battery

Abstract

An electrochemical cell comprising: an anode comprising a lithium or sodium metal, or a lithium or sodium metal alloy; an ion-conducting cathode comprising an electroactive sulfur material; and a liquid electrolyte comprising one or more lithium salts or one or more sodium salts, wherein the polysulfide solubility of the electrolyte is less than 500 mM.

Description

Technology Field

[0001] The present invention relates to a battery, in particular to a lithium-sulfur battery. Background Technology

[0002] Rechargeable batteries, such as lithium-sulfur batteries, can be recharged by applying an external current to the battery. This type of rechargeable battery has a wide range of applications. Important considerations when developing lithium-sulfur rechargeable batteries include weight and volumetric energy, cycle life, and ease of battery assembly. Another example of a rechargeable battery is the sodium-sulfur battery.

[0003] A typical lithium-sulfur battery comprises an anode (negative electrode) formed of lithium metal or a lithium metal alloy and a cathode (positive electrode) formed of elemental sulfur or other electroactive sulfur materials. Sulfur or other electroactive sulfur-containing materials may be mixed with electrically conductive materials, such as carbon, to improve electrical conductivity.

[0004] Traditionally, high-energy lithium-sulfur batteries use a liquid electrolyte. The cathode typically contains carbon mixed with (or containing) sulfur. During discharge, the electroactive sulfur material (e.g., elemental sulfur) is converted into lithium polysulfide species Sn 2-It is reduced to (n≥2, e.g., n = 2 to 8). This species is generally soluble in the electrolyte. In the second stage of discharge, the polysulfide species is reduced to insoluble lithium sulfide Li2S. When the battery is charged, this two-stage mechanism occurs in reverse, where lithium sulfide is oxidized to lithium polysulfide species and then oxidized to sulfur. However, polysulfide shuttling due to the high solubility of polysulfides in the electrolyte can affect cycling performance and reduce Coulombic efficiency. In particular, during the cycling of traditional lithium-sulfur batteries, the concentration of polysulfide species increases within traditional electrolyte formulations due to the high solubility of polysulfide species in the electrolyte. This process complicates the operation of traditional lithium-sulfur batteries, reduces available capacity (usable energy), shortens cycle life, and decreases Coulombic efficiency.

[0005] One alternative to traditional lithium-sulfur batteries is the all-solid-state lithium-sulfur (ASSLiS) battery. This battery contains a solid electrolyte, such as a solid-state polymer or ceramic electrolyte, instead of the liquid electrolyte found in "traditional" lithium-sulfur batteries. The use of a solid electrolyte can be advantageous in terms of safety and volumetric-to-grain energy density. Using an all-solid-state battery avoids the formation of polysulfide species that solvate within the liquid electrolyte, thereby avoiding problems associated with the presence of these species. Consequently, all-solid-state lithium-sulfur (ASSLiS) batteries can theoretically achieve high gravimetric and volumetric energies. However, ASSLiS batteries face major issues, such as poor interfacial contact between the electrolyte and the electrodes.

[0006] In light of the above, there remains a need for high-energy lithium-sulfur batteries capable of solving the above problem.

[0007] Before describing specific examples of the invention, it should be understood that the present disclosure is not limited to the specific batteries, methods, or materials disclosed herein. It should also be understood that the terms used herein are for describing specific examples and are not intended to be limiting, and the scope of protection will be defined by the claims and their equivalents.

[0008] In describing and claiming the battery and method of the present invention, the following terms will be used: the singular form includes the plural form unless the context clearly indicates otherwise. Thus, for example, "cathode" includes a reference to one or more of these elements.

[0009] According to one aspect of the present invention, an electrochemical cell comprising the following is provided:

[0010] An anode comprising lithium or sodium metal, or a lithium or sodium metal alloy;

[0011] An ion-conducting cathode containing an electroactive sulfur material; and

[0012] A liquid electrolyte comprising one or more lithium salts or one or more sodium salts, wherein the polysulfide solubility of the electrolyte is less than 500 mM.

[0013] The battery according to the present invention combines the advantages associated with traditional lithium-sulfur batteries and all-solid-state lithium-sulfur batteries. First, using a low-porous solid-state cathode (i.e., a cathode structure having a low interfacial contact area between the electrolyte component and the cathode) together with a redox-active sulfur component that undergoes reduction and oxidation reactions without the formation of soluble intermediate polysulfide species can produce a high-energy lithium-sulfur battery. Second, using a liquid electrolyte with low solubility for lithium polysulfide species can ensure good interfacial contact between the electrolyte and each electrode. The advantages derived from this type of hybrid liquid / solid-state battery include high weight- and volumetric energy, high cycle life, improved safety characteristics, improved Coulomb efficiency, and a voltage profile favorable for BMS (Battery Management System) control.

[0014] According to another aspect of the present invention, an electrochemical cell comprising the following is provided:

[0015] An anode comprising lithium or sodium metal, or a lithium or sodium metal alloy;

[0016] An ion-conducting cathode containing an electroactive sulfur material; and

[0017] A liquid electrolyte comprising one or more lithium salts or one or more sodium salts, wherein the concentration of one or more lithium salts or sodium salts in the electrolyte is 75% or more of the saturation concentration of the electrolyte.

