and causes acute aquatic toxicity.

Suspensions of Al dust in air may pose a severe explosion hazard [208,210]. Explosion or fire hazards may be present when the above-mentioned dust and fines or molten Al are in contact with water or certain metal oxides including rust and copper oxide [211]. Al dust or fumes are nuisance particulates [208].

As reported in [211], Al dust and/or fumes may pose a physiological hazard after inhalation or ingestion. They can induce an influenza-like illness and lung cancer when chronically overexposed.

According to [212], Al metal foil is toxic to lungs. If it is heated or in a dust form, it can irritate respiratory tract. Heating it can emit Al₂O₃ fumes and induce fume metal fever after inhalation. Chronic exposure to Al dust may cause dyspnea, cough, asthma, chronic obstructive lung disease, pulmonary fibrosis, pneumothorax, pneumoconiosis, encephalopathy, weakness, incoordination and epileptiform seizures, and other neurological symptoms.

Contact with the Al dust may cause mechanical irritation of the skin or eyes [211]. Moreover, according to [212], Al metal foil is a slight irritant in contact with skin.

As reported in [213], stainless steel foil containing Fe, Cr, and Ni was subjected to processes generating particulates can cause hazards to health or environmental effects presented in Table 2. Similarly, according to [214], stainless steel foil containing Mn, Ni, Cr, Mo, Cu, Al, W, Co, and Sn can also cause hazards to health or environmental effects presented in Table 2.

According to [215], stainless steel in the powdered form is poisonous to aquatic life and reactive in contact with water, and also exhibits pyrophoricity, flammability, self-heating capabilities, carcinogenicity, and acute toxicity. During the production of stainless steel, dust, fumes, or particulates are generated. Exposure to such dust or fumes can irritate the eyes, skin, and respiratory tract. Fine particulates dispersed in the air may present an explosion hazard. Inhalation of such dust and fumes can induce metal fume fever.

There was no information found about the hazards related to C-coated Al foil; however, they are akin to those related to aluminum and graphite, as presented in Table 2. According to [216], Al is very poisonous to aquatic life, also with prolonged effects.

According to [217], graphite powder causes serious eye irritation and may also cause respiratory irritation and cancer by inhalation. It can also damage organs via long-term or repeated exposure.

As reported in [218,219], Cu foil is not considered a hazardous material. However, according to [220], Cu dusts, mists or fumes can occur when Cu foil is cut or laminated. They can irritate eyes and respiratory tract. If they comprise arsenic, they are carcinogenic to humans. Sharp edges of Cu foil can induce cuts during its production.

Moreover, as reported in [221], Cu foil is fatal if swallowed or inhaled, and is very poisonous to aquatic life. It causes serious eye irritation, and may cause allergic skin reactions, genetic defects, and damage to the digestive system, hematopoietic system, kidneys, nose, respiratory tract, and/or skin, via long-term or repeated exposure if inhaled. Additionally, it can produce combustible dust.

According to [222], Inconel in the solid form can be allergic to people sensitive to the metals contained in it. User-generated dust or fumes can irritate the skin and eyes. Chronic exposure can induce dermatitis or conjunctivitis. Excessive inhalation of fumes released during welding may pose prolonged health effects. According to [223], Inconel 625 dust clouds may be explosive and can irritate the eyes. High dust levels may irritate the respiratory system.

Additionally, edges of Inconel 625 strips [224] may be sharp and can cause cuts. Hot metal and UV radiation produced can cause burns. Metal (Al, Mn, Mo, Cr, Ni, Co, Nb, Cu, Ti, Fe, W, and V) ingestion can cause toxic effects. The inhalation of welding or spraying fumes may cause damage to the lungs and respiratory tract. Co and Ni are animal carcinogens and inhalation of their fumes and dusts should be avoided. The prolonged inhalation of Mn fumes and dust may cause irreversible damage to the nervous system, resulting in Parkinson’s disease-like symptoms.

While Cu is usually unstable when mated with chloride-containing electrolytes [225], the application of Cu current collectors below 1.7 V versus Mg/Mg²⁺ allows the use of an S cathode with the Grignard-based nucleophilic all-phenyl complex (APC) electrolyte [95]. The electrochemical behavior of such cells is better than the ones with SS current collectors. The copper sulfides can form at the interface between S and Cu, partially protecting the free S in the cathode from reactions with APC electrolytes (vide supra). No such copper sulfides occurred on cathodes based on SS current collectors dried at 50 °C [95].

Muthuraj et al. [226] developed a 3D porous current collector, made of a N-, S-dually doped carbon cloth (DCC), that is stable if mated with corrosive electrolytes and capable of catching PSs. It was and possessed a 3D interconnected porous structure that ensures high cycle stability and conductivity.

There was no information found about hazards directly related to a N-, S-dually doped carbon cloth; however, some information is available related to the N-doped porous carbon, the N/S co-doped graphene presented in Table 2 and the N/S co-doped carbon nanodots.

According to [227], N-doped graphitic porous carbon can be cancerogenic. Additionally, hazardous decomposition products such as carbon oxides are formed under fire conditions.

As reported in [228], N/S co-doped graphene powder causes serious eye irritation, and may cause respiratory irritation.

Ji et al. [229] reported that the N, S-doped C nanodots (N,S-CNDs), usually exhibited a high antioxidative ability in free radical scavenging in physicochemical conditions. During studies conducted using two cell lines, the uptake of the N,S-CNDs initiated the formation of intracellular reactive oxygen species (ROS), thus inducing oxidative stress and deleteriousness to both cell lines. The mitochondrial membrane potential enhanced with the concentration of the CNDs. The N,S-CNDs supports ROS generation via interactions with the electron transport chain in the mitochondrial membrane because of the S composite in the CNDs.

Various hazards related to the use of materials for current collectors in Mg–S cells are presented in Figure 9. It is visible that the highest number of the hazards identified belonged to the hazard group related to the toxic effects on aquatic life. Two sets of seven hazards identified belonged to the hazard groups related to the toxic or allergic effects on the respiratory tract and to the generation of damage to organs, respectively. Additionally, only three pairs of the identified hazards belonged to the hazard groups related to the toxic or allergic effects on the gastrointestinal tract, the generation of genetic defects, and damages to fertility or an unborn child, respectively. No hazard was identified related to the corrosion.

Materials for current collectors belong to the group posing much more hazards related to their use compared to the case of anode materials and separator materials. However, hazards related to the materials of current collectors are less numerous and less varied compared to the case of the cathode materials.

6. Binders

Various binders are used in the cathodes of Mg–S batteries. The most commonly used is 10%wt. [12,15,21,64,65,66,67,68,90,93,94,98] or about 10%wt. [131] of polyvinylidene fluoride (PVdF) as a binder. Table 1 also shows that the most commonly used binder (bind) is the PVdF one.

Li et al. [13] also utilized a PVDF binder during their studies on Mg–S batteries.

According to [230], poly(vinylidene fluoride) irritates the skin and seriously irritates the eyes. It can also irritate the respiratory tract.

Kim et al. [25] utilized a 4%wt. poly(tetrafluoroethylene) (PTFE) as a binder in Mg–S batteries.

Zou et al. [28] applied a 5%wt. PTFE binder into the cathode of an Mg–S battery.

There were three pieces of information found about the toxicity of PTFE.

Sajid and Ilyas [231] found that PTFE-coated cookware emits different gases and chemicals of mild to severe toxicity. Further studies are need into the toxicity and fate of ingested PTFE coatings. The poisonous perfluorinated carboxylic acid (PFOA) is also utilized during the production of PTFE. The PFOA can exist in the gas phase emitted from the cooking utensils under normal cooking temperatures. Therefore, PFOA is replaced with GenXs, although the latter can also have a similar level of toxicity. Therefore, more research is necessary on the human exposure and poisonous effects of PTFE, PFOA, GenX, and other alternatives.

Shimizu et al. [232] stated that PTFE can induce polymer fume fever in humans.

According to [233], polytetrafluoroethylene is of low oral toxicity but can irritate gastrointestinal tract. Dust and vapors, or fumes, evolved during thermal processing can irritate the respiratory system. It can irritate the skin and eyes. It is also low-level poisonous to aquatic organisms.

Sheng et al. [52] utilized a mixture of 5% sodium carboxyl methyl cellulose (NaCMC) and 5% styrene butadiene rubber (SBR) as a binder in an Mg–S battery.

According to [234], sodium carboxymethyl cellulose is detrimental to aquatic life, also with long-lasting effects (Table 2).

