Additive for lithium-sulfur batteries

Abstract

The disclosed technology relates to a rechargeable electrochemical cell comprising an electroactive sulfur-containing material and an ionically conductive salt, and a thiophosphate / ester / salt redox mediator.

Description

Background Technology

[0001] The disclosed technology relates to a rechargeable electrochemical battery comprising an electroactive sulfur-containing material and an ionicly conductive salt, as well as a thiophosphate / ester / salt redox mediator.

[0002] Lithium-sulfur (Li-sulfur) battery packs are a group of battery pack technologies that possess and will exceed some of the theoretical limits of the performance properties of lithium-ion battery packs. Optimized Li-sulfur battery packs are expected to be safer, cheaper, and have a lower environmental impact than Li-ion battery packs in full commercialization. In particular, elemental sulfur used in the cathode construction is abundant and is generated as a waste product of the oil and gas industry. Unlike Li-ion battery packs or next-generation metal-air battery packs, Li-sulfur battery packs do not require compounds composed of rare or low-abundance elements such as Ni, Mn, Co, Pt, Au, and / or Ag (in most iterations). One advantage of Li-sulfur battery packs over Li-ion battery packs is their potentially higher mass energy density (Wh kg⁻¹), meaning they will be suitable for electrification applications where weight reduction is a priority. This is particularly relevant in the aerospace industry, including electric aircraft, satellites, UAVs (unmanned aerial vehicles), and other military applications, as well as applications such as electrified heavy-duty trucks and marine applications. To achieve the required mass energy density for lithium-sulfur battery packs to be used in a wider range of applications, such as electrified trucks, it is necessary to improve the utilization of sulfur contained in the battery, and more specifically, the utilization of sulfur contained in the cathode material. For these reasons, many companies and academic consortia are actively developing lithium-sulfur battery packs as the next generation of battery pack devices.

[0003] In a basic lithium-sulfur secondary battery, discharge involves a complex multi-step redox cascade that occurs from elemental sulfur (S₈) to lithium sulfide (Li₂S) according to the following proposed reaction: S8 + 16Li+ + 16e- → Li₂S₈ + 14Li⁺ + 14e⁻ →( Li2S6 or Li2S4 or Li2S3 ) Soluble polysulfides → 4Li₂S₂ + 8Li⁺ + 8e⁻ → 8Li2S Both sulfur and lithium sulfide are electrically insulating and practically insoluble in electrolytes. However, lithium polysulfide intermediates in redox cascades are highly soluble (in available liquid electrolytes) and can migrate away from the cathode region and even reach the anode region of the battery, causing battery cycling problems due to competitive chemical reduction that can occur when sulfur-containing intermediates migrate to the anode. This reduces the amount of sulfur available for subsequent electrochemical cycles and allows for unlimited recharge cycles, where polysulfide material "shuttles" between the anode and cathode, undergoing chemical redox cycles instead of electrochemical redox cycles. Furthermore, this shuttle phenomenon can corrode the anode and shorten battery life. Additives that can rapidly mediate electrochemical redox conversions can suppress this phenomenon and enable batteries to maintain higher capacity for longer periods.

[0004] Furthermore, only a portion of the insulating sulfur present as a dispersed fine powder in the cathode composite material is in electrical contact with the conductive carbon matrix of the cathode. To improve the utilization rate of sulfur in the battery pack (during battery discharge), mobile additives and redox intermediates that can enter the non-electrically contacted regions of both S8 (during battery discharge) and deposited Li2S (during battery charging) can bridge this gap through additional redox processes and catalysis. Such additives will allow for more efficient utilization of deposited battery pack sulfur, charging and discharging products.

[0005] Therefore, there is a need for an additive for battery packs containing electroactive sulfur and ionic conductive salts (such as lithium-sulfur battery packs) to mediate electrochemical redox conversion and more fully utilize the charging and discharging products of this conversion. Summary of the Invention

[0006] Therefore, the disclosed technology provides a thiophosphate / ester / salt redox mediator additive for battery packs containing electroactive sulfur and ionic conductive salts to mediate electrochemical redox conversion and more fully utilize the charging and discharging products of the conversion.

[0007] Specifically, this technology includes an electrolyte composition containing a medium (such as a polymeric medium or an organic solvent), a metal salt, and a thiophosphate / ester / salt redox mediator. The metal salt may include, for example, an alkali metal, an alkaline earth metal, a transition metal, or a post-transition metal.

[0008] It also provides cathodes containing materials with electroactive sulfur and redox mediators of thiophosphate / ester / salt.

[0009] More specifically, the electrolyte and cathode can be used together in an electrochemical cell containing a cathode, an anode, and an electrolyte. The cathode itself contains an electroactive sulfur-containing material and a thiophosphate / ester / salt redox mediator. The electrolyte contains a polymer medium or solvent, an ionicly conductive salt, and a thiophosphate / ester / salt redox mediator, provided that the concentration of the thiophosphate / ester / salt redox mediator in at least one of the cathode and the electrolyte is not zero.

[0010] This technology also includes a method for conductive chemical redox conversion in an electrochemical cell containing an ionicly conductive salt and electroactive sulfur, the method comprising preparing an electrochemical cell comprising a) a cathode containing an electroactive sulfur material, b) an anode, and c) an electrolyte, and preparing said electrolyte comprising i) a polymer medium or solvent, ii) an ionicly conductive salt, and iii) a thiophosphate / ester / salt redox mediator, and operating said electrochemical cell.

[0011] This technology also provides the application of thiophosphate / ester / salt redox mediators in conducting chemical redox conversions in electrochemical cells containing ionicly conductive salts and electroactive sulfur. Detailed Implementation

[0012] The preferred features and implementation schemes will now be described in a non-restrictive manner.

[0013] One aspect of the provided technology is a method for conductive chemical redox conversion in an ionicly conductive salt-containing electroactive sulfur rechargeable electrochemical cell using a thiophosphate / ester / salt redox mediator. The thiophosphate / ester / salt redox mediator can be placed in the electrolyte or cathode of the ionicly conductive salt-containing electroactive sulfur rechargeable electrochemical cell. The electrolyte within the electrochemical cell can be liquid, gel, or solid.

[0014] In one embodiment, the technology includes an electrolyte containing a medium, a metal salt, and a thiophosphate / ester / salt redox mediator.

[0015] Electrolytes can be in liquid, quasi-solid, or solid form at room temperature.

