Alkali-sulfur secondary battery and use thereof

Abstract

The invention relates to an alkali-sulfur battery, and to a use thereof. The alkali-sulfur secondary battery contains or consists of: a cathode which contains or consists of a sulfur source, an electrically conductive carbon material and an alkali-metal-ion-conductive solid electrolyte; an anode; and an organic electrolyte which contains or consists of an organic ether and a conductive salt. The organic electrolyte contacts the cathode and the anode and is characterized in that, at a temperature in the range of 20°C to 100°C, it has a solubility for sulfur-containing components of the cathode that lies in the range of ≤ 10 mmol of sulfur atoms per liter of organic electrolyte. The alkali-sulfur secondary battery according to the invention has a very high specific energy density and, at the same time, high durability. In fact, a specific energy density is achieved which significantly exceeds the specific energy density of all previously known alkali-sulfur secondary batteries.

Description

[0001] Alkaline-sulfur secondary battery and use thereof

[0002] An alkali-sulfur battery is provided and a use thereof is proposed. The alkali-sulfur secondary battery contains a cathode that contains or consists of a sulfur source, an electrically conductive carbon material, and an alkali metal ion-conductive solid electrolyte, an anode, and an organic electrolyte that contains or consists of an organic ether and a conductive salt. The organic electrolyte contacts the cathode and the anode and is characterized in that, at a temperature in the range of 20°C to 100°C, it has a solubility for sulfur-containing components of the cathode that is in the range of <10 mmol of sulfur atoms per liter of organic electrolyte. The alkali-sulfur secondary battery according to the invention has a very high specific energy density and, at the same time, a high longevity.In fact, a specific energy density is achieved that significantly exceeds that of all previously known alkaline-sulfur secondary batteries. Alkaline-sulfur secondary batteries, such as lithium-sulfur secondary batteries, theoretically possess a very high specific energy density (2600 Wh / kg - based on the active materials). However, the current state of the art has so far only achieved a fraction of this theoretical specific energy density (max. 470 Wh / kg). The reason for this is the high proportion of passive materials, particularly the electrolyte used in the known lithium-sulfur secondary batteries.

[0003] By using solid electrolytes instead of liquid electrolytes, the weight of the secondary batteries introduced via the passive materials can be minimized. This would, in principle, make it possible to exceed the current limits in specific energy density. However, there is currently no suitable anode concept for this type of secondary battery: Direct contact between metallic lithium anodes and the solid electrolyte leads 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, with conventional sulfur cathodes, these would again result in a high passive weight, which would reduce the achievable specific energy densities.

[0005] Essentially, three different concepts or approaches for producing an alkaline-sulfur secondary battery are known in the prior art. A first approach is to use a liquid electrolyte and a "soluble" sulfur cathode. However, this approach leads to a high passive weight due to the liquid electrolyte and thus to a low specific energy density. A second approach uses a liquid electrolyte and a "bound" sulfur cathode ("encapsulation / bonding concept"). This approach is also characterized by a high passive weight and a low specific energy density.A third approach uses a solid electrolyte, which reduces the passive weight and increases the specific energy density. However, it has the disadvantage that the longevity of the produced lithium-sulfur secondary batteries is reduced, as short circuits and a rapidly progressing degradation of the secondary battery components occur quickly during their operation. Based on this, the object of the present invention was to provide an alkali-sulfur secondary battery that overcomes at least one disadvantage of the prior art. In particular, the alkali-sulfur battery should have a maximum specific energy density while simultaneously maintaining a high longevity. Furthermore, uses of the alkali-sulfur secondary battery should be proposed.

[0006] The object is achieved by the alkali-sulfur secondary battery having the features of claim 1 and the use having the features of claim 15. The dependent claims show advantageous developments.

[0007] According to the invention, an alkali-sulfur secondary battery is provided, containing or consisting of: a) a cathode which contains or consists of a sulfur source, an electrically conductive carbon material and an alkali metal ion-conductive, sulfidic solid electrolyte; b) an anode; and c) an organic electrolyte which contains or consists of an organic ether and a conducting salt, wherein the electrolyte contacts the cathode and the anode; characterized in that the organic electrolyte, at a temperature in the range of 20 °C to 100 °C (optionally: at 100 °C), has a solubility for sulfur-containing components of the cathode (ie at least for the sulfur source and the sulfidic solid electrolyte of the cathode taken together) which is in the range of < 10 mmol of sulfur atoms per liter of organic electrolyte.

[0008] The solubility of the organic electrolyte for sulfur-containing components of the cathode (total atomic sulfur concentration) can be determined by contacting the sulfur-containing components of the cathode with the organic electrolyte at a temperature range of 20 °C to 100 °C (preferably 100 °C) for a period of 24 hours. The amount of sulfur dissolved in the organic electrolyte can then be determined by complete oxidation with hydrogen peroxide (H2O2) and subsequent precipitation with barium sulfate (gravimetric determination). If the conducting salt contains sulfur, the contribution of the sulfur introduced into the organic electrolyte via the conducting salt must be subtracted to determine the solubility of the organic electrolyte for sulfur-containing components of the cathode (i.e., to avoid obtaining falsely high values ​​for said solubility).Alternatively, the amount of sulfur dissolved in the organic electrolyte (without contribution from the conducting salt, if it contains sulfur) can be determined by drying the organic electrolyte followed by CHNOS analysis.

