Alkali metal-sulfur secondary battery and use thereof

Abstract

The invention relates to an alkali metal-sulfur cell and the use thereof. The alkali metal-sulfur secondary battery comprises or consists of: a positive electrode comprising or consisting of a sulfur source, a conductive carbon material, and an alkali metal ion conductive solid electrolyte; a negative electrode; and an organic electrolyte comprising or consisting of an organic ether and a conductive salt. The organic electrolyte is in contact with the positive electrode and the negative electrode, and is characterized in that the organic electrolyte has a solubility for sulfur-containing components of the positive electrode of < = 10 mmol sulfur atoms per liter of the organic electrolyte at a temperature of 20 DEG C to 100 DEG C. The alkali metal-sulfur secondary battery according to the present invention has a very high specific energy density and at the same time has a long service life. Actually, the specific energy density achieved by the alkali metal-sulfur secondary battery is remarkably higher than that of all previously known alkali metal-sulfur secondary batteries.

Description

[0001] An alkali metal-sulfur battery is provided and its uses are proposed. The alkali metal-sulfur secondary battery comprises: a positive electrode containing or constituting a sulfur source, a conductive carbon material, and an alkali metal ion-conducting solid electrolyte; a negative electrode; and an organic electrolyte containing or constituting an organic ether and a conductive salt. The organic electrolyte is in contact with both the positive and negative electrodes, and is characterized in that, at a temperature of 20°C to 100°C, its solubility for the sulfur-containing component of the positive electrode is ≤10 millimoles of sulfur per liter of organic electrolyte. The alkali metal-sulfur secondary battery according to the invention exhibits a very high specific energy density while also having a long service life. In fact, the specific energy density it achieves significantly exceeds that of all previously known alkali metal-sulfur secondary batteries.

[0002] Alkali metal-sulfur secondary batteries, such as lithium-sulfur batteries, theoretically possess very high specific energy densities (2600 Wh / kg – based on the active material). However, in existing technologies, only a fraction of this theoretical specific energy density has been achieved to date (a maximum of 470 Wh / kg). This is due to the high proportion of passive materials, particularly the electrolyte, used in known lithium-sulfur secondary batteries.

[0003] Using a solid electrolyte instead of a liquid electrolyte can minimize the weight of secondary batteries introduced by passive materials. In principle, this could potentially exceed current limits in terms of specific energy density. However, there is currently no suitable anode concept for such secondary batteries: direct contact between a lithium metal anode and a solid electrolyte can lead to short circuits and rapid degradation.

[0004] Lithium anodes work particularly well and reversibly when in contact with liquid or polymer-based ether electrolytes. However, these electrolytes introduce high passive weights for conventional sulfur cathodes, thus reducing the achievable specific energy density.

[0005] Essentially, three different concepts or methods are known in the prior art for manufacturing alkali metal-sulfur secondary batteries. The first method uses a liquid electrolyte and a "soluble" sulfur cathode. However, this method results in a higher passive weight due to the liquid electrolyte, leading to a lower specific energy density. The second method uses a liquid electrolyte and a "fixed" sulfur cathode ("encapsulated / fixed concept"). This method also suffers from high passive weight and low specific energy density. The third method uses a solid electrolyte, which reduces passive weight and increases specific energy density, but the disadvantage is a shortened lifespan for the resulting lithium-sulfur secondary batteries due to rapid short circuits and rapid degradation of the battery assembly during operation.

[0006] Therefore, the object of the present invention is to provide an alkali metal-sulfur secondary battery that overcomes at least one drawback of the prior art. In particular, the alkali metal-sulfur battery should have maximized specific energy density and high durability. Furthermore, the uses of this alkali metal-sulfur secondary battery should also be proposed.

[0007] This objective is achieved by an alkali metal-sulfur secondary battery having the features of claim 1 and by use having the features of claim 15. The dependent claims describe advantageous improvements.

[0008] According to the present invention, an alkali metal-sulfur secondary battery is provided, comprising or consisting of:

[0009] a) A positive electrode comprising or consisting of a sulfur source, conductive carbon material, and an alkali metal ion-conducting sulfide solid electrolyte;

[0010] b) Negative electrode; and

[0011] c) An organic electrolyte comprising or consisting of an organic ether and a conductive salt, wherein the electrolyte is in contact with the positive electrode and the negative electrode;

[0012] The organic electrolyte is characterized in that, at a temperature of 20°C to 100°C (optionally: 100°C), the solubility of the sulfur-containing component of the positive electrode (i.e., at least the sulfur source and sulfide solid electrolyte of the positive electrode) is ≤10 millimoles of sulfur per liter of organic electrolyte.

[0013] The solubility of the sulfur-containing component of the cathode in the organic electrolyte (“total atomic sulfur concentration”) can be determined by contacting the sulfur-containing component of the cathode with the organic electrolyte for 24 hours at a temperature of 20°C to 100°C (preferably 100°C). The amount of sulfur dissolved in the organic electrolyte can then be determined by complete oxidation with hydrogen peroxide (H₂O₂) followed by precipitation with barium sulfate (gravimetric determination). If the conductive salt contains sulfur, the contribution of sulfur introduced into the organic electrolyte through the conductive salt must be subtracted to determine the solubility of the sulfur-containing component of the cathode in the organic electrolyte (i.e., to avoid erroneously obtaining an overestimated solubility value). Alternatively, the amount of sulfur dissolved in the organic electrolyte (excluding the contribution of the conductive salt, if it contains sulfur) can be determined by drying the organic electrolyte and then performing CHNOS analysis.

[0014] The alkali metal-sulfur secondary battery according to the present invention exhibits a very high specific energy density and a long lifespan. In fact, the specific energy density it achieves significantly exceeds that of all previously known alkali metal-sulfur secondary batteries. The reason for this is speculated as follows:

[0015] The low passive weight and the resulting high specific energy density are achieved through the solid composition of the positive electrode (solid positive electrode). This means that the positive electrode cannot be permeated by organic electrolytes, at least in certain areas; that is, in the case of organic liquid electrolytes, only a small amount of electrolyte is needed, which reduces the weight contribution of the organic electrolyte. Ion transport in the positive electrode occurs primarily through the alkali metal ion-conducting solid electrolyte of the positive electrode, while electron transport occurs through the conductive carbon material of the positive electrode. Surprisingly, it has also been shown that the alkali metal-sulfur secondary battery according to the invention can operate at low pressures (i.e., at pressures <0.5 MPa). The advantage here is that manufacturing the alkali metal-sulfur secondary battery requires lighter or simpler fixtures, which can achieve additional weight savings and potentially further improve the specific energy density.

