battery

Abstract

To provide high energy lithium-sulfur cells capable of solving such problems that the operation of traditional lithium-sulfur cells is made complicated, and the available capacity (available useful energy), the cycle life, and the coulombic efficiency are reduced.SOLUTION: There is provided an electrochemical cell comprising an anode, an ionically conductive cathode, and a liquid electrolyte. The anode comprises: lithium metal or sodium metal; or a lithium metal alloy or a sodium metal alloy, the ionically conductive cathode comprises an electroactive sulfur material, and the liquid electrolyte comprises at least one lithium salt or at least one sodium salt. The polysulfide solubility of the electrolyte is less than 500 mM.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to cells, and more particularly to lithium-sulfur cells (or lithium-sulfur batteries). [Background technology]

[0002] Secondary batteries, such as lithium-sulfur cells, can be recharged by passing an external current through the cell. This type of rechargeable cell has a wide range of potential applications. Important considerations in developing lithium-sulfur secondary batteries include gravimetric and volumetric energy, cycle life, and ease of cell assembly. Another example of a secondary battery is the sodium-sulfur cell. Summary of the Invention [Problem to be solved by the invention]

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

[0004] Traditionally, high-energy lithium-sulfur cells use a liquid electrolyte. The cathode typically comprises carbon mixed with or incorporating sulfur. During discharge, the electroactive sulfur material (e.g., elemental sulfur) is converted into lithium polysulfide species S n 2-(n ≥ 2, e.g., n = 2-8). These species are generally soluble within the electrolyte. In the second stage of discharge, the polysulfide species are reduced to insoluble lithium sulfide, LiS. When the cell is charged, this two-step mechanism occurs in reverse, with lithium sulfide being oxidized to lithium polysulfide (or sulfide) species and then to sulfur. However, polysulfide shuttles, due to the high solubility of polysulfides in the electrolyte, can affect cycling performance and reduce coulombic efficiency. In particular, during cycling of conventional lithium-sulfur cells, the concentration of polysulfide species increases in conventional electrolyte formulations due to the high solubility of these species in the electrolyte. This process complicates the operation of conventional lithium-sulfur cells, resulting in a decrease in available capacity (available useful energy), a decrease in cycle life, and a decrease in coulombic efficiency.

[0005] One alternative to conventional lithium-sulfur cells is all-solid-state lithium-sulfur (ASSLiS) batteries. Instead of the liquid electrolyte found in "conventional" lithium-sulfur cells, these comprise a solid electrolyte, such as a solid-state polymer or ceramic electrolyte. The use of a solid electrolyte can be advantageous in terms of safety and volumetric / mass energy density. The use of solid-state batteries avoids the formation of solvated polysulfide species in the liquid electrolyte, thus avoiding the problems associated with the presence of these species. Thus, all-solid-state lithium-sulfur cells can theoretically achieve high mass energy and high volumetric energy. However, ASSLiS batteries suffer from significant problems, such as poor interfacial contact between the electrolyte and the electrodes.

[0006] In view of the above, there is a need for a high energy lithium-sulfur cell that can address the above challenges. [Brief explanation of the drawings]

[0007] Various aspects of the present invention will now be described, by way of example, with reference to the accompanying figures. [Figure 1] FIG. 1 shows electrochemical performance data for a cell containing a conventional sulfur cathode, a liquid electrolyte containing a lithium salt at a concentration greater than 75% of saturation, and a lithium metal foil anode. [Figure 2] FIG. 2 shows electrochemical performance data for a cell according to the present invention. [Figure 3] FIG. 3 shows a comparison of the discharge profiles for cycle 2 from the electrochemical performance in FIGS. DETAILED DESCRIPTION OF THE INVENTION

[0008] Before particular examples of the present invention are described, it is to be understood that the disclosure is not limited to the particular cells, methods, or materials disclosed herein, and that the terminology used herein is used only to describe particular examples and is not intended to be limiting, as the scope of protection is defined by the claims and their equivalents.

[0009] In describing and claiming the cells and methods of the present invention, the following terminology is used: the singular forms "a," "an," and "the" include the plural forms unless the context clearly dictates otherwise. Thus, for example, "cathode" includes reference to one or more of such elements.

[0010] According to one aspect of the present invention, there is provided an electrochemical cell comprising an anode, an ionically conductive cathode, and a liquid electrolyte, wherein the anode comprises lithium metal and sodium metal, or a lithium metal alloy and a sodium metal alloy, the ionically conductive cathode comprises an electroactive sulfur material, and the liquid electrolyte comprises at least one lithium salt or at least one sodium salt, wherein the solubility of polysulfides in the electrolyte is less than 500 mM.