[0018] electrochemical cell

[0019] The electrochemical cell according to the present invention may be a lithium-sulfur cell. Another example of the electrochemical cell according to the present invention is a sodium-sulfur cell. The lithium-sulfur cell may include a lithium anode and a cathode comprising an electroactive sulfur material, for example, elemental sulfur. The electrolyte may include at least one solvent or ionic liquid and a salt, for example, a lithium salt. In another example, the electrochemical cell is a sodium-sulfur cell. When the electrochemical cell is a sodium-sulfur cell, the cell may include a sodium anode and a cathode comprising an electroactive sulfur material, for example, elemental sulfur. The electrolyte may include at least one solvent or ionic liquid and a salt, for example, a sodium salt.

[0020] Anode

[0021] In a lithium-sulfur battery, the lithium anode comprises an electroactive substrate containing lithium. The electroactive substrate may comprise lithium metal or a lithium metal alloy. Preferably, the electroactive substrate comprises a foil formed of lithium metal or a lithium metal alloy. Examples of lithium alloys include lithium aluminum alloys, lithium magnesium alloys, and lithium boron alloys. Preferably, a lithium metal foil is used. If the battery is a sodium-sulfur battery, the anode comprises sodium metal or a sodium metal alloy. Preferably, the anode comprises a foil formed of sodium metal or a sodium metal alloy. Examples of sodium alloys include sodium aluminum alloys, sodium magnesium alloys, and sodium boron alloys. Preferably, a sodium metal foil is used.

[0022] cathode

[0023] The cathode of an electrochemical cell contains an electroactive sulfur material. The cathode is ion-conductive. That is, in the solid state, it contains ions (i.e., alkali cations, Li). + or Na +It enables the conduction of ). Accordingly, the electrochemistry of the battery according to the present invention can proceed with little or no dissolution of active species, such as polysulfides, in the electrolyte. In one embodiment, 10% or less, preferably 5% or less, e.g. 2% or less of the polysulfides formed during charging / discharging may be dissolved in the electrolyte. In one embodiment, the polysulfides are not dissolved in the electrolyte. The chemistry associated with charging and discharging the battery according to the present invention is similar to that observed in a full-solid-state lithium-sulfur battery in which polysulfides are not dissolved in the electrolyte.

[0024] Electroactive sulfur materials may include elemental sulfur, sulfur-based organic compounds, sulfur-based inorganic compounds, and sulfur-containing polymers. Preferably, elemental sulfur or Li2S is used. In one embodiment, the cathode comprises a sulfur-carbon complex. The cathode may also comprise an electroactive sulfur material that may be ion-conductive. This material may comprise additional elements such as Li, Na, Mg, P, N, Si, Ge, Ti, Zr, Sn, B, A, F, Cl, Br, I, O, or combinations thereof, in addition to sulfur. Examples of ion-conductive sulfur-containing materials are LGPS, Li3PS4, or Li7P3S 11 It includes. In one embodiment, the cathode may also include an ion-conductive sulfur-carbon composite.

[0025] The cathode may further comprise a solid electrically conductive material. The solid electrically conductive material may be any suitable conductive material. Preferably, this solid electrically conductive material may be formed of carbon. Examples include carbon black, carbon fibers, graphene, reduced graphene oxide, and carbon nanotubes. Other suitable materials include metals (e.g., flakes, fillers, and powders) and conductive polymers. Examples of conductive polymers include polypyrrole, polythiophene, polyaniline, polyacetylene, polyphenylene vinylene, and poly(3,4-ethylenedioxythiophene). Preferably, carbon black is used. In one embodiment, if the cathode comprises a sulfur-carbon composite, the additional solid electrically conductive material may not be present in the cathode.

[0026] The cathode is an ion-conducting material, particularly solid Li + or Na + It may additionally include an ion conductor. The ion-conducting material is 10 at 25°C -7 Greater than S / cm, e.g., 10 -6 It can have bulk ionic conductivity greater than S / cm. The cathode is Li3PS4 or Li x P y S zWhen including an electroactive ion-conducting material such as, there may be no additional ion-conducting material. In some examples, the lithium-ion conductive material includes a ceramic material. The ceramic material may have a crystalline, polycrystalline, partial crystalline, or amorphous structure. Suitable ceramic materials include, but are not limited to, oxides, carbonates, nitrides, carbides, sulfides, oxysulfides, and / or oxynitrides of metals and / or metalloids. In some cases, the ceramic material includes lithium. Non-limiting examples of suitable solid-state electrolytes having sufficient ionic conductivity include lithium-containing ceramic materials, such as lithium oxides (e.g., Li2O, LiO, LiO2, LiRO2, where R is scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and / or lutetium), lithium carbonates (Li2CO3), lithium nitrides (e.g., Li3N), lithium oxysulfides, lithium oxynitrides, lithium garnet-type oxides (e.g., Li7La3Zr2O2). 12 ), Li 10 GeP2S 12 It can be produced by combinations of various lithium compounds, such as lithium phosphate oxynitride, lithium silicosulfide, lithium germanosulfide, lithium lanthanum oxide, lithium titanium oxide, lithium borosulfide, lithium aluminosulfide, lithium phosphosulfide, lithium silicate, lithium borate, lithium aluminate, lithium phosphate, lithium halides, and combinations thereof. In certain cases, the ceramic material comprises lithium oxide, lithium nitride, or lithium oxysulfide. In some embodiments, the ceramic comprises carbonates and / or carbides.