[0016] High long-term stability is achieved through an organic electrolyte. This organic electrolyte contains or consists of organic ethers and conductive salts, and has a solubility of ≤10 millimoles of sulfur atoms per liter of organic electrolyte for the sulfur-containing component of the positive electrode (i.e., at least for the sum of the sulfur source and the sulfide solid electrolyte) at temperatures from 20°C to 100°C.

[0017] The organic ether is characterized by good compatibility with the negative electrode, thereby improving long-term stability. The extremely low or even non-existent solubility of the sulfur-containing components at the positive electrode results in high compatibility with the sulfide solid electrolyte and the sulfur source at the positive electrode; that is, the sulfide solid electrolyte and the sulfur source do not dissolve in the organic electrolyte. Liquid electrolytes with high solubility of the sulfur-containing components at the positive electrode would cause the positive electrode components (including the sulfur source and the sulfide solid electrolyte) to react and dissolve, leading to rapid degradation of the positive electrode. Furthermore, dissolved sulfur-containing components at the positive electrode (e.g., polysulfides) may cause an electrochemical "shuttle" effect, reducing battery efficiency or causing self-discharge. The low solubility of the sulfur-containing components at the positive electrode can be achieved, for example, by selecting an appropriately high concentration of conductive salts in the organic electrolyte. Alternatively or additionally, this can be achieved by selecting a suitable organic ether or by mixing the organic ether with other organic electrolytes (e.g., fluorinated ethers).

[0018] The sulfur source for the positive electrode can be selected from sulfur, sulfur compounds, and combinations thereof. The sulfur source preferably comprises or consists of organosulfur compounds, transition metal sulfides, and / or alkali metal sulfides. The organosulfur compound is particularly preferably a sulfurized polyacrylonitrile. The transition metal sulfide is particularly preferably selected from vanadium sulfide, iron sulfide, molybdenum sulfide, bismuth sulfide, cobalt sulfide, titanium sulfide, copper sulfide, tin sulfide, nickel sulfide, and combinations thereof. The alkali metal sulfide is particularly preferably selected from Li₂S, Na₂S, and combinations thereof.

[0019] Furthermore, the sulfur source of the positive electrode may be present in the positive electrode in an amount of at least 20% by weight, preferably at least 30% by weight, particularly preferably at least 40% by weight, very particularly preferably at least 45% by weight, and optionally at most 75% by weight, relative to the total weight of the positive electrode.

[0020] Furthermore, the sulfur source in the positive electrode may exist in particulate form within the positive electrode, wherein the particle size in at least one dimension (optionally in all three dimensions) is preferably <1µm, wherein the particle size refers to the particle size that can be measured by electron microscopy. Preferably, the sulfur source is uniformly distributed in the positive electrode, i.e., uniformly mixed (and preferably pressed) with other components of the positive electrode.

[0021] The conductive carbon material for the positive electrode can be selected from carbon black, porous carbon, carbon nanotubes, carbon nanofibers, graphene, graphite and combinations thereof.

[0022] Furthermore, the conductive carbon material of the positive electrode may be present in the positive electrode in an amount of 5% to 50% by weight, preferably 10% to 40% by weight, particularly preferably 15% to 30% by weight, and especially 18% to 25% by weight relative to the total weight of the positive electrode.

[0023] Furthermore, the conductive carbon material of the positive electrode can exist in the positive electrode in particulate form, wherein the particle size in at least one dimension (optionally in all three dimensions) is preferably <1µm, wherein the particle size refers to the particle size that can be measured by electron microscopy. Preferably, the conductive carbon material is uniformly distributed in the positive electrode, i.e., uniformly mixed (and preferably pressed) with other components of the positive electrode.

[0024] The alkali metal ion conductive solid electrolyte at the positive electrode can be an inorganic alkali metal ion conductive solid electrolyte or an inorganic-organic alkali metal ion conductive solid electrolyte.

[0025] Furthermore, the alkali metal ion-conducting solid electrolyte at the positive electrode can be selected from sulfide alkali metal ion-conducting solid electrolytes. Preferably, the alkali metal ion-conducting solid electrolyte is selected from sulfide alkali metal ion-conducting solid electrolytes having thiophosphate groups.

[0026] In addition, the alkali metal ion-conducting solid electrolyte at the positive electrode can be selected from Li2S-P2S5; Li7P3S 11;Li2S-GeS2; Li2S-B2S3; Li6PS5Cl; Li2S-SiS2; Li2S-P2S5-LiX, where X=Cl, Br or I; Li2S-P2S5-Li2O; Li2S-P2S5-Li2O- LiI; Li2S-SiS2-LiI; Li2S-SiS2-LiBr; Li2S-SiS2-LiCl; Li2S-SiS2-B2S3-LiI; Li2S-SiS2-P2S5-LiI; Li2S-P2S5-Z m S n Where m and n are integers and M is selected from P, Si, Sb, Sn or Ge; Li3PS4-2LiBH4; Li2S-SiS2-Li3PO4; Li2S-SiS2-Li p MO q Where p and q are integers and M is selected from P, Si, or Ge; Na2S-P2S5; Na2S-GeS2; Na2S-B2S3; Na6PS5Cl; Na2S-SiS2; Na2S-P2S5-NaX, where X = Cl, Br, or I; Na2S-P2S5-Na2O; Na2S-P2S5-Na2O-NaI; Na2S-SiS2-NaI; Na2S-SiS2-NaBr; Na2S-SiS2-NaCl; Na2S-SiS2-B2S3-NaI; Na2S-SiS2-P2S5-NaI; Na2S-P2S5-Z m S n Where m and n are integers and M is selected from P, Si, Sb, Sn or Ge; Na2S-SiS2-Na3PO4; Na2S-SiS2-Na p MO q , where p and q are integers and M is selected from P, Si or Ge; or combinations thereof.