[0011] The cell of the present invention combines the advantages associated with conventional lithium-sulfur cells and all-solid-state lithium-sulfur cells. First, the use of a low-porosity solid cathode (i.e., a cathode structure with a small interfacial contact area between the electrolyte component and the cathode) with a redox-active sulfur component that undergoes reduction and oxidation reactions without forming soluble intermediate polysulfide species can result in a high-energy lithium-sulfur cell. Second, the use of a liquid electrolyte with low solubility for lithium polysulfide species can ensure good interfacial contact between the electrolyte and each electrode. Benefits derived from this type of hybrid liquid / solid cell include high mass and volumetric energy, high cycle life, improved safety characteristics, improved coulombic efficiency, and a favorable voltage profile for BMS (battery management system) control.

[0012] According to another aspect of the present invention, there is provided an electrochemical cell comprising an anode, an ion-conducting cathode, and a liquid electrolyte, wherein the anode comprises lithium metal or sodium metal, or a lithium metal alloy or a sodium metal alloy, the ion-conducting cathode comprises an electroactive sulfur material, and the liquid electrolyte comprises at least one lithium salt or at least one sodium salt, wherein the concentration of the at least one lithium salt or sodium salt in the electrolyte is at least 75% of the saturation concentration of the electrolyte. electrochemical cell

[0013] The electrochemical cell according to the present invention may be a lithium-sulfur cell. A further example of an electrochemical cell according to the present invention is a sodium-sulfur cell. The lithium-sulfur cell may comprise a lithium anode and a cathode comprising an electroactive sulfur material, e.g., elemental sulfur. The electrolyte may comprise at least one solvent or ionic liquid and a salt, e.g., 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 comprise a sodium anode and a cathode comprising an electroactive sulfur material, e.g., elemental sulfur. The electrolyte may comprise at least one solvent or ionic liquid and a salt, e.g., a sodium salt. anode

[0014] In a lithium-sulfur cell, 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 may comprise a foil formed of lithium metal or a lithium metal alloy. Examples of lithium alloys include lithium aluminum alloy, lithium magnesium alloy, and lithium boron alloy. Preferably, a lithium metal foil is used. When the cell is a sodium-sulfur cell, 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 alloy, sodium magnesium alloy, and sodium boron alloy. Preferably, a sodium metal foil is used. Cathode

[0015] The cathode of the electrochemical cell comprises an electroactive sulfur material. The cathode is ionically conductive, i.e., it can conduct ions (i.e., alkali cations, Li) in the solid state. + or Na +) conduction. Thus, the electrochemistry of a cell according to the 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 charge / discharge may dissolve in the electrolyte. In one embodiment, the polysulfides are not dissolved in the electrolyte. The chemistry involved in charging and discharging a cell according to the invention is similar to that observed in all-solid-state lithium-sulfur cells in which polysulfides are not dissolved in the electrolyte.

[0016] Electroactive sulfur materials 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 composite material. The cathode may comprise an electroactive sulfur material that may also be ionically conductive. This material may contain sulfur and additional elements such as Li, Na, Mg, P, N, Si, Ge, Ti, Zr, Sn, B, A, F, Cl, Br, I, O, or any combination thereof. Examples of sulfur-containing materials that are also ionically conductive are LGPS, Li3PS4, or Li7P3S. 11 In one embodiment, the cathode may comprise a sulfur-carbon composite material that is also ionically conductive.

[0017] The cathode may further comprise a solid electronically conductive (or electrically conductive) material. The solid electronically conductive material may be any suitable conductive material. Preferably, the solid electronically conductive material may be formed of carbon. Examples include carbon black, carbon fiber, graphene, reduced graphene oxide, carbon nanotubes, etc. Other suitable materials include metals (e.g., flakes, fillings, 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 an embodiment in which the cathode comprises a sulfur-carbon composite, no additional solid electronically conductive material may be present in the cathode.