[0016] In one embodiment, the electrolyte may be in liquid form at room temperature. In some liquid electrolytes, the medium may include an aprotic organic solvent (or simply abbreviated as "solvent"). Suitable solvents include any of the alkaline (cationically complexed) aprotic polar solvents known or commonly used in lithium-sulfur battery packs, such as polyethers, ethers such as dimethoxyethane, sulfolane, dimethyl sulfoxide, dimethylacetamide, tetramethylurea, N-methylpyrrolidone, tetraethylsulfonamide; ethers such as tetrahydrofuran, methyl-THF, 1,3-dioxane, diethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether and mixtures thereof; carbonates such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, etc.; and esters such as methyl acetate, ethyl acetate, propyl acetate and γ-butyrolactone. Fluorinated solvents, eutectic solvents and solvates (salts in the solvent) may also be used. The electrolyte may contain a single such solvent or a mixture of such solvents. Any of the polar aprotic polymers known in the field of battery packs can be used as a single polymer, as part of a polymer mixture, or as part of a medium along with a solvent. Polymer materials can take the form of a gel. Suitable polymers for electrolytes can include, for example, polyethylene oxide, polyethersulfone, polyvinyl alcohol, and polyimide. Such liquid media are known in the art.

[0017] Liquid electrolytes can also be ionic liquids or sulfone electrolytes. Ionic liquids known in the art are liquids at room temperature and are composed entirely of ions. Sulfone electrolytes are also known in the art, and particularly acyclic aliphatic sulfones, such as ethylmethyl sulfone, exhibit high chemical and thermal stability.

[0018] Liquid electrolyte media can be distributed between compartments in an electrochemical cell. One compartment may contain the electrolyte in contact with the cathode (the electrolyte in such a compartment may be called the cathode electrolyte). Another compartment may contain the electrolyte in contact with the anode (the electrolyte in such a compartment may be called the anodic electrolyte). The anodic and cathode electrolytes may be the same or different from each other, and only one or both of them may contain a thiophosphate / ester / salt redox mediator.

[0019] Electrolytes can also be in solid form, with the medium including solid polymer media. Such solid polymer media are known in the art. Examples of solid polymer media may include sulfide-based solid polymer media, which may include, for example, lithium, phosphorus, and halogen components, as well as metals, metalloids, and lanthanides.

[0020] Electrolytes can also be in quasi-solid form, which contains a certain amount of liquid electrolyte within a solid electrolyte.

[0021] In addition to having a solid and / or liquid medium, the electrolyte composition will also contain one or more salts that impart ionic and / or ionic conductivity to the electrolyte medium. This can include metal salts. The metal of the metal salt can be an alkali metal, alkaline earth metal, transition metal, or post-transition metal. Examples of metals include lithium, sodium, magnesium, and aluminum, as well as their alloys or composites. Conductive salts are well known in the battery pack industry and include lithium salts such as (CF3SO2)2N-, CF3SO3-, CH3SO3-, ClO4-, PF6-, AsF6-, halogens, etc.

[0022] Typically, the conductive salts are lithium salts, such as LiPF6, LiBF4, LiClO4, LiAsF6, LiCF3SO3, and LiC(CnF2n+1SO2)3; lithium imides, such as LiN(CnF2n+1SO2)2 (where n can be an integer from 1 to 20), LiN(SO2F)2, Li2SiF6, LiSbF6, and LiAlCl4; and salts of the general formula (CnF2n+1SO2)mXLi, where m can be defined as follows: m=1 when X can be selected from oxygen and sulfur, m=2 when X can be selected from nitrogen and phosphorus, and m=3 when X can be selected from carbon and silicon. Preferred conductive salts are selected from LiC(CF3SO2)3, LiN(CF3SO2)2, LiPF6, LiBF4, and LiClO4, with LiPF6 and LiN(CF3SO2)2 being particularly preferred.

[0023] In one embodiment, the ionicly conductive salt may include an alkali metal salt, such as a lithium salt. Sodium and other alkali metal salts, as well as mixtures thereof, may also be used.

[0024] The electrolyte composition will further comprise a thiophosphate / ester / salt redox mediator. The electrolyte may comprise one thiophosphate / ester / salt redox mediator or a mixture of several different thiophosphate / ester / salt redox mediators. Thiophosphates / esters / salts that can be used as thiophosphate / ester / salt redox mediators are known in the art and in the literature, and may include, for example, amide-containing dithiophosphites, dithiophosphate diamide esters, dithiophosphate esters, and mixtures thereof.

[0025] Thiophosphate / ester / salt redox mediators can be ionic salts or covalent (nonionic) compounds. Typical thiophosphate / ester / salt compounds that can also be used as redox mediators include dialkyl-substituted thiophosphate / ester / salts, and include mono- and dithiophosphate esters, amine or ammonium salts of acids, and any combination thereof. Esters of thiophosphates include hydrocarbon esters containing 4 to 20 carbon atoms, or 6 to 12 carbon atoms, or 6 to 8 carbon atoms. The hydrocarbon group can be a straight-chain or branched aliphatic or aromatic group.

[0026] In one embodiment, the thiophosphate / ester / salt redox mediator can be a dithiophosphate ester containing a branched alkyl group with 6 to 12 carbon atoms. In one embodiment, the ester group of the thiophosphate ester may contain an acylated hydrocarbon group. The acylated hydrocarbon group includes ester and amide bonds and contains 4 to 20 carbon atoms or 4 to 12 carbon atoms. The thiophosphate / ester / salt redox mediator can be represented by formula (I):

[0027] (I)

[0028] Where X is oxygen or sulfur; each R1 is independently a straight-chain or branched aliphatic hydrocarbon group containing 3 to 18 carbon atoms, 3 to 10 carbon atoms, or 6 to 8 carbon atoms; R2 is a branched or straight-chain hydrocarbon group containing 4 to 20 carbon atoms, or an acylated hydrocarbon group (-R3-(C=O)-Y-R4) containing 4 to 20 carbon atoms; and R3 is a hydrocarbon group containing 1 to 6 carbon atoms, Y is O or N-R5, and R4 and R5 are each independently a hydrocarbon group containing 1 to 12 carbon atoms. Suitable alkyl groups (R1 and R2) include ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, pentyl, methylpentyl, n-pentyl, n-hexyl, n-octyl, isooctyl, 2-ethylhexyl, n-decyl, isodecyl, n-dodecyl, 2,4,4-trimethylpentyl, 2-octyl, 2-decyl, and 2-dodecyl.

[0029] In one embodiment, the thiophosphate may be a thiophosphate of formula (II) with an acylated hydrocarbon group:

[0030] (II)

[0031] Where X is oxygen or sulfur; each R 1 Independently, it is a straight-chain or branched aliphatic hydrocarbon group containing 3 to 18 carbon atoms, 3 to 10 carbon atoms, or 6 to 8 carbon atoms; Y is O or NR. 5 ;R 4 and R 5 Each is independently an H or a hydrocarbon group with 1 to 12 carbon atoms; and R 6 It is a hydrogen or hydrocarbon group with one to four carbon atoms. A suitable alkyl group (R...) 4 and R 5 () includes methyl, ethyl, propyl, butyl, sec-butyl, pentyl, hexyl, and 2-ethylhexyl. In some embodiments, R 4 It can be a hydrocarbon group attached to two or more amide nitrogen atoms, thereby producing a bridging dimer, oligomer, or even polymeric composition.

