CATHOD WITH A FLUOR-CONTAINING POLYMER AND A SOLID BATTERY WITH THE CATHOD

Description

[0001] The invention relates to a cathode and a solid-state battery with the cathode.

[0002] In the following, the term "solid-state battery" is used synonymously for all terms commonly used in the prior art for galvanic cells and cells that use at least one solid electrolyte as an ion-conducting connection between the cathode and anode, such as metal solid-state battery, metal solid-state accumulator, all-solid-state battery (ASSB), cell, solid-state cell, polymer cell, and accumulator. Rechargeable batteries (secondary batteries) are specifically included. The terms "battery," "cell," and "electrochemical cell" are also used synonymously with the term "solid-state battery."

[0003] Solid-state batteries represent a further development of batteries with liquid electrolytes. In these batteries, the porous, liquid-soaked separator, which is responsible for ion transport and thus charge equalization between the cathode and anode, is replaced by an ion-conducting solid.

[0004] A preferred variant of the solid-state battery is the lithium-ion solid-state battery.

[0005] Lithium-ion solid-state batteries known from the prior art have two different electrodes: a positive electrode (cathode) and a negative electrode (anode). In a lithium-ion solid-state battery, the cathode comprises a cathode active material capable of reversibly absorbing and releasing lithium ions. The anode can comprise an anode active material, which may be lithium metal, a lithium-containing alloy, or an alternative material also designed to reversibly absorb and release lithium ions. Examples of materials commonly used in the prior art include graphite, silicon, and silicon suboxide (SiO₂x with Ox < 2).

[0006] If the anode of a solid-state lithium-ion battery contains no lithium metal immediately after its manufacture, but at least some lithium metal is deposited during the first few charging cycles, it is referred to as a "lithium-free" anode design. In this context, "lithium-free" means that the anode is free of metallic lithium in its uncharged state after manufacturing and before the cell is formed. Metallic lithium is only formed at the anode during a charging process.

[0007] The two electrodes are connected via a solid-state separator, which conducts lithium ions. Furthermore, the solid-state separator spatially separates the cathode from the anode. It ensures the transport of lithium ions between the cathode and the anode. Thus, the solid-state separator conducts the electric current through lithium ion transport within the solid. Therefore, the solid-state separator constitutes a solid-state lithium-ion conductor.

[0008] Solid-state separators can be classified into ceramic, polymer-based, and gel-based solid electrolytes. Sulfide and oxide solid electrolytes are particularly common as ceramic solid electrolytes, gaining increasing importance due to their electrochemical stability combined with high lithium-ion conductivity. Polymer-based solid electrolytes, on the other hand, are solvent-free and rely on ionic conduction along polymer chains. Polyethylene oxide with a lithium-containing conductive additive, for example, can be used as a polymer-based solid electrolyte. Gel-based solid electrolytes contain a solid polymer matrix permeated by a liquid electrolyte, which ensures ionic conductivity.

[0009] US Patent 2019 / 0157723 A1 describes a lithium-ion solid-state battery comprising a cathode with a cathode active material and an anode with an anode active material. The anode also includes an anode current collector. The anode active material is selected to form an alloy or compound with metallic lithium. The anode active material and the cathode active material are spatially separated by a solid electrolyte. The solid electrolyte consists of a sulfide material, such as Li₆P₅Cl with an argyrodite structure. The cathode active material consists, in particular, of known lithium-containing layered oxides such as NMC. The anode active material can be selected from the group consisting of amorphous carbon, gold, platinum, palladium, silicon, silver, aluminum, bismuth, tin, and zinc, as well as combinations thereof.

[0010] The lithium-ion solid-state battery described above uses a lithium-free anode design, as metallic lithium is deposited between the anode current collector and the anode active material during the initial charging cycles. Therefore, metallic lithium is not initially present in the cell after manufacturing.

[0011] WO 2020 0725524 A1 discloses a lithium-ion solid-state battery comprising an anode current collector, a solid electrolyte, and a transition layer between the anode current collector and the solid electrolyte. The transition layer is selected from the group consisting of zinc, tin, magnesium, silver, aluminum, indium, bismuth, lithium alloy, lithium oxide, and lithium peroxide, as well as combinations thereof. In particular, the solid electrolyte consists of a lithium-containing garnet, preferably lithium lanthanum zirconate (LLZO) with the chemical formula Li₇La₃Zr₂O₁₂, which ensures charge balance between the anode and cathode by transporting lithium ions. A lithium-free anode design is also employed here.

[0012] From US patent 2021 / 01226281 A1, ceramic solid-state electrolytes are known which can be described by the general formula: Li 1-abcd P a T b A c X d where 0 ≤ a ≤ 0.129, 0 ≤ b ≤ 0.096, 0.316 ≤ c ≤ 0.484, 0.012 ≤ d ≤ 0.125 and where T is an element from the group consisting of As, Si, Ge, Al and B, X is one or more halogens or N, and A is one or more of S and Se.