[0018] The cathode is an ionically conducting material, specifically solid Li + or Na + The ionically conductive material may further comprise an ion conductor. -7 S / cm, e.g., 10 -6 The cathode can have a bulk ionic conductivity of more than 100 S / cm. x P y S zIn some cases, the lithium ion conducting material includes an electroactive ion conducting material such as lithium ion conductor, and no additional ion conducting material may be present. In some examples, the lithium ion conducting material includes a ceramic material. The ceramic material may have a crystalline, polycrystalline, partially 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 electrolytes with sufficient ion conductivity can be produced by combining various lithium compounds, such as lithium-containing ceramic materials. Lithium-containing ceramic materials include lithium oxide (e.g., Li2O, LiO, LiO2, LiRO2, where R is scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, yterbium, and / or lutetium), lithium carbonate (Li2CO3), lithium nitride (e.g., Li3N), lithium oxysulfide, lithium oxynitride, and garnet-type lithium oxide (e.g., Li7La3Zr2O 12 ), Li 10 GeP2S 12, lithium phosphorus oxynitride, lithium silicon sulfide, lithium germanosulfide, lithium lanthana oxide (lithium lanthanum oxide), lithium titanium oxide (lithium titanate), lithium borosulfide, lithium aluminosulfide, lithium phosphosulfide, lithium silicate, lithium borate, lithium aluminate, lithium phosphate, lithium halide, and combinations of the above. In some cases, the ceramic material comprises lithium oxide, lithium nitride, or lithium oxysulfide. In some embodiments, the ceramic comprises a carbonate and / or carbide.

[0019] In some embodiments, the lithium ion conducting material can be selected from species capable of donating an electron pair (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, yterbium, and / or lutetium), lithium carbonate (Li2CO3), lithium nitrides (e.g., Li3N), lithium oxysulfides, lithium oxynitrides, garnet-type lithium oxides (e.g., Li7La3Zr2O 12 ), Li 10 GeP2S 12 , lithium phosphorus oxynitride, lithium silicon sulfide, lithium germanosulfide, lithium lanthana oxide, lithium titanium oxide, lithium borosulfide, lithium aluminosulfide, lithium phosphosulfide, lithium silicate, lithium borate, lithium aluminate, lithium phosphate, lithium halides, and combinations of the above.

[0020] Examples of ceramic materials that can be used as lithium ion conducting materials include Li-containing oxides, such as Li 3.3 La 0.56TiO3; Nasicon structure (e.g.: LiTi(PO4)3); LiSICON (Li 14 Zn(GeO4)4);Li 10 GeP2Si 12 ;Garnet: Li7La3Zr2O 12 Li2O; other oxides, such as Al2O3, TiO2, ZrO2, SiO2, ZnO; sulfides, such as Li2S-P2S5; antiperovskites, such as Li3OCl; hydrides, such as LiBH4, LiBH4-LiX (X=Cl, Br, I), LiNH, LiNH2, Li3AlH6, Li2NH; borates or phosphates, such as Li2B4O7, Li3PO4, LiPON; carbonates or hydroxides, such as LiCO 3、 These include LiOH; fluorides, such as LiF; nitrides, such as LiN; and sulfides, such as lithium borosulfide, lithium phosphosulfide, lithium aluminosulfide, oxysulfides, and praseodymium oxide. At least one of the above ceramic materials, or a combination thereof, may be used. Sodium-sulfur cells (sodium-sulfur batteries) may utilize the sodium ion equivalent of any of these conductive materials.

[0021] In some examples, the lithium ion conducting material may be formed from an inherently ionically conducting polymer material, such as Nafion. -7Polymers blended with lithium (or sodium) salts that can achieve bulk conductivities (or electrical conductivities, or electrical conductivities) of greater than 10 ... In one embodiment, a coblock polymer such as Nafion may be used. At least one of the above polymeric materials, or a combination thereof, may be used. In one embodiment, the cathode comprises ceramic particles combined with one or more ion-conducting polymers.

[0022] The cathode allows both electrons and ions to be conducted in the solid-state, which allows the electrochemical reactions at the cathode during charging or discharging to occur in the solid state without the need to form soluble intermediates in the form of polysulfide species.

[0023] The cathode may further comprise a binder to bind the cathode components together. The cathode may also bind the cathode components to an electronically conductive current collector. By doing so, the binder may provide the cathode with improved mechanical robustness or improve the processability of the cathode. The binder may be a polymer binder, such as a polyether, such as poly(ethylene oxide), polyethylene glycol, polypropylene glycol, polytetramethylene glycol (PTMG), or polytetramethylene ether glycol (PTMEG).

[0024] The binder may be selected from halogenated polymers, more preferably from fluorinated polymers. Examples of suitable binders include poly(vinylidene fluoride) (PVDF), preferably α-phase poly(vinylidene fluoride), poly(trifluoroethylene) (PVF3), polytetrafluoroethylene (PTFE), copolymers of vinylidene fluoride with either hexafluoropropylene (HFP), trifluoroethylene (VF3), tetrafluoroethylene (TFE), or chlorotrifluoroethylene (CTFE), fluoroethylene / propylene (FEP) copolymers, copolymers of ethylene with either fluoroethylene / propylene (FEP), 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.