[0009] The alkaline-sulfur secondary battery according to the invention exhibits a very high specific energy density combined with a high longevity. In fact, a specific energy density is achieved that significantly exceeds the specific energy density of all previously known alkaline-sulfur secondary batteries. The following is suspected to be the reason for this:

[0010] The low passive weight and the resulting high specific energy density are achieved by the solid components of the cathode (solid cathode). As a result, the cathode cannot be penetrated by the organic electrolyte, at least in some areas, i.e. in the case of an organic liquid electrolyte, only a small amount of electrolyte is required, whereby the weight contribution of the organic electrolyte is reduced. The ion transport in the cathode occurs predominantly through the alkali metal ion-conductive solid electrolyte of the cathode, and the electron transport in the cathode occurs through the electrically conductive carbon material of the cathode. It has also surprisingly been found that the alkali-sulfur secondary battery according to the invention can be operated at low pressure (i.e. at a pressure < 0.5 MPa). The advantage here is that lighter orless complex clamping devices are required for the production of the alkali-sulfur secondary battery, which enables additional weight savings and can further increase the specific energy density.

[0011] The high long-term stability is achieved by the organic electrolyte. This contains or consists of an organic ether and a conductive salt and, at a temperature range of 20 °C to 100 °C, exhibits a solubility for sulfur-containing components of the cathode (i.e., at least for the sulfur source and the sulfide solid electrolyte combined) of < 10 mmol sulfur atoms per liter of organic electrolyte.

[0012] The organic ether is characterized by good compatibility with the anode, which increases long-term stability. The very low to nonexistent solubility for the sulfur-containing components of the cathode results in high compatibility with the sulfide solid electrolyte in the cathode and with the sulfur source of the cathode. This means that the sulfide solid electrolyte and the sulfur source do not dissolve in the organic electrolyte. Liquid electrolytes with high solubility for sulfur-containing components of the cathode would lead to a reaction and dissolution of the cathode components (including the sulfur source and the sulfide solid electrolyte), thus leading to rapid degradation of the cathode. Furthermore, dissolved sulfur-containing components of the cathode (e.g., polysulfides) can lead to electrochemical "shuttle" and reduce battery efficiency or cause self-discharge.The low solubility for sulfur-containing components of the cathode can be achieved, for example, by selecting a suitably high conducting salt concentration in the organic electrolyte. Alternatively or additionally, this can be achieved by selecting a suitable organic ether or mixtures of the organic ether with other organic electrolytes (e.g., fluoroethers).

[0013] The sulfur source of the cathode can be selected from the group consisting of sulfur, sulfur compound, and combinations thereof. The sulfur source preferably contains or consists of an organosulfur compound, a transition metal sulfide, and / or an alkali metal sulfide. The organosulfur compound is particularly preferably sulfurized polyacrylonitrile. The transition metal oxide is particularly preferably selected from the group consisting of 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 the group consisting of U2S, Na2S, and combinations thereof. Furthermore, the sulfur source of the cathode can be present 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 a maximum of 75 wt.-%, based on the total weight of the cathode, are present in the cathode.

[0014] In addition, the sulfur source of the cathode can be present as particles in the cathode, with the particle size in at least one dimension (optionally in all three dimensions) preferably being < 1 pm, where the particle size refers to a particle size determinable by electron microscopy. Preferably, the sulfur source is homogeneously distributed in the cathode, i.e., homogeneously mixed (and preferably compressed) with the other components of the cathode.

[0015] The electrically conductive carbon material of the cathode can be selected from the group consisting of carbon black, porous carbons, carbon nanotubes, carbon nanofibers, graphene, graphite and combinations thereof.

[0016] Furthermore, the electrically conductive carbon material of the cathode can be present in the cathode in an amount of 5 to 50 wt.%, preferably 10 to 40 wt.%, particularly preferably 15 to 30 wt.%, in particular 18-25 wt.%, based on the total weight of the cathode.

[0017] Furthermore, the electrically conductive carbon material of the cathode can be present as particles in the cathode, with the particle size in at least one dimension (optionally in all three dimensions) preferably being < 1 pm, wherein the particle size refers to a particle size determinable by electron microscopy. Preferably, the electrically conductive carbon material is homogeneously distributed in the cathode, i.e., homogeneously mixed (and preferably pressed) with the other components of the cathode.

[0018] The alkali metal ion-conductive solid electrolyte of the cathode can be an inorganic alkali metal ion-conductive solid electrolyte or an inorganic-organic alkali metal ion-conductive solid electrolyte. Furthermore, the alkali metal ion-conductive solid electrolyte of the cathode can be selected from the group consisting of sulfidic alkali metal ion-conductive solid electrolytes. Preferably, the alkali metal ion-conductive solid electrolyte is selected from the group consisting of sulfidic alkali metal ion-conductive solid electrolytes that have a thiophosphate group.