[0032] Other covalent thiophosphate / ester compounds that can be used as redox mediators include disulfide compounds of formula (III):

[0033] (III)

[0034] Where X is oxygen or sulfur; n is 0, 1, or 2; each R 1 Independently, it is a straight-chain or branched aliphatic hydrocarbon group containing 3 to 18 carbon atoms, 3 to 10 carbon atoms, or 6 to 8 carbon atoms. Suitable alkyl groups (R1) include ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, pentyl, methylpentyl, n-pentyl, n-hexyl, n-octyl, isooctyl, 2-ethylhexyl, n-decyl, isodecyl, and n-dodecyl.

[0035] Ionic thiophosphate compounds include metal, amine, and ammonium salts of dialkyl-thiophosphate. As described above, these thiophosphates can be mono- or dithiophosphates or mixtures thereof. In one embodiment, the thiophosphate can be a salt of dialkyl-thiophosphate, wherein the alkyl group is independently a straight-chain or branched aliphatic hydrocarbon group containing 3 to 18 carbon atoms, 3 to 10 carbon atoms, or 6 to 8 carbon atoms.

[0036] The amine salt of the thiophosphate can be a salt of a primary, secondary, or tertiary alkyl amine, wherein each alkyl group independently contains 1 to 20 carbon atoms; 4 to 12 carbon atoms; or 6 to 10 carbon atoms. In one embodiment, a secondary or tertiary amine may be selected such that two or more alkyl groups together form one or more 5- or 6-membered cyclic structures. Suitable amines include ethylamine, diethylamine, triethylamine, propylamine, isopropylamine, dipropylamine, diisopropylamine, butylamine, dibutylamine, sec-butylamine, tert-butylamine, pentylamine, 2-ethylhexylamine, bis(2-ethylhexylamine), tri(2-ethylhexylamine), decylamine, undecylamine, dodecylamine, piperidine, tetramethylpiperidine, aniline, and alkylated aniline.

[0037] Ammonium dithiophosphate can be a salt of quaternary ammonium or a mixture thereof. The cationic form of the ammonium salt can be represented by formula (IV):

[0038] (IV)

[0039] Among them, R a R b R c and R dEach is independently an H or a hydrocarbon group with 2 to 24 carbon atoms, 4 to 20 carbon atoms, or 6 to 18 carbon atoms. Examples of suitable hydrocarbon groups include ethyl, propyl, butyl, pentyl, methylpentyl, pentyl, n-hexyl, n-octyl, isooctyl, 2-ethylhexyl, n-decyl, isodecyl, n-dodecyl, isodecyl, n-tetradecyl, n-hexadecyl, n-octadecyl, oleyl, and other commonly named groups such as lauryl, cocoyl, oleyl, tallow, stearyl, cetyl, and benzyl.

[0040] In one embodiment, the phosphorus-containing ionic compound may be a metal salt of dialkyl dithiophosphate, which may include zinc dialkyl dithiophosphate. Such salts are commonly referred to as dialkyl dithiophosphates (DDP) or simply dithiophosphates (DP). They are well-known to those skilled in the art of lubricant formulation and are readily available. Metal dithiophosphates (MDDP or MDP) include salts of zinc, antimony, calcium, magnesium, lithium, copper, cobalt, iron, manganese, molybdenum, tungsten, vanadium, tin, and combinations thereof. In one embodiment, the metal dithiophosphate may be zinc or lithium. Examples of suitable metal dialkyl dithiophosphates that can be used as redox mediators for thiophosphates / esters / salts include metal salts of formula (V):

[0041] (V)

[0042] Each R 1 Independently, it is a straight-chain or branched aliphatic hydrocarbon group containing 3 to 18 carbon atoms, 3 to 10 carbon atoms, or 6 to 8 carbon atoms; n is an integer of 1, 2, 3, or 4 that matches the valence of the metal; and M is a metal with the valence "n", and typically includes zinc, copper, iron, cobalt, antimony, lithium, manganese, and combinations thereof.

[0043] Broadly speaking, the concentration of the redox mediator in the electrolyte composition can range from 0 mM or 0.1 mM to 100 mM, and can be in the range of 0.5 mM to 50 mM, or 1 mM to 40 mM, or even 1.5 mM to 30 mM. In many embodiments, the concentration of the redox mediator in the electrolyte composition can be in the range of 0 mM or 0.5 mM to 10 mM, particularly 1 mM to 9 mM or 1.5 mM to 8 mM.

[0044] The electrolyte described above can be used in an electrochemical cell that further includes an anode (i.e., the oxidation electrode during discharge cycles) and a cathode (i.e., the reduction electrode during discharge cycles). In a battery pack used as a device for converting chemical energy into electrical energy, the electrode with the higher electrochemical potential is called the positive electrode, and the electrode with the lower electrochemical potential is called the negative electrode. As used herein, conventional battery pack nomenclature is employed, where the terms "cathode" or "positive electrode" and "anode" or "negative electrode" refer to the electrochemical function of the electrode that converts stored chemical energy into electrical energy during battery discharge. During the charging portion of a cycle, the actual electrochemical function of the electrode is the opposite of the electrochemical function that occurs during discharge.

[0045] The cathode can be prepared from an electroactive sulfur-containing material as described above and optionally a thiophosphate / ester / salt redox mediator. Broadly speaking, the concentration of the redox mediator in the cathode can range from 0 mM or 0.1 mM to 100 mM, and can be in the range of 0.5 mM to 50 mM, or in the range of 1 mM to 40 mM, or even in the range of 1.5 mM to 30 mM. In many embodiments, the concentration of the redox mediator in the electrolyte composition can be in the range of 0 mM to 10 mM, or in the range of 0.5 mM to 10 mM, or 1 mM to 9 mM, or 1.5 mM to 8 mM.

[0046] The cathode comprises elemental sulfur, elemental selenium, or a mixture of elemental chalcogenides. In one embodiment, the cathode is further composed of one or more materials containing electroactive sulfur. The cathode may additionally and / or alternatively comprise a polymeric medium and / or conductive additives. Suitable polymeric media include, for example, polyvinyl alcohol, polyacrylonitrile, polyvinylidene fluoride (PVDF), polyvinyl fluoride, polytetrafluoroethylene (PTFE), copolymers of tetrafluoroethylene and hexafluoropropylene, copolymers of vinylidene fluoride and hexafluoropropylene, copolymers of vinylidene fluoride and tetrafluoroethylene, ethylene-propylene-diene monomer rubber (EPDM), and polyvinyl chloride (PVC). Conductive additives may be, for example, carbon in a conductive form, such as graphite, graphene, carbon fibers, carbon nanotubes, carbon black, or carbon in a pre-conductive form, such as polyacrylonitrile or pitch, or soot (e.g., lamp or furnace soot). The cathode may be present in a battery pack or electrochemical cell in combination with a current collector (such as any current collector known in the field of battery packs or electrochemical cells). For example, the cathode may be coated on the surface of a metal current collector.