[0025] Other examples of suitable binders include polyacrylonitrile, polyurethane, PVDF-acrylic copolymer, polyacrylic acid, polyimide, and polyvinyl alcohol. Further suitable binders include rubber (e.g., styrene butadiene rubber), cellulose (e.g., carboxymethyl cellulose), or gelatin.

[0026] 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 can comprise polyethylene oxide or PVDF.

[0027] The cathode may comprise 0.05 to 20 wt %, preferably 0.5 to 10 wt %, such as 1 to 5 wt %, for example 2 to 3 wt %, of binder based on the total weight of the cathode. electrolyte

[0028] The electrolyte according to the present invention can be a liquid electrolyte. Liquid electrolytes provide good physical contact between the electrolyte and the electrodes as a result of the electrolyte wetting the cathode and anode. This is in contrast to solid-state batteries, where a solid electrolyte cannot provide sufficient interfacial contact between the electrolyte and the anode / cathode due to lack of wetting. This is particularly problematic during cycling of an ASSLiS cell when volume changes occur at the anode and cathode due to reactions occurring during charge or discharge. As a result of these volume changes, it is very difficult to maintain intimate contact at the anode-electrolyte and cathode-electrolyte interfaces.

[0029] Any suitable solvent system or liquid or gel or mixture of liquids and / or gels can be used for the electrolyte. The electrolyte is liquid over the operating temperature range of the cell, which may be from -30 to 120°C, preferably from -10 to 90°C, for example, from 0 to 60°C. The operating pressure of the cell may be from 5 mbar to 100 bar, preferably from 10 mbar to 50 bar, for example, from 100 mbar to 20 bar. In one example, the cell can be operated at room temperature and pressure. The high concentration of the electrolyte according to the present invention means that the electrolyte has a lower vapor pressure than standard electrolytes. Therefore, the cell according to the present invention may perform better at low pressures than standard lithium-sulfur electrolytes. The liquid electrolyte can be a gel electrolyte.

[0030] Suitable organic solvents for use in the electrolyte include ethers (e.g., linear ethers, diethyl ether (DEE), diglyme (2-methoxyethyl ether), tetraglyme, tetrahydrofuran, 2-methyltetrahydrofuran, dimethoxyethane (DME), dioxolane (DIOX)); carbonates (e.g., dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl 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, methyl propionate, ethyl propionate, ethyl amine, ethyl methyl ... acetate, and methyl butyrate); ketones (e.g., methyl ethyl ketone); nitriles (e.g., acetonitrile, proprionitrile, 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., trimethylphosphate, triethylphosphate, tributylphosphate); phosphoramides (e.g., hexamethylphosphoramide). Further suitable solvents include toluene, benzene, heptane, xylene, dichloromethane, and pyridine.

[0031] Any of the 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.

[0032] Any combination of one or more of the above solvents is included in the electrolyte.

[0033] In an alternative embodiment, the electrolyte may include one or more ionic liquids as a solvent, which may be organic cations such as imidazolium, ammonium, pyrrolidinium, and / or bis(trifluoromethanesulfonyl)imide TFSI. - , bis(fluorosulfonyl)imide FSI - , triflate, tetrafluoroborate BF4 - , dicyanamide DCA - , chloride Cl -Ionic liquids are liquids at room temperature (20°C). Examples of suitable ionic liquids include (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) ... 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-methyl N-trimethyl-N-butylammonium 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 nium 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, N-methyl-N-butyl-piperidinium bis(trifluoromethanesulfonyl)imide, N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide, and combinations thereof.

[0034] Alternatively or additionally, the liquid electrolyte can be a gel electrolyte. The gel electrolyte can include a gelled liquid electrolyte, for example, polyethylene oxide with an ether, such as dimethyl ether. In one example, the electrolyte can include polyethylene oxide in combination with LiTFSI in dimethyl ether.

[0035] Any combination of the above solvents may be used in the electrolyte. For example, the electrolyte may include 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 detailed above may be envisioned.

[0036] In a preferred embodiment, the solvent is an ether, such as dimethoxyethane (DME), dioxolane (DIOX), diglyme, triglyme, tetraglyme, or a mixture thereof. In another preferred embodiment, the solvent is a fluorinated ether.

[0037] When the cell is a lithium-sulfur cell, the electrolyte dissolved in the solvent comprises a lithium salt. Suitable lithium salts include lithium hexafluoroarsenate (LiAsF), lithium hexafluorophosphate (LiPF), lithium perchlorate (LiCLO), lithium sulfate (LiSO), lithium nitrate (LiNO), lithium trifluoromethanesulfonate (LiOTf), lithium bis(trifluoromethane)sulfonimide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiDFOB), lithium bis(pentafluoroethanesulfonyl)imide (LiBETI), lithium 2-trifluoromethyl-4,5-dicyanoimidazole (LiTDI), and combinations thereof.