[0019] Apart from that, the alkali metal ion-conductive solid electrolyte of the cathode can be selected from the group consisting of IJ2S-P2S5, IJ7P3S11, IJ2S-GeS2, U2S-B2S3, LiePSsCI, Li2S-SiS2, Li2S-P2Ss-LiX, where X = CI, Br or I, IJ2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCI, Li2S-SiS2-B2S3-I.I.I, Li2S-SiS2-P2Ss-LiI, Li2S-P2S5-Zm S n , where m and n are integers and M is selected from P, Si, Sb, Sn or Ge, Li3PS4-2LiBH4, Li2S-SiS2-LisPO4, Li2S-SiS2-Li p . MOq, where p and q are integers and M is selected from P, Si or Ge, Na2S-P2Ss, Na2S-GeS2, Na2S-B2S3, NaePSsCl, Na2S-SiS2, Na2S-P2Ss-NaX, where X=Cl, Br or I, Na2S-P2S5-Na2O, Na2S-P2S5-Na2O-Nal, Na2S-SiS2-Nal, Na2S-SiS2-NaBr, Na2S-SiS2-NaCl, Na2S-SiS2-B2S3-Nal, Na2S-SiS2-P2S5-Nal, 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 a combination thereof.

[0020] In addition, the alkali metal ion-conductive solid electrolyte of the cathode may be present in the cathode in an amount of 15 to 55 wt.%, preferably 20 to 50 wt.%, particularly preferably 25 to 45 wt.%, in particular 30 to 40 wt.%, based on the total weight of the cathode.

[0021] In addition, the alkali metal ion-conductive solid electrolyte of the cathode can be present as particles in the cathode, wherein the particle size in at least one dimension (optionally in all dimensions) is preferably < 1 pm, wherein the particle size refers to a particle size determinable by electron microscopy. Preferably, the alkali metal ion-conductive solid electrolyte is homogeneously distributed in the cathode, i.e., it is homogeneously mixed (and preferably pressed) with the other components of the cathode.

[0022] The cathode of the alkaline-sulfur secondary battery may further contain a binder. The binder may contain or consist of a fluoropolymer, with the fluoropolymer preferably being PTFE.

[0023] Furthermore, the binder may be present in the cathode in an amount of 0.1 to 10 wt.%, based on the total weight of the cathode.

[0024] In addition, the binder can be present as fibrils (i.e. in the form of fibrils) in the cathode.

[0025] The cathode may have a coating consisting of an alkali metal ion-conductive solid electrolyte on at least one surface that contacts the organic electrolyte.

[0026] Here, the alkali metal ion-conductive solid electrolyte is preferably an oxidic alkali metal ion-conductive solid electrolyte or a sulfidic alkali metal ion-conductive solid electrolyte.

[0027] Furthermore, the coating can preferably have a thickness in the range of 0.1 to 10 pm, wherein the thickness refers to an extension of the coating in the direction perpendicular to its planar extension.

[0028] In a preferred embodiment, the cathode is designed such that it cannot be penetrated by the organic electrolyte, at least in a volume of the cathode facing away from the organic electrolyte. This volume of the cathode is preferably at least 60 vol.%, particularly preferably at least 70 vol.%, most preferably at least 80 vol.%, optionally at least 90 vol.%, of the total volume of the cathode. The larger the volume, the less organic electrolyte can penetrate into the cathode and the smaller the amount of organic electrolyte required in the alkaline-sulfur secondary battery, i.e., the higher its specific energy density.

[0029] In a further preferred embodiment, the cathode has indentations on a side facing the organic electrolyte, which contain the organic electrolyte. The indentations are preferably selected from the group consisting of pores, trenches, impressions, and combinations thereof. This embodiment has the advantage that the cathode exposes a large surface area and thus a contact area to the organic electrolyte, thereby reducing the contact resistance between the cathode and the organic electrolyte and thus improving the electrical properties of the alkaline-sulfur battery.

[0030] Furthermore, the cathode can contact a flat layer on a side facing away from the organic electrolyte, which contains or consists of an electrically conductive material (cathode conductor). The electrically conductive material is preferably selected from the group consisting of metals, metal alloys, carbons, and combinations thereof. The electrically conductive material is particularly preferably selected from the group consisting of stainless steel, aluminum, aluminum alloys, carbon nanotubes, and combinations thereof. Stainless steel has the advantage of imparting high mechanical strength to the cathode.

[0031] The anode of the alkali-sulfur secondary battery may contain or consist of an alkali metal or an alkali metal alloy, preferably lithium metal, a lithium metal alloy, sodium metal and / or a sodium metal alloy.

[0032] In an optional embodiment, the anode does not contain any alkali metal and contains or consists of porous carbon.