[0047] Therefore, in a simple embodiment, the present technology provides an electrochemical cell having a cathode, an anode, and an electrolyte, the cathode itself having an electroactive sulfur-containing material and an optional (e.g., 0 mM to 100 mM) thiophosphate / ester / salt redox mediator, the electrolyte containing a polymeric medium or solvent, an ionicly conductive salt, and an optional (e.g., 0 mM to 100 mM) thiophosphate / ester / salt redox mediator; provided that the concentration of at least one of the cathode thiophosphate / ester / salt redox mediator and the electrolyte thiophosphate / ester / salt redox mediator is not zero.

[0048] Electroactive sulfur-containing materials for cathodes are known in the art and can be covalent compounds such as elemental sulfur or polymers containing polysulfide bridges, or ionic compounds such as sulfides or polysulfide salts. Preferred electroactive sulfur-containing materials are those containing at least one Li-S- group, such as Li2S, lithium polysulfides (Li2S2 to Li2S), or lithium thiols (lithium thiols), especially Li2S.

[0049] In one embodiment, the cathode containing electroactive sulfur can be Li2S.

[0050] During the charging process of an electrochemical cell, as more and more SS bonds are formed, the cathode can include a mixture of different electroactive sulfur-containing materials.

[0051] In addition to materials containing electroactive sulfur, the cathode may also include one or more other components. For example, the cathode may contain carbon in a conductive polymorph, such as selected from graphite, carbon black, carbon nanotubes, graphene, or carbon in a pre-conductive form, such as polyacrylonitrile or pitch, or a mixture of at least two of the foregoing. Suitable carbon in a conductive polymorph is described on page 4, line 30 to page 6, line 22 of WO 2012 / 168851, which is incorporated herein by reference.

[0052] In addition, the cathode may include one or more polymeric media, such as one or more organic polymers. Suitable polymeric media are described on page 6, line 40 to page 7, line 30 of WO 2012 / 168851, which is incorporated herein by reference. Polymeric media particularly suitable for use as cathodes include polyvinyl alcohol, poly(ethylene oxide), carboxymethyl cellulose (CMC), and halogenated (co)polymers, such as polyvinyl chloride or polyvinylidene chloride, especially fluorinated (co)polymers, such as polyvinylidene fluoride, and especially polyvinylidene fluoride, lithium-ion Nafion, and polytetrafluoroethylene.

[0053] In one embodiment, based on the total mass of all materials containing electroactive sulfur, all carbon in conductive polymorphs, and all polymer media, the cathode may include sulfur in the range of 10 wt% to 80 wt%, preferably 30 wt% to 60 wt%, as determined by elemental analysis.

[0054] In one embodiment, based on the total mass of all electroactive sulfur-containing materials, all carbon in conductive polymorphs, and all polymer media, the cathode may contain conductive polymorphic carbon in the range of 0.1 wt% to 60 wt%, preferably 1 wt% to 40 wt%. This carbon can also be determined by elemental analysis, for example, in which case the evaluation of elemental analysis must take into account the fact that carbon is also present in the organic polymers representing the polymer media, as well as other possible sources.

[0055] In one embodiment, based on the total mass of all materials containing electroactive sulfur, all carbon in conductive polymorphs, and all polymer media, the cathode may contain polymer media in the range of 0.1 wt% to 20 wt%, preferably 1 wt% to 15 wt%, more preferably 3 wt% to 10 wt%.

[0056] In addition, the cathode can have other components that are conventional to it, such as a current collector, which can be configured in the form of metal wire, metal grid, metal mesh, stretched metal, metal sheet, metal foil, or carbon paper / cloth. Suitable metal foil is especially aluminum foil.

[0057] In one embodiment, the cathode has a thickness in the range of 25 μm to 200 μm, preferably 30 μm to 100 μm, based on the thickness without a current collector.

[0058] The anode of an electrochemical cell can be made of a material, for example, capable of accepting Li ions in metallic form, such as an alkali metal, such as lithium or sodium, or another active material or composition. Anode materials can include metallic lithium, lithium alloys, metallic sodium, sodium alloys, alkali metals or alloys thereof, metal powders, alloys of lithium with aluminum, bismuth, magnesium, copper, silicon and / or tin, alkali metal-carbon and alkali metal-graphite intercalations, hard carbon, soft carbon, graphitic carbon, amorphous carbon, graphene, graphite (and especially mixtures of graphite, intercalated graphite, and two or more of the aforementioned carbons), compounds capable of reversibly oxidizing and reducing with alkali metal ions, and mixtures thereof. The metal or metal alloy (e.g., metallic lithium) can be contained within the battery pack as a film, or as several films optionally separated by a ceramic material. Suitable ceramic materials include, for example, silicon dioxide, alumina, or lithium-containing glassy materials such as lithium phosphate, lithium aluminate, lithium silicate, lithium phosphorus nitride, lithium tantalum oxide, lithium aluminosilicate, lithium titanium oxide, lithium silicon sulfide, lithium germanium sulfide, lithium aluminum sulfide, lithium boron sulfide, lithium phosphorus sulfide, and mixtures thereof.

[0059] The anode may further contain one or more polymer media. The selected polymer media may be one or more of the aforementioned polymer media specified in the context of the description of the cathode.

[0060] In addition, the anode can have other components that are conventional to it, such as a current collector that can be configured in the form of metal wire, metal grid, metal mesh, stretched metal, or metal foil or sheet. Suitable metal foil is, in particular, copper foil.

[0061] In one embodiment, the anode has a thickness in the range of 15 μm to 1000 μm, preferably 30 μm to 750 μm or 60 μm to 500 μm, based on the thickness without a current collector.

[0062] The rechargeable electrochemical batteries described above can also have their own conventional components, such as separators, cable connections, and casings.

[0063] The rechargeable electrochemical cells described in this article offer high voltage, and notably, high energy density and good stability. More specifically, due to the thiophosphate / ester / salt redox mediator, they exhibit increased capacity and improved cycle stability.

[0064] The rechargeable electrochemical battery of the present invention can be assembled into an alkali metal ion battery pack, preferably a rechargeable alkali metal ion battery pack, and especially a rechargeable lithium ion battery pack.

[0065] The rechargeable electrochemical battery of the present invention can be combined with each other, for example, in series or in parallel, in the rechargeable alkali metal ion battery pack of the present invention, especially in the rechargeable lithium ion battery pack. Series connection is preferred.

[0066] The notable features of the rechargeable electrochemical battery of the present invention are its exceptionally high capacity, high performance even after repeated charging, and significantly delayed battery failure. The rechargeable electrochemical battery of the present invention is well-suited for use in motor vehicles, electric bicycles (e.g., e-bikes), aircraft, ships, or stationary energy storage devices. This application constitutes another part of the subject matter of the invention.