[0038] The electrolyte may comprise one or more lithium salts. Combinations of salts may be used, for example, lithium triflate in combination with lithium nitrate.

[0039] Alternatively, when the cell is a sodium-sulfur cell, the electrolyte comprises at least one sodium salt dissolved in an organic solvent. Suitable sodium salts include sodium hexafluoroarsenate, sodium hexafluorophosphate, sodium perchloride, sodium sulfate, sodium nitrate, sodium trifluoromethanesulfonate, sodium bis(trifluoromethane)sulfonimide, sodium bis(fluorosulfonyl)imide, sodium bis(oxalato)borate, sodium difluoro(oxalato)borate, sodium bis(pentafluoroethanesulfonyl)imide, sodium 2-trifluoromethyl-4,5-dicyanoimidazole, and combinations thereof. The electrolyte can comprise one or more of the above sodium salts. In one embodiment, the electrolyte can comprise a combination of a lithium salt and a sodium salt.

[0040] The electrolyte may have low solubility for polysulfides, or in some cases, the electrolyte may not dissolve polysulfides at all. 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, preferably less than 200 mM, more preferably less than 100 mM, for example less than 50 mM, for example less than 1 mM, at room temperature. Correspondingly, the electrolyte may generally have low solubility for sulfur-containing species (such as 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 polysulfide solubility of less than 400 mM, preferably less than 200 mM, more preferably less than 100 mM, for example less than 50 mM, for example less than 1 mM, at room temperature.

[0041] The lithium salt or sodium salt can be present in the electrolyte at a high concentration, i.e., at a level close to the saturation concentration of the electrolyte. For example, the concentration of the lithium salt or sodium salt, or one or more lithium salts or sodium salts, in the electrolyte can be in the range of 0.05M to 10M, preferably 1M to 5M, e.g., 3M. The concentration of at least one lithium salt or sodium salt in the solvent can be at least 75% of the saturation concentration of the solvent system, preferably at least 80% of the saturation concentration of the solvent, e.g., at least 85% of the saturation concentration of the solvent, e.g., at least 90% of the saturation concentration of the solvent. In one example, the concentration of the solvent can be about 100% of the saturation concentration, i.e., the electrolyte can be completely saturated.

[0042] The term "saturation concentration" refers to the limit (or degree or extent) of a particular solubility of a substance in a particular solvent. When saturation concentration is reached, adding more solute (e.g., adding a lithium salt) does not increase the concentration of the solution. Instead, the excess solute precipitates from the solution. Saturation concentration is measured at room temperature, e.g., 25°C.

[0043] The use of electrolytes with low or no polysulfide solubility, such as those containing lithium salts at near-saturation concentrations, can inhibit polysulfide shuttles within the electrolyte and thus is beneficial in cells such as lithium-sulfur cells. The polysulfide shuttle effect is undesirable because it results in a loss of coulombic efficiency. Without wishing to be bound by theory, the presence of high electrolyte concentrations and lithium (or sodium) salts at near-saturation concentrations allows only a small amount of polysulfides to dissolve in the electrolyte, meaning that little or no polysulfide shuttles can occur. Therefore, the concentration of alkali metal salts in the electrolyte means that the electrolyte has low solubility for polysulfides. The use of electrolytes containing lithium salts at near-saturation concentrations in "conventional" lithium-sulfur cells tends to result in poor electrochemical performance due to low utilization of the active sulfur species. This is due to the inability of intermediate species to be solvated by the electrolyte, due to the near-solvation nature of the electrolyte. Without solvation of the intermediate species in a conventional cathode, there is insufficient lithium ion transport to the active sulfur species present, which significantly reduces utilization and performance under normal operating conditions. However, combining a low-porosity solid cathode with an electrolyte having low polysulfide solubility mitigates this problem due to the lack of polysulfide dissolution during cycling. In the present invention, electrolytes with low polysulfide solubility, such as electrolytes containing salts at concentrations close to the electrolyte saturation concentration, can be used efficiently in combination with a solid cathode. While conventional high-energy lithium-sulfur cells require a non-viscous electrolyte with a concentration far from the electrolyte saturation concentration, the chemistry involved in the cells of the present invention does not require the electrolyte to be non-viscous, and the electrolyte concentration need not be far from the saturation concentration of the dissolved lithium salt (or sodium salt in the case of sodium-sulfur cells).