As reported in [235], the SBR binder is flammable under high heat and flame and can generate toxic and combustible fumes, such as carbon monoxide, chlorinated and hydrocarbon compounds, and soot. It may cause skin and eye irritation. An excessive inhalation of it can cause headache, nausea, and irritation.

Various hazards related to the use of materials for binders in Mg–S cells are shown in Figure 10. It is visible that the highest number of the hazards identified belonged to the hazard group related to the toxic effects on aquatic life. Only three single hazards were identified and referred to the hazard groups related to the toxic or allergic effects on the skin, eyes, and respiratory tract, respectively.

Similarly, in the case of the anode materials, it can be noticed that only a few materials are used for the binders accompanied with cathode materials in Mg–S batteries. Such binder materials pose only a few hazards associated with their use.

7. Electrolyte Systems

There are some limitations to the electrolyte systems usable for Mg–S batteries [11,119,120,121,122]. Many kinds of electrolytes in Mg batteries are of a nucleophilic nature and therefore are incompatible with S cathodes. Therefore, the transformation of the cathode material is needed for compatibility with the nucleophilic electrolytes [73,94,95]. Moreover, new non-nucleophilic electrolytes compatible with S cathodes have been developed. Various hazards related to the use of nucleophilic electrolytes were discussed in subchapter 7.1. Such hazards related to the non-nucleophilic ones were described in subchapter 7.2. Subchapter 7.3. comprises a summary of electrolyte systems for Mg–S battery electrolytes, and hazards associated with them.

7.1. Nucleophilic Electrolytes

Initially, the APC electrolyte obtained from the reaction between PhMgCl and AlCl₃ has been found to be incompatible with S-based conversion cathodes, because of the nucleophilicity of the organomagnesium compounds [12,150]. Therefore, at the beginning, the APC electrolyte seemed to be not predestined for use in Mg–S cells. Since an appropriate current collector [95] and cathode materials [73] have been developed, the APC electrolyte has come back for use in Mg–S batteries.

There was no information found about hazards relative to APC electrolyte.

Table 2 presents some information about hazards related to the use of AlC_l3, PhMgCl, and LiCl.

According to [236], AlCl₃ causes severe skin burns and eye damage. Additionally, it may cause respiratory irritation [237].

As reported in [238], chlorophenylmagnesium causes severe skin burns and serious eye damage.

The use of a Cu-based current collector instead of an SS one allows effective cycling of a cell based on an S₈ cathode and an APC electrolyte [95]. Moreover, the addition of LiCl into the nucleophilic electrolyte improves cycle performance of such a cell [95].

The electrochemical effectiveness of an Mg–S battery can be increased by using microporous carbon as the cathode material, Cu as a current collector, and a nucleophilic APC electrolyte containing LiCl as an additive ([94] Table 1).

The SGDY cathode is also compatible with the nucleophilic APC electrolyte, even though the current collector in the Mg–S battery is made of Al instead of Cu [73].

According to [239], LiCl is detrimental if swallowed it causes skin irritation and serious eye irritation.

7.2. Non-Nucleophilic Electrolytes

The high electrophilicity of the S cathode allows the use of non-nucleophilic electrolytes in many Mg–S cells [56,240]. The less/non-nucleophilic electrolytes in Mg–S cells can be qualified into two groups, including chloride-comprising ones and chloride-free, noncorrosive ones. Various hazards related to the use of chloride containing non/less nucleophilic electrolytes were discussed in subchapter 7.2.1. The hazards related to the utilization of non/less corrosive, non-nucleophilic electrolytes for Mg–S batteries were presented in subchapter 7.2.2.

7.2.1. Chloride-Containing, Non/Less Nucleophilic Electrolytes

Electrolytes in Mg–S batteries are obtained using Mg salts combining an Mg complex comprising a non-nucleophilic base, including [HMDS]₂Mg ([14,15] Table 1), HMDSMgCl [241], magnesium bis(diisopropyl)amide [98] with a B- or Al-containing Lewis acid ([13] Table 1). Liebenow et al. [241] found that the Hauser base-derived magnesium hexamethyldisilazide chloride (HMDSMgCl) electrolyte facilitated the Mg stripping and plating in Mg cells.

There was no information found about hazards related to the use of HMDSMgCl.

Table 2 presents some information of hazards related to the use of BF₃, hexamethyldisilazane, and magnesium bis(hexamethyldisilazide).

According to [242], boron trifluoride (BF₃) contains gas under pressure and may explode if heated. It induces severe skin burns and damage of eyes and even serious one. It can irritate the respiratory tract and damage organs via long-term or repeated exposure. It is also detrimental to aquatic life.

As reported in [243], hexamethyldisilazane is a highly flammable liquid and vapor. It is detrimental if swallowed or inhaled and poisonous if in contact with the skin. It is also detrimental to aquatic life, with prolonged effects.

According to [244], magnesium bis(hexamethyldisilazide) induces severe skin burns and damage to the eyes, even serious ones.

As reported in [245], magnesium bis(diisopropyl)amide is a highly flammable liquid and vapor and, in contact with water, releases flammable gas. It may be fatal after swallowing and entering the airways; it is poisonous after inhalation. It induces severe skin burns and damage to the eyes. It may cause respiratory irritation and genetic defects, and probably induce cancer. It is also detrimental to aquatic life, with prolonged effects.

Kim et al. [25] increased the performance of the HMDSMgCl electrolyte by creating molecular species with a [Mg₂(µ-Cl)₃][HMDSAlCl₃] species after adding AlCl₃.

Kim et al. [25] also obtained cell with a purified [Mg₂(µ-Cl)₃][HMDSAlCl₃] within tetrahydrofuran (THF) as an electrolyte, an elemental S/carbon black composite as the cathode, and Mg foil as the anode (Table 1). In addition, the active compound [Mg₂(µ-Cl)₃⸱6THF]+[HMDSAlCl₃]⁻ could only be received from THF [12].

There was no information found about the hazards relative to [Mg₂(µ-Cl)₃][HMDSAlCl₃] and Mg₂(µ-Cl)₃.

Table 2 presents some information about hazards related to the use of tetrahydrofuran. According to [246], it is a highly flammable liquid and vapor. It is detrimental if it is swallowed and suspected of causing cancer. It causes serious eye irritation and may cause respiratory irritation.

Zhao-Karger et al. [90] obtained the electrolytes by a one-step reaction between magnesium bis(hexamethyldisilazide) [(HMDS)₂Mg], AlCl₃ in diglyme, and tetraglyme (Table 1). Such a reaction results in an electrochemically active combination, [Mg₂Cl₃][HMDSAlCl₃], dissolvable both in diglyme and tetraglyme. Additionally, the desirable Mg plating and stripping also occurs when the ionic liquid (IL) N-methyl-N-butyl-piperidinium TFSI (PP14TFSI) is added to the above-mentioned electrolyte.

Such an electrolyte was also studied by ([24,93] Table 1, [91,227]) but with the other sets of cathodes, anodes, and current collectors.

Ford et al. [30] also utilized an electrolyte comprising a mixture of (HMDS)₂Mg and AlCl₃ within THF as a solvent.

There was no information found about hazards relative to N-methyl-N-butyl-piperidinium TFSI, and [Mg₂Cl₃][HMDSAlCl₃].

Table 2 presents some information on hazards related to the use of diglyme and tetraglyme.

According to [247], 2-methoxyethyl ether is a flammable liquid and vapor. It may form explosive peroxides and may damage fertility or an unborn child.

As reported in [248], tetraethylene glycol dimethyl ether can damage an unborn child and probably fertility as well.

Sheng et al. [52] utilized a mixture of Mg(HMDS)₂, AlCl₃, and MgCl₂ (1:2:1) within DEG or TEG as an electrolyte for the Mg–S batteries studied (Table 1).

Zou et al. [28] utilized an Mg-HMDS (mixture of 49 wt.% Mg(HMDS)₂, 38 wt.% AlCl₃, and 13 wt.% MgCl₂ within a tetraethylene glycol dimethyl ether TEGDME) as an electrolyte for the Mg–S batteries investigated (Table 1).

Table 2 contains one hazard related to the use of TEGDME that may damage fertility or an unborn child [249]. As reported in [250], tetraethylene glycol dimethyl ether (TEGDME) causes eye irritation and may cause skin and respiratory tract irritation. It is air-sensitive and hygroscopic.

Gao et al. [22] investigated a cell comprising an electrolyte of 0.1 m (HMDS)₂Mg–2AlCl₃–MgCl₂ with the addition of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), active carbon cloth/elemental S as the cathode and Mg foil as the anode (Table 1).

Zhou et al. [68] also found LiTFSI as an effective additive for Mg–S cells (Table 1).