[0013] WO 2019 / 051305 A1 discloses a cathode, anode, and a solid electrolyte arranged between the cathode and the anode. At least the cathode, anode, or solid electrolyte comprises a ceramic material containing lithium (Li), boron (B), and sulfur (S). The ceramic material exhibits several crystalline phases and has an overall composition characterized by an a:b:c molar ratio of Li:B:S, where c / b is in the range of approximately 1 to approximately 3.

[0014] EP 3 496 202 A1 describes lithium-ion-conducting lithium yttrium halides of the general formula Li 6-3z Y z X 6 , wherein 0 <z<2 ist und X Cl oder Br bedeutet. Die Lithium-Yttriumhalogenide werden als Festkörperelektrolyt in einer Lithiumionen-Festkörperbatterie verwendet.

[0015] US 10 811 688 B2 and US 2017 / 0338492 A1 disclose a lithium-ion solid-state battery with a solid-state electrolyte based on an ion-conducting polymer, an ion source such as Li₂O, Na₂O, MgO, CaO, ZnO, KOH, NaOH, CaCl₂, AlCl₃, MgCl₂, LiTFSI (lithium bis-trifluoromethanesulfonimide), LiBOB (lithium bis(oxalate)borate), or combinations thereof, and an electron acceptor. Liquid crystal polymers, polyetheretherketone (PEEK), polyphenylene sulfide (PPS), and semicrystalline polymers with a crystallinity greater than 30% are specified as lithium-ion-conducting polymers.

[0016] US patent 2019 / 0051939 A1 discloses a lithium-ion solid-state battery containing a polylithium acrylate as a polymer-based solid electrolyte. The solid electrolyte further comprises a hydrophilic polymer, a lithium salt, and a Lewis acid.

[0017] To ensure sufficient ionic conduction between the electrode and the solid electrolyte, close contact between the active materials of the cathode and the solid electrolyte is essential. This is achieved by integrating the solid electrolyte into the cathode. This is accomplished by using so-called composite electrodes, which are a mixture of the solid electrolyte and the active material.

[0018] However, the combination of solid electrolyte and cathode active material entails a number of problems.

[0019] During the regular operation of a lithium-ion solid-state battery, the continuous re- and de-lithiation of the active materials can lead to volume changes within these materials. Over time, these volume changes can cause mechanical stresses in the cell. These mechanical stresses, in turn, can lead to cracks within the solid electrolyte, which can impair the proper functioning of the cell. Crack formation is a particular problem for rigid ceramic solid-state electrolytes.

[0020] Furthermore, the production of ceramic solid-state electrolytes often requires a sintering step at temperatures between 650° and 1200°. However, such temperatures can irreparably damage a composite cathode, especially the cathode active material present in the composite cathode.

[0021] This problem can be remedied by using either organic binders or polymer electrolytes such as polyethylene oxide (PEO) in the cathode composite. However, organic binders lack ionic conductivity, and the oxidative stability of polymers like PEO is often insufficient for the potentials of the electrode materials on the cathode side (> 4V).

[0022] The invention is based on the objective of avoiding the disadvantages of solid-state batteries known from the prior art and providing a solid-state battery that is easy to manufacture and can be operated stably over a longer period of time.

[0023] The problem is solved according to the invention by providing a cathode for a solid-state battery according to claim 1.

[0024] Advantageous embodiments of the cathode according to the invention for a solid-state battery are specified in the dependent claims, which can be optionally combined with one another.

[0025] According to the invention, the cathode for a solid-state battery comprises the following components: (A) at least one cathode active material; (B) at least one first fluorine-containing polymer with an at least partially fluorinated or perfluorinated backbone, wherein the first fluorine-containing polymer contains at least one ionic group of the following formula (I): wherein M is a cation selected from the group consisting of protons and alkali metals; n is an integer from 1 to 4; Z is a central ion selected from the group consisting of aluminum and boron; and R is a monovalent, optionally fluorine-substituted hydrocarbon residue selected from the group consisting of C1-C8 alkyl, C2-C10 alkenyl, C2-C10 alkynyl, C6-C12 cycloalkyl and C6-C12 aryl; wherein the ionic group is connected to the backbone of the first fluorine-containing polymer via at least one bridging oxygen atom of the ionic group.

[0026] The invention is based on the basic idea of ​​providing a combination of a cathode active material and a first fluorine-containing polymer for the cathode of a solid-state battery, wherein the combination proposed according to the invention has a number of advantageous properties.