[0044] The use of the electrolyte and cathode combination according to the present invention allows for the use of small amounts of electrolyte in the cell, despite the low solubility of polysulfides in the electrolyte system. Conventional lithium-sulfur cells require an electrolyte with high solubility for lithium polysulfide species, and the capacity of such cells depends on the solubility and, therefore, the amount of electrolyte available in the cell. Highly concentrated electrolytes have low solubility for polysulfide intermediates. Therefore, when highly concentrated electrolytes are used in combination with conventional cathodes, more electrolyte is needed to solubilize the active material, and therefore, more electrolyte is needed to achieve high capacity. Large amounts of electrolyte are disadvantageous because they increase the size and weight of the cell and lower the specific energy (or energy density).

[0045] In the present invention, the chemistry occurring at the cathode means that polysulfide formation is inhibited or avoided, and therefore the cell does not rely on the solubility and volume of the electrolyte for achievable capacity during charge and discharge. This allows for the use of relatively small amounts of highly concentrated electrolyte to obtain high capacity. In one embodiment, approximately 0.1 to 3 microliters of electrolyte per gram of active sulfur is present in a cell according to the present invention, preferably 0.5 to 2 microliters of electrolyte per gram of active sulfur, e.g., 1 microliter of electrolyte per gram of active sulfur.

[0046] The use of a high-concentration electrolyte also improves the performance of the lithium metal anode. For example, the high-concentration electrolyte effectively passivates the anode and forms a stable solid electrolyte interface (SEI), which allows the cell to be cycled safely and provides a long cycle life.

[0047] The electrolyte may also contain additional salts in addition to the lithium (or sodium) salts described above. For example, the electrolyte may contain further metal salts such as sodium salts, lithium salts, potassium salts, rubidium salts, cesium salts, calcium salts, magnesium salts, etc. Examples of the additional salts may 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 wt. % of the total amount of salts in the electrolyte, preferably 5 to 30 wt. %, for example 10 to 20 wt. %. method

[0048] Cells according to the present invention can be fabricated by any suitable method. For example, a mixture of electroactive sulfur materials can be mixed and applied to a current collector in the form of a slurry in a solvent (e.g., water or an organic solvent). The electroactive sulfur materials can be mixed with, for example, an ionically and / or electronically conductive material and any additional optional components, such as a binder, before forming the slurry. The solvent can then be removed, and the resulting structure can be calendered to form a composite structure, which can be cut into the desired shape to form the cathode. A separator can then be placed on the cathode, and an anode can be placed on the separator to form a stack, followed by the addition of electrolyte to form the cell. [Example]

[0049] [Example 1] The electrochemical performance of a lithium-sulfur cell with a "conventional" cathode is presented. The cathode (positive electrode) comprised 70 wt.% sulfur as the active material, 20 wt.% Ketjen black as a conductive additive, and 10 wt.% PEO as a binder. The cell's liquid electrolyte contained a lithium salt at a concentration greater than 75% of saturation. The liquid electrolyte consisted of LiFSI dissolved in dimethoxyethane (DME) to a molar concentration of 4.5 M. A 100-micron-thick lithium metal foil was utilized as the negative electrode (anode). The liquid electrolyte components were contained within an inert separator placed between the electrodes.

[0050] The cell has a theoretical sulfur capacity of 1672 mAhg based on the total sulfur content of the cathode as measured by mass (or mass, or mass spectrometry). -1 Assuming that the voltage was 0.1 V, the capacitor was cycled between 1.5 and 2.8 V under an applied current corresponding to a rate of C / 50.

[0051] The electrochemical performance data of the cell is provided in FIG.

[0052] The use of an electrolyte with a saturation concentration >75% allowed for the limited formation of polysulfide species, which reduced or prevented the shuttling phenomenon. However, the utilization of the active material was low.

[0053] [Example 2] Electrochemical performance data for the cell of the present invention are shown in Figure 2. The cathode (positive electrode) prepared in accordance with the present invention comprised 50 wt. % solid ionically conductive ceramic (prepared by combining 75 wt. % Li2S and 25 wt. % P2S5), 30 wt. % elemental sulfur as the active material, and 10 wt. % Ketjen Black as an electronically conductive additive. A liquid electrolyte containing a lithium salt at a concentration greater than 75% of its saturation concentration and a lithium metal foil anode (negative electrode) were used. The liquid electrolyte components were held within an inert separator disposed between the electrodes. The sulfur contained in the solid electrolyte components was accounted for in the capacity calculation.

[0054] In this cell, utilization of the active sulfur material was significantly enhanced, limiting the formation of soluble polysulfide species, and no shuttling was observed. A comparison of the discharge profiles for cycle 2 in Figures 1 and 2 is shown in Figure 3. This comparison demonstrates that the present invention, combined with an electrolyte with a saturation concentration greater than 75%, enabled significant performance improvements compared to conventional sulfur cathodes. The present invention enabled high utilization of the active material while avoiding the formation of solvated polysulfide species, and therefore no shuttling was observed.