[0027] In some embodiments, the lithium-ion-conducting material may be selected from species capable of providing electron pairs (e.g., Lewis bases). Examples of suitable electron-donating materials include lithium oxides (e.g., Li2O, LiO, LiO2, LiRO2, where R is scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and / or lutetium), lithium carbonates (Li2CO3), lithium nitrides (e.g., Li3N), lithium oxysulfides, lithium oxynitrides, lithium garnet-type oxides (e.g., Li7La3Zr2O2). 12 ), Li 10 GeP2S 12 Lithium phosphate oxynitride, lithium silicosulfide, lithium germanosulfide, lithium lanthanum oxide, lithium titanium oxide, lithium borosulfide, lithium aluminosulfide, lithium phosphosulfide, lithium silicate, lithium borate, lithium aluminate, lithium phosphate, lithium halides, and combinations thereof are included but not limited thereto.

[0028] Examples of ceramic materials that can be used as lithium ion conductive materials are Li-containing oxides, for example, Li 3.3 La 0.56 TiO3; Nasicon structure (e.g., LiTi(PO4)3); LiSICON (Li 14 Zn(GeO4)4); Li 10 GeP2S 12 ; Garnet: Li7La3Zr2O 12　; Li2O; other oxides, e.g., Al2O3, TiO2, ZrO2SiO2, ZnO; sulfides, e.g., Li2S-P2S5; antiperovskites, e.g., Li3OCl; hydrides, e.g., LiBH4, LiBH4-LiX (X=Cl, Br, I), LiNH, LiNH2, Li3AlH6, Li2NH; borates or phosphates, e.g., Li2B4O7, Li3PO4, LiPON; carbonates or hydroxides, e.g., Li2CO3, LiOH; fluorides, e.g., LiF; nitrides, e.g., Li3N; sulfides, e.g., lithium borosulfide, lithium phosphosulfide, lithium aluminosulfide, oxysulfide, praseodymium oxide. At least one of the above ceramic materials or a combination thereof may be used. In a sodium-sulfur battery, a sodium ion equivalent of such a conductive material may be used.

[0029] In some examples, the lithium-ion conductive material may be formed from an intrinsically ion-conductive polymer material, such as Nafion. Alternatively, 10 -7Polymers mixed with lithium (or sodium) salts capable of achieving bulk conductivity of S / cm or higher may also be used. Examples of suitable polymers include EO-based polymers (e.g., PEO); acrylate-based polymers (e.g., PMMA); polyamines (polyethyleneimine); siloxanes (poly(dimethylsiloxane)); polyheteroaromatic compounds (e.g., polybenzimidazole); polyamides (e.g., nylon); polyimides (e.g., Kapton); and polyvinyls (e.g., polyacrylamide, poly(2-vinylpyridine), poly(N-vinylpyrrolidone), poly(methylcyanoacrylate), poly(vinyl acetate), poly(vinyl alcohol), poly(vinyl chloride), poly(vinyl fluoride)). It includes inorganic polymers (e.g., polysilane, polysilazane, polyphosphazene, polyphosphonate), polyurethane, polyolefin (e.g., polypropylene, polytetrafluoroethylene), and polyester (e.g., polycarbonate, polybutylene terephthalate). In one embodiment, a co-block polymer such as Nafion may be used. One or more of the above polymer materials or a combination thereof may be used. In one embodiment, the cathode comprises ceramic particles combined with one or more ion-conducting polymers.

[0030] At the cathode, both electrons and ions can be conducted in a solid state. This allows electrochemical reactions at the cathode during charging or discharging to occur in a solid state without the need to form soluble intermediates in the form of polysulfide species.

[0031] The cathode may additionally include a binder for bonding the cathode components together. The cathode may also bond the cathode components to an electrically conductive current collector. By doing so, the binder may provide improved mechanical rigidity to the cathode or improve the processability of the cathode. The binder may be a polymeric binder, for example, a polyether, such as poly(ethylene oxide), polyethylene glycol, polypropylene glycol, polytetramethylene glycol (PTMG), or polytetramethylene ether glycol (PTMEG).