[0033] Furthermore, the anode can contact a flat layer on a side facing away from the organic electrolyte, which contains or consists of an electrically conductive material (anode conductor), wherein the electrically conductive material is preferably selected from the group consisting of metals, metal alloys, and combinations thereof. Particularly preferably, the electrically conductive material is selected from the group consisting of stainless steel, copper, copper alloy, nickel, nickel alloy, and combinations thereof.

[0034] The organic electrolyte of the alkaline-sulfur secondary battery can be liquid at a temperature of 25 °C and a pressure of 1013 hPa (liquid electrolyte). The liquid organic electrolyte can contain an organic ether selected from organic ethers that are liquid at 25 °C and a pressure of 1013 hPa. The ether is preferably an cyclic ether with the chemical formula A-(OB) n -OC, where O represents an oxygen atom and A, B and C each represent a saturated or unsaturated, linear or cyclic hydrocarbon radical, where B contains at least 2 carbon atoms and n is > 1, and where the ether is particularly preferably selected from the group consisting of 1,2-dimethoxyethane, 1,3-dioxolane, 2-methoxyethyl ether, bis(2-(2-methoxyethoxy)ethyl) ether and mixtures thereof.

[0035] Furthermore, the conducting salt can be present in the liquid organic electrolyte at a concentration that (at a temperature in the range of 20 °C to 100 °C) corresponds to a solubility limit of the liquid organic electrolyte for the conducting salt (or is even higher; see the following paragraph). This high amount of conducting salt ensures, on the one hand, that the organic liquid electrolyte has high ionic conductivity and, on the other hand, that no polysulfides can dissolve in the organic liquid electrolyte. Optionally, the conducting salt can be present in the liquid organic electrolyte at a concentration in the range of 0.5 M to 15 M, preferably in the range of 1 M to 10 M, particularly preferably in the range of 2 M to 5 M.

[0036] Furthermore, the alkali-sulfur secondary battery (e.g. its organic electrolyte, its cathode, its anode and / or optionally its separator) can contain an amount of conducting salt which exceeds the solubility limit (i.e. saturation limit) of conducting salt in the organic electrolyte at a temperature in the range from 20°C to 100°C. In this case, the alkali-sulfur battery contains conducting salt which is at least partially not present in dissolved form at a temperature in the range from 20°C to 100°C (preferably at a temperature of 100°C). The conducting salt can be present in partially undissolved form (directly) in the organic electrolyte. Alternatively or additionally, the conducting salt can be present in a coating of the cathode, the anode and / or a separator of the alkali-sulfur secondary battery which contains or consists of the conducting salt.The advantage of this is that it can be even better ensured that the organic electrolyte has a solubility for sulfur-containing components of the cathode within the temperature range of 20 °C to 100 °C that is in the range of < 10 mmol sulfur atoms per liter of organic electrolyte. For example, it can also be ensured that during operation of the alkaline-sulfur battery or during temperature fluctuations, the solubility of the organic electrolyte for sulfur-containing components of the cathode does not exceed the range of < 10 mmol sulfur atoms per liter of organic electrolyte.

[0037] Alternatively, the organic electrolyte can be gel-like at a temperature of 25 °C and a pressure of 1013 hPa (gel electrolyte). This has the advantage that the weight of the alkaline-sulfur battery is lower than that of a liquid electrolyte, thus increasing its specific energy density. Furthermore, the gel electrolyte is less likely to leak, resulting in greater safety during operation of the alkaline-sulfur secondary battery.

[0038] The gel-like organic electrolyte may contain an organic ether selected from organic ethers that are liquid at 25 °C and a pressure of 1013 hPa. Preferably, the ether is an cyclic ether with the chemical formula A-(OB) n-OC, where O represents an oxygen atom and A, B and C each represent a saturated or unsaturated, linear or cyclic hydrocarbon radical, where B contains at least 2 carbon atoms and n is > 1, and where the ether is particularly preferably selected from the group consisting of 1,2-dimethoxyethane, 1,3-dioxolane, 2-methoxyethyl ether, bis(2-(2-methoxyethoxy)ethyl) ether and mixtures thereof.

[0039] In a preferred embodiment, the gel-like organic electrolyte contains a gelling agent, which is preferably a polymer. The polymer is particularly preferably selected from the group consisting of PEO, PEG-DME, and combinations thereof.

[0040] Furthermore, the conducting salt is present in the gel-like organic electrolyte at a concentration that, at a temperature in the range of 20°C to 100°C, corresponds to or exceeds the solubility limit of the gel-like organic electrolyte for the conducting salt. This high amount of conducting salt ensures, on the one hand, that the gel electrolyte has high ionic conductivity and, on the other hand, that no polysulfides can dissolve in the gel electrolyte. Optionally, the conducting salt is present in the gel-like organic electrolyte at a concentration in the range of 0.5 M to 15 M, preferably in the range of 1 M to 10 M, particularly preferably in the range of 2 M to 5 M.