By adding an excess of metallic Li into the [HMDS]₂Mg-based electrolyte, Zuo et al. [251] obtained an increase in the electrochemical performance of the Mg–S cells (Table 1).

Table 2 presents some information of the hazards related to the use of LiTFSI and Li.

As reported in [252], bis(trifluoromethane)sulfonimide lithium is poisonous when swallowed or in contact with the skin. It induces severe skin burns and damage to the eyes. It can also damage organs via long-term or repeated exposure. It is detrimental to aquatic life, with prolonged effects.

According to [253], contact of Li with water results in the release of flammable gases capable to spontaneous ignition. It also induces severe skin burns and damage to the eyes.

Nuli et al. [97,254] investigated an electrolyte for Mg–S cells comprised of magnesium bis(diisopropylamide) MBA and AlCl₃ dissolved in THF. The electron-rich amide in MBA weakens the anodic stability of the salt, but the addition of AlCl₃ improves the stabilization of the Mg-N bonds in MBA. The molar ratio of MBA and AlCl₃ varied from 2:1 to 1:2 [97].

Zhao et al. [97] also compared the oxidation stability of the 0.25 m MBA–AlCl₃/THF electrolyte with the nucleophilic 0.4 m APC electrolyte, (PhMgCl)₂–AlCl₃/THF, obtaining the better stability of the MBA–2AlCl₃/THF electrolyte than that of the APC electrolyte mating with an Al or SS working electrode.

The electrochemical performance was further increased when it was also dissolved with 1 mol L⁻¹ of LiCl into 0.25 mol L⁻¹ MBA/0.5 mol L⁻¹ of AlCl₃ in THF, effectively limiting the amount of Mg–PSs in the electrolyte [97].

Du et al. [65] developed an organic Mg–B-based (OMBB) electrolyte via a reaction between tris(hexafluoroisopropyl) borate B[HFP]₃, MgCl₂, and excessive Mg powder in DME. The optimal MgCl₂: B[HFP]₃ ratio was equal to 1:2 (Table 1).

There was no information found about hazards relative to organic Mg B-based OMBB electrolyte. Table 2 presents some information about hazards related to the use of B[HFP]₃.

According to [255], tris(2H-hexafluoroisopropyl) borate causes skin irritation, serious eye irritation, and may also cause respiratory irritation.

Ha et al. [21] studied the compatibility of 0.3 m Mg(TFSI)₂ in glyme/diglyme with an S-based cathode in the Mg-CMK/S cell (Table 1).

Similarly, Itaoka et al. [96] investigated Mg–S cells utilizing elemental S and a bis(alkenyl) compound with a crown ether (18-Crown 6-Ether) unit (S-BUMB₁₈C₆) and a linear ether unit (S-UOEE) as cathode materials jointly with an electrolyte comprising Mg(TFSI)₂.

There was no information found about hazards relative to the use of S-BUMB₁₈C₆ and S-UOEE [96]. Table 2 presents some information about hazards related to the use of 18-Crown 6-Ether.

The incompatibility between a glyme-based solvent and Mg(TFSI)₂ induced the development of dendrites on the Mg anode as reported in [256,257]. Mixtures of diglyme and Mg(TFSI)₂ are chemically unstable because of water impurities found in commercial salts [258]. To improve the chemical purity of Mg(TFSI)₂, it can be added to C₈H₁₈Mg [92,257,259].

Li et al. [70] used a small concentration (below 50 × 10⁻³ m) of iodine (I₂) as an additive into an electrolyte comprising Mg(TFSI)₂ within DME as a solvent.

There was no information found about the hazards related to the use of Mg(TFSI)₂:I₂/DME electrolyte.

According to [259], iodine is detrimental after swallowing, inhalation, or contact with skin. It causes skin irritation and serious eye irritation and may cause respiratory irritation. It also damages organs (thyroid gland) via long-term or repeated exposure by swallowing. It is very poisonous to aquatic life.

Table 2 presents some information about hazards related to the use of C₈H₁₈Mg, trifluoromethanesulfonic acid, Mg(TFSI)₂, butane, and Mg(OH)₂.

According to [260], magnesium bis(trifluoromethanesulfonimide) causes severe skin burns and eye damage.

As reported in [261], contact of dibutylmagnesium with air results in a spontaneous fire. Its contact with water results in the release of flammable gases capable of spontaneous ignition. It also induces severe skin burns and damage to the eyes.

According to [262], trifluoromethanesulfonic acid may induce corrosion in contact with metals and is detrimental if swallowed. It induces severe skin burns and damage to the eyes and may cause respiratory irritation.

As reported in [263], butane is a gas of very high flammability. Under pressure, it may explode if heated.

According to [264], magnesium oxide may be detrimental if inhaled, swallowed, or absorbed through the skin. It may cause respiratory tract irritation, skin irritation, and eye irritation.

As reported in [265], magnesium hydroxide causes skin irritation and serious eye irritation. It may also cause respiratory irritation.

According to [266], 18-crown 6-ether is detrimental if swallowed and causes serious eye irritation.

Gao et al. [74] studied the Mg–S/ACC cell with a 1 M Mg(TFSI)₂/MgCl₂/DME electrolyte comprising the MgCl₂ addition (Table 1).

Ford et al. [30] utilized an electrolyte comprising a mixture of MgTFSI₂ and MgCl₂ within DME as a solvent (Table 1).

Sheng et al. [52] reported the use of two mixtures as the electrolytes for the Mg–S batteries studied. The first one comprised Mg(TFSI)₂, MgCl₂ (1:0.8) within DME, DEG, or TEG solvent; the second one comprised Mg(TFSI)₂ and MgCl₂ (1:0.8) within pure DOL and DOL/DME mix (1:3; 1:1; 3:1) solvent (Table 1).

As reported in [267], MgCl₂ releases flammable gases when in contact with water.

According to [268], magnesium chloride hexahydrate causes skin irritation and serious eye irritation, and also may cause respiratory irritation.

As reported in [269], magnesium chloride can irritate the eyes, skin, and respiratory tract, it can damage kidneys and it irritates the gastrointestinal tract. Inhalation of its fumes can induce metal fume fever.

Yang et al. [64] developed a new electrolyte containing magnesium trifluoromethanesulfonate (Mg(CF₃SO₃)₂)–AlCl₃–MgCl₂–anthracene–LiCl dissolved in THF and tetraglyme (Table 1). An Mg–S microporous carbon cell comprising 0.125 m Mg(CF₃SO₃)₂ + 0.25 m AlCl₃ + 0.25 m MgCl₂ + 0.025 m anthracene/THF and tetraglyme (1:1, v:v) electrolyte was studied.

Gao et al. [22] added LiCl and 0.5 M LiCF₃SO₃, respectively, to a 0.125 m Mg(CF₃SO₃)₂ + 0.25 m AlCl₃ + 0.25 m MgCl₂ + 0.025 m anthracene/THF and tetraglyme (1:1, v:v) solution.

Table 2 contains some information about hazards related to the use of anthracene, Mg(CF₃SO₃)₂, and LiCF₃SO₃.

According to [270], magnesium trifluoromethanesulfonate induces severe skin burns and eye damage.

As reported in [271], anthracene is detrimental if swallowed. It causes serious eye irritation and may cause respiratory irritation. It exhibits acute aquatic toxicity, and is very poisonous to aquatic life with prolonged effects.

According to [272], lithium trifluoromethanesulfonate causes skin irritation and serious eye irritation, and may also cause respiratory irritation.

Nakayama et al. [26] utilized an Mg electrolyte composed of magnesium chloride (MgCl₂) and ethyl n-propyl sulfone (EnPS), which was the simplest, non-Grignard, Lewis acid-free electrolyte.

There was no information found about hazards related to the use of EnPS; however, according to [273], propyl sulfone can irritate the eyes, skin, respiratory tract, and digestive tract. As reported in [274], dipropyl sulfone may decompose upon combustion, or in high temperatures, to generate poisonous fume.

7.2.2. Non/Less Corrosive, Nonnucleophilic Electrolytes

Muldoon et al. [225] found that corrosion caused by chlorides in the electroactive species [Mg₂(µ-Cl)₃·6THF] and the unwanted bulky nature of the cations, such as the two octahedrally coordinated Mg atoms linked by three chlorides, forced the use of chloride-free salts for Mg–S cells.

Li et al. ([13] Table 1) obtained a chloride-free electroactive salt, [Mg(THF)₆][AlCl₄]₂, from the reaction of MgCl₂ with two analogues of AlCl₃ in THF and an IL, i.e., N-methyl-N-butyl pyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR14TFSI).