[0032] The binder may be selected from halogenated polymers, and more preferably from fluorinated polymers. Examples of suitable binders include poly(vinylidene fluoride) (PVDF) (preferably, α-form), poly(trifluoroethylene) (PVF3), polytetrafluoroethylene (PTFE), copolymers of vinylidene fluoride and hexafluoropropylene (HFP) or trifluoroethylene (VF3) or tetrafluoroethylene (TFE) or chlorotrifluoroethylene (CTFE), fluoroethylene / propylene (FEP) copolymers, copolymers of ethylene and fluoroethylene / propylene (FEP) or tetrafluoroethylene (TFE) or chlorotrifluoroethylene (CTFE), perfluoropropyl vinyl ether (PPVE), perfluoroethyl vinyl ether (PEVE), and copolymers of ethylene and perfluoromethyl vinyl ether (PMVE), or blends thereof.

[0033] Other examples of suitable binders include polyacrylonitrile, polyurethane, PVDF-acrylic copolymer; polyacrylic acid, polyimide, and polyvinyl alcohol. Additional suitable binders include rubber (e.g., styrene butadiene rubber), cellulose (e.g., carboxymethyl cellulose), or gelatin.

[0034] In some examples, the binder is selected from at least one of PEO, PVDF, Nafion, polypyrrole, polythiophene, polyaniline, polyacetylene, polyphenylene vinylene, poly(3,4-ethylenedioxythiophene), and polyphenylene sulfide. For example, the binder may include polyethylene oxide or PVDF.

[0035] The cathode may contain 0.05 to 20 weight%, preferably 0.5 to 10 weight%, for example 1 to 5 weight%, for example 2 to 3 weight% of a binder based on the total weight of the cathode.

[0036] electrolytes

[0037] The electrolyte according to the present invention may be a liquid electrolyte. A liquid electrolyte provides excellent physical contact between the electrolyte and the electrodes because the electrolyte wets the cathode and the anode. This is in contrast to all-solid-state batteries, where the solid electrolyte lacks wettability and cannot provide satisfactory interfacial contact between the electrolyte and the anode / cathode. This becomes a problem, particularly during the cycling of an ASSLiS battery, when volume changes occur at the anode and cathode due to reactions occurring during charging or discharging. As a result of these volume changes, it is very difficult to maintain close contact at the anode-electrolyte and cathode-electrolyte interfaces.

[0038] Any suitable solvent system, or a liquid or gel, or a mixture of liquid and / or gel, may be used as the electrolyte. The electrolyte is a liquid over an operating temperature range of the battery that may be -30 to 120°C, preferably -10 to 90°C, for example 0 to 60°C. The operating pressure of the battery may be 5 mbar to 100 bar, preferably 10 mbar to 50 bar, for example 100 mbar to 20 bar. In one example, the battery may be operated at room temperature and pressure. According to the present invention, a high concentration of the electrolyte means that the electrolyte has a lower vapor pressure than a standard electrolyte. Therefore, the battery according to the present invention can exhibit better performance than a standard lithium-sulfur battery at low pressure. The liquid electrolyte may be a gel electrolyte.

[0039] Organic solvents suitable for use in electrolytes include ethers (e.g., linear ether, diethyl ether (DEE), deglaime (2-methoxyethyl ether), tetraglaime, tetrahydrofuran, 2-methyltetrahydrofuran, dimethoxyethane (DME), dioxolane (DIOX)); carbonates (e.g., dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, methylpropyl carbonate, ethylene carbonate (EC), propylene carbonate (PC)); sulfones (e.g., dimethyl sulfone (DMS), ethyl methyl sulfone (EMS), tetramethyl sulfone (TMS)); esters (e.g., methyl formate, ethyl formate, methyl propionate, methylpropyl propionate, ethyl propyl propionate, ethyl acetate, and methyl butyrate); and ketones (e.g., methyl ethyl ketone). Nitriles (e.g., acetonitrile, propionitrile, isobutyronitrile); amides (e.g., dimethylformamide, dimethylacetamide, hexamethylphosphoamide, N,N,N,N-tetraethylsulfamide), lactams / lactones (e.g., N-methyl-2-pyrrolidone, butyrolactone), ureas (e.g., tetramethylurea), sulfoxides (e.g., dimethyl sulfoxide); phosphates (e.g., trimethyl phosphate, triethyl phosphate, tributyl phosphate); phosphoramides (e.g., hexamethylphosphoramide). Additional suitable solvents include toluene, benzene, heptane, xylene, dichloromethane, and pyridine.

[0040] Any of ethers, carbonates, sulfones, esters, ketones, nitriles, amides, lactams, ureas, phosphates, and phosphoramides may be fluorinated. An example of a fluorinated ether is 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0041] Any combination of one or more of the above solvents may be included in the electrolyte.