[0067] The present invention further provides the use of the rechargeable electrochemical battery of the present invention as described above in motor vehicles, electric bicycles, aircraft, ships or stationary energy storage devices.

[0068] Using the rechargeable metal-ion battery pack of the present invention, especially the rechargeable lithium-ion battery pack, in a device has the advantages of extended operating time before recharging and less capacity loss during the extended operating time. If the intention is to achieve the same operating time with an electrochemical battery having a lower energy density, the higher weight of the electrochemical battery must be accepted.

[0069] Therefore, the present invention further provides the use of the rechargeable metal-ion battery pack, and in particular the rechargeable lithium-ion battery pack, of the present invention in devices, especially mobile devices. Examples of mobile devices are vehicles, such as motor vehicles (including cars, trucks, buses, and any other motor vehicles), bicycles, airplanes, or water vehicles such as boats or ships. Other examples of mobile devices are portable ones, such as computers, especially laptops, telephones, or electrical devices, such as those from the construction field, especially drill bits, battery-powered screwdrivers, or battery-powered trackers. The use provides an increase in battery capacity relative to a baseline (i.e., without thiophosphate / ester / salt redox mediators), and a continuous increase in battery capacity relative to a baseline during battery pack cycling.

[0070] The present invention further provides an apparatus comprising at least one rechargeable electrochemical battery as described above.

[0071] This technology further provides a method for conductive chemical redox conversion in an electrochemical cell containing an ionicly conductive salt and electroactive sulfur. The method includes preparing an electrochemical cell comprising a) a cathode containing an electroactive sulfur material, b) an anode, and c) an electrolyte; preparing the electrolyte comprising i) a polymer medium or solvent, ii) an ionicly conductive salt, and iii) a thiophosphate / ester / salt redox mediator; and operating the electrochemical cell.

[0072] Additionally, the application of thiophosphate / ester / salt redox mediators in conducting chemical redox conversions in electrochemical cells containing ionicly conductive salts and electroactive sulfur is provided.

[0073] As used herein, the term "hydrocarbon group" refers to a group having carbon atoms directly connected to the remainder of the molecule, wherein the group comprises at least carbon and hydrogen atoms. If the hydrocarbon group contains more than one carbon atom, these carbons do not necessarily have to be connected to each other. For example, at least two carbons may be connected via suitable elements or groups. In various embodiments, the term "hydrocarbon group" refers to a group having carbon atoms directly connected to the remainder of the molecule, wherein the group consists of carbon, hydrogen, and optionally one or more heteroatoms, provided that the heteroatoms do not alter the predominantly hydrocarbon nature of the substituent. Heteroatoms may connect at least two carbons in the hydrocarbon group and optionally no more than two non-hydrocarbon substituents. Suitable heteroatoms will be apparent to those skilled in the art and include, for example, sulfur, nitrogen, oxygen, phosphorus, and silicon. When the hydrocarbon group contains heteroatoms, optionally, no more than two heteroatoms will be present for every ten carbon atoms in the hydrocarbon group. Suitable non-hydrocarbon substituents will also be apparent to those skilled in the art and include, for example, halogenated, hydroxyl, alkoxy, mercapto, alkyl mercapto, nitro, nitroso, and thionyl groups.

[0074] Therefore, examples of hydrocarbon groups in the context of this technology include: Hydrocarbon groups, selected from aliphatic (e.g., alkyl or alkenyl), alicyclic (e.g., cycloalkyl, cycloalkenyl, cyclodienyl) and aromatic groups; The substituted hydrocarbon group is selected from the hydrocarbon group defined in (i) that is substituted by no more than two non-hydrocarbon substituents and / or one or more hydrocarbon substituents, wherein the non-hydrocarbon substituents are selected from the group consisting of: halogen, hydroxyl, alkoxy, mercapto, alkyl mercapto, nitro, nitroso and thionyl. A hydrocarbon group containing heteroatoms is selected from hydrocarbon groups defined in (i) that contain one or more heteroatoms in a ring or chain, provided that no more than two heteroatoms are present for every ten carbon atoms in the group, and the heteroatoms are selected from sulfur, nitrogen, oxygen, phosphorus, and silicon. A hydrocarbon group containing heteroatoms may be substituted by no more than two non-hydrocarbon substituents and / or one or more hydrocarbon substituents.

[0075] In some implementations, the term "hydrocarbon group" refers to a group having carbon atoms directly attached to the rest of the molecule, wherein the group consists of carbon atoms and hydrogen atoms.

[0076] It is known that some of the substances described above can interact in the final formulation, such that the composition of the final formulation may differ from those initially added. For example, metal ions can migrate to other acidic or anionic sites of other molecules. The resulting products, including those formed when the compositions of the present invention are used for their intended purpose, may not be easily described. However, all such modifications and reaction products are included within the scope of the present invention; the present invention includes compositions prepared by mixing the above-described components.

[0077] Examples of methods for preparing the three dithiophosphates of Examples 1 to 12 : Dithiophosphate 1: S-hydrodithiophosphate O,O-di(isooctyl ester)

[0078] Isooctanol (100 ol) (352 g) was charged into a 1 L flanged flask in a heating mantle and heated to 70 °C. The flask was equipped with a PTFE stirrer and thermocouple, an N2 inlet at the top of a powder feeding funnel with a rubber stopper, a water-cooled condenser with venting, and a Dreschel alkaline washer containing up to 20 wt% bleach. P2S5 (150 g) was added in portions of 20 g over 1 hour. The powder feeding funnel was then replaced with a subsurface N2 bubbling system, and the reaction was heated to 110 °C for 2 hours, followed by cooling to room temperature. The mixture was then filtered to give dithiophosphate 1 as a pale yellow liquid in quantitative yield.

[0079] Dithiophosphate 2: a mixture of diisobutyl and pentyl dithioic acid

[0080] A mixture of 61 / 39 wt% pentanol and isobutanol (396 g) was charged into a 1 L flanged flask in a heating mantle and heated to 65 °C. The flask was equipped with a PTFE stirrer and thermocouple, an N2 inlet at the top of a powder feeding funnel with a rubber stopper, a water-cooled condenser with venting, and a Dreschel alkaline washer containing up to 20 wt% bleach. Phosphorus pentasulfide (V) (200 g) was added in portions of 20 g each over 1 hour. The powder feeding funnel was then replaced with a subsurface N2 inlet, and the mixture was heated to 100 °C for 2 hours. The reaction was then reconfigured for vacuum distillation, and residual alcohol was removed under reduced pressure to give dithiophosphate 2 as a pale yellow liquid in quantitative yield.