[0041] Alternatively, the organic electrolyte can be solid at a temperature of 25 °C and a pressure of 1013 hPa (solid electrolyte). This has the advantage that the weight of the alkaline-sulfur battery is lower than that of a liquid electrolyte or a gel electrolyte, thus increasing its specific energy density. Furthermore, the solid electrolyte cannot leak, resulting in greater safety during operation of the alkaline-sulfur secondary battery.

[0042] The solid organic electrolyte can contain an organic ether selected from organic ethers that are solid at 25 °C and a pressure of 1013 hPa (e.g., an organic polyether). In particular, the solid organic electrolyte (e.g., solid organic ethers) has no intrinsic ionic conductivity for alkali metal ions. Due to the lack of intrinsic ionic conductivity for alkali metal ions, the conductivity for alkali metal ions is mediated solely by the conductive salt present in the solid organic electrolyte.

[0043] Furthermore, the solid organic electrolyte can contain an organic polyether, wherein the organic polyether is preferably selected from the group consisting of PEO, PEG-DME, and combinations thereof. In particular, the end groups of the molecules of the solid organic electrolyte (e.g., the solid organic polyether) do not have an OH group and optionally have an alkyl group. The absence of an OH group at the end groups has the advantage of increasing the stability of the organic electrolyte and further improving the long-term stability of the alkaline-sulfur secondary battery.

[0044] Furthermore, the conducting salt can be present in the solid organic electrolyte in an amount of at least 10 wt.%, based on the total weight of the solid organic electrolyte. The amount of conducting salt in the solid organic electrolyte is typically in the range of 10 to 80 wt.%. This high amount of conducting salt ensures, on the one hand, that the solid electrolyte has high ionic conductivity and, on the other hand, that no polysulfides can accumulate on the solid electrolyte or be incorporated into the solid electrolyte.

[0045] In a preferred embodiment, the organic electrolyte further contains another organic ether which differs from the (first) organic ether.

[0046] The additional organic ether preferably has a lower solubility for the conducting salt than the (first) organic ether of the organic electrolyte. The advantage here is that the amount or concentration of conducting salt required to reduce the solubility of the electrolyte for polysulfide ions to a solubility in the range of < 5 mM can be lower. This can represent a weight advantage and thus further increase the specific energy density of the alkali-sulfur battery. Furthermore, this can represent an economic advantage if the addition of the additional organic ether is more cost-effective than a corresponding increase in the amount or concentration of conducting salt.

[0047] The further organic ether may be contained in the organic electrolyte in an amount of 10 to 90 vol.%, based on the sum of the volume of the organic ether and the volume of the further organic ether.

[0048] The further organic ether can be 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 pentyl ether, ethyl pentyl ether, propyl pentyl ether, butyl pentyl ether, dipentyl ether, l-(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, pentylhexyl ether, dihexyl ether, methoxycyclohexane, phenetole, 2-methoxypropane, 2-methoxybutane, 2-methoxypentane, 2-methoxyhexane, 2-ethoxypropane, 2-ethoxybutane, 2-ethoxypentane, 2-ethoxyhexane, and mixtures thereof. Furthermore, the further organic ether can be an organic fluoroether, wherein the fluoroether 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-Pentafluoropropyldifluoromethyl 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 isopentyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, l,l,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, Hexafluoroisopropyl methyl ether, l,l,3,3,3-pentafluoro-2-trifluoromethyl- propyl 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, wherein the fluoroether is preferably a 1,1,2,2-tetrafluoroethyl propyl ether, particularly preferably 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether.

[0049] The conducting salt contained in the electrolyte can be 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, LiIl, LiCI, LiF, LiPF5(SO2CF3), LiPF4(SO2CF3)2 and combinations thereof, preferably selected from the group consisting of LiFSI, LiTFSI and combinations thereof.

[0050] The alkaline-sulfur secondary battery may also contain a porous separator (e.g., in the case of a liquid electrolyte or gel electrolyte). The porous separator allows ion transport through the pores of the porous separator.

[0051] The porous separator may contain or consist of an organic material and / or a ceramic material. The organic material is preferably selected from the group consisting of polyolefins. The ceramic material is preferably Al2O3.

[0052] Furthermore, the porous separator can have a thickness, in a direction perpendicular to a planar extent of the porous separator, in the range of 1 μm to 80 μm, preferably in the range of 2 μm to 40 μm, particularly preferably in the range of 5 μm to 20 μm, most particularly preferably in the range of 10 μm to 15 μm. The thinner the separator, the lower its weight contribution to the total weight of the alkali-sulfur secondary battery and the higher the specific energy density of the alkali-sulfur secondary battery.

[0053] The invention further proposes the use of the alkali-sulfur secondary battery according to the invention as an energy source in an i) stationary device, preferably in a building; and / or ii) mobile device, preferably in a mobile electronic device and / or a means of transport, wherein the means of transport is preferably selected from the group consisting of automobile, aircraft, drone, train, and combinations thereof.