[0042] In an alternative embodiment, the electrolyte may comprise one or more ionic liquids as a solvent. The ionic liquids are organic cations, e.g., imidazolium, ammonium, pyrrolidinium, and / or organic anions, e.g., bis(trifluoromethanesulfonyl)imide TFSI. - , bis(fluorosulfonyl)imide FSI - , trilate, tetrafluoroborate BF4 - , dicyanamide DCA - , chloride Cl -It may contain a salt containing [it]. The ionic liquid is a liquid at room temperature (20°C). Examples of suitable ionic liquids are (N,N-diethyl-N-methyl-N(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl), N,N-diethyl-N-methyl-N-propylammonium bis(fluorosulfonyl)imide, N,N-diethyl-N-methyl-N-propylammonium bis(fluorosulfonyl)imide, N,N-dimethyl-N-ethyl-N-(3-methoxypropyl)ammonium bis(fluorosulfonyl)imide, N,N-dimethyl-N-ethyl-N-(3-methoxypropyl)ammonium bis(trifluoromethanesulfonyl)imide, N,N-dimethyl-N-ethyl-N-benzylammonium bis(trifluoromethanesulfonyl)imide, N,N-dimethyl-N-ethyl-N-phenylethylammonium bis(trifluoromethanesulfonyl)imide, N-ethyl-N,N-dimethyl-N-(2-methoxyethyl)ammonium bis(fluorosulfonyl)imide, N-ethyl-N,N-dimethyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)imide, N-tributyl-N-methylammonium bis(trifluoromethanesulfonyl)imide, N-tributyl-N-methylammonium dicyanamide, N-tributyl-N-methylammonium iodide, N-trimethyl-N-butylammonium bis(trifluoromethanesulfonyl)imide, N-trimethyl-N-butylammonium bromide, N-trimethyl-N-hexylammonium bis(trifluoromethanesulfonyl)imide, N-trimethyl-N-propylammonium bis(fluorosulfonyl)imide, N-trimethyl-N-propylammonium Bis(trifluoromethanesulfonyl)imide, (N,N-diethyl-N-methyl-N(2-methoxyethyl)ammonium bis(fluorosulfonyl)imide, 1-butyl-1-methylpyrrolidinium bis(fluorosulfonyl)imide, 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide, 1-methyl-1-(2-methoxyethyl)pyrrolidinium bis(fluorosulfonyl)imide, N,N-diethyl-N-methyl-N-propylammonium bis(fluorosulfonyl)imide, N-ethyl-N,N-dimethyl-N-(2-methoxyethyl)ammonium bis(fluorosulfonyl)imide, N-propyl-N-methylpiperidinium bis(fluorosulfonyl)imide, N-trimethyl-N-butylammonium Bis(fluorosulfonyl)imide,Includes N-methyl-N-butyl-piperidinium bis(trifluoromethanesulfonyl)imide, N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide, and combinations thereof.

[0043] Alternatively or additionally, the liquid electrolyte may be a gel electrolyte. The gel electrolyte may comprise polyethylene oxide and a gelling liquid electrolyte, such as an ether, for example, dimethyl ether. In one example, the electrolyte may comprise polyethylene oxide together with LiTFSI in dimethyl ether.

[0044] Any combination of the above solvents may be used in the electrolyte. For example, the electrolyte may comprise a combination of an ionic liquid and a fluorinated ether, or a combination of an ionic liquid in a gel, or a combination of a fluorinated ether in a gel. Any other combination of two or more of the liquids and / or gels described in detail above may also be considered.

[0045] In a preferred embodiment, the solvent is an ether, for example, dimethoxyethane (DME), dioxolane (DIOX), deglaim, triglaim, tetraglaim, or a mixture thereof. In another preferred embodiment, the solvent is a fluorinated ether.

[0046] When the battery is a lithium-sulfur battery, the electrolyte comprises a lithium salt dissolved in a solvent. Suitable lithium salts include lithium hexafluoroarsenate LiAsF6, lithium hexafluorophosphate LiPF6, lithium perchlorate LiClO4, lithium sulfate Li2SO4, lithium nitrate LiNO3, lithium trifluoromethanesulfonate LiOTf, lithium bis(trifluoromethane)sulfonimide LiTFSI, lithium bis(fluorosulfonyl)imide LiFSI, lithium bis(oxalic acid)borate LiBOB, lithium difluoro(oxalic acid)borate LiDFOB, lithium bis(pentafluoroethanesulfonyl)imide LiBETI, lithium 2-trifluoromethyl-4,5-dicyanomidazole LiTDI, and combinations thereof.

[0047] The electrolyte may contain one or more lithium salts. A combination of salts may also be used, for example, lithium trilate may be used together with lithium nitrate.

[0048] Alternatively, if the battery is a sodium-sulfur battery, the electrolyte comprises one or more sodium salts dissolved in an organic solvent. Suitable sodium salts include sodium hexafluoroarsenate, sodium hexafluorophosphate, sodium perchlorate, sodium sulfate, sodium nitrate, sodium trifluoromethanesulfonate, bis(trifluoromethane)sulfonimide, bis(fluorosulfonyl)imide, sodium bis(oxalic acid)borate, sodium difluoro(oxalic acid)borate, sodium bis(pentafluoroethanesulfonyl)imide, sodium 2-trifluoromethyl-4,5-dicyanomidazole, and combinations thereof. The electrolyte may also comprise one or more of the above sodium salts. In one embodiment, the electrolyte may comprise a combination of lithium and sodium salts.