Bi et al. [72] combined MgCl₂/AlCl₃/Mg (ratio of 1:1:1) within a DME (MMAC) electrolyte with IL, such as 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (Pyr14TFSI), obtaining, as result, an MMAC-IL electrolyte of much better performance compared to the MMAC one.

There was no information found about the hazards relative to [Mg(THF)₆][AlCl₄]_2.

According to [275], 1-Butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide exhibits no known hazards. However, as reported in [276], it causes skin irritation and serious eye irritation, and may cause respiratory irritation (Table 2).

The other Lewis acid for the electrolyte of Mg–S cells is also a subject of investigation.

Xu et al. [131] developed a Y-based electrolyte by changing AlCl₃ with YCl₃. This was obtained from the reaction of MgCl₂ and two analogues of YCl₃ with the IL PYR14TFSI and diglyme (Table 1).

According to [277], yttrium trichloride causes skin irritation and serious eye irritation and may cause respiratory irritation (Table 2).

Zuo et al. [278] developed the other two electrolytes, dissolving 0.2–0.8 mol L⁻¹ of AlCl₃ and 0.006–0.024 mol L⁻¹ of TiCl₄ in an ether-based solvent. Moreover, an excess of Mg was introduced with a weight ratio between Mg and the solution equal to 3:10 and 12:10, respectively.

According to [279], titanium tetrachloride is detrimental if swallowed and fatal if inhaled. It induces severe skin burns and potentially severe eye damage. It can also irritate the respiratory tract (Table 2).

One group of noncorrosive electrolytes utilizes weakly coordinating anions (WCAs), which can be applied to the production of novel salts for electrolytes utilized in Mg–S cells [280,281,282].

Zhao-Karger et al. [71] developed a fluorinated magnesium alkoxyborate-based electrolyte. They obtained the conductive salts from the reaction of Mg[BH₄]₂ with fluorinated alcohols (RF-OH) in ethereal solvents (such as DME). By using hexafluoro-2-propanol (hfip), the conductive salt, Mg[B(hfip)₄]₂⸱3 DME was received when solvent has been removed. This type of Mg salt was insensitive to water and air.

Zhao-Karger et al. examined a 0.6 m Mg[B(hfip)₄]₂·3 DME/DME electrolyte [71].

The same group of researchers also used 0.8 m of Mg[B(hfip)₄]₂ in diglyme/tetraglyme as an electrolyte for Mg–S cells with an S/CMK-3 cathode, and an Mg plate anode [71].

These authors also studied the effect of the concentration of conductive salt in the electrolyte, Mg[B(hfip)₄]₂⸱3 DME, on battery cyclability by using ACC-based S composites as cathode materials [66].

According to [283], 1,1,1,3,3,3-hexafluoro-2-propanol causes severe skin burns and potentially serious eye damage, and it probably can damage an unborn child. It can also damage organs via long-term or repeated exposure.

Xiu et al. [284] reported that magnesium tetrakis(hexafluoroisopropyloxy) borate is non-corrosive.

According to [285], Mg[B(hfip)₄]₂ is a non-corrosive electrolyte.

Zhang et al. [67] obtained a so-called B-centered base Mg (BCM) electrolyte from the reaction of tris(2H-hexafluoroisopropyl) borate (THFPB) with MgF₂ within a DME solvent (Table 1). Such an electrolyte was also utilized during studies conducted by ([98] Table 1).

Xu et al. [69] utilized a mixture of Mg(BH₄)₂ and THFPB within a DGM solvent as an electrolyte for the Mg–S battery studied (Table 1).

According to [286], contact of Mg(BH₄)₂ with water results in the release of flammable gases. It is toxic if swallowed, inhaled, or comes into contact with the skin. It also induces severe skin burns and damage to the eyes (Table 2).

There was no information found about hazards relative to boron-centered base magnesium (BCM) electrolyte.

According to [255], the tris(2H-hexafluoroisopropyl) borate causes skin irritation and serious eye irritation and may cause respiratory irritation (Table 2).

Similarly, as reported in [287], magnesium fluoride also causes skin irritation and serious eye irritation and may cause respiratory irritation (Table 2).

According to [288], 1,2-dimethoxyethane is a highly flammable liquid and vapor. It is detrimental if swallowed or inhaled and may also damage fertility or an unborn child (Table 2). It may also form explosive peroxides.

Hintennach [289] modified this electrolyte by the addition of a mixture of two thiobarbituric acid derivatives, including thiobarbital and 2-thiobarbituric acid, with a concentration in the range of 0.01–1.9 wt.%.

There was no information found about the hazards related to the use of such a modified electrolyte. However, according to [290], thiobarbituric acid causes skin, serious eye irritation, and may cause respiratory irritation (Table 2). Additionally, as reported in [291], 2-thiobarbituric acid exhibits no known hazards.

7.3. Summary of Electrolyte Systems for Mg–S Batteries

Various hazards related to the use of materials for electrolytes in Mg–S cells are shown in Figure 11. The highest number of the hazards identified and referred to the hazard group related to the toxic effects on skin. Two sets of twenty hazards identified belonged to the hazard groups related to the toxic or allergic effects on the eyes and respiratory tract, respectively. Only two single hazards identified belonged to the hazard groups related to the generation of genetic defects and cancers, respectively. Only a pair of the hazards identified and referred to the hazard group related to corrosion. Moreover, only three hazards identified belonged to the hazard group related to the generation of damages to organs.

Various electrolyte systems applicable to Mg–S batteries are still being investigated. Their development is limited by their need for compatibility with an S cathode and are strongly affected by the effective syntheses of noncorrosive Mg salts and the use of various solvents and additives. The promising Mg salts include B- or Al-centered weakly coordinating anions. Moreover, polymer-based electrolytes should also be under consideration. However, their incompatibility with the Mg anode and a low Mg ion transfer number is still not resolved. Electrolytes are also the group causing the majority of the hazards related to the Mg–S cells, both due to the number of new types of electrolytes and substances used to produce them. Such hazards vary widely in type and degree of danger, much more so than in the case of the mentioned earlier cathode materials.

Table 1. Materials for components of Mg–S batteries.