[0027] Furthermore, the alkali metal ion-conducting solid electrolyte of the positive electrode may be present in the positive electrode in an amount of 15% to 55% by weight, preferably 20% to 50% by weight, particularly preferably 25% to 45% by weight, and especially 30% to 40% by weight relative to the total weight of the positive electrode.

[0028] Furthermore, the alkali metal ion-conducting solid electrolyte of the positive electrode can exist in the positive electrode in particulate form, wherein the particle size in at least one dimension (optionally in all dimensions) is preferably <1µm, the particle size referring to the particle size that can be measured by electron microscopy. Preferably, the alkali metal ion-conducting solid electrolyte is uniformly distributed in the positive electrode, i.e., uniformly mixed (and preferably pressed) with other components of the positive electrode.

[0029] The positive electrode of an alkali metal-sulfur secondary battery may also contain a binder.

[0030] The adhesive may comprise or consist of a fluoropolymer, wherein the fluoropolymer is preferably PTFE.

[0031] Furthermore, the binder may be present in the positive electrode in an amount of 0.1% to 10% by weight relative to the total weight of the positive electrode.

[0032] In addition, the binder can exist in the positive electrode as a fibril (i.e. in the form of a fibril).

[0033] The positive electrode may have a coating composed of an alkali metal ion-conducting solid electrolyte on at least one surface in contact with the organic electrolyte.

[0034] In this case, the alkali metal ion conductive solid electrolyte is preferably an oxide alkali metal ion conductive solid electrolyte or a sulfide alkali metal ion conductive solid electrolyte.

[0035] Furthermore, the thickness of the coating is preferably from 0.1µm to 10µm, where thickness refers to the dimension of the coating in the direction perpendicular to its plane extension.

[0036] In a preferred embodiment, the positive electrode is configured such that the organic electrolyte cannot permeate into at least a portion of the volume of the positive electrode facing away from the organic electrolyte. This portion of the positive electrode preferably comprises at least 60% of the total positive electrode volume, particularly preferably at least 70% of the total volume, most preferably at least 80% of the total volume, and optionally at least 90% of the total volume. The larger this volume, the less organic electrolyte can permeate into the positive electrode, resulting in a smaller amount of organic electrolyte required for the alkali metal-sulfur secondary battery, i.e., a higher specific energy density.

[0037] In other preferred embodiments, the positive electrode has an indentation containing the organic electrolyte on the side facing the organic electrolyte, wherein the indentation is preferably selected from pores, trenches, imprints, and combinations thereof. The advantage of this embodiment is that the positive electrode exposes a large surface area, thereby increasing the contact area with the organic electrolyte, which reduces the transition resistance between the positive electrode and the organic electrolyte, thus improving the electrical performance of the alkali metal-sulfur battery.

[0038] Furthermore, on the side facing away from the organic electrolyte, the positive electrode may contact a planarization layer, which comprises or constitutes a conductive material (positive electrode conductor), wherein the conductive material is preferably selected from metals, metal alloys, carbon, and combinations thereof. The conductive material is particularly preferably selected from stainless steel, aluminum, aluminum alloys, carbon nanotubes, and combinations thereof. Stainless steel has the advantage of imparting high mechanical strength to the positive electrode.

[0039] The negative electrode of an alkali metal-sulfur secondary battery may contain or be composed of alkali metal or alkali metal alloy, preferably lithium metal, lithium metal alloy, sodium metal and / or sodium metal alloy.

[0040] In an optional embodiment, the negative electrode does not contain any alkali metal, but rather contains or is composed of porous carbon.

[0041] Furthermore, on the side opposite to the organic electrolyte, the negative electrode may contact a planarization layer, which comprises or constitutes a conductive material (negative electrode conductor), wherein the conductive material is preferably selected from metals, metal alloys, and combinations thereof. The conductive material is particularly preferably selected from stainless steel, copper, copper alloys, nickel, nickel alloys, and combinations thereof.

[0042] The organic electrolyte in alkali metal-sulfur secondary batteries can be liquid (liquid electrolyte) at a temperature of 25°C and a pressure of 1013 hPa.

[0043] The liquid organic electrolyte may comprise an organic ether selected from organic ethers that are liquid at 25°C and 1013 hPa. Preferably, the ether has the chemical formula A-(OB). n -OC is an acyclic ether, wherein O represents an oxygen atom, and A, B and C each represent a saturated or unsaturated, straight-chain or cyclic hydrocarbon group, wherein B contains at least 2 carbon atoms and n≥1, and the ether is particularly preferably selected from 1,2-dimethoxyethane, 1,3-dioxolane, bis(2-methoxyethyl) ether, bis[2-(2-methoxyethoxy)ethyl] ether and mixtures thereof.

[0044] Furthermore, the conductive salt can be present in the liquid organic electrolyte at a concentration (at a temperature of 20°C to 100°C) corresponding to the solubility limit of the conductive salt in the liquid organic electrolyte (or even higher; see below). This high concentration of the conductive salt ensures, on the one hand, that the organic liquid electrolyte has high ionic conductivity, and on the other hand, that the polysulfides cannot dissolve in the organic liquid electrolyte. Optionally, the concentration of the conductive salt in the liquid organic electrolyte can be from 0.5M to 15M, preferably from 1M to 10M, and particularly preferably from 2M to 5M.

[0045] Furthermore, the alkali metal-sulfur secondary battery (e.g., its organic electrolyte, its positive electrode, its negative electrode, and / or its optional separator) may contain an amount of conductive salt exceeding the solubility limit (i.e., saturation limit) of the conductive salt in the organic electrolyte at temperatures from 20°C to 100°C. In this case, the alkali metal-sulfur battery contains conductive salt that is at least partially insoluble at temperatures from 20°C to 100°C (preferably at 100°C). The conductive salt may be present (directly) in the organic electrolyte in a partially undissolved form. Alternatively or additionally, the conductive salt may be present in the coating of the positive electrode, negative electrode, and / or separator of the alkali metal-sulfur secondary battery, the coating comprising or constituting the conductive salt. The advantage here is that the solubility range of the sulfur-containing component of the positive electrode in the organic electrolyte at temperatures from 20°C to 100°C can be more effectively ensured to be ≤10 mmol sulfur atoms per liter of organic electrolyte. For example, it can also ensure that during the operation of alkali metal-sulfur batteries or during temperature fluctuations, the solubility of the sulfur-containing components of the positive electrode in the organic electrolyte does not exceed ≤10 millimoles of sulfur per liter of organic electrolyte.