[0054] When using the alkali-sulfur secondary battery according to the invention, the alkali-sulfur secondary battery can be operated at room temperature (temperature in the range of 20 °C to 30 °C) or at a higher temperature in the range of 60 °C to 100 °C. Operation at a higher temperature is advantageous because at higher temperatures the ionic conductivity of the organic electrolyte is increased, thus improving the conversion kinetics of the cathode.

[0055] The subject matter of the invention will be explained in more detail with reference to the following example and the following figures, without wishing to restrict it to the specific embodiments shown here.

[0056] Figure 1 shows schematically a structure of an alkali-sulfur secondary battery according to the invention.

[0057] Figure 2 shows schematically a structure of another alkali-sulfur secondary battery according to the invention.

[0058] Figure 3 shows the result of an electrochemical investigation (specific capacity and coulombic efficiency) of an alkali-sulfur secondary battery according to the invention (electrolyte is DME with 12 IVI LiFSI; see triangular symbols) in comparison with a non-inventive alkali-sulfur battery (electrolyte is DME with only 4 M LiFSI; see square symbols).

[0059] Example - Production of an alkali-sulfur battery according to the invention

[0060] The cathode material for the alkali-sulfur secondary battery according to the invention was prepared in an argon-filled glove box. Sulfur (Sigma Aldrich), carbon (Printex XE2B, Orion), and solid electrolyte (NEI) were mixed in a mass ratio of 3:2:5 and ground into 5 mm balls using a ball mill (Retsch PM100) for 4 hours at a rotation speed of 400 rpm.

[0061] To produce a free-standing cathode dry film, 0.5 wt.% PTFE, based on the total weight of the cathode material, was added to the prepared cathode composite. The mixture was then poured into a heated mortar and ground under shear forces until a continuous cathode film was formed. This film was rolled out on a heated plate to a homogeneous thickness of approximately 50 μm. The free-standing dry film was subsequently laminated to a carbon-coated aluminum foil. 13 mm die cuts were produced for characterization in button cells, and the cathodes were laser-assembled for characterization in pouch cells.

[0062] The cell concept was evaluated in button cells (CR2016). For this purpose, the manufactured cathodes (13 mm diameter) were mounted against a lithium anode (250 pm, 16.5 mm on a 1000 pm steel spacer). A 12 pm PE separator was used as the separator.

[0063] Two different electrolyte compositions were used and compared. 40 μl of electrolyte was used in each case, meaning 20 μl of electrolyte was applied to the cathode and another 20 μl of electrolyte was applied to the separator.

[0064] The first electrolyte composition (reference electrolyte) was (only) 4 M LiFSI in DME, which corresponds to a concentration of the conducting salt LiFSI well below the solubility limit of LiFSI in DME. The organic electrolyte thus exhibited a solubility for polysulfide ions well above 5 mM and above 10 mM, respectively, at a temperature range of 20 °C to 100 °C.

[0065] The second electrolyte composition (inventive electrolyte) was 12 M LiFSI in DME, which corresponds to a concentration of the conducting salt LiFSI at the solubility limit of LiFSI in DME. The organic electrolyte thus exhibited a solubility for polysulfide ions of < 5 mM at a temperature range of 20 °C to 100 °C. Figure 1 shows a schematic structure of this alkali-sulfur battery.

[0066] The cells produced with the respective electrolyte compositions were each tested in the voltage range from 1.6 V to 2.7 V. The first 10 cycles were charged and discharged symmetrically at a current rate of 0.05 C, the following at 0.1 C. During charging, a constant voltage step at 2.7 V followed the charging process with constant current in all cycles. Figure 3 shows the result of this electrochemical investigation of the alkali-sulfur secondary battery according to the invention (electrolyte according to the invention, DME with 12 M LiFSI) in comparison with a non-inventive alkali-sulfur battery (reference electrolyte, DME with only 4 M LiFSI).

[0067] The cell with the reference electrolyte initially showed a specific capacity of approximately 1500 Ah per kg of sulfur, but this dropped sharply after the second cycle and was only approximately 100 Ah per kg of sulfur by the fifth cycle.

[0068] In contrast, the cell with the electrolyte according to the invention initially exhibited a specific capacity of approximately 1700 Ah per kg of sulfur, which was still approximately 1400 Ah per kg of sulfur even after the 20th cycle. Thus, unlike the reference alkaline-sulfur secondary battery, the alkaline-sulfur secondary battery according to the invention is capable of maintaining a high specific capacity and thus a high specific energy density over a long operating period. For the tested alkaline-sulfur secondary battery according to the invention, a specific energy density of 588 Wh per kg of electrode stack of the alkaline-sulfur secondary battery was obtained.

[0069] 1: Cathode of the alkaline-sulfur secondary battery;

[0070] 2: Anode of the alkaline-sulfur secondary battery;

[0071] 3: organic electrolyte of the alkaline-sulfur secondary battery;

[0072] 4: porous separator of alkaline-sulfur secondary battery;

[0073] 5: flat layer containing or consisting of an electrically conductive material and contacting the cathode (cathode conductor);

[0074] 6: Indentations of the cathode containing the electrolyte (here: impressions).