[0027] The fluorine-containing polymer exhibits ionic groups as a key characteristic. These ionic groups enable virtually unimpeded ion transport within the cathode. The first fluorine-containing polymer is therefore an ionic conductor. The addition of conventional conducting salts such as lithium hexafluorophosphate is thus unnecessary. Ionic conduction occurs via the fluorine-containing polymer itself. Due to these functional ionic groups, the first fluorine-containing polymer also exhibits a transport number close to 1.

[0028] At the same time, fluorinated polymers with at least a partially fluorinated or perfluorinated backbone possess high chemical and electrochemical stability. Consequently, they are particularly suitable for use in a cathode for a solid-state battery.

[0029] The first fluorine-containing polymer is also mechanically flexible and elastic. The polymers can therefore compensate for the volume changes of the cathode material during cell operation. The cathode material can thus expand and contract freely during re- and de-lithiation. The combination of the cathode material and the first fluorine-containing polymer can compensate for these volume changes and prevent mechanical stresses within the cell.

[0030] Furthermore, a synergistic effect occurs between the cathode active material as the "rigid" component and the fluorine-containing polymer as the "soft" component. The fluorine-containing polymer, as the "soft" component, can preferentially adapt to the rigid shape of the cathode active material. This increases the contact area and ensures ionic conduction between the fluorine-containing polymer and the cathode active material.

[0031] Suitable cathode active materials for the cathode can be any cathode active materials known in the prior art.

[0032] Preferred cathode active materials for the cathode according to the invention include lithium cobalt oxide (LCO), lithium nickel oxide (LNO), lithium nickel cobalt aluminum oxide (NCA), lithium nickel manganese cobalt oxide (NMC), lithium and manganese-rich lithium nickel manganese cobalt oxide or lithium nickel manganese oxide (LMR), lithium manganese oxide (LMO), lithium iron phosphate (LFP), lithium manganese iron phosphate (LMFP), lithium nickel manganese oxide spinel (LNMO) and derivatives as well as combinations thereof.

[0033] Lithium nickel manganese cobalt compounds are also known by the abbreviation NMC, and occasionally alternatively by the technical abbreviation NCM. NMC-based cathode materials are used particularly in lithium-ion batteries for vehicles. NMC as a cathode material exhibits an advantageous combination of desirable properties, such as high specific capacity, reduced cobalt content, high high-current capability, and high intrinsic safety, which is demonstrated, for example, by sufficient stability under overcharging conditions.

[0034] NMCs can be described using the general formula unit Li α Ni x Mn y Co z O 2 with x+y+z = 1, where α denotes the stoichiometric proportion of lithium and is usually between 0.8 and 1.15. Certain stoichiometries are given in the literature as numerical triples, for example, NMC 811, NMC 622, NMC 532, and NMC 111. The numerical triplet indicates the relative content of nickel : manganese : cobalt. In other words, NMC 811, for example, is a cathode material with the general formula unit LiNi 0.8 Mn 0.1 Co 0.1 O 2 , i.e., with α = 1. Furthermore, the so-called lithium- and manganese-rich NMCs or LMRs with the general formula unit Li 1+ε (Ni x Mn y Co z ) 1-ε O 2 can also be used, where ε is in particular between 0.1 and 0.6, preferably between 0.2 and 0.4. These lithium-rich layered oxides are also known as Overlithitated (Layered) Oxides (OLO).

[0035] According to the invention, the first fluorine-containing polymer contains at least one ionic group of general formula (I).

[0036] The ionic group is an ion comprising a cation M+< and an anion [-(O)n-Z-(OR)4-n]-<.

[0037] In the general formula (I), the negative charge of the anion is stoichiometrically balanced by the positive charge of the cation.

[0038] The cation is selected from the group consisting of protons and alkali metals. Lithium is the preferred cation.

[0039] In formula (I), Z represents a central ion selected from the group consisting of aluminum and boron. The ionic groups are therefore either aluminates or borates, and the anions of formula (I) are accordingly singly negatively charged.

[0040] The R groups each represent a monovalent, optionally fluorine-substituted hydrocarbon residue and are independently selected from the group consisting of C1-C8 alkyl, C2-C10 alkenyl, C2-C10 alkynyl, C6-C12 cycloalkyl, and C6-C14 aryl. For the purposes of the invention, monovalent means that the hydrocarbon residues R each bind to the central ion Z via a single oxygen atom.

[0041] For the purposes of the invention, the term C1-C8 alkyl comprises linear or branched saturated hydrocarbon residues with one to eight carbon atoms. Preferred hydrocarbon residues include, for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, iso-butyl, tert-butyl, n-pentyl, iso-pentyl, 2,2-dimethylpropyl, n-hexyl, iso-hexyl, 2-ethylhexyl, n-heptyl, iso-heptyl, n-octyl, and iso-octyl.