[0046] Alternatively, the organic electrolyte can be gel-type (gel electrolyte) at a temperature of 25°C and a pressure of 1013 hPa. This has the advantage that the alkali metal-sulfur battery weighs less than that of a liquid electrolyte, thereby increasing its specific energy density. Furthermore, gel electrolytes are less prone to leakage, thus improving the safety of the alkali metal-sulfur secondary battery during operation.

[0047] The gel-type organic electrolyte may contain organic ethers selected from organic ethers that are liquid at 25°C and 1013 hPa. Preferably, the ether has the chemical formula A-(OB). n -OC is an acyclic ether, wherein O represents an oxygen atom, and A, B and C each represent a saturated or unsaturated, straight-chain or cyclic hydrocarbon group, wherein B contains at least 2 carbon atoms and n≥1, and the ether is particularly preferably selected from 1,2-dimethoxyethane, 1,3-dioxolane, bis(2-methoxyethyl) ether, bis[2-(2-methoxyethoxy)ethyl] ether and mixtures thereof.

[0048] In a preferred embodiment, the gel-type organic electrolyte comprises a gelling agent, wherein the gelling agent is preferably a polymer. The polymer is particularly preferably selected from PEO, PEG-DME, and combinations thereof.

[0049] In addition, the conductive salt is present in the gel-type organic electrolyte at a concentration corresponding to or exceeding the solubility limit of the conductive salt in the gel-type organic electrolyte at a temperature of 20°C to 100°C. This high concentration of conductive salt ensures, on the one hand, that the gel electrolyte has high ionic conductivity, and on the other hand, that polysulfides cannot dissolve in the gel electrolyte. Optionally, the concentration of the conductive salt in the gel-type organic electrolyte can be from 0.5M to 15M, preferably from 1M to 10M, and particularly preferably from 2M to 5M.

[0050] Alternatively, the organic electrolyte can be solid (solid electrolyte) at a temperature of 25°C and a pressure of 1013 hPa. This has the advantage that the alkali metal-sulfur battery is lighter than liquid and gel electrolytes, thereby increasing its specific energy density. Furthermore, the solid electrolyte does not leak, thus improving the safety of the alkali metal-sulfur secondary battery during operation.

[0051] The solid organic electrolyte may comprise organic ethers (e.g., organic polyethers) selected from organic ethers that are solid at 25°C and 1013 hPa. Specifically, the solid organic electrolyte (e.g., solid organic ether) does not possess intrinsic ionic conductivity to alkali metal ions. Due to the lack of intrinsic ionic conductivity to alkali metal ions, conduction to alkali metal ions is mediated solely by the conductive salts present in the solid organic electrolyte.

[0052] Furthermore, the solid organic electrolyte may comprise an organic polyether, preferably selected from PEO, PEG-DME, and combinations thereof. Specifically, the terminal groups of the solid organic electrolyte molecule (e.g., the solid organic polyether) do not have OH groups, but optionally have alkyl groups. The absence of OH groups at the terminal groups has the advantage of improving the stability of the organic electrolyte and further enhancing the long-term stability of alkali metal-sulfur secondary batteries.

[0053] Furthermore, the conductive salt may be present in the solid organic electrolyte in an amount of at least 10% by weight relative to the total weight of the solid organic electrolyte. The content of the conductive salt in the solid organic electrolyte is particularly between 10% and 80% by weight. This high concentration of conductive salt ensures, on the one hand, that the solid electrolyte has high ionic conductivity, and on the other hand, that polysulfides do not accumulate on or accumulate in the solid electrolyte.

[0054] In a preferred embodiment, the organic electrolyte further comprises other organic ethers different from the (first) organic ether.

[0055] Other organic ethers preferably have lower solubility for the conductive salt than the (first) organic ether of the organic electrolyte. The advantage here is that the amount or concentration of the conductive salt required to reduce the solubility of the electrolyte for polysulfide ions to the ≤5 mM range may be lower. This could be a weight advantage, thereby further increasing the specific energy density of the alkali metal-sulfur battery. Furthermore, if adding other organic ethers is more cost-effective than correspondingly increasing the amount or concentration of the conductive salt, this could represent an economic advantage.

[0056] Other organic ethers may be included in the organic electrolyte at a volume percentage of 10% to 90% relative to the sum of the volumes of the organic ethers and other organic ethers.

[0057] Other organic ethers may be selected from ethylpropyl ether, dipropyl ether, diisopropyl ether, di-(1,2-dimethylpropyl) ether, methyl butyl ether, ethyl butyl ether, propyl butyl ether, dibutyl ether, diisobutyl ether, methyl pentyl ether, ethyl pentyl ether, propyl pentyl ether, butyl pentyl ether, dipentyl ether, 1-(2,2-dimethylpropoxy)-2,2-dimethylpropane, isopentyl ether, di-(1,2-dimethylpropyl) ether, methyl hexyl ether, ethyl hexyl ether, propyl hexyl ether, butyl hexyl ether, pentyl hexyl ether, dihexyl ether, methoxycyclohexane, phenethyl ether, 2-methoxypropane, 2-methoxybutane, 2-methoxypentane, 2-methoxyhexane, 2-ethoxypropane, 2-ethoxybutane, 2-ethoxypentane, 2-ethoxyhexane and mixtures thereof.