[0049] The electrolyte may have low solubility for polysulfides, or in some cases, the electrolyte may not dissolve polysulfides. The electrolyte may have a polysulfide solubility of less than 500 mM at room temperature (20°C). For example, the electrolyte may have a polysulfide solubility of less than 400 mM at room temperature, preferably less than 200 mM, more preferably less than 100 mM, for example less than 50 mM, for example less than 1 mM. Thus, the electrolyte may generally have low solubility for sulfur-containing species (e.g., polysulfides and sulfur). For example, the electrolyte may have a sulfur solubility of less than 500 mM at room temperature (20°C). For example, the electrolyte may have a sulfur solubility of less than 400 mM at room temperature, preferably less than 200 mM, more preferably less than 100 mM, for example less than 50 mM, for example less than 1 mM.

[0050] Lithium or sodium salts may be present in the electrolyte at high concentrations, that is, at levels close to the saturation concentration of the electrolyte. For example, the concentration of lithium or sodium salts or salts in the electrolyte may be in the range of 0.05 M to 10 M, preferably in the range of 1 M to 5 M, for example, 3 M. The sodium salt in the solvent may be at least 75% of the saturation concentration of the solvent system, preferably at least 80% of the saturation concentration of the solvent, for example, at least 85% of the saturation concentration of the solvent, for example, at least 90% of the saturation concentration of the solvent. In one example, the concentration of the solvent is about 100% of the saturation concentration, that is, the electrolyte may be completely saturated.

[0051] The term "saturation concentration" refers to the degree of solubility of a specific substance in a specific solvent. Once saturation concentration is reached, adding more solute (e.g., more lithium salt) does not increase the concentration of the solution. Instead, the excess solute precipitates from the solution. Saturation concentration is determined at room temperature (e.g., 25°C).

[0052] The use of electrolytes with poor or no polysulfide solubility, such as electrolytes containing lithium salts at concentrations close to saturation, can suppress polysulfide shuttle within the electrolyte and is therefore beneficial for batteries like lithium-sulfur batteries. The polysulfide shuttle effect is undesirable due to the resulting loss of Coulomb efficiency. Without being bound by theory, the presence of high-concentration electrolytes and lithium (or sodium) salts at concentrations close to saturation causes only a small amount of polysulfide to dissolve in the electrolyte, which means that little to no polysulfide shuttle can occur. Therefore, the concentration of alkali metal salts in the electrolyte implies that the electrolyte has low solubility for polysulfides. In "traditional" lithium-sulfur batteries, using an electrolyte containing lithium salts at concentrations close to saturation tends to degrade electrochemical performance due to the low utilization of active sulfur species. This occurs because intermediate species cannot be solvated by the electrolyte since the electrolyte is nearly solvated. Without solvation of intermediate species within a traditional cathode, lithium ion transfer to the active sulfur species present is insufficient, and thus utilization and performance are significantly reduced under normal operating conditions. However, a combination of a low-porosity solid-state cathode and an electrolyte with poor polysulfide solubility mitigates this problem due to the absence of polysulfide dissolution during cycling. In the present invention, an electrolyte with poor polysulfide solubility, for example, an electrolyte containing a salt at a concentration close to the saturation concentration of the electrolyte, can be efficiently used in combination with a solid-state cathode.In traditional high-energy lithium-sulfur batteries, the cathode requires a non-viscous electrolyte with a concentration different from the saturation concentration of the electrolyte, but the chemistry associated with the battery of the present invention means that the electrolyte does not need to be non-viscous and the concentration of the electrolyte does not need to differ from the saturation concentration of the dissolved lithium salt (or, in the case of a sodium-sulfur battery, the sodium salt).

[0053] By using a combination of an electrolyte and a cathode according to the present invention, a small volume of electrolyte can be used in the battery despite the low solubility of polysulfides within the electrolyte system. In traditional lithium-sulfur batteries, an electrolyte with high solubility for lithium polysulfide species is required, and the capacity of such batteries depends on solubility, and thus on the volume of usable electrolyte within the battery. Highly concentrated electrolytes have low solubility for polysulfide intermediates. Therefore, when using a highly concentrated electrolyte in combination with a traditional cathode, much more electrolyte is required to dissolve the active material, and thus much more electrolyte is required to achieve high capacity. A larger volume of electrolyte is disadvantageous as it increases the size and weight of the battery and results in lower specific energy.

[0054] In the present invention, the chemistry occurring at the cathode means that the formation of polysulfides is suppressed or avoided, and accordingly, the battery does not depend on the solubility and volume of the electrolyte for the achievable capacity during charging and discharging. This allows for the use of a relatively small amount of highly concentrated electrolyte to obtain a high capacity. In one embodiment, about 0.1 to 3 μl of electrolyte per 1 g of active sulfur is present in the battery according to the present invention, preferably 0.5 to 2 μl of electrolyte per 1 g of active sulfur, for example, 1 μl of electrolyte per 1 g of active sulfur is present.