Claims

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

2. Alkali-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 compound and combinations thereof, wherein the sulfur source preferably contains or consists of an organosulfur compound, a metal sulfide and / or an alkali metal sulfide, wherein the sulfur source particularly preferably contains or consists of sulfurized polyacrylonitrile, vanadium sulfide, iron sulfide, molybdenum sulfide, bismuth sulfide, cobalt sulfide, titanium sulfide, copper sulfide, tin sulfide, nickel sulfide, U2S, and / or Na2S; and / or ii) 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 at most 75 % by weight, based on the total weight of the cathode, in the cathode; and / or iii) is present as particles in the cathode, wherein the particle size in at least one dimension is preferably < 1 µm, wherein the particle size refers to a particle size determinable by electron microscopy.

3. Alkali-sulfur secondary battery according to 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 carbons, carbon nanotubes, carbon nanofibers, graphene, graphite, and combinations thereof; and / or ii) is present in the cathode in an amount of 5 to 50 wt. %, preferably 10 to 40 wt. %, particularly preferably 15 to 30 wt. %, in particular 18-25 wt. %, based on the total weight of the cathode; and / or iii) is present as particles in the cathode, wherein the particle size in at least one dimension is preferably < 1 pm, wherein the particle size refers to a particle size determinable by electron microscopy.

4. Alkali-sulfur secondary battery according to one of the preceding claims, characterized in that the alkali metal ion-conductive solid electrolyte of the cathode i) is an inorganic alkali metal ion-conductive solid electrolyte or an inorganic-organic alkali metal ion-conductive solid electrolyte; and / or ii) is selected from the group consisting of sulfidic alkali metal ion-conductive solid electrolytes, preferably selected from the group consisting of sulfidic alkali metal ion-conductive solid electrolytes which have a thiophosphate group; and / or iii) is selected from the group consisting of IJ2S-P2S5, IJ7P3S11, Li2S-GeS2, U2S-B2S3, Li6PS5CI, Li2S-SiS2, Li2S-P2S5-LiX, where X = CI, Br or I, Li2S-P2Ss-Li2O, Li2S-P2Ss-Li2O-LiIl, Li2S-SiS2-LiIl, Li2S-SiS2-Li Br, Li2S-SiS2-LiCI, Li2S-SiS2-B2S3-Li I, Li2S-SiS2 _P2Ss-Li I, Li2S-P2S5-ZmSn, 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, U3PS4-2IJBH4, Na2S-P2S5, Na2S-GeS2, Na2S-B2S3, Na6PS5Cl, Na2S-SiS2, Na2S-P2S5-NaX, where X=Cl, Br or I, Na2S-P2S5-Na2O, Na2S-P2S5-Na2O-Nal, Na2S-SiS2-Nal, Na2S-SiS2-NaBr, Na2S-SiS2-NaCl, Na2S-SiS2-B2S3-Nal, Na2S-SiS2-P2Ss-Nal, Na2S-P2S5-Z m S n , where m and n are integers and M is selected from P, Si or Ge, Na2S-SiS2-NasPC, Na2S-SiS2-Na pMOq, where p and q are integers and M is selected from P, Si, Sb, Sn or Ge, or a combination thereof; and / or iv) is present in the cathode in an amount of 15 to 55 wt.%, preferably 20 to 50 wt.%, particularly preferably 25 to 45 wt.%, in particular 30 to 40 wt.%, based on the total weight of the cathode; and / or v) is present as particles in the cathode, wherein the particle size in at least one dimension is preferably < 1 pm, wherein the particle size refers to a particle size determinable by electron microscopy.

5. An alkali-sulfur secondary battery according to any one of the preceding claims, characterized in that the cathode further contains a binder, wherein the binder preferably i) contains or consists of a fluoropolymer, wherein the fluoropolymer is preferably PTFE; and / or ii) is present in the cathode in an amount of 0.1 to 10 wt.%, based on the total weight of the cathode; and / or iii) is present as fibrils in the cathode.

6. Alkali-sulfur secondary battery according to one of the preceding claims, characterized in that the cathode has, at least on a surface that contacts the organic electrolyte, a coating consisting of an alkali metal ion-conductive solid electrolyte, wherein preferably i) the alkali metal ion-conductive solid electrolyte is an oxidic alkali metal ion-conductive solid electrolyte or sulfidic alkali metal ion-conductive solid electrolyte; and / or ii) the coating preferably has a thickness in the range of 0.1 to 10 pm, wherein the thickness relates to an extension of the coating in the direction perpendicular to its planar extension.