[0058] In addition, other organic ethers may be organofluorinated ethers, wherein the fluorinated ethers are preferably selected from 2,2,2-trifluoroethyl methyl ether, 2,2,2-trifluoroethyl difluoromethyl ether, 2,2,3,3,3-pentafluoropropyl methyl ether, 2,2,3,3,3-pentafluoropropyl difluoromethyl ether, 2,2,3,3,3-pentafluoropropyl-1,1,2,2-tetrafluoroethyl ether, 1,1,2,2-tetrafluoroethyl methyl ether, 1,1,2,2-tetrafluoroethyl ethyl ether, 1,1,2,2-tetrafluoroethyl propyl ether, 1,1,2,2-tetrafluoroethyl butyl ether, 1,1,2,2-tetrafluoroethyl isobutyl ether, 1,1,2,2-tetrafluoroethyl ethyl ether, and 1,1,2,2-tetrafluoroethyl ethyl ether. The fluorinated ethers are 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, hexafluoroisopropylmethyl ether, 1,1,3,3,3-pentafluoro-2-trifluoromethylpropylmethyl ether, 1,1,2,3,3,3-hexafluoropropylmethyl ether, 1,1,2,3,3,3-hexafluoropropylethyl ether, 2,2,3,4,4,4-hexafluorobutyl difluoromethyl ether and mixtures thereof, wherein the fluorinated ether is preferably 1,1,2,2-tetrafluoroethylpropyl ether, and particularly preferably 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0059] The conductive salt contained in the electrolyte can be selected from LiFSI, LiTFSI, LiPF6, LiBF4, LiClO4, LiSO3CF3, LiN(SO2F)2, LiN(SO2CF3)2, LiN(SO2F)(SO2CF3), LiN(SO2F)(SO2C4F9), LiN(SO2CF2CF3)2, LiC(SO2CF2CF3)3, LiC(SO2CF3)3, LiI, LiCl, LiF, LiPF5(SO2CF3), LiPF4(SO2CF3)2 and combinations thereof, preferably LiFSI, LiTFSI and combinations thereof.

[0060] Alkali metal-sulfur secondary batteries may also include a porous membrane (e.g., in the case of a liquid electrolyte or a gel electrolyte). The porous membrane allows ions to be transported through the pores of the membrane.

[0061] The porous membrane may comprise or consist of organic materials and / or ceramic materials. The organic material is preferably selected from polyolefins. The ceramic material is preferably Al2O3.

[0062] Furthermore, the thickness of the porous membrane in its direction perpendicular to its plane can be from 1µm to 80µm, preferably from 2µm to 40µm, particularly preferably from 5µm to 20µm, and very particularly preferably from 10µm to 15µm. The thinner the membrane, the smaller its contribution to the total weight of the alkali metal-sulfur secondary battery, and the higher the specific energy density of the alkali metal-sulfur secondary battery.

[0063] The present invention also proposes the use of the alkali metal-sulfur secondary battery according to the present invention as an energy source in the following devices:

[0064] i) In stationary installations, preferably in buildings; and / or

[0065] ii) In mobile devices, preferably in mobile electronic devices and / or vehicles, wherein the vehicles are preferably selected from automobiles, airplanes, drones, trains and combinations thereof.

[0066] When using the alkali metal-sulfur secondary battery according to the invention, the battery can operate at room temperature (20°C to 30°C) or at higher temperatures of 60°C to 100°C. Operating at higher temperatures is advantageous because the ionic conductivity of the organic electrolyte increases at higher temperatures, which can improve the conversion kinetics of the cathode.

[0067] The following examples and figures are intended to explain the subject matter of the invention in more detail, but are not intended to limit it to the specific embodiments shown herein.

[0068] Figure 1 A schematic diagram of the alkali metal-sulfur secondary battery structure according to the present invention is shown.

[0069] Figure 2 The structure of another alkali metal-sulfur secondary battery according to the present invention is illustrated schematically.

[0070] Figure 3 Electrochemical studies (specific capacity and coulombic efficiency) of an alkali metal-sulfur secondary battery according to the invention (electrolyte is a DME with 12M LiFSI; see triangle symbol) and an alkali metal-sulfur battery not according to the invention (electrolyte is a DME with only 4M LiFSI; see square symbol) are shown.

[0071] Example – Manufacturing of an alkali metal-sulfur battery according to the present invention

[0072] The cathode material for the alkali metal-sulfur secondary battery according to the present invention was prepared in an argon-filled glove box. For this purpose, sulfur (Sigma Aldrich), carbon (Printex XE2B, Orion), and solid electrolyte (NEI) were mixed in a mass ratio of 3 / 2 / 5 and milled for 4 hours using a ball mill (Retsch PM100) at a speed of 400 rpm, with the grinding balls having a diameter of 5 mm.

[0073] To prepare a free-standing dry cathode film, 0.5% by weight of PTFE relative to the total weight of the cathode material was added to the prepared cathode composite material. The mixture was then placed in a heated mortar and ground under shear force until a coherent cathode film was formed. It was then rolled on a heated plate to a uniform thickness of approximately 50 µm. The free-standing dry film was then laminated onto carbon-coated aluminum foil. For characterization of coin cells, stamped sheets with a diameter of 13 mm were prepared; for characterization of pouch cells, the cathode was assembled using laser technology.

[0074] The battery concept was evaluated in a coin cell (CR2016). For this purpose, a fabricated positive electrode (13 mm in diameter) was assembled with a lithium negative electrode (250 µm, 16.5 mm, located on a 1000 µm steel pad). A 12 µm PE separator was used.

[0075] Two different electrolyte compositions were used and compared. In each case, 40 µl of electrolyte was used, i.e., 20 µl of electrolyte was applied to the positive electrode and another 20 µl of electrolyte was applied to the diaphragm.

[0076] The first electrolyte composition (reference electrolyte) is a DME with 4M LiFSI (only), which corresponds to a concentration of the conductive salt LiFSI that is far below the solubility limit of LiFSI in DME. Therefore, this organic electrolyte has a solubility for polysulfide ions that is much higher than 5mM and also higher than 10mM at temperatures ranging from 20°C to 100°C.

[0077] The second electrolyte composition (the electrolyte according to the invention) is a DME with 12M LiFSI, which corresponds to the concentration of the conductive salt LiFSI reaching the solubility limit of LiFSI in the DME. Therefore, this organic electrolyte has a solubility of ≤5mM for polysulfide ions at temperatures from 20°C to 100°C. Figure 1 A schematic diagram of the alkali metal-sulfur battery structure is shown.