[0081] Dithiophosphate 3: S-hydrodithiophosphate O,O-bis(4-methylpentan-2-ester)

[0082] 312 g of 4-methyl-2-pentanol (MPL) was charged into a 1 L flanged flask in a heating mantle and heated to 70 °C. The flask was equipped with a PTFE stirrer and thermocouple, an N2 inlet at the top of a powder feeding funnel with a rubber stopper, a water-cooled condenser with venting, and a Dreschel alkaline washer containing up to 20 wt% bleach. P2S5 (150 g) was added in portions of 20 g over 1 hour. The powder feeding funnel was then replaced with a subsurface N2 bubbling system, and the reaction was heated to 110 °C for 2 hours, followed by cooling to room temperature. The reaction was then reconfigured for vacuum distillation, and residual alcohol was removed under reduced pressure to give a pale yellow liquid dithiophosphate 3 in quantitative yield.

[0083] Preparation Examples (1-12) : Example 1: bis(dithiophosphate)S,S'-((methylenebis(azanediyl))bis(3-oxopropane-3,1-di) Ester))O,O,O',O'-Tetra(isooctyl ester)

[0084] Dithiophosphate 1 (483 g) was heated to 65°C in a 1 L flanged flask containing an N2 inlet, a condenser, a PTFE thermocouple, a top-mounted stirrer, and a caustic Dreschel flask. N,N'-methylenebisacrylamide (84 g) was added in portions over 45 minutes, and the reaction was maintained at 65°C for 4 hours. After completion, the reactants were absorbed into heptane (100 ml), washed with 1 M NaOH (3 × 50 ml), dried (MgSO4), and concentrated under reduced pressure to give Example 1 (245 g), a pale yellow oil.

[0085] Example 2: Methyl 3-((dialkoxythiophosphoryl)thio)propionate (alkyl = isobutyl and pentyl)

[0086] Phosphothiophosphate 2 (100 g) was added to a 250 ml round-bottom flask equipped with an N2 inlet, condenser, PTFE thermocouple, stir bar, and caustic Dreschel flask on a hot plate stirrer and heated to 65 °C. Methyl acrylate (31 g) was added in portions over 30 minutes via a dropping funnel, maintaining the temperature below 70 °C. After complete addition, the reaction was maintained at 60 °C for 4 hours, then cooled to room temperature. The resulting oil was absorbed in heptane (100 ml) and washed with 1 M NaOH (3 × 50 ml), then dried (MgSO4) and concentrated under reduced pressure to give Example 2 (115 g), a pale yellow oil.

[0087] Example 3: Tris(dithiophosphoric acid)S,S',S''-((1,3,5-triazine-1,3,5-triyl)tris(3-oxopropyl) Alkyl-3,1-diester))O,O,O',O',O'',O''-hexa(isooctyl ester)

[0088] Phosphophosphate 1 (50 g) was heated to 65°C in a 100 mL round-bottom flask equipped with an N2 inlet, condenser, PTFE thermocouple, stir bar, and caustic Dreschel flask on a hot plate stirrer. 1,3,5-Triacryloylhexahydro-1,3,5-triazine (10.5 g) was added in portions over 45 minutes, and the reaction was maintained at 65°C for 4 hours. After completion, the reactants were absorbed into heptane (100 mL), washed with 1 M NaOH (3 × 50 mL), dried (MgSO4), and concentrated under reduced pressure. Further purification was possible by column chromatography, eluting with EtOAc / heptane (1:9 → 1:1 gradient). This yielded Example 3 (15 g), a pale yellow oil.

[0089] Example 4: Dithiophosphate S-(3-(diethylamino)-3-oxopropyl ester)O,O-di(isooctyl ester)

[0090] Phosphophosphate 1 (50 g) was heated to 65°C in a 100 mL round-bottom flask equipped with an N2 inlet, condenser, PTFE thermocouple, stir bar, and caustic Dreschel flask on a hot plate stirrer. Diethylacrylamide (16 g) was added in portions via a dropping funnel over 45 minutes, and the reaction was maintained at 65°C for 4 hours. After completion, the reactants were absorbed into heptane (100 mL), washed with 1 M NaOH (3 × 50 mL), dried (MgSO4), and concentrated under reduced pressure. Further purification was achieved by column chromatography, eluting with EtOAc / heptane (1:9 to 1:1 gradient). This yielded Example 4 (13 g), a pale yellow oil.

[0091] Example 5: Methyl 3-((bis(isooctyloxy)thiophosphoryl)thio)propionate

[0092] Phosphophosphate 1 (50 g) was heated to 65°C in a 100 mL round-bottom flask equipped with an N2 inlet, condenser, PTFE thermocouple, stir bar, and caustic Dreschel flask on a hot plate stirrer. Methyl acrylate (10.8 g) was added in portions via a dropping funnel over 45 minutes, and the reaction was maintained at 65°C for 4 hours. After completion, the reactants were absorbed into heptane (100 mL), washed with 1 M NaOH (3 × 50 mL), dried (MgSO4), and concentrated under reduced pressure. Further purification was possible by column chromatography, eluting with EtOAc / heptane (1:9 to 1:1 gradient). This yielded the title compound Example 5 (20 g), a pale yellow oil.

[0093] Example 6: 2-Ethylhexyl 3-((dialkoxythiophosphoryl)thio)propionate (alkyl = isobutyl and pentyl)

[0094] Phosphophosphate 2 (25 g) was heated to 65°C in a 100 mL round-bottom flask equipped with an N2 inlet, condenser, PTFE thermocouple, stir bar, and caustic Dreschel flask on a hot plate stirrer. 2-Ethylhexyl propionate (16.6 g) was added in portions via a dropping funnel over 45 minutes, and the reaction was maintained at 65°C for 4 hours. After completion, the reactants were absorbed into heptane (100 mL), washed with 1 M NaOH (3 × 50 mL), dried (MgSO4), and concentrated under reduced pressure. Further purification was achieved by column chromatography, eluting with EtOAc / heptane (1:9 → 1:1 gradient). This yielded Example 6 (10 g), a pale yellow oil.

[0095] Example 7: Dithiophosphate S-(3-amino-3-oxopropyl ester)O,O-di(isooctyl ester)

[0096] Phosphophosphate 1 (50 g) was heated to 65°C in a 100 mL round-bottom flask equipped with an N2 inlet, condenser, PTFE thermocouple, stir bar, and caustic Dreschel flask on a hot plate stirrer. Methyl acrylate (9 g) was added in portions over 45 minutes, and the reaction was maintained at 65°C for 4 hours. After completion, the reactants were absorbed into heptane (100 mL), washed with 1 M NaOH (3 × 50 mL), dried (MgSO4), and concentrated under reduced pressure. Further purification was possible by column chromatography, eluting with EtOAc / heptane (1:9 → 1:1 gradient). This yielded Example 7 (7 g), a pale yellow oil.