[0042] For the purposes of the invention, the term C2-C10-alkenyl comprises linear or branched, at least partially unsaturated hydrocarbon residues with two to ten carbon atoms, wherein the hydrocarbon residues have at least one C-C double bond. Preferred hydrocarbon residues include, for example, ethenyl, 1-propenyl, 2-propenyl, 1-n-butenyl, 2-n-butenyl, isobutenyl, 1-pentenyl, 1-hexenyl, 1-heptenyl, 1-octenyl, 1-nonenyl, and 1-decenyl.

[0043] The term C2-C10-alkynyl, as used in the invention, comprises linear or branched, at least partially linear, unsaturated hydrocarbon residues with two to ten carbon atoms, wherein the hydrocarbon residues have at least one C-C triple bond. Preferred hydrocarbon residues include, for example, ethynyl, 1-propynyl, 2-propynyl, 1-n-butynyl, 2-n-butynyl, iso-butynyl, 1-pentynyl, 1-hexynyl, 1-heptynyl, 1-octynyl, 1-nonynyl, and 1-decinyl.

[0044] For the purposes of the invention, the term C6-C12 cycloalkyl comprises cyclic, saturated hydrocarbon residues with six to twelve carbon atoms. Preferred hydrocarbon residues include, for example, cyclopropyl, cyclobutyl, cyclopentyl, cyclohepyl, cyclohepyl, cyclocononyl, and cyclodecanyl.

[0045] For the purposes of the invention, the term C6-C14 aryl comprises aromatic hydrocarbon residues with six to twelve carbon atoms. Preferred hydrocarbon residues include, for example, phenyl, naphthyl, and anthracyl.

[0046] In a preferred embodiment, the hydrocarbon residues R are at least partially fluorinated, preferably completely fluorinated.

[0047] Fluorine-substituted hydrocarbon residues yield anions that form particularly stable ionic groups of formula (I).

[0048] n is an integer from 1 to 4. Thus, n defines the number of bonds between the central ion Z and the at least partially fluorinated or perfluorinated backbone of the first fluorine-containing polymer. The bond between the central ion Z and the first fluorine-containing polymer always occurs via at least one bridging oxygen atom of the ionic group.

[0049] The number of -OR groups is given as 4-n in the general formula (I). Thus, the number of -OR groups is directly linked to the number of bonds (n) of the central ion Z to the at least partially fluorinated or perfluorinated backbone of the first fluorine-containing polymer.

[0050] The degree of linkage of the ionic group can be adjusted depending on the value of n. Generally, two types of linkages are possible depending on the choice of n: ionic end groups (n=1); and ionic crosslinking groups (n=2, 3 or 4).

[0051] In one embodiment, the first fluorine-containing polymer has at least one ionic end group of general formula (I), wherein n is equal to 1.

[0052] If n in formula (I) equals 1, the central ion Z is connected to the backbone of the first fluorine-containing polymer via a bridging oxygen atom in the ionic group. Such a central ion Z then bonds to three -OR substituents. An example of such an ionic end group is given by the following formula (II):

[0053] In a further embodiment, the first fluorine-containing polymer has at least one ionic crosslinking group of the general formula (I), wherein n is equal to 2, 3 or 4.

[0054] If n in formula (I) equals 2, the central ion Z is linked to the backbone of a first fluorine-containing polymer via two bridging oxygen atoms in the ionic group. Such a central ion Z then binds to two -OR substituents. An example of such an ionic structure is given by the following formula (III):

[0055] If n in formula (I) is equal to 3, the central ion Z is connected to the backbone of a first fluorine-containing polymer via three bridging oxygen atoms in the ionic group. Such a central ion Z then binds to a residue -OR. An example of such an ionic structure is given by the following formula (IV):

[0056] If n in formula (I) equals 4, the central ion Z is linked to the backbone of a first fluorine-containing polymer via four bridging oxygen atoms in the ionic group. Such a central ion Z does not bind to any -OR substituents. An example of such an ionic structure is given by the following formula (V):

[0057] In general, the first fluorine-containing polymer can have both ionic end groups of formula (II) and ionic crosslinking groups of formulas (III) to (V). However, it is also conceivable that the first fluorine-containing polymer contains only ionic end groups or only ionic crosslinking groups.

[0058] In a preferred embodiment, the general formula (I) has at least one or more of the following features: Z means aluminum; M means lithium; and R represents a linear branched or cyclic C1-C4 perfluoroalkyl group.

[0059] For the purposes of the invention, the term C1-C4-perfluoroalkyl comprises linear or branched saturated perfluorinated hydrocarbon residues with 1 to 4 carbon atoms.