[0078] Batteries manufactured using their respective electrolyte compositions were tested at voltages ranging from 1.6V to 2.7V. The first 10 cycles were performed with symmetrical charge-discharge at a current rate of 0.05C, followed by subsequent cycles at 0.1C. In all cycles, a constant current charge was followed by a constant voltage step at 2.7V during the charging process. Figure 3 Electrochemical results are shown for an alkali metal-sulfur secondary battery according to the invention (electrolyte according to the invention, DME with 12M LiFSI) and an alkali metal-sulfur battery not according to the invention (reference electrolyte, DEM with only 4M LiFSI).

[0079] The battery using the reference electrolyte initially showed a specific capacity of about 1500 Ah / kg sulfur, but this dropped sharply after the second cycle, reaching only about 100 Ah / kg sulfur by the fifth cycle.

[0080] In contrast, the battery using the electrolyte according to the invention initially exhibited a specific capacity of approximately 1700 Ah / kg sulfur, and maintained a specific capacity of approximately 1400 Ah / kg sulfur even after 20 cycles. This means that, unlike the reference alkali metal-sulfur secondary battery, the alkali metal-sulfur secondary battery according to the invention is able to maintain a high specific capacity during long-term operation, thereby maintaining a high specific energy density. The tested alkali metal-sulfur secondary battery according to the invention has a specific energy density of 588 Wh / kg electrode stack.

[0081] List of reference numerals

[0082] 1: The positive electrode of an alkali metal-sulfur secondary battery;

[0083] 2: The negative electrode of an alkali metal-sulfur secondary battery;

[0084] 3: Organic electrolytes for alkali metal-sulfur secondary batteries;

[0085] 4: Porous separator for alkali metal-sulfur secondary batteries;

[0086] 5: A planar layer (positive conductor) that contains or constitutes a conductive material and is in contact with the positive electrode;

[0087] 6: Positive electrode indentation containing electrolyte (here, imprint).

Claims

1. An alkali metal-sulfur secondary battery comprising or consisting of: a) a cathode comprising or consisting of a sulfur source, an electrically conductive carbon material, and an alkali metal ion-conducting sulfide solid electrolyte; b) an anode; and c) an organic electrolyte comprising or consisting of an organic ether and an electrically conductive salt, wherein the organic electrolyte is in contact with the cathode and the anode; characterized in that the organic electrolyte has a solubility for the sulfur-containing components of the cathode of < 10 millimoles of sulfur atoms per liter of organic electrolyte at a temperature of 20 °C to 100 °C.

2. The alkali-metal-sulfur secondary battery according to the preceding claim, characterized in that the sulfur source of the cathode i) is selected from the group consisting of sulfur, sulfur compounds, and combinations thereof, wherein the sulfur source preferably comprises or consists of an organic sulfur compound, a metal sulfide, and / or an alkali metal sulfide, wherein the sulfur source particularly preferably comprises or consists of a sulfonated polyacrylonitrile, a vanadium sulfide, an iron sulfide, a molybdenum sulfide, a bismuth sulfide, a cobalt sulfide, a titanium sulfide, a copper sulfide, a tin sulfide, a nickel sulfide, Li2S, and / or Na2S; and / or ii) is present in the cathode in an amount of at least 20 wt.-%, preferably at least 30 wt.-%, particularly preferably at least 40 wt.-%, very particularly preferably at least 45 wt.-%, optionally up to 75 wt.-%, relative to the total weight of the cathode; and / or iii) is present in the cathode in particulate form, wherein the particle size in at least one dimension is preferably < 1 pm, wherein the particle size refers to the particle size measurable by electron microscopy.

3. The alkali-metal-sulfur secondary battery according to any one of the preceding claims, characterized in that, the electrically conductive carbon material of the cathode i) is selected from the group consisting of carbon black, porous carbon, carbon nanotubes, carbon nanofibers, graphene, graphite, and combinations thereof; and / or ii) is present in the cathode in an amount of 5 wt.-% to 50 wt.-%, preferably 10 wt.-% to 40 wt.-%, particularly preferably 15 wt.-% to 30 wt.-%, in particular 18 wt.-% to 25 wt.-%, relative to the total weight of the cathode; and / or iii) is present in the cathode in particulate form, wherein the particle size in at least one dimension is preferably < 1 pm, wherein the particle size refers to the particle size measurable by electron microscopy.

4. The alkali-metal-sulfur secondary battery according to any one of the preceding claims, characterized in that, the alkali metal ion-conducting solid electrolyte of the cathode i) is an inorganic alkali metal ion-conducting solid electrolyte or is an inorganic-organic alkali metal ion-conducting solid electrolyte; and / or ii) is selected from the group consisting of sulfide alkali metal ion-conducting solid electrolytes, preferably from sulfide alkali metal ion-conducting solid electrolytes having thiophosphonate groups; and / or iii) selected from Li2S-P2S5; Li7P3S 11 ; Li2S-GeS2; Li2S-B2S3; Li6PS5Cl; Li2S-SiS2; Li2S-P2S5-LiX, where X = Cl, Br or I; Li2S-P2S5-Li2O; Li2S-P2S5-Li2O-LiI; Li2S-SiS2-LiI; Li2S-SiS2-LiBr; Li2S-SiS2-LiCl; Li2S-SiS2-B2S3-LiI; Li2S-SiS2-P2S5-LiI; Li2S-P2S5-Z m S n , where m and n are integers and M is selected from P, Si or Ge; Li2S-SiS2-Li3PO4; Li2S-SiS2-Li p MO q , where p and q are integers and M is selected from P, Si, Sb, Sn or Ge; Li3PS4-2LiBH4; Na2S-P2S5; Na2S-GeS 2； Na2S-B2S3; Na6PS5Cl; Na2S-SiS2; Na2S-P2S5-NaX, where X = Cl, Br or I; Na2S-P2S5-Na2O; Na2S-P2S5-Na2O-NaI; Na2S-SiS2-NaI; Na2S-SiS2-NaBr; Na2S-SiS2-NaCl; Na2S-SiS2-B2S3-NaI; Na2S-SiS2-P2S5-NaI; Na2S-P2S5-Z m S n , where m and n are integers and M is selected from P, Si or Ge; Na2S-SiS2-Na3PO4; Na2S-SiS2-Na p MO q , where p and q are integers and M is selected from P, Si, Sb, Sn or Ge; or combinations thereof; and / or iv) is present in the cathode in an amount of 15 wt.-% to 55 wt.-%, preferably 20 wt.-% to 50 wt.-%, particularly preferably 25 wt.-% to 45 wt.-%, in particular 30 wt.-% to 40 wt.-%, relative to the total weight of the cathode; and / or v) is present in the cathode in particulate form, wherein the particle size in at least one dimension is preferably < 1 pm, the particle size referring to the particle size measurable by electron microscopy.