Electrolyte	Cell Type	Anode	Separator	Cathode	Current Collector	Ref.
HMDSMgCl:AlCl3/THF	CR2032 coin cell	Mg foil	PTFE	S/C (S/C (61% S, 35% CB, 4% PTFE (bind)) on C substrate)	n.a.	[25]
(HMDS)2Mg:AlCl3/TEG	Swagelok cell	Mg:CB	borosilicate glass fiber	S/CMK (75% S/CMK, 15% Super P, 10% PVdF (bind) NMP or CMC (bind) water)	Inconel 625	[90]
(HMDS)2Mg:AlCl3:LiTFSI/TEG	Swagelok cell	Mg foil	Whatman glass fiber	S/ACC (impregnation of activated carbon cloth with sulfur)	Inconel	[22]
[Mg(THF)6][AlCl4]2 PYR14TFSI/THF	CR2016 coin cells	Mg disk	Celgard 2400	S/NG (S, N-doped GO, Super P, PVDF (bind))	Al	[13]
(HMDS)2Mg:AlCl3/TEG	Swagelok cell	Mg/C pellets	Celgard 2500	S/rGO (75% S/rGO, 15 % Super P, 10% PVdF (bind) NPM)	Inconel 625	[93]
(HMDS)2Mg:AlCl3/TEG	coin cell	Mg foil disc	CNF-coated glass fiber	S/CNF (preactivated CNF matrix filled with S)	CNF	[24]
MgTFSI2-MgCl2-DME	coin-cell	Mg foil disk	glass fiber	S/ACC (impregnation of active carbon cloth with S).	Inconel, Mo, or W laminate layer	[74]
THFPB-MgF2-DME	CR2032 coin cell	Mg foil	glass fiber	S/C (80 % S/C, 10% acetylene black, 10% PVdF (bind) NPM)	SS foil, Ni foil, Cu foil, pyrolytic graphitic film	[67]
B(HFP)3-MgCl2-Mg/DME	CR2032 coin cell	Mg disc	glass microfiber	S/CNTs (80% S-C (S-AMC, S-CNT or S-CMK), 10 % Super P, 10 % PVdF (bind) NMP)	Cu foil	[73]
([Mg(DG)2] [HMDSAlCl3])2/DG	coin cell	Mg	n.a.	S/CNT (80% S/C (8:2), 10% GO/CNT, 10% PVdF (bind) NMP)	n.a.	[15]
PhMgCl:AlCl3/THF	CR2016 coin cell	Mg	ENTEK PE membrane	S/MC (70% S@MC, 20% Super P, 10% PVdF (bind) NMP)	Cu foil	[94]
PhMgCl:AlCl3:LiCl/THF	CR2016 coin cell	Mg	ENTEK PE membrane	S/MC (70% S@MC, 20% Super P, 10% PVdF (bind)-NMP)	Cu foil	[94]
(HMDS)2Mg-AlCl3-LiTFSI-DG	CR2032 coin cell	Mg foil	Whatman glass fiber with/without RGO layer	S/MOFs (70% ZIF (NPs with Zn)-C-S (various S loading), 20% Super P, 10% PVdF (bind) NMP)	SS or Mo	[68]
Mg(BH4)2:THFPB/DGM	coin cell	Mg foil	n.a.	S/C (80% S/C, 10% acetylene black, 10% PVdF (bind) NPM)	Al, GF, SS, Ni, Cu, and Ag	[69]
Mg(TFSI)2:I2/DME	Swagelok cell	Mg foil	glass microfiber	S/ACC	n.a.	[70]
MgCl2:YCl3-PYR14TFSI/DG	CR2032 coin cell	Mg	n.a.	MgPS/G-CNTs (30% MgS8, 60% G-CNT, 10% PVdF (bind)-NMP)	n.a.	[131]
Mg(CF3SO3)2:MgCl2:AlCl3- AT/THF/TG	CR2016 coin cell	Mg ribbon	ENTEK PE	S/MC (80% S@MC, 10% Super P, 10% PVdF (bind)-NPM)	Cu foil	[64]
Mg(CF3SO3)2:MgCl2:AlCl3:LiCl- AT/THF/TG	CR2016 coin cell	Mg ribbon	ENTEK PE	S/MC (80% S@MC, 10% Super P, 10% PVdF (bind)-NPM)	Cu foil	[64]
Mg(CF3SO3)2:MgCl2:AlCl3:LiCF3SO3- AT/THF/TG	CR2016 coin cell	Mg ribbon	ENTEK PE	S/MC (80% S@MC, 10% Super P, 10% PVdF (bind)-NPM)	Cu foil	[64]
THFPB-MgF2-DME	CR2032 coin cell	Mg metallic	glass-wool	S/CB (60% (S8, Cu2S, or CuS), 30% Super P, 10% PVdF (bind)-NMP {- THF for S8})	Cu foil	[98]
MgCl2/EnPS	CR2016 coin cell	Mg	glass fiber	S/C Pellet type (S or MgS, conductive carbon, PTFE (bind)-acetone Sheet type (S or MgS, conductive carbon, SBR, CMC (bind)–water:ethanol)	Ni	[26]
Mg(TFSI)2/glyme/diglyme	CR2032 coin cell	Mg disc	microporous PE film	CMK/S (70 % CMK/S, 20% Super P, 10% PVdF (bind)-NMP)	Al	[21]
Mg[B(hfip)4]2); MgBOR(hfip)/DEG–TEG	Swagelok cell	Mg foil	borosilicate glass fiber	CMK/S (75 wt.% S/CMK, 15 wt.% CB, 10 wt.% CMC (bind)-NMP)	SS	[12]
(Mg/MgCl2/AlCl3 {1:1 ratio}-DME (MMAC)/Pyr14TFSI	coin cell	Mg foil	Whatman glass fiber	CMK/S (80% CMK/S, 10% CB, 10 wt.% PVdF (bind)-NMP)	Mo foil	[72]
Mg(TFSI)2:MgCl2 {1:0.8}-DME, DEG or TEG Mg(TFSI)2:MgCl2 {1:0.8}-pure DOL or DOL:DME {1:3; 1:1 or 3:1} Mg(HMDS)2:AlCl3:MgCl2 {1:2:1}-DEG or TEG	CR2032 coin cell	Mg foil	Whatman glass fiber	CMK/S (80% CMK/S, 10% Super P, 5% NaCMC, 5% SBR (bind)-deionized water)	C-Al foil	[52]
MgTFSI2/MgCl2-DME; MgHMDS2/AlCl3 -THF	CR2032 coin cell	Mg disc	glass fiber or Celgard 2325	ACC/S	SS	[30]
Mg-HMDS (Mg(HMDS)2:AlCl3:MgCl2 {49:38:13}-TEGDME	n.a.	Mg foil	Whatman glass fiber	S/KB/PTFE (95 wt.% S/KB (8:2), 5 wt.% PTFE (bind)-IPA)	SS	[28]
Mg[B(hfip)4]2-3DME	pouch cell	Mg disc	Mix (60 wt.% Mo6S8, 30 wt.% SuperP, 10 wt.% PVDF) on Celgard 2340 or 90 wt.% SuperP and 10 wt.% PVDF	S/C (80 wt.% S/C, 10 wt.% Super P, 10 wt.% PVdF (bind)–NMP); also a variant of mix (90 wt.% S/C, 10 wt.% Mo6S8) instead of pure S/C	Al foil	[29]

Table 1. Materials for components of Mg–S batteries.