[0060] Examples of suitable perfluoroalkyl groups are trifluoromethyl, perfluoro-ethyl, perfluoro-propyl, perfluoro-isopropyl, perfluoro-n-butyl, perfluoro-sec-butyl, perfluoro-iso-butyl and perfluoro-tert-butyl.

[0061] In a particularly preferred embodiment, the ionic group is an ionic end group of the following formula (VI):

[0062] In one embodiment, the backbone of the first fluorine-containing polymer is fully fluorinated and features repeating units of tetrafluoroethylene (-C₂F₄-). The backbone of the first fluorine-containing polymer is thus derived from polytetrafluoroethylene (PTFE). Furthermore, the backbone is unbranched (linear) and consists essentially of fluorine and carbon.

[0063] The first fluorine-containing polymer can comprise at least one perfluorinated side chain. The perfluorinated side chain serves to link the backbone and an ionic group of the general formula (I).

[0064] The invention is not limited with respect to the perfluorinated side chain. All perfluorinated side chains known in the prior art for perfluorinated polymers can be used. In particular, the perfluorinated side chains known from DE 28 17 315, to which reference is made here, can be used.

[0065] In a preferred embodiment, the basic structure of the first fluorine-containing polymer contains at least one side chain of the following formula (VII): wherein Y represents a fluorine atom or a linear, branched, or cyclic C1-C8 perfluoroalkyl group; m is 0, 1, or 2; and v is 0 or 1; where the ionic group of general formula (I) is attached to the CY 2 -Rest of the side chain is bound.

[0066] The central ion Z of an ionic group of general formula (I) can be bonded to the CY2 residue of the side chain via a bridging oxygen atom of the ionic group. The side chain thus represents a linking element between the backbone and the ionic group.

[0067] An ionic end group is bound to the backbone of the first fluorine-containing polymer via only one side chain. Ionic crosslinking groups, on the other hand, are bound to the backbone of a fluorine-containing polymer via several side chains. However, it is also conceivable that the ionic crosslinking groups crosslink the backbones of several initial fluorine-containing polymers together.

[0068] For example, if n equals 2 in the general formula (I), the ionic crosslinking group is bound to the backbone of a first polymer via two side chains.

[0069] In another embodiment, the first fluorine-containing polymer is a copolymer of the following formulas (VIII) or (IX): wherein, m is 0, 1 or 2; p is 1 to 10; r is 1 to 10; s is 1 to 15; and Y is a fluorine atom or a linear, branched or cyclic C1-C10 perfluoroalkyl group; and T is an ionic group of general formula (I).

[0070] Here too, the ionic group T of general formula (I) bonds to the -CY2 residue. The ionic group of general formula (I) can thus be easily integrated into the fluorine-containing polymer.

[0071] Furthermore, due to the fluorine substitution, the side chains are chemically stable against the oxidative stresses during cell operation.

[0072] The first fluorine-containing polymer can be prepared via the synthesis of hydroxy-group-containing fluoropolymers, which can be reacted with lithium aluminum hydride (LiAlH₄) in perfluorohexane (C₆F₁₄) at 70–80°C in the presence of perfluoroalcohols. The cathode can further comprise a second fluorine-containing polymer, wherein the second fluorine-containing polymer is selected from the group of sulfonated perfluorinated polymers.

[0073] With regard to the sulfonated perfluorinated polymers, the invention is not further limited. In principle, all sulfonated perfluorinated polymers commonly used in the prior art can be employed.

[0074] For example, the polymers known from DE 28 17 315 ​​can be used.

[0075] In a preferred embodiment, the sulfonated perfluorinated polymers are based on or derived from polytetrafluoroethylene such as NAFION®.

[0076] In a further embodiment, the sulfonated perfluorinated polymers have perfluoroalkyl side chains with functional groups.

[0077] With regard to the functional groups of the perfluoroalkyl side chains, the second fluorine-containing polymer is not restricted. In principle, all functional groups commonly used in the prior art can be employed for perfluoroalkyl side chains, provided they are ionic and contain lithium ions as cations.

[0078] Preferably, the sulfonated perfluorinated polymers based on polytetrafluoroethylene SO 3 Li-containing, SO 2 -N -< Li +< -SO 2 CF 3 -containing and / or SO 2 C(CN) 2 Li-containing perfluoroalkyl side chains.

[0079] Suitable examples of SO₂C(CN)₂Li-containing perfluoroalkyl side chains are structures of the following formula (X):

[0080] Suitable examples of SO3 Li-containing perfluoroalkyl side chains are structures of the following formula (XI):

[0081] Suitable examples of SO2-N< Li+< SO2CF3-containing perfluoroalkyl side chains are structures of the following formula (XII):

[0082] The perfluoroalkyl side chains are not restricted with respect to the examples mentioned above, in particular not to the perfluoroethoxy and perfluoroisopropoxy groups shown. In principle, the proposed SO₃Li-containing, SO₂-N< Li+< SO₂CF₃-containing, and / or SO₂C(CN)₂Li-containing perfluoroalkyl side chains can have any branched or unbranched perfluoroalkoxy groups.