5. The alkali-metal-sulfur secondary battery according to any one of the preceding claims, characterized in that, the cathode further comprises a binder, wherein the binder preferably i) comprises or consists of a fluorine-containing polymer, wherein the fluorine-containing polymer is preferably PTFE; and / or ii) is present in the cathode in an amount of 0.1 wt.-% to 10 wt.-%, relative to the total weight of the cathode; and / or iii) is present in the positive electrode as fibrils.

6. The alkali-metal-sulfur secondary battery according to any one of the preceding claims, characterized in that, The positive electrode has at least on the surface facing the organic electrolyte a coating consisting of an alkali metal ion-conducting solid electrolyte, wherein preferably i) the alkali metal ion-conducting solid electrolyte is an oxide alkali metal ion-conducting solid electrolyte or a sulfide alkali metal ion-conducting solid electrolyte; and / or ii) the coating preferably has a thickness of 0.1 pm to 10 pm, wherein the thickness refers to the dimension of the coating in the direction perpendicular to the extension of its plane.

7. The alkali-metal-sulfur secondary battery according to any one of the preceding claims, characterized in that, The positive electrode i) is configured such that the organic electrolyte cannot penetrate into at least a part of the volume of the positive electrode facing away from the organic electrolyte, wherein this part of the volume of the positive electrode preferably comprises at least 60 vol.-%, particularly preferably at least 70 vol.-%, very particularly preferably at least 80 vol.-%, optionally at least 90 vol.-%, of the total volume of the positive electrode; and / or ii) has on the side facing the organic electrolyte an indentation comprising the organic electrolyte, wherein the indentation is preferably selected from the group consisting of pores, grooves, embossings, and combinations thereof; and / or iii) contacts on the side facing away from the organic electrolyte a flat layer comprising or consisting of an electrically conductive material, wherein the electrically conductive material is preferably selected from the group consisting of metals, metal alloys, carbon, and combinations thereof, wherein the electrically conductive material is particularly preferably selected from the group consisting of stainless steel, aluminum, aluminum alloys, carbon nanotubes, and combinations thereof.

8. The alkali-metal-sulfur secondary battery according to any one of the preceding claims, characterized in that, The negative electrode i) comprises or consists of an alkali metal or an alkali metal alloy, preferably lithium metal, a lithium metal alloy, sodium metal, and / or a sodium metal alloy; and / or ii) does not comprise an alkali metal and comprises or consists of a porous carbon; and / or iii) contacts on the side facing away from the organic electrolyte a flat layer comprising or consisting of an electrically conductive material, wherein the electrically conductive material is preferably selected from the group consisting of metals, metal alloys, and combinations thereof, wherein the electrically conductive material is particularly preferably selected from the group consisting of stainless steel, copper alloys, nickel, nickel alloys, and combinations thereof.

9. The alkali-metal-sulfur secondary battery according to any one of the preceding claims, characterized in that, The organic electrolyte is liquid at a temperature of 25 °C and a pressure of 1013 hPa, wherein preferably i) the organic electrolyte comprises an organic ether selected from the group of organic ethers which are liquid at 25 °C and a pressure of 1013 hPa; ii) The organic electrolyte comprises an organic ether having the chemical formula A-(OB). n -OC acyclic ethers, wherein O represents an oxygen atom, and A, B, and C each represent a saturated or unsaturated, straight-chain or cyclic hydrocarbon group, wherein B contains at least 2 carbon atoms and n≥1, and wherein the ether is particularly preferably selected from 1,2-dimethoxyethane, 1,3-dioxolane, bis(2-methoxyethyl) ether, bis[2-(2-methoxyethoxy)ethyl] ether, and mixtures thereof; and / or iii) the concentration of the electrically conductive salt in the liquid organic electrolyte corresponds to or is higher than the solubility limit of the liquid organic electrolyte for the electrically conductive salt at a temperature of 20 °C to 100 °C, wherein optionally the electrically conductive salt is present in the liquid organic electrolyte at a concentration of 0.5 M to 15 M, preferably 1 M to 10 M, particularly preferably 2 M to 5 M.

10. The alkali-metal-sulfur secondary battery according to any one of claims 1 to 8, characterized by, The organic electrolyte is of the gel type at a temperature of 25 °C and a pressure of 1013 hPa, wherein preferably i) the organic electrolyte comprises an organic ether selected from the group of organic ethers which are liquid at 25 °C and a pressure of 1013 hPa; and / or ii) The organic electrolyte comprises an organic ether having the chemical formula A-(OB). n -OC acyclic ethers, wherein O represents an oxygen atom, and A, B, and C each represent a saturated or unsaturated, straight-chain or cyclic hydrocarbon group, wherein B contains at least 2 carbon atoms and n≥1, and wherein the ether is particularly preferably selected from 1,2-dimethoxyethane, 1,3-dioxolane, bis(2-methoxyethyl) ether, bis[2-(2-methoxyethoxy)ethyl] ether, and mixtures thereof; and / or iii) the organic electrolyte comprises a gelling agent, wherein the gelling agent is preferably a polymer, wherein the polymer is particularly preferably selected from the group consisting of PEO, PEG-DME, and combinations thereof; and / or iv) the concentration of the electrically conductive salt in the liquid organic electrolyte corresponds to or is higher than the solubility limit of the liquid organic electrolyte for the electrically conductive salt at a temperature of 20 °C to 100 °C, wherein optionally the electrically conductive salt is present in the liquid organic electrolyte at a concentration of 0.5 M to 15 M, preferably 1 M to 10 M, particularly preferably 2 M to 5 M. iv) the concentration of the electrically conductive salt in the gel-type organic electrolyte corresponds to or is higher than the solubility limit of the gel-type organic electrolyte for the electrically conductive salt at a temperature of 20 °C to 100 °C, wherein, optionally, the electrically conductive salt is present in the gel-type organic electrolyte at a concentration of 0.5 M to 15 M, preferably 1 M to 10 M, particularly preferably 2 M to 5 M.