7. Alkali-sulfur secondary battery according to one of the preceding claims, characterized in that the cathode i) is designed such that it cannot be penetrated by the organic electrolyte at least in a volume of the cathode which is remote from the organic electrolyte, this volume of the cathode preferably being 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 cathode; and / or ii) on a side facing the organic electrolyte, has indentations which contain the organic electrolyte, wherein the indentations are preferably selected from the group consisting of pores, trenches, impressions and combinations thereof; and / or iii) on a side facing away from the organic electrolyte, contacts a flat layer which contains or consists of an electrically conductive material, wherein the electrically conductive material is preferably selected from the group consisting of metals, metal alloys, carbons and combinations thereof, wherein the electrically conductive material is particularly. is preferably selected from the group consisting of stainless steel, aluminum, aluminum alloy, carbon nanotubes and combinations thereof.

8. Alkali-sulfur secondary battery according to one of the preceding claims, characterized in that the anode i) contains 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) contains no alkali metal and contains or consists of porous carbon; and / or iii) on a side facing away from the organic electrolyte, contacts a flat layer which contains or consists 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, copper alloy, nickel, nickel alloy and combinations thereof.

9. Alkali-sulfur secondary battery according to 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 contains an organic ether selected from organic ethers that are liquid at 25 °C and a pressure of 1013 hPa; ii) the organic electrolyte contains an organic ether that is an cyclic ether having the chemical formula A-(OB) n -OC, where O represents an oxygen atom and A, B and C each represent a saturated or unsaturated, linear or cyclic, hydrocarbon radical, where B contains at least 2 carbon atoms and n is > 1, and where the ether is particularly preferably selected from the group consisting of 1,2-dimethoxyethane, 1,3-dioxolane, 2-methoxyethyl ether, bis(2-(2-methoxyethoxy)ethyl) ether and mixtures thereof; and / or iii) the conducting salt is present in the liquid organic electrolyte at a concentration which, at a temperature in the range from 20°C to 100°C, corresponds to or is higher than a solubility limit of the liquid organic electrolyte for the conducting salt, where optionally the conducting salt is present in the liquid organic electrolyte at a concentration in the range from 0.5 M to 15, preferably in the range from 1 M to 10 M, particularly preferably in the range from 2 M to 5 M.

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

11. Alkali-sulfur secondary battery according to one of claims 1 to 8, characterized in that the organic electrolyte is solid at a temperature of 25 °C and a pressure of 1013 hPa, wherein preferably i) the organic electrolyte contains an organic ether which is selected from organic ethers which are solid at 25 °C and a pressure of 1013 hPa and have no intrinsic ionic conductivity for alkali metal ions; ii) the organic electrolyte contains 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 molecules of the polyether do not have an OH group, optionally having an alkyl group; and / or iii) the conducting salt is present in the solid organic electrolyte in an amount which is at least 10 wt.%, based on the total weight of the solid organic electrolyte, wherein the amount of conducting salt in the solid organic electrolyte is in particular in the range from 10 to 80 wt.%.

12. An alkali-sulfur secondary battery according to any one of the preceding claims, characterized in that the organic electrolyte further contains another organic ether which is different from organic ether, wherein the further organic ether preferably i) has a lower solubility for the conducting salt than the organic ether of the organic electrolyte; and / or ii) is contained in the organic electrolyte in an amount of 10 to 90 vol.%, based on the sum of the volume of the organic ether and the volume of the further organic ether;and / or 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 pentyl ether, ethyl pentyl ether, propyl pentyl ether, butyl pentyl ether, dipentyl ether, l-(2,2-dimethylpropoxy)-2,2-dimethylpropane, isopentyl ether, di-(1,2-dimethylpropyl) ether, methylhexyl ether, ethylhexyl ether, propylhexyl ether, butylhexyl ether, pentylhexyl ether, dihexyl ether, methoxycyclohexane, phenetole, 2-methoxypropane, 2-methoxybutane, 2-methoxypentane, 2-methoxyhexane, 2-ethoxypropane, 2-ethoxybutane, 2-ethoxypentane, 2-ethoxyhexane, and mixtures thereof, or an organic fluoroether, wherein the fluoroether 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 isopentyl ether, l,l,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. Alkali-sulfur secondary battery according to one of the preceding claims, characterized in that the conducting salt is selected from the group consisting of LiFSI, LiTFSI, LiPFe, LiBF4, LiClC, LiSO3CF3, LiN(SO2F)2, LiN(SO2CF3)2, LiN(SO2F)(SO2CF3), LiN(SO2F)(SO2C4Fg), LiN(SO2CF2CF3)2, LiC(SO2CF2CF3)3, LiC(SO2CF3)3, LiIl, LiCl, LiF, LiPFs(SO2CF3), LiPF4(SO2CF3)2 and combinations thereof, preferably selected from the group consisting of LiFSI, LiTFSI and combinations thereof.

14. Alkali-sulfur secondary battery according to one of the preceding claims, characterized in that the alkali-sulfur secondary battery further contains a porous separator, wherein the porous separator preferably i) contains 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 Al2O3; and / or ii) has a thickness, in a direction perpendicular to a planar extent of the porous separator, in the range from 1 pm to 80 pm, preferably in the range from 2 pm to 40 pm, more preferably in the range from 5 pm to 20 pm, most preferably in the range from 10 pm to 15 pm.

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

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