[0083] Preferably, the lithium content of the cathode can be precisely controlled by incorporating a second fluorine-containing polymer. Additionally, the lithium-ion conductivity of the cathode can also be adjusted. The lithium-ion conductivity is primarily controlled by selecting the functional group of the perfluoroalkyl side chains. Thus, the second fluorine-containing polymer acts as a second lithium-ion conductor.

[0084] In a preferred embodiment, the cathode comprises at least one solvent component, wherein the solvent component is selected from the group consisting of perfluorocarbonates, perfluoroaromatics, perfluoroethers and perfluoroesters, as well as combinations and derivatives thereof.

[0085] Hexafluorobenzene, for example, can be used as a perfluoroaromatic.

[0086] The solvent component preferably forms a gel with the first and / or second fluorine-containing polymer. This gel acts as a gel electrolyte, ensuring ion transport in the cathode. The gel electrolyte is mechanically flexible, allowing it to compensate for volume changes in the cathode active material during cell operation. This prevents damage to the solid-state cell due to mechanical stress.

[0087] In a particularly preferred embodiment, the cathode comprises the following components, each based on the total weight of the cathode: (A) 40–98 wt.% of at least one cathode active material; (B) 0.1–30 wt.% of at least one first fluorine-containing polymer; (C) 0–30 wt.% of at least one second fluorine-containing polymer, preferably selected from the group of sulfonated perfluorinated polymers, preferably based on polytetrafluoroethylene (PTFE) with SO₃Li-containing, SO₂-N<<Li+<<-SO₂CF₃-containing and / or SO₂C(CN)₂Li-containing perfluoroalkyl side chains; and (D) 0–70 wt.%, preferably 0.1–70 wt.% of at least one solvent component consisting of perfluorocarbonates, perfluoroaromatics, perfluoroethers and perfluoroesters, as well as combinations and derivatives thereof; where the proportions of components (A) to (D) add up to 100 wt. %.

[0088] Furthermore, the cathode can contain additional additives known from the prior art, such as binders and conductive additives. The invention is not limited with regard to these additional additives.

[0089] Furthermore, the invention relates to a solid-state battery comprising a cathode, an anode and a solid-state separator which spatially separates the cathode from the anode and is in ion-conducting contact with the cathode and anode.

[0090] The solid separator comprises at least one ceramic polymer-based or gel-based solid electrolyte or combinations thereof.

[0091] The invention is not limited with regard to the solid-state electrolyte used as a solid-state separator. In principle, all separators known in the prior art based on solid-state electrolytes can be used.

[0092] The solid-state separator can comprise at least one solid-state electrolyte, in particular at least one ceramic, polymer-based or gel-based solid-state electrolyte and combinations thereof.

[0093] In one embodiment, the solid electrolyte comprises a lithium phosphorus sulfide and / or a lithium boron sulfide with the general formula Li c T y S z R q , where T represents boron or phosphorus, and R represents a halogen, and where 2≤ c ≤7, 1≤y≤7, 3≤z≤13, 0≤ q ≤1.

[0094] Further examples of suitable solid electrolytes include the compounds of the general formula Li 1-abcd P a T b A c X d known from US 2021 / 0126281 A1, where 0 ≤ a ≤ 0.129, 0 ≤ b ≤ 0.096, 0.316 ≤ c ≤ 0.484, 0.012 ≤ d ≤ 0.125, and where T is an element from the group consisting of As, Si, Ge, Al and B, X is one or more halogens or N, and A is one or more of S and Se, and the compositions known from WO 2019 / 051305 A1 based on lithium (Li), boron (B) and sulfur (S), characterized by an a:b:c molar ratio of Li:B:S, where c / b is in a range of about 1 up to about 3.

[0095] In another embodiment, the solid electrolyte comprises a lithium-containing garnet with the general formula Li n La m M' p M" q Zr s O t , wherein 4 <n<8,5, 1,5<m<4, 0≤p≤2, 0≤q≤2, 0≤s≤2,5 und 10<t≤13 ist, und wobei M' und M" unabhängig voneinander ausgewählt sind aus der Gruppe bestehend aus Aluminium, Molybdän, Wolfram, Niob, Antimon, Calcium, Barium, Strontium, Cerium, Hafnium, Rubidium, Gallium und Tantal.

[0096] In a further development of the invention, the lithium-containing garnet comprises a compound with the general formula Li w La v Zr k O h · gAl 2 O 3 , wherein 5≤w≤8, 2≤v≤5, 0≤k≤3, 10≤h≤13 and 0≤g≤1.