Electrolyte	Cell Type	Anode	Separator	Cathode	Current Collector	Ref.
HMDSMgCl:AlCl3/THF	CR2032 coin cell	Mg foil	PTFE	S/C (S/C (61% S, 35% CB, 4% PTFE (bind)) on C substrate)	n.a.	[25]
(HMDS)2Mg:AlCl3/TEG	Swagelok cell	Mg:CB	borosilicate glass fiber	S/CMK (75% S/CMK, 15% Super P, 10% PVdF (bind) NMP or CMC (bind) water)	Inconel 625	[90]
(HMDS)2Mg:AlCl3:LiTFSI/TEG	Swagelok cell	Mg foil	Whatman glass fiber	S/ACC (impregnation of activated carbon cloth with sulfur)	Inconel	[22]
[Mg(THF)6][AlCl4]2 PYR14TFSI/THF	CR2016 coin cells	Mg disk	Celgard 2400	S/NG (S, N-doped GO, Super P, PVDF (bind))	Al	[13]
(HMDS)2Mg:AlCl3/TEG	Swagelok cell	Mg/C pellets	Celgard 2500	S/rGO (75% S/rGO, 15 % Super P, 10% PVdF (bind) NPM)	Inconel 625	[93]
(HMDS)2Mg:AlCl3/TEG	coin cell	Mg foil disc	CNF-coated glass fiber	S/CNF (preactivated CNF matrix filled with S)	CNF	[24]
MgTFSI2-MgCl2-DME	coin-cell	Mg foil disk	glass fiber	S/ACC (impregnation of active carbon cloth with S).	Inconel, Mo, or W laminate layer	[74]
THFPB-MgF2-DME	CR2032 coin cell	Mg foil	glass fiber	S/C (80 % S/C, 10% acetylene black, 10% PVdF (bind) NPM)	SS foil, Ni foil, Cu foil, pyrolytic graphitic film	[67]
B(HFP)3-MgCl2-Mg/DME	CR2032 coin cell	Mg disc	glass microfiber	S/CNTs (80% S-C (S-AMC, S-CNT or S-CMK), 10 % Super P, 10 % PVdF (bind) NMP)	Cu foil	[73]
([Mg(DG)2] [HMDSAlCl3])2/DG	coin cell	Mg	n.a.	S/CNT (80% S/C (8:2), 10% GO/CNT, 10% PVdF (bind) NMP)	n.a.	[15]
PhMgCl:AlCl3/THF	CR2016 coin cell	Mg	ENTEK PE membrane	S/MC (70% S@MC, 20% Super P, 10% PVdF (bind) NMP)	Cu foil	[94]
PhMgCl:AlCl3:LiCl/THF	CR2016 coin cell	Mg	ENTEK PE membrane	S/MC (70% S@MC, 20% Super P, 10% PVdF (bind)-NMP)	Cu foil	[94]
(HMDS)2Mg-AlCl3-LiTFSI-DG	CR2032 coin cell	Mg foil	Whatman glass fiber with/without RGO layer	S/MOFs (70% ZIF (NPs with Zn)-C-S (various S loading), 20% Super P, 10% PVdF (bind) NMP)	SS or Mo	[68]
Mg(BH4)2:THFPB/DGM	coin cell	Mg foil	n.a.	S/C (80% S/C, 10% acetylene black, 10% PVdF (bind) NPM)	Al, GF, SS, Ni, Cu, and Ag	[69]
Mg(TFSI)2:I2/DME	Swagelok cell	Mg foil	glass microfiber	S/ACC	n.a.	[70]
MgCl2:YCl3-PYR14TFSI/DG	CR2032 coin cell	Mg	n.a.	MgPS/G-CNTs (30% MgS8, 60% G-CNT, 10% PVdF (bind)-NMP)	n.a.	[131]
Mg(CF3SO3)2:MgCl2:AlCl3- AT/THF/TG	CR2016 coin cell	Mg ribbon	ENTEK PE	S/MC (80% S@MC, 10% Super P, 10% PVdF (bind)-NPM)	Cu foil	[64]
Mg(CF3SO3)2:MgCl2:AlCl3:LiCl- AT/THF/TG	CR2016 coin cell	Mg ribbon	ENTEK PE	S/MC (80% S@MC, 10% Super P, 10% PVdF (bind)-NPM)	Cu foil	[64]
Mg(CF3SO3)2:MgCl2:AlCl3:LiCF3SO3- AT/THF/TG	CR2016 coin cell	Mg ribbon	ENTEK PE	S/MC (80% S@MC, 10% Super P, 10% PVdF (bind)-NPM)	Cu foil	[64]
THFPB-MgF2-DME	CR2032 coin cell	Mg metallic	glass-wool	S/CB (60% (S8, Cu2S, or CuS), 30% Super P, 10% PVdF (bind)-NMP {- THF for S8})	Cu foil	[98]
MgCl2/EnPS	CR2016 coin cell	Mg	glass fiber	S/C Pellet type (S or MgS, conductive carbon, PTFE (bind)-acetone Sheet type (S or MgS, conductive carbon, SBR, CMC (bind)–water:ethanol)	Ni	[26]
Mg(TFSI)2/glyme/diglyme	CR2032 coin cell	Mg disc	microporous PE film	CMK/S (70 % CMK/S, 20% Super P, 10% PVdF (bind)-NMP)	Al	[21]
Mg[B(hfip)4]2); MgBOR(hfip)/DEG–TEG	Swagelok cell	Mg foil	borosilicate glass fiber	CMK/S (75 wt.% S/CMK, 15 wt.% CB, 10 wt.% CMC (bind)-NMP)	SS	[12]
(Mg/MgCl2/AlCl3 {1:1 ratio}-DME (MMAC)/Pyr14TFSI	coin cell	Mg foil	Whatman glass fiber	CMK/S (80% CMK/S, 10% CB, 10 wt.% PVdF (bind)-NMP)	Mo foil	[72]
Mg(TFSI)2:MgCl2 {1:0.8}-DME, DEG or TEG Mg(TFSI)2:MgCl2 {1:0.8}-pure DOL or DOL:DME {1:3; 1:1 or 3:1} Mg(HMDS)2:AlCl3:MgCl2 {1:2:1}-DEG or TEG	CR2032 coin cell	Mg foil	Whatman glass fiber	CMK/S (80% CMK/S, 10% Super P, 5% NaCMC, 5% SBR (bind)-deionized water)	C-Al foil	[52]
MgTFSI2/MgCl2-DME; MgHMDS2/AlCl3 -THF	CR2032 coin cell	Mg disc	glass fiber or Celgard 2325	ACC/S	SS	[30]
Mg-HMDS (Mg(HMDS)2:AlCl3:MgCl2 {49:38:13}-TEGDME	n.a.	Mg foil	Whatman glass fiber	S/KB/PTFE (95 wt.% S/KB (8:2), 5 wt.% PTFE (bind)-IPA)	SS	[28]
Mg[B(hfip)4]2-3DME	pouch cell	Mg disc	Mix (60 wt.% Mo6S8, 30 wt.% SuperP, 10 wt.% PVDF) on Celgard 2340 or 90 wt.% SuperP and 10 wt.% PVDF	S/C (80 wt.% S/C, 10 wt.% Super P, 10 wt.% PVdF (bind)–NMP); also a variant of mix (90 wt.% S/C, 10 wt.% Mo6S8) instead of pure S/C	Al foil	[29]

Table 2. Hazard statements related to materials utilized in Mg–S batteries.

Element of Mg–S Battery	Material	Class of EC 1272/2008	References
Anode	Mg	H228, H261	[75]
		H228, H252, H261	[77]
	Al2O3	H319, H335, H372	[87]
Separator	CNF	H226, H312 + H332, H319, H360D.	[103]
	TiS2	H261, H315, H319, H335	[107]
Current collector	Al foil	H228, H400	[210]
		H400, H410	[216]
	Al Sheet and Foil (mixture)	H228, H251, H252, H261, H400, H410, H411	[211]
	Graphite	H319, H335, H350i, H373	[217]
	Stainless steel	H242, H300, H310, H317, H331, H332, H351, H410	[213]
		H316, H320, H334, H317, H341, H351, H360/H361, H370, H371, H335, H372, H373, H413	[214]
	Cu	H300, H330, H317, H319, H340, H373, H400	[221]
	Inconel 625 powder	H317, H334, H351, H372	[223]
	N-doped Graphitic Porous Carbon	H351	[227]
	N/S co-doped Graphene powder	H319, H335	[228]
Cathode	MoS2 Powder	H319, H335	[136]
	MoS2	H315, H319, H335	[196]
	MnO2	H302, H332	[141]
	MoO3	H301, H319, H335, H351, H412	[144]
	V2O5	H302, H332, H335, H341, H361d, H372, H411	[142]
	C8H8O4	H302, H315, H319, H335	[145]
	Fullerenes	H315, H319, H351, H335	[147]
	CuF2	H314, H318	[153]
	AgCl	H400, H410	[155]
	Sulfur	H315, H228	[158]
		H303, H313, H315, H333	[159]
	Activated carbon	H252	[170]
		H320, H335	[169]
	Mesoporous Carbon CMK-3	H351	[179]
	Mesoporous Carbon	H351	[180]
	Carbon Nanofiber	H319, H335	[186]
	Carbon Nanotube	H319, H335	[185]
	MgS	H302, H311, H314, H400	[190]
	FeS2	H334, H410	[194]
	SnS2	H315, H319, H335	[195]
	Ni2S3	H317, H341, H350i, H372, H410	[188]
	CoS2	H317, H410	[197]
	O2 (compressed)	H270, H280	[152]
Binder	polyvinylidene fluoride	H315, H319, H335	[230]
	Na carboxymethyl cellulose	H402, H412	[234]
Electrolyte	Tetrahydrofuran	H225, H302, H319, H335, H351	[246]
	AlCl3	H314	[236]
	PhMgCl	H314, H318	[238]
	LiCl	H302, H315, H319	[239]
	BF3	H280, H330, H314, H318, H335, H373, H402	[242]
	Hexamethyldisilazane	H225, H302 + H332, H311, H412	[243]
	Mg bis(hexamethyldisilazide)	H314, H318	[244]
	Mg bis(diisopropyl)amide	H225, H261, H304, H314, H331, H335, H341, H351, H412	[245]
	2-Methoxyethyl ether	H226, H360FD	[247]
	Tetraethylene glycol dimethyl ether	H360Df	[248]
	C2F6LiNO4S	H301, H311, H314, H373, H412	[252]
	Li	H260, H314	[253]
	Anthracene	H302, H319, H335, H400, H410	[271]
	B[HFP]3	H315, H319, H335	[255]
	C8H18Mg	H250, H260, H314	[261]
	Trifluoromethanesulfonic acid	H290, H302, H314, H335	[262]
	Mg(TFSI)2	H314	[260]
	Butane	H220, H280	[263]
	Mg(OH)2	H315, H319, H335	[265]
	18-Crown 6-Ether	H302, H319	[266]
	LiCF3SO3	H315, H319, H335	[272]
	Cl2H12MgO6	H315, H319, H335	[268]
	Mg(CF3SO3)2	H314, H318	[270]
	C11H20F6N2O4S2	H315, H319, H335	[276]
	MgCl2	H261	[267]
	YCl3	H315, H319, H335	[277]
	TiCl4	H302, H314, H318, H330, H335	[279]
	(CF3)2CHOH	H314, H318, H361, H373	[283]
	tris(2H-hexafluoroisopropyl) borate	H315, H319, H335	[255]
	MgF2	H315, H319, H335	[287]
	1,2-dimethoxyethane	H225, H303, H332, H360	[288]
	Thiobarbituric Acid	H315, H319, H335	[290]
	Mg(BH4)2	H261, H301, H311, H331, H314	[286]
	TEGDME	H360	[249]
	Iodine	H302, H312, H315, H319, H332, H335, H372, H400	[259]