11. The alkali-metal-sulfur secondary battery according to any one of claims 1 to 8, characterized by, The organic electrolyte is a solid at a temperature of 25 °C and a pressure of 1013 hPa, wherein, preferably i) the organic electrolyte comprises an organic ether selected from the group consisting of organic ethers which are solid at 25 °C and a pressure of 1013 hPa and do not have an intrinsic ionic conductivity for alkali metal ions; ii) the organic electrolyte comprises an organic polyether, wherein the organic polyether is preferably selected from the group consisting of PEO, PEG-DME and combinations thereof, wherein in particular the end groups of the polyether molecules do not have OH groups, optionally with alkyl groups; and / or iii) the electrically conductive salt is present in the solid organic electrolyte in an amount of at least 10 wt.-% relative to the total weight of the solid organic electrolyte, wherein the amount of the electrically conductive salt in the solid organic electrolyte is in particular 10 wt.-% to 80 wt.-%.

12. The alkali-metal-sulfur secondary battery of any one of the preceding claims, characterized in that, The organic electrolyte further comprises a further organic ether different from the organic ether of the organic electrolyte, wherein the further organic ether is preferably i) has a lower solubility for the electrically conductive salt than the organic ether of the organic electrolyte; and / or ii) is contained in the organic electrolyte in an amount of 10 vol.-% to 90 vol.-% relative to the sum of the volume of the organic ether and the volume of the further organic ether; and / or iii) is present in the organic electrolyte in an amount of 0.1 wt.-% to 20 wt.-% relative to the total weight of the organic electrolyte. iii) is selected from the group consisting of ethyl propyl ether, dipropyl ether, diisopropyl ether, di-(1,2-dimethylpropyl) ether, methyl butyl ether, ethyl butyl ether, propyl butyl ether, dibutyl ether, diisobutyl ether, methyl amyl ether, ethyl amyl ether, propyl amyl ether, butyl amyl ether, diamyl ether, 1 -(2,2-dimethylpropoxy)-2,2-dimethylpropane, isoamyl ether, di-(1,2-dimethylpropyl) ether, methyl hexyl ether, ethyl hexyl ether, propyl hexyl ether, butyl hexyl ether, amyl hexyl ether, dihexyl ether, methoxycyclohexane, phenyl ethyl ether, 2-methoxypropane, 2-methoxybutane, 2-methoxy pentane, 2-methoxyhexane, 2-ethoxypropane, 2-ethoxybutane, 2-ethoxy pentane, 2-ethoxyhexane, and mixtures thereof, or is an organofluorinated ether, wherein the fluorinated ether is preferably selected from the group consisting of 2,2,2-trifluoroethyl methyl ether, 2,2,2-trifluoroethyl difluoromethyl ether, 2,2,3,3,3-pentafluoropropyl methyl ether, 2,2,3,3,3-pentafluoropropyl difluoromethyl ether, 2,2,3,3,3-pentafluoropropyl-1,1,2,2-tetrafluoroethyl ether, 1,1,2,2-tetrafluoroethyl methyl ether, 1,1,2,2-tetrafluoroethyl ethyl ether, 1,1,2,2-tetrafluoroethyl propyl ether, 1,1,2,2-tetrafluoroethyl butyl ether, 1,1,2,2-tetrafluoroethyl isobutyl ether, 1,1,2,2-tetrafluoroethyl isoamyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, hexafluoroisopropyl methyl ether, 1,1,3,3,3-pentafluoro-2-trifluoromethylpropyl methyl ether, 1,1,2,3,3,3-hexafluoropropyl methyl ether, 1,1,2,3,3,3-hexafluoropropyl ethyl ether, 2,2,3,4,4,4-hexafluorobutyl difluoromethyl ether, and mixtures thereof.

13. The alkali-metal-sulfur secondary battery of any of the preceding claims, characterized in that, The electrically conductive salt is selected from the group consisting of LiFSI, LiTFSI, LiPF6, LiBF4, LiCIO4, LiSO3CF3, LiN(SO2F)2, LiN(SO2CF3)2, LiN(SO2F)(SO2CF3), LiN(SO2F)(SO2C4F9), LiN(SO2CF2CF3)2, LiC(SO2CF2CF3)3, LiC(SO2CF3)3, LiI, LiCI, LiF, LiPF5(SO2CF3), LiPF4(SO2CF3)2, and combinations thereof, preferably from the group consisting of LiFSI, LiTFSI, and combinations thereof.

14. The alkali-metal-sulfur secondary battery of any one of the preceding claims, characterized in that, The alkali metal-sulfur secondary battery further comprises a porous separator, wherein the porous separator is preferably i) comprises or consists of an organic material and / or a ceramic material, wherein the organic material is preferably selected from the group consisting of polyolefins and / or the ceramic material is preferably AI2O3; and / or ii) a thickness in the direction of extension perpendicular to the plane of the porous separator of 1 µm to 80 µm, preferably 2 µm to 40 µm, particularly preferably 5 µm to 20 µm, very particularly preferably 10 µm to 15 µm.

15. Use of the alkali metal-sulfur secondary battery according to any of the preceding claims as an energy source in: i) a stationary device, preferably in a building; and / or ii) a mobile device, preferably in a mobile electronic device and / or a vehicle, wherein the vehicle is preferably selected from the group consisting of a car, an airplane, a drone, a train, and combinations thereof.

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