[0097] In a preferred embodiment, the solid electrolyte is a lithium-containing garnet with the general formula Li j La 3 Zr b O 12 · gAl 2 O 3 , wherein 5≤j≤8, 0 <b≤2,5, und 0≤g≤1 ist.

[0098] Suitable polymer-based solid electrolytes include, in particular, mixtures of polyethylene oxide and its derivatives with a lithium-containing conducting salt. Further examples include ion-conducting polymers based on liquid crystal polymers, polyetheretherketone (PEEK), polyphenylene sulfide (PPS), and semicrystalline polymers with a crystallinity of more than 30%, such as the compositions known from US 2017 / 0338492 A1 and US 10 811 688 B2, to which reference is made.

[0099] Furthermore, the solid-state electrolytes described in US 2019 / 0051939 A1, which contain a polylithium acrylate together with a hydrophilic polymer, a lithium salt and a Lewis acid, can also be used.

[0100] Furthermore, the lithium-ion-conducting lithium yttrium halides of general formula Li 6-3z Y z X 6 described in EP 3 496 202 A1 can be used as a solid electrolyte, wherein 0 <z<2 ist und X Cl oder Br bedeutet. Die Lithium-Yttriumhalogenide können als Festkörperelektrolyt in einer Lithiumionenbatterie eingesetzt werden.

[0101] The solid-state separator comprises at least one solid-state electrolyte. However, it is also conceivable that several different solid-state electrolytes are used.

[0102] Preferably, the solid separator comprises one of the above-mentioned oxide solid electrolytes, particularly preferably a lithium-containing garnet such as lithium lanthanum zirconate (LLZO).

[0103] Preferably, the solid-state separator is configured as a single layer, which can be single or multi-layered. In particular, several layers with different solid-state separators can be present. The composition of the layers can vary stepwise or gradually. Preferably, an oxide solid-state electrolyte is arranged on the anode side.

[0104] The anode comprises an anode current collector and optionally an anode layer.

[0105] The anode current collector can be made of any material known in the art for anode current collectors. Preferably, the anode current collector is made of copper.

[0106] The anode layer of the solid-state battery can comprise all structures and materials for anodes known in the prior art.

[0107] For example, the anode layer can include an anode active material and / or a nucleation layer.

[0108] Furthermore, the anode layer can be a composite layer comprising a mixture of anode active materials and other components such as binders, conductive additives and solid electrolytes, as well as combinations thereof.

[0109] Finally, the anode layer can be single-layered or multi-layered.

[0110] Preferred components for the anode active material in the lithium-ion solid-state battery include lithium metal, zinc, magnesium, silver, aluminum, indium, tin, bismuth, silicon, silicon suboxide, graphite, silicon-carbon composite, tin-carbon composite, silicon alloy and lithium alloy, as well as combinations thereof.

[0111] In one embodiment, the anode contains no lithium metal in its uncharged state after manufacturing. The lithium metal is only deposited on the anode during a charging process after the lithium-ion solid-state battery has been manufactured.

[0112] Therefore, lithium metal is deposited on the anode current collector or optionally on a seed layer that can be applied to the anode current collector.

[0113] However, unlike the anode active material, the seed layer is not capable of completely absorbing the lithium metal deposited at the anode during charging of the lithium-ion solid-state battery. For this reason, the seed layer fulfills a different function than the anode active material, namely to control lithium deposition at the anode during the charging process of the lithium-ion solid-state battery. This can be achieved by using a seed layer with a thickness of 1 nm to 10 µm, preferably 5 nm to 3 µm, and particularly preferably 10 to 2000 nm. In a further embodiment, a porous seed layer can be provided.

[0114] In general, the nucleation layer can comprise the same components as the anode active material described above, except for lithium or lithium alloys.

[0115] Suitable examples of components for the nucleation layer include zinc, magnesium, silver, aluminum, indium, tin, bismuth, silicon, silicon suboxide, graphite, silicon-carbon composite, tin-carbon composite, silicon alloy, and combinations thereof.

[0116] The cathode comprises a cathode current collector and a cathode layer on the cathode current collector.

[0117] The cathode current collector can be made of any material known in the prior art for cathode current collectors. Preferably, the cathode current collector is made of aluminum.

[0118] The cathode layer comprises at least one cathode active material and a first fluorine-containing polymer.

[0119] Suitable cathode active materials for the cathode according to the invention include lithium cobalt oxide (LCO), lithium nickel oxide (LNO), lithium nickel cobalt aluminum oxide (NCA), lithium nickel manganese cobalt oxide (NMC), lithium and manganese-rich lithium nickel manganese cobalt oxide or lithium nickel manganese oxide (LMR), lithium manganese oxide (LMO), lithium iron phosphate (LFP), lithium manganese iron phosphate (LMFP), lithium nickel manganese oxide spinel (LNMO) and derivatives as well as combinations thereof.