[0055] Throughout this description and the claims, the terms "comprise" and "contain" and variations thereof mean "including but not limited to" and are not intended to (and do not) exclude other moieties, additives, components, integers, or steps. Throughout this description and the claims, the singular encompasses the plural unless the context requires otherwise. In particular, when the indefinite article is used, it should be understood that the specification contemplates the plural as well as the singular unless the context requires otherwise.

[0056] It should be understood that any feature, integer, property, compound, chemical moiety, or group described in connection with a particular aspect, embodiment, or example of the invention is applicable to any other aspect, embodiment, or example described herein, unless incompatible therewith. All features disclosed herein (including the accompanying claims, abstract, and drawings), and / or all steps of any method or process so disclosed, may be combined in any combination, except combinations in which at least some of such features and / or steps are mutually exclusive. The invention is not limited to the details of the foregoing embodiments. The invention extends to any novel combination of features disclosed herein (including the accompanying claims, abstract, and drawings), or any novel combination of steps of any method or process disclosed.

[0057] The reader's attention is directed to all articles and documents filed contemporaneously with or prior to this application in connection with this application and which are hereby open to public inspection, and the contents of all such articles and documents are hereby incorporated by reference. A preferred embodiment of the present invention is as follows. [1] an anode, an ion-conducting cathode, and a liquid electrolyte; the anode comprises lithium metal or sodium metal, or a lithium metal or sodium metal alloy; the ion-conducting cathode comprises an electroactive sulfur material; and the liquid electrolyte comprises at least one lithium salt or at least one sodium salt, and the solubility of the polysulfide in the electrolyte is less than 500 mM; Electrochemical cell. [2] 10. The electrochemical cell according to claim 1, wherein the concentration of the at least one lithium salt or sodium salt in the electrolyte is at least 75% of the saturated concentration of the electrolyte. [3] 10. The 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. [4] The electrochemical cell according to [3], wherein the conductive ceramic particles are selected from at least one of LLZO, LATP, LGPS, and Li2S-P2S5. [5] The electrochemical cell according to any one of [1] to [4], wherein the cathode further comprises a solid electron-conducting material comprising an electron-conducting carbon material or an ion-conducting polymer. [6] The electrochemical cell according to [5], wherein the electron-conductive carbon material is selected from at least one of carbon nanotubes, carbon nanofibers, graphene, reduced graphene oxide, and carbon black. [7] The electrochemical cell according to [5], wherein the ion-conducting polymer is selected from at least one of polypyrrole, polythiophene, polyaniline, polyacetylene, polyphenylene vinylene, and poly(3,4-ethylenedioxythiophene). [8] 10. The electrochemical cell of claim 1, wherein the cathode comprises a carbon-sulfur composite material. [9] The electrochemical cell according to any one of [1] to [8], wherein the cathode contains 1 to 60 wt % of an ion-conductive material based on the total weight of the cathode.

[10] The electrochemical cell according to any one of [1] to [9], wherein the electroactive sulfur material comprises elemental sulfur or Li2S.

[11]

[10] The electrochemical cell according to any one of [1] to

[10] , wherein the at least one lithium salt is selected from 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(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiDFOB), lithium bis(pentafluoroethanesulfonyl)imide (LiBETI), lithium 2-trifluoromethyl-4,5-dicyanoimidazole (LiTDI), and combinations thereof.

[12] The electrolytes include linear ethers, 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, hexamethylphosphoramide, toluene, benzene, heptane, xylene, and dichloromethane; ionic liquids, fluorinated ethers, gels, and mixtures thereof.

[13] The electrochemical cell according to any one of [1] to

[12] , wherein the saturation concentration is at least 80%, preferably at least 90%.

[14] The electrochemical cell according to any one of [1] to

[13] , wherein the cathode further comprises a binder, and the binder is preferably selected from at least one of PEO, PVDF, Nafion, polypyrrole, polythiophene, polyaniline, polyacetylene, polyphenylene vinylene, poly(3,4-ethylenedioxythiophene), and polyphenylene sulfide.

[15] The electrochemical cell according to

[14] , wherein the binder is contained in an amount of 1 to 30 wt % of the total weight of the electrode.

[16] The electrochemical cell according to any one of [1] to

[15] , wherein the solubility of the polysulfide in the electrolyte is less than 400 mM, preferably less than 200 mM, for example less than 100 mM.

[17] The electrochemical cell according to any one of [1] to

[16] , wherein the electrochemical cell is a lithium-sulfur cell.