Note: H225-Highly flammable liquid and vapor; H226-Flammable liquid and vapor; H228-Flammable solid; H242-Heating may cause a fire; H251-Self-heating, may catch fire; H252-Self-heating substances/mixtures, in large quantities may catch fire; H260-In contact with water releases flammable gases that may ignite spontaneously; H261-Substance and mixture that, in contact with water, emits flammable gas; H270: May cause or intensify fire, oxidizer; H280 Contains gas under pressure, may explode if heated; H290-May be corrosive to metals; H300-Fatal if swallowed; H301-Toxic if swallowed; H302-Harmful if swallowed; H303-May be harmful if swallowed; H304-May be fatal if swallowed and enters airways; H310-Fatal in contact with skin; H311-Toxic in contact with skin; H312 + H332-Harmful in contact with skin or if inhaled; H313-May be harmful in contact with skin; H314-Causes severe skin burns and eye damage; H315-Causes skin irritation; H316-Mild skin irritation; H317-May cause an allergic skin reaction; H-318-Causes serious eye damage; H319-Causes serious eye irritation; H320-Causes eye irritation; H330-Fatal if inhaled; H331-Toxic if inhaled; H332-Harmful if inhaled; H333-May be harmful if inhaled; H334-May cause allergy or asthma symptoms or breathing difficulties if inhaled; H335-May cause respiratory irritation; H340-May cause genetic defects; H341-May cause genetic defects; H350i-May cause cancer by inhalation; H351-Suspected of causing cancer; H360F/D-May damage fertility or an unborn child; H360/H361-May damage fertility or an unborn child; H361d-Suspected of damaging an unborn child; H370-Causes damage to organs; H371-May cause damage to organs; H372-Causes damage to organs through prolonged or repeated exposure; H373-May cause damage to organs through prolonged or repeated exposure; H400-Acute aquatic toxicity; H402-Harmful to aquatic life; H410-Very toxic to aquatic life with long-lasting effects; H411-Toxic to aquatic life with long-lasting effects; H412-Harmful to aquatic life with long lasting effects; H413-May cause long lasting harmful effects to aquatic life.

Table 2. Hazard statements related to materials utilized in Mg–S batteries.

Element of Mg–S Battery	Material	Class of EC 1272/2008	References
Anode	Mg	H228, H261	[75]
		H228, H252, H261	[77]
	Al2O3	H319, H335, H372	[87]
Separator	CNF	H226, H312 + H332, H319, H360D.	[103]
	TiS2	H261, H315, H319, H335	[107]
Current collector	Al foil	H228, H400	[210]
		H400, H410	[216]
	Al Sheet and Foil (mixture)	H228, H251, H252, H261, H400, H410, H411	[211]
	Graphite	H319, H335, H350i, H373	[217]
	Stainless steel	H242, H300, H310, H317, H331, H332, H351, H410	[213]
		H316, H320, H334, H317, H341, H351, H360/H361, H370, H371, H335, H372, H373, H413	[214]
	Cu	H300, H330, H317, H319, H340, H373, H400	[221]
	Inconel 625 powder	H317, H334, H351, H372	[223]
	N-doped Graphitic Porous Carbon	H351	[227]
	N/S co-doped Graphene powder	H319, H335	[228]
Cathode	MoS2 Powder	H319, H335	[136]
	MoS2	H315, H319, H335	[196]
	MnO2	H302, H332	[141]
	MoO3	H301, H319, H335, H351, H412	[144]
	V2O5	H302, H332, H335, H341, H361d, H372, H411	[142]
	C8H8O4	H302, H315, H319, H335	[145]
	Fullerenes	H315, H319, H351, H335	[147]
	CuF2	H314, H318	[153]
	AgCl	H400, H410	[155]
	Sulfur	H315, H228	[158]
		H303, H313, H315, H333	[159]
	Activated carbon	H252	[170]
		H320, H335	[169]
	Mesoporous Carbon CMK-3	H351	[179]
	Mesoporous Carbon	H351	[180]
	Carbon Nanofiber	H319, H335	[186]
	Carbon Nanotube	H319, H335	[185]
	MgS	H302, H311, H314, H400	[190]
	FeS2	H334, H410	[194]
	SnS2	H315, H319, H335	[195]
	Ni2S3	H317, H341, H350i, H372, H410	[188]
	CoS2	H317, H410	[197]
	O2 (compressed)	H270, H280	[152]
Binder	polyvinylidene fluoride	H315, H319, H335	[230]
	Na carboxymethyl cellulose	H402, H412	[234]
Electrolyte	Tetrahydrofuran	H225, H302, H319, H335, H351	[246]
	AlCl3	H314	[236]
	PhMgCl	H314, H318	[238]
	LiCl	H302, H315, H319	[239]
	BF3	H280, H330, H314, H318, H335, H373, H402	[242]
	Hexamethyldisilazane	H225, H302 + H332, H311, H412	[243]
	Mg bis(hexamethyldisilazide)	H314, H318	[244]
	Mg bis(diisopropyl)amide	H225, H261, H304, H314, H331, H335, H341, H351, H412	[245]
	2-Methoxyethyl ether	H226, H360FD	[247]
	Tetraethylene glycol dimethyl ether	H360Df	[248]
	C2F6LiNO4S	H301, H311, H314, H373, H412	[252]
	Li	H260, H314	[253]
	Anthracene	H302, H319, H335, H400, H410	[271]
	B[HFP]3	H315, H319, H335	[255]
	C8H18Mg	H250, H260, H314	[261]
	Trifluoromethanesulfonic acid	H290, H302, H314, H335	[262]
	Mg(TFSI)2	H314	[260]
	Butane	H220, H280	[263]
	Mg(OH)2	H315, H319, H335	[265]
	18-Crown 6-Ether	H302, H319	[266]
	LiCF3SO3	H315, H319, H335	[272]
	Cl2H12MgO6	H315, H319, H335	[268]
	Mg(CF3SO3)2	H314, H318	[270]
	C11H20F6N2O4S2	H315, H319, H335	[276]
	MgCl2	H261	[267]
	YCl3	H315, H319, H335	[277]
	TiCl4	H302, H314, H318, H330, H335	[279]
	(CF3)2CHOH	H314, H318, H361, H373	[283]
	tris(2H-hexafluoroisopropyl) borate	H315, H319, H335	[255]
	MgF2	H315, H319, H335	[287]
	1,2-dimethoxyethane	H225, H303, H332, H360	[288]
	Thiobarbituric Acid	H315, H319, H335	[290]
	Mg(BH4)2	H261, H301, H311, H331, H314	[286]
	TEGDME	H360	[249]
	Iodine	H302, H312, H315, H319, H332, H335, H372, H400	[259]

Note: H225-Highly flammable liquid and vapor; H226-Flammable liquid and vapor; H228-Flammable solid; H242-Heating may cause a fire; H251-Self-heating, may catch fire; H252-Self-heating substances/mixtures, in large quantities may catch fire; H260-In contact with water releases flammable gases that may ignite spontaneously; H261-Substance and mixture that, in contact with water, emits flammable gas; H270: May cause or intensify fire, oxidizer; H280 Contains gas under pressure, may explode if heated; H290-May be corrosive to metals; H300-Fatal if swallowed; H301-Toxic if swallowed; H302-Harmful if swallowed; H303-May be harmful if swallowed; H304-May be fatal if swallowed and enters airways; H310-Fatal in contact with skin; H311-Toxic in contact with skin; H312 + H332-Harmful in contact with skin or if inhaled; H313-May be harmful in contact with skin; H314-Causes severe skin burns and eye damage; H315-Causes skin irritation; H316-Mild skin irritation; H317-May cause an allergic skin reaction; H-318-Causes serious eye damage; H319-Causes serious eye irritation; H320-Causes eye irritation; H330-Fatal if inhaled; H331-Toxic if inhaled; H332-Harmful if inhaled; H333-May be harmful if inhaled; H334-May cause allergy or asthma symptoms or breathing difficulties if inhaled; H335-May cause respiratory irritation; H340-May cause genetic defects; H341-May cause genetic defects; H350i-May cause cancer by inhalation; H351-Suspected of causing cancer; H360F/D-May damage fertility or an unborn child; H360/H361-May damage fertility or an unborn child; H361d-Suspected of damaging an unborn child; H370-Causes damage to organs; H371-May cause damage to organs; H372-Causes damage to organs through prolonged or repeated exposure; H373-May cause damage to organs through prolonged or repeated exposure; H400-Acute aquatic toxicity; H402-Harmful to aquatic life; H410-Very toxic to aquatic life with long-lasting effects; H411-Toxic to aquatic life with long-lasting effects; H412-Harmful to aquatic life with long lasting effects; H413-May cause long lasting harmful effects to aquatic life.