[0055] The use of highly concentrated electrolytes can also enhance the performance of lithium metal anodes. For example, highly concentrated electrolytes can effectively passivate the anode to form a stable solid-electrolyte interface (SEI). This can enable safe cycling of the battery and provide a long cycle life.

[0056] The electrolyte may contain additional salts in addition to the lithium (or sodium) salts described above. For example, the electrolyte may contain additional metal salts such as sodium, lithium, potassium, rubidium, cesium, calcium, and magnesium salts. Examples of additional salts include NaTFSI, KTFSI, RbTFSI, CsTFSI, Ca(TFSI)2, Mg(TFSI)2, NaPF6, and NaFSI. The additional salts may be present in an amount of 1 to 50 weight%, preferably 5 to 30 weight%, for example 10 to 20 weight%, of the total amount of salts in the electrolyte.

[0057] method

[0058] A battery according to the present invention can be manufactured by any suitable method. For example, a mixture of electroactive sulfur materials can be mixed by applying it to a current collector in the form of a slurry in a solvent (e.g., water or an organic solvent). Before forming the slurry, the electroactive sulfur materials may be mixed with, for example, an ion-conducting material and / or an electrically conductive material, and additional optional components, such as a binder. Then, the solvent may be removed, and the resulting structure may be calendered to form a composite structure, which may then be cut into a desired shape to form a cathode. Subsequently, a separator may be placed on the cathode and an anode on the separator to form a stack, and then an electrolyte may be added to form a battery. Brief explanation of the drawing

[0059] Various embodiments of the present invention are described by way of example with reference to the accompanying drawings, where Figure 1 shows electrochemical performance data of a battery containing a traditional sulfur cathode, a liquid electrolyte containing a lithium salt at a concentration greater than 75% of the saturation concentration, and a lithium metal foil anode. Figure 2 shows electrochemical performance data of a battery according to the present invention. Figure 3 illustrates a comparison of the cycle 2 discharge profiles from the electrochemical performance data of Figures 1 and 2. Specific details for implementing the invention

[0060] Examples

[0061] Example 1

[0062] The electrochemical performance of a lithium-sulfur battery having a "traditional" cathode is provided. The cathode (positive electrode) contained 70 wt% sulfur as an active material, 20 wt% Ketjen black as a conductive additive, and 10 wt% PEO as a binder. The liquid electrolyte of the battery contained a lithium salt at a concentration exceeding 75% of the saturation concentration. The liquid electrolyte consisted of LiFSI dissolved in dimethoxyethane (DME) at a molar concentration of 4.5 M. A 100-micron thick lithium metal foil was used as the negative electrode (anode). The liquid electrolyte components were retained within an inert separator placed between the electrodes.

[0063] The above battery is measured by mass, and the theoretical capacity of sulfur is 1672 mAh g -1 Assuming that, it was cycled between 1.5V and 2.8V under an applied current corresponding to a ratio of C / 50 based on the total sulfur content of the cathode.

[0064] Electrochemical performance data of the above battery is provided in Fig. 1.

[0065] Using an electrolyte with a saturation concentration exceeding 75% can limit the formation of polysulfide species. This reduces or prevents the shuttle phenomenon. However, the utilization rate of the active material is poor.

[0066] Example 2

[0067] Electrochemical performance data for a battery according to the present invention is provided in FIG. 2. The cathode (positive electrode) prepared according to the present invention comprises 50 wt% solid ion-conducting ceramic (produced by combining 75 wt% Li2S with 25 wt% P2S5), 30 wt% elemental sulfur as an active material, and 10 wt% Ketjen black as an electrically conductive additive. A liquid electrolyte containing a lithium salt at a concentration exceeding 75% of the saturation concentration and a lithium metal foil anode (negative electrode) were used. The liquid electrolyte components were retained within an inert separator placed between the electrodes. Sulfur contained in the solid electrolyte components is taken into account in the capacity calculation.

[0068] The utilization rate of active sulfur material in this battery is greatly improved, the formation of soluble polysulfide species is limited, and no shuttles are observed.

[0069] Figure 3 provides a comparison of the cycle 2 discharge profiles of Figures 1 and 2. This comparison shows that using the cathode (anode) described in the present invention with the electrolyte at a saturation concentration exceeding 75% achieves a significant improvement in performance compared to a traditional type of sulfur cathode. The present invention allows for a high utilization rate of the active material while avoiding the formation of solvated polysulfide species (thus no shuttle phenomenon is observed).

[0070] Throughout the description and claims of this specification, the words “comprising” and “containing” and variations thereof mean “comprising but not limited thereto” and are not intended to exclude other moiety, additive, component, integer, or step (i.e., not excluding them). Throughout the description and claims of this specification, the singular includes the plural unless the context otherwise requires. In particular, where an indefinite article is used, the specification should be understood to consider the plural as well as the singular unless the context otherwise requires.