[0097] Example 8: bis(phosphoric acid thiophosphate)S,S'-((methylenebis(azanediyl))bis(3-oxopropane-3,1-di) Ester))O,O,O',O'-Tetra(isooctyl ester)

[0098] Dithiophosphate 1 (50 g) was heated to 65 °C for 12 hours in a 100 ml round-bottom flask equipped with an N2 inlet, condenser, PTFE thermocouple, stirrer, and caustic Dreschel flask on a hot plate stirrer with a N2 inlet, condenser, PTFE thermocouple, stirrer, and caustic Dreschel flask. Then, N,N'-methylenebisacrylamide (8.6 g) was added in portions over 45 minutes, and the reaction was maintained at 65 °C for 4 hours. After completion, the reactants were absorbed into heptane (100 ml), washed with 1 M NaOH (3 × 50 ml), dried (MgSO4), and concentrated under reduced pressure. Further purification was achieved by column chromatography, eluting with acetone / SBP-3 (1:9 to 1:1 gradient). This yielded Example 8 (8 g), a pale yellow oil.

[0099] Example 9: O,O-di(isooctyl)-2-ethylhexylammonium dithiophosphate

[0100] Dithiophosphate 1 (50 g) was charged into a 100 ml round-bottom flask equipped with an N2 inlet, condenser, PTFE thermocouple, stir bar, and caustic Dreschel flask mounted on a hot plate stirrer. 2-Ethylhexylamine (18.2 g) was added dropwise through a dropping funnel over 45 minutes, maintaining the reaction temperature below 30°C. After complete addition, the reaction was heated to 60°C and maintained for 4 hours. This yielded Example 9, a pale yellow oil, in quantitative yield.

[0101] Example 10: bis(dithiophosphate)S,S'-((methylenebis(azanediyl))bis(3-oxopropane-3,1-di) Ester))O,O,O',O'-Tetra(4-methylpentane-2-ester)

[0102] Phosphothiophosphate 3 (207 g) was heated to 65°C in a 500 ml round-bottom flask equipped with an N2 inlet, condenser, PTFE thermocouple, stir bar, and caustic Dreschel flask on a hot plate stirrer. N,N'-methylenebisacrylamide (52 g) was added in portions over 45 minutes, and the reaction was maintained at 65°C for 4 hours. After completion, the reactants were absorbed into heptane (100 ml), washed with 1 M NaOH (3 × 50 ml), dried (MgSO4), and concentrated under reduced pressure to give Example 10 (121 g), a pale yellow oil.

[0103] Example 11: O,O-bis(4-methylpentane-2-ester) disulfide of dithiophosphate

[0104] Dithiophosphate 3 (1476 g) was added to a 3 L jacketed vessel equipped with an N2 inlet, a dropping funnel, a PTFE top stirrer and PTFE thermocouple, a condenser, and an alkaline washer, and the mixture was heated to 35 °C. H2O2 (364 g) was pumped in over 2 hours using a peristaltic pump (approximately 3.1 g / min). The reaction was then maintained at 35 °C for 3 hours, followed by cooling and standing overnight. The aqueous layer was separated, and the organic layer (MgSO4) was dried. The mixture was then concentrated under reduced pressure to a quantitative yield of Example 11, a pale yellow liquid.

[0105] Example 12: O,O-bis(4-methylpentan-2-ester)S-(oct-2-ester) dithiophosphate

[0106] Dithiophosphate 3 (182 g) and 1-octene (68 g) were heated to 90 °C in a 500 ml round-bottom flask equipped with an N2 inlet, condenser, PTFE thermocouple, stir bar, and caustic Dreschel flask on a hot plate stirrer. After completion, the reactants were absorbed into heptane (100 ml), washed with 1 M NaOH (3 × 50 ml), dried (MgSO4), and concentrated under reduced pressure to give Example 12 (230 g), a pale yellow liquid.

[0107] It has been found that, with low treatment and low contribution (e.g., 1% additional sulfur) to the total battery pack sulfur content, thiophosphate / ester / salt redox mediators have increased the cyclic discharge capacity of model lithium-sulfur rechargeable battery packs in the form factor of standard Swagelok batteries. The improvement in discharge capacity is impressive, with an improvement of >70% relative to the unadded battery within the first 20 cycles.

[0108] New materials and electrolytes for lithium-sulfur battery packs should be tested in terms of the scale and form factor at which they will eventually be used; however, the use of coin cells is necessary for screening purposes. Additional testing at the 1 amp-hour pouch cell scale can demonstrate performance for similar commercially viable battery pack configurations in more realistic scenarios.

[0109] Tests related to the above samples were conducted using three different battery configurations: Swagellock batteries, button batteries, and pouch batteries. The following is a description of the configurations and materials required for button battery manufacturing that can be replicated by those skilled in the art.

[0110] Button cell construction: All button cell construction was carried out in a glove box under an argon atmosphere.

[0111] Electrolyte composition: The electrolyte composition consists of a 1:1 dioxacyclopentane (DOL):dimethoxyethane (DME) (anhydrous) solvent. In addition to the solvent, the following materials are also present: 1M LiTFSI (lithium bis(trifluoromethane)sulfonylimide) and up to 0.8M LiNO3, but for the data contained in Table 1, the LiNO3 concentration used in the embodiments of the present invention is 5mM. The electrolyte solution is prepared in a glove box under an argon atmosphere. The solvent is further dried on a molecular sieve before use. The LiTFSI is weighed, followed by the LiNO3 (in an amount sufficient to achieve a final molar concentration of 0.8M), and then they are combined and then added to the premixed DOL:DME solution.

[0112] Cathode: The cathode material used is a commercially available sulfur-carbon composite material (supplied by NEI). Before being used in button cells, the cathode material is cut into 10mm to 12mm discs and then dried at room temperature under vacuum.

[0113] Diaphragm: The diaphragm is Celguard-2400, pre-stamped into a 15mm disc, and dried under vacuum at 40°C for 72 hours.

[0114] Anode preparation: The anode used is a lithium metal disc (held in a glove box under an argon atmosphere) and is stamped into a disc of 12mm to 14mm. Before button cell construction, the surface of the lithium needs to be gently rubbed with a plastic tool to remove any layers formed by contaminants / surface reactions. The lithium is then gently flattened to avoid any dimensional changes during button cell winding.

[0115] Button battery assembly: Before use, dry the following materials under vacuum at 70°C and then store them in a glove box under an argon atmosphere; Button battery top casing (large) Button battery bottom casing (small) Button battery gasket (usually already attached to the bottom casing of the button battery) 2 x 0.5mm stainless steel spacers Button battery wave spring Electrolyte solution 15mm Celgard 2400 diaphragm 12mm to 14mm lithium (anode) disks, and 10mm to 12mm cathode disk.

[0116] Construct the battery as follows, adding each of the following components to the initial bottom casing: spacer disk, lithium disk, diaphragm disk, electrolyte added via micropipette (electrolyte volume depends on sulfur load; the electrolyte-to-sulfur ratio is typically kept below 30 μL / Mg), cathode, spacer disk, wave spring, and the top casing of the coin cell (finished product). After construction, roll the coin cell to 50 kg m -2 The pressure.