Claims

1. an anode, an ion-conducting cathode, and a liquid electrolyte; the anode comprises lithium metal or sodium metal, or a lithium metal alloy or a sodium metal alloy; The ion-conducting cathode comprises an electroactive sulfur material and a －７ S / cm; The ion-conductive material is conductive ceramic particles that are at least one of LLZO, NLZO, LATP, NATP, LGPS, Na 10 GeP 2 S 12, Li 2 S—P 2 S 5 , or Na 2 S—P 2 S 5 , and / or a polymer blended with a lithium or sodium salt, wherein the polymer is at least one of an acrylate-based polymer, a polyamine, a siloxane, a polyheteroaromatic compound, a polyamide, a polyimide, a polyvinyl, a poly(N-vinylpyrrolidone), a poly(methyl cyanoacrylate), a poly(vinyl acetate), a poly(vinyl alcohol), a poly(vinyl chloride), a poly(vinyl fluoride), a polysilane, a polysilazane, a polyphosphazene, a polyphosphonate, a polyurethane, a polyolefin, or a polyester; and, The liquid electrolyte comprises at least one lithium salt or at least one sodium salt, and the solubility of polysulfides in the liquid electrolyte is less than 500 mM at 20°C. Electrochemical cell.

2. 10. The electrochemical cell of claim 1, wherein the concentration of the at least one lithium or sodium salt in the liquid electrolyte is at least 75% of a saturation concentration of the liquid electrolyte.

3. An electrochemical cell as described in claim 2, wherein the concentration of the at least one lithium salt or sodium salt is at least 80% of the saturated concentration.

4. 4. The electrochemical cell of claim 1, wherein the cathode further comprises a solid electronically conductive material comprising an electronically conductive carbon material or an electronically conductive polymer.

5. 5. The electrochemical cell of claim 4, wherein the electronically conductive carbon material is selected from at least one of carbon nanotubes, carbon nanofibers, graphene, reduced graphene oxide, and carbon black.

6. 5. The electrochemical cell of claim 4, wherein the electronically conductive polymer is selected from at least one of polypyrrole, polythiophene, polyaniline, polyacetylene, polyphenylene vinylene, and poly(3,4-ethylenedioxythiophene).

7. 7. The electrochemical cell of claim 1, wherein the cathode comprises a carbon-sulfur composite material.

8. 8. The electrochemical cell of claim 1, wherein the cathode comprises 1 to 60 wt. % of an ion-conducting material, based on the total weight of the cathode.

9. The electroactive sulfur material is elemental sulfur or Li ２ 9. The electrochemical cell of claim 1, comprising S.

10. At least one lithium salt of the liquid electrolyte is lithium hexafluoroarsenate LiAsF ６ , lithium hexafluorophosphate LiPF ６ , lithium perchlorate LiCLO ４ , lithium sulfate Li ２ SO ４ , lithium nitrate LiNO ３ 10. The electrochemical cell of any one of claims 1 to 9, wherein the lithium ion exchange catalyst is selected from the group consisting of lithium trifluoromethanesulfonate LiOTf, lithium bis(trifluoromethane)sulfonimide LiTFSI, lithium bis(fluorosulfonyl)imide LiFSI, lithium bis(oxalato)borate LiBOB, lithium difluoro(oxalato)borate LiDFOB, lithium bis(pentafluoroethanesulfonyl)imide LiBETI, lithium 2-trifluoromethyl-4,5-dicyanoimidazole LiTDI, and combinations thereof.

11. The liquid electrolyte may be selected from the group consisting of linear ethers, 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), methyl butyrate (MB), methyl ethyl ketone, and acetonitrile (ACN). , propionitrile (PN), isobutyronitrile (iBN), dimethylformamide (DMF), dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), tetramethylurea (TMU), dimethyl sulfoxide (DMSO), trimethyl phosphate, triethyl phosphate, hexamethylphosphoramide, toluene, benzene, heptane, xylene, and dichloromethane; ionic liquids, fluorinated ethers, and mixtures thereof.

12. 12. The electrochemical cell of claim 1, wherein the cathode further comprises a binder, the binder being selected from at least one of PEO, PVDF, and polyphenylene sulfide.

13. 13. The electrochemical cell of claim 12, wherein the binder comprises 1 to 30 wt % of the total weight of the electrode.

14. 14. An electrochemical cell according to any one of claims 1 to 13, wherein the solubility of polysulfides in the liquid electrolyte is less than 400 mM.

15. 15. The electrochemical cell of any one of claims 1 to 14, wherein the electrochemical cell is a lithium-sulfur cell.

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