[0071] Features, integers, properties, compounds, chemical moieties, or groups described in connection with specific aspects, embodiments, or examples of the present invention should be understood to be applicable to any other aspects, embodiments, or examples described herein, except where incompatible. All features and / or steps of any disclosed method or process disclosed herein (including the appended claims, summary, and drawings) may be combined in any combination, except for mutually exclusive combinations of at least some of such features and / or steps. The present invention is not limited to the details of any previously described embodiments. The present invention extends to any novel features or any novel combinations of features disclosed herein (including the appended claims, summary, and drawings), or any novel features or any novel combinations of steps of any disclosed method or process.

[0072] Readers may note all papers and documents submitted simultaneously with or prior to this specification and disclosed together with this specification in connection with this application (the contents of all such papers and documents are incorporated herein by reference).

Claims

Claim 1 An anode comprising lithium or sodium metal, or a lithium or sodium metal alloy; an electroactive sulfur material; 10 at 25°C -7 An electrochemical cell comprising: an ion-conducting material having a bulk ion conductivity greater than S / cm; and a solid electrically conductive material comprising an electrically conductive carbon material or an electrically conductive polymer; an ion-conducting cathode comprising; and a liquid electrolyte comprising one or more lithium salts or one or more sodium salts, wherein the liquid electrolyte is sulfur, the polysulfide solubility of the liquid electrolyte at 20°C is less than 500 mM. Claim 2 An electrochemical cell according to claim 1, wherein the concentration of the liquid electrolyte is saturated at 75% or more when measured at 25°C. Claim 3 An electrochemical cell according to claim 1, wherein the cathode further comprises an ion-conducting material selected from at least one of conductive ceramic particles and an ion-conducting polymer. Claim 4 An electrochemical cell according to claim 3, wherein the conductive ceramic particles are selected from at least one of LLZO, LATP, LGPS, or Li2S-P2S5. Claim 5 An electrochemical cell according to any one of claims 1 to 4, wherein the electrically conductive carbon material is selected from at least one of carbon nanotubes, carbon nanofibers, graphene, reduced graphene oxide, or carbon black. Claim 6 An electrochemical cell according to any one of claims 1 to 4, wherein the electrically conductive polymer is selected from at least one of polypyrrole, polythiophene, polyaniline, polyacetylene, polyphenylenevinylene, or poly(3,4-ethylenedioxythiophene). Claim 7 An electrochemical cell according to any one of claims 1 to 4, wherein the cathode comprises a carbon-sulfur composite material. Claim 8 An electrochemical cell according to any one of claims 1 to 4, wherein the cathode contains 1 to 60 weight percent of an ion-conducting material based on the total weight of the cathode. Claim 9 An electrochemical cell according to any one of claims 1 to 4, wherein the electroactive sulfur material comprises elemental sulfur or Li2S. Claim 10 An electrochemical cell according to any one of claims 1 to 4, wherein one or more lithium salts are selected from lithium hexafluoroarsenate (LiAsF6), lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium sulfate (Li2SO4), lithium nitrate (LiNO3), lithium trifluoromethanesulfonate (LiOTf), bis(trifluoromethane)sulfonimide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(oxalic acid)borate (LiBOB), lithium difluoro(oxalic acid)borate (LiDFOB), lithium bis(pentafluoroethanesulfonyl)imide (LiBETI), lithium 2-trifluoromethyl-4,5-dicyanomidazole (LiTDI), and combinations thereof. Claim 11 In any one of claims 1 to 4, the liquid electrolyte is linear ether, diethyl ether (DEE), tetrahydrofuran (THF), dimethoxyethane (DME), dioxolane (DIOX), diglyme, dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), methyl formate (MF), ethyl formate (EF), methyl propionate (MP), ethyl acetate (EA) and methyl butyrate (MB), methyl ethyl ketone, acetonitrile (ACN), propionitrile (PN), isobutyronitrile (iBN), dimethylformamide (DMF), dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), tetramethylurea (TMU), dimethyl sulfoxide (DMSO), trimethyl phosphate, triethyl phosphate, An electrochemical cell comprising a solvent selected from at least one of hexamethylphosphoramide, toluene, benzene, heptane, xylene, and dichloromethane; ionic liquids, fluorinated ethers, and mixtures thereof. Claim 12 In claim 2, an electrochemical cell in which the liquid electrolyte is saturated by 80% or more. Claim 13 An electrochemical cell according to any one of claims 1 to 4, wherein the cathode further comprises a binder, and the binder is selected from at least one of PEO, PVDF, polypyrrole, polythiophene, polyaniline, polyacetylene, polyphenylenevinylene, poly(3,4-ethylenedioxythiophene) or polyphenylene sulfide. Claim 14 An electrochemical cell according to claim 13, wherein the binder accounts for 1 to 30 weight percent of the total weight of the anode. Claim 15 An electrochemical cell according to any one of claims 1 to 4, wherein the polysulfide solubility of the liquid electrolyte is less than 400 mM. Claim 16 An electrochemical cell according to any one of claims 1 to 4, wherein the battery is a lithium-sulfur battery. Claim 17 delete

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