[0117] Button cell battery testing: After assembly, remove the button cells from the glove box and place them in an oven, where they are cycled at 40°C. Let them rest for 8 hours. Begin with a discharge process applying a negative current, using a constant current between the potential limits of 1.8V and 2.6V to achieve constant current cycling (from the start of discharge). Do not use a constant voltage step.

[0118] In the formation process, the battery undergoes three cycles at a symmetrical charge-discharge rate of 1 / 20C, after which the desired test can begin with a symmetrical charge-discharge cycle at a rate of 1 / 10C. A 1C cycle rate corresponds to the current required to fully charge or discharge the battery within one hour. Therefore, a charge-discharge rate of, for example, 1 / 10C means that the charge-discharge current should allow the expected capacity to be fully charged or discharged within 10 hours. The exact current depends on the total sulfur mass in the battery (because these batteries are constructed with the sulfur-containing cathode as a rate-limiting factor).

[0119] The performance of button cells was studied by charge-discharge cycling using commercially available battery cyclers (e.g., Ivium, BioLogic).

[0120] Table 1

[0121] It is noteworthy that the battery packs used above are constructed with commercially available carbon-sulfur cathodes, rather than highly optimized custom cathodes. This makes the improvement all the more impressive and may mean that this discovery will contribute to improving the performance of commercially manufactured lithium-sulfur battery packs (through the high-throughput manufacturing techniques currently known in the art). It is believed that the additive brings about this improvement by advantageously interacting with sulfur via a multi-step redox process to form Li₂S, and this interaction increases the utilization of available sulfur in the battery, thus bringing the battery closer to its theoretical maximum capacity. Advantageously, the additive disclosed herein is also free of rare metals and relatively easy to produce compared to other redox mediators demonstrated in the literature, making the additive cost-effective and contributing to the production of more sustainable battery packs with lower environmental impact.

[0122] Each of the documents mentioned above is incorporated herein by reference. Any reference to any document is not an admission that the document conforms to the prior art or constitutes general knowledge of a person skilled in the art in any jurisdiction. Unless expressly stated in the examples or otherwise, all numerical quantities of substances, reaction conditions, molecular weights, number of carbon atoms, etc., specified in this specification should be understood to be modified by the word “about.” It should be understood that the upper and lower limits of the quantities, ranges, and proportions described herein can be combined independently. Similarly, the ranges and quantities of each element of the invention can be used in conjunction with the ranges or quantities of any other element. As used herein, the expression “consisting substantially of…” allows for the inclusion of substances that do not materially affect the basic and novel properties of the composition under consideration.

Claims

1. An electrolyte composition comprising a. a medium, b. an ionically conductive salt, and c. a thiophosphoric acid / ester / salt redox mediator.

2. The electrolyte composition of claim 1, wherein the medium comprises a polymeric medium.

3. The electrolyte composition of claim 1, wherein the medium comprises an aprotic organic solvent.

4. The electrolyte composition of any one of the preceding claims, wherein the ionically conductive salt comprises a metal salt.

5. The electrolyte composition of claim 4, wherein metal comprises an alkali metal.

6. The electrolyte composition of claim 4, wherein the metal comprises an alkaline earth metal.

7. The electrolyte composition of claim 4, wherein the metal comprises a transition metal or a post-transition metal.

8. The electrolyte composition of claim 4, wherein the metal comprises lithium, sodium, magnesium, aluminum, and alloys or composites thereof.

9. The electrolyte composition of any one of the preceding claims, wherein the thiophosphoric acid / ester / salt compound comprises a compound of Formula (I) (I) wherein X is oxygen or sulfur; each R 1 is independently a linear or branched aliphatic hydrocarbon group containing 3 to 18 carbon atoms; R 2 is a branched or linear hydrocarbon group containing 4 to 20 carbon atoms, or an acylated hydrocarbon group containing 4 to 20 carbon atoms (-R 3 -(C=0)-Y-R 4 ), wherein R 3 is a hydrocarbon group containing 1 to 6 carbon atoms, Y is O or N-R 5 , and R 4 and R 5 are each independently H or a hydrocarbon group of 1 to 12 carbon atoms.

10. The electrolyte composition of any one of the preceding claims, wherein the thiophosphoric acid / ester / salt compound comprises a compound of Formula (II) (II) wherein X is oxygen or sulfur; each R 1 independently is a linear or branched aliphatic hydrocarbon group containing 3 to 18 carbon atoms; Y is O or NR 5 ; R 4 and R 5 each independently is a hydrocarbyl group of 1 to 12 carbon atoms; and R 6 is hydrogen or a hydrocarbyl group of 1 to 4 carbon atoms.

11. The electrolyte composition of any one of the preceding claims, wherein the thiophosphoric acid / ester / salt compound comprises a compound of Formula (III) (III) wherein X is oxygen or sulfur; each R 1 independently is a straight-chain or branched aliphatic hydrocarbon group containing 3 to 18 carbon atoms.

12. The electrolyte composition of any one of the preceding claims, wherein the thiophosphoric acid / ester / salt compound comprises a dialkyl thiophosphoric acid.

13. The electrolyte composition of any one of the preceding claims, wherein the thiophosphoric acid / ester / salt compound comprises an amine salt of a thiophosphoric acid ester.

14. The electrolyte composition of any one of the preceding claims, wherein the thiophosphoric acid / ester / salt compound comprises an ammonium dithiophosphate.

15. The electrolyte composition of any one of the preceding claims, wherein the thiophosphoric acid / ester / salt compound comprises a metal salt of a dialkyldithiophosphoric acid.

16. A cathode comprising a. an electrically active sulfur-containing material, and b. a thiophosphoric acid / ester / salt redox mediator.

17. An electrochemical cell comprising a. a cathode comprising i. an electrically active sulfur-containing material, and ii. 0 mM to 100 mM of a thiophosphoric acid / ester / salt redox mediator, b. an anode, and c. an electrolyte comprising i. a medium, ii. an ionically conductive salt, and iii. 0 mM to 100 mM of a thiophosphoric acid / ester / salt redox mediator, as long as at least one of a(ii) and c(iii) is not 0.

18. A method of mediating electrochemical redox transformations in an ionically conductive salt-electroactive sulfur-containing electrochemical cell, the method comprising: Preparation of an electrochemical cell comprising a) a cathode comprising an electrically active sulfur-containing material, b) an anode, and c) an electrolyte, and preparation of the electrolyte comprising i) a polymeric medium or a solvent, ii) an ionically conductive salt, and iii) a thiophosphoric acid / ester / salt redox mediator, and operation of the electrochemical cell.

19. Use of a thiophosphoric acid / ester / salts redox mediator to mediate electrochemical redox transformations in an ionically conductive salt-electroactive sulfur electrochemical cell.

20. The use of claim 18, wherein the use provides an increase in capacity of the cell relative to baseline (i.e., without the thiophosphoric acid / ester / salts redox mediator).

21. The use of claim 18, wherein the use provides a sustained increase in capacity of the cell relative to baseline over cell cycling.

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