8. Handling of Mg–S Battery Materials with Hazards Related to Their Use

In addition to the rather natural tendency to avoid (what is sometimes impossible) and minimize direct contact with hazardous substances, a few general recommendations can be made, as have been discussed in the many reference safety data sheets also presented in this review.

• In contact with flammable substances, it can be necessary to wear a self-contained breathing apparatus in pressure-demand, Mine Safety and Health Administration/National Institute for Occupational Safety & Health (MSHA/NIOSH) approved, or the equivalent one, and full protective gear;
• In the case of fire occurrence, it is needed to use the appropriate extinguishing media, including water, dry chemicals, chemical foam, or alcohol-resistant foam;
• If the substance causes, or may cause, irritation or allergy to the eyes, it is required to wear appropriate protective eyeglasses or chemical safety goggles as described by the Occupational Safety and Health Administration (OSHA’s) eye and face protection regulations in 29 Code of Federal Regulations (CFR) 1910.133 or European Standard EN166;
• If the substance causes or may cause irritation or allergy to the skin, it is needed to wear appropriate protective gloves to prevent skin exposure. Moreover, it is necessary to wear appropriate protective clothing to prevent skin exposure;
• If the substance causes, or may cause, irritation or allergy of the respiratory tract, and particularly if the exposure limit can be exceeded, it is required to use a NIOSH/MSHA or European Standard EN 149 approved respirator;
• If the substance causes, or may cause, irritation or allergy of the gastrointestinal tract, it is necessary to use good personal hygiene practices, including washing hands before eating, drinking, smoking, or using the toilet;
• If spills or leaks of a dangerous substance may occur, it is needed to absorb the spill with an inert material (e.g., vermiculite, sand, or earth), then place it in a suitable container. It is also necessary to clean up spills immediately, following precautions in the Protective Equipment section, and provide an adequate intensity of ventilation;
• When in contact with a hazardous substance, it is necessary to wash thoroughly after handling. Before the planned reuse, it is needed to remove contaminated or soiled clothing and wash them.

Usually, hazardous substances should be stored in a cool, dry, well-ventilated area away from incompatible substances. The containers used for the storage of such substances should be kept tightly closed.

The use of various materials, particularly in the case of the Mg–S cells, is always associated with identified, partly identified, or non-identified hazards. This aspect can be significant in relation to the further recycling of such materials [292].

To complete the hazard identification, it is needed to collect, up to reaching completeness, information in the following three categories:

• Chemical identity;
• Physical and chemical properties;
• Health effects.

The main sources of information related to chemical identification comprise the following:

• Company records;
• SDSs and product safety bulletins from manufacturers or suppliers;
• OSHA chemical sampling information pages;
• The Merck Index [293];
• ChemID;
• Trade associations’ documents.

The main sources of information related to the physical and chemical properties comprise the following:

• Fire Protection Guide to Hazardous Materials [294];
• USA Department of Transportation Emergency Response Guidebook [295];
• OSHA Occupational Chemical Database [296];
• Hazardous Substances Data Bank (HSDB) [297];
• Product safety bulletins from manufacturers or suppliers;
• National Institute for Occupational Safety and Health (NIOSH) documents [298],
• NIOSH Pocket Guide to Chemical Hazards [299],
• International Chemical Safety Cards [300],
• OECD eChemPortal [301],
• The Merck Index [293],
• CRC Handbook of Chemistry and Physics [302],
• Sax’s Dangerous Properties of Industrial Materials [303],
• Bretherick’s Handbook of Reactive Chemicals Hazards [304],
• Trade associations’ documents.

Some recommended reference sources for health effects include:

• Frank R. Lautenberg Chemical Safety for the 21st Century Act [305];
• Company-sponsored research reports;
• SDSs and product safety bulletins from manufacturers and suppliers;
• OSHA Occupational Chemical Database [296];
• Hazardous Substances Data Bank (HSDB) [297];
• National Institute of Occupational Safety and Health (NIOSH) documents [298];
• NIOSH Pocket Guide to Chemical Hazards [299];
• Centers for Disease Control and Prevention (CDC) documents [306];
• Agency for Toxic Substances and Disease Registry (ATSDR) documents [307];
• International Chemical Safety Cards [300];
• NIOSH Registry of Toxic Effects of Chemical Substances (RTECS) [308];
• OSHA chemical sampling information pages;
• IARC Monographs on the Identification of Carcinogenic Hazards to Humans [309];
• NTP Annual Report on Carcinogens [310];
• ACGIH Threshold Limit Values (TLVs) and Biological Exposure Indices (BEIs) [311];
• OECD eChemPortal [301];
• Hawley’s Condensed Chemical Dictionary [312];
• Sax’s Dangerous Properties of Industrial Materials [303];
• Trade associations’ documents.

From the point of view of the further development of the materials used to produce Mg–S batteries, it is important to deal with material mixtures (materials of cathodes, separators, and electrolytes) because each material included in the mixture creates different hazards separately or together with other components of the mixture. The procedure for dealing with such mixtures, and for determining their resultant hazards, is described in [313].

Particularly important and useful for the determination of hazards of mixtures are those determined for several hazard classes for the classified ingredients of the mixtures.

It can be expected that further types of materials will be successively involved in the production of new Mg–S batteries, bringing new or already identified hazards related to their use of these materials. Therefore, it is important to subject each new, or existing, material for which such hazards have not been identified, so far, to a certain group of identification tests. Such identification tests include experimental studies of chemical reactions with various active substances, in particular substances modeling aggressive environmental impacts (oxidation and corrosion), and simulation tests in models based on the mixture rule. In addition, identification studies include in vitro studies on mammalian cell lines [314,315], and in vivo studies in mouse, rat, and rabbit models [316,317] for the toxic and allergic effects on skin, eyes, digestive and respiratory systems, pregnancy, cancer generation, and the selection of appropriate therapies. Using software [318], these results can be extrapolated to different groups of people and their organs. However, clinical trials will be required over a longer period. Having the results of these studies for individual component materials, it will be possible to estimate their impact on humans and animals if they are used as components of mixtures in accordance with the methodology described in [313]. Furthermore, the cut-off values and the concentration limits can also be determined using these tests, especially in vivo tests.

9. Methods

Using ‘logical’ database searches, the set of publications (literature) from electronic databases including ‘ISI Web of Science’, ‘Scopus’, and ‘Google Scholar’ was obtained. The period studied in the literature on Mg–S cells ranged from 1974 to 2022. Mostly, articles published in English are comprised, as they are widely accessible to readers around the world. Only a few were published in Germany.

10. Summary

Various hazards related to the use of materials in Mg–S cells are presented in Figure 12. It is visible that the highest number of the hazards identified belonged to the hazard group related to the toxic effects on skin. Two other hazard groups are also characterized by many hazards identified, namely, those related to toxic or allergic effects on the eyes and respiratory tract, respectively. The lowest number of the hazards identified belonged to the hazard group related to corrosion. Additionally, only five of the hazards identified referred to in the hazard group related to the generation of genetic defects. Two other groups are also characterized by a relatively small number of identified hazards, equal to nine—the first one related to the generation of cancers and the second one related to the generation of damages to fertility, or an unborn child, respectively.

The ratio of the number of the hazards identified related to the single component of the Mg–S cell and the total number of the hazards identified related to the Mg–S cell versus the Mg–S related group of hazards is shown in Figure 13. The highest value of such a ratio characterizes the electrolyte-related group of the hazards identified. Additionally, the relatively high values of such a ratio were obtained for the cathode-related and current collector-related groups of the hazards identified.

Therefore, when developing a new Mg–S cell configuration, it can be carefully assumed that the group of the life-related hazards characterized by a whole Mg–S cell is well determined by those related to the electrolyte, cathode, and current collector of such a cell.

The Mg–S batteries utilized a lot of materials for their anodes, separators, current collectors, binders, cathodes, and electrolytes. These materials pose various hazards related to their use. The most numerous groups of hazards are posed by the material groups of cathodes and electrolytes. Even for the two latter groups, such hazards vary widely in type and degree of danger. One group of the mentioned hazards is related directly to the human body, involving the eyes, skin, respiratory and digestive tract, and also fertility or an unborn child. The other group of such hazards is related to aquatic life. Yet another group is related to the flammability of materials or the release of flammable or toxic gases by them. Interestingly, some of the described hazards are similar to those found in the case of Li–S batteries’ cathodes, separators, or binders, but some are clearly different, as in the case of anodes [319]. Additionally, the popular Celgard separators are applicable also for Li-ion batteries [320], which environmental and human health impacts were discussed in [321]. Moreover, it should be postulated that pregnant women should not be involved in the production or recycling processes related to Mg–S cells.