[0120] In an advantageous embodiment of the invention, the solid-state battery is a lithium-ion solid-state battery.

[0121] The lithium-ion solid-state battery comprises a cathode with a cathode layer comprising a cathode active material and a first fluorine-containing polymer, an anode, and a solid-state separator based on a ceramic, in particular an oxide, solid-state electrolyte.

[0122] In this embodiment, a synergistic effect occurs between the cathode according to the invention and the ceramic solid-state separator. Firstly, the fluorine-containing polymer enables ionic bonding of the cathode to the oxide separator; secondly, the solid-state separator can be manufactured separately from the cathode. In other words, the ceramic solid-state separator, in particular an oxide solid-state electrolyte, can be sintered separately at high temperatures and only subsequently joined with the cathode. Consequently, the cathode does not need to be exposed to high temperatures during manufacturing. Nevertheless, due to the solid-state electrolyte based on a fluorine-containing polymer used in the cathode according to the invention, intimate contact with the ceramic solid-state electrolyte is established.

[0123] Another advantageous combination results from the composition of a lithium-ion solid-state battery consisting of the cathode described above, an oxide solid-state separator and an anode comprising an anode layer, wherein the anode layer comprises a lithium metal.

[0124] In this arrangement, the ceramic, particularly oxide, solid-state separator serves as a particularly stable protective layer between the lithium metal of the anode layer and the active material of the cathode layer. This prevents an undesirable reaction between the cathode components and the lithium metal of the anode. Consequently, no oxidative decomposition occurs on the anode side. On the cathode side, the first fluorine-containing polymer remains intact because it is spatially separated from the lithium metal of the anode by the protective layer. The performance of the lithium-ion solid-state battery is therefore only minimally, if at all, impaired.

[0125] The proposed lithium-ion solid-state batteries are easy to manufacture and exhibit improved cycle stability.

[0126] The cyclic aging resistance of the test cells can be determined via the number of cycles. The test cells are initially charged with a constant charging current up to a maximum permissible cell voltage. The upper cutoff voltage is held constant until the charging current drops to a predefined value or the maximum charging time is reached. This is also known as I / V charging. Subsequently, the test cells are discharged with a constant discharge current down to a given cutoff voltage. The charging process can be repeated depending on the desired number of cycles. The upper and lower cutoff voltages, as well as the given charging and discharging currents, must be selected experimentally. This also applies to the value to which the charging current has dropped.

[0127] The invention is described in more detail below with reference to exemplary embodiments and the accompanying drawings. The drawings show: Figure 1 in a schematic representation a lithium-ion solid-state battery with only one first fluorine-containing polymer; Figure 2 in a schematic representation the lithium-ion solid-state battery made of Figure 1 with a second fluorinated polymer; and Figure 3 in a schematic representation the lithium-ion solid-state battery made of Figure 2 with a solvent component.

[0128] Figure 1 Figure 1 shows a lithium-ion solid-state battery 10. The lithium-ion solid-state battery 10 has an anode 16 and a cathode 26. The anode 16 and the cathode 26 are ionically conductively connected to each other via a solid-state separator 18. Furthermore, the solid-state separator 18 spatially separates the anode 16 from the cathode 26.

[0129] In this context, ionically conductive refers to the conduction of lithium ions within the solid separator 18.

[0130] The anode 16 comprises an anode current collector 12 and an anode layer 14 on the anode current collector 12.

[0131] Anode current collectors are known and are usually made of a metallic material. The anode current collector 12 is intended for the electrical contact of the anode layer 14. The anode current collector 12 can, for example, be made of copper.

[0132] The anode layer 14 comprises at least one anode active material.

[0133] The anode active material is designed to reversibly absorb and release lithium ions. Preferably, the anode active material is composed of components from the group consisting of lithium metal, zinc, magnesium, silver, aluminum, indium, tin, bismuth, silicon, silicon suboxide, graphite, silicon-carbon composite, tin-carbon composite, silicon alloy, and lithium alloy, as well as combinations thereof.

[0134] The anode active material preferably comprises a lithium metal.

[0135] The cathode 26 comprises a cathode current collector 24 and a cathode layer 25 on the cathode current collector 24.

[0136] Cathode current collectors are typically made of a metallic material such as aluminum.

[0137] The cathode layer 25 is a composite and comprises a mixture of a cathode active material 20 and a first fluorine-containing polymer 22. In particular, the cathode active material 20 is distributed in a matrix of the first fluorine-containing polymer 22.

[0138] The cathode active material 20 is preferably selected from the group consisting of lithium cobalt oxide (LCO), lithium nickel oxide (LNO), lithium nickel cobalt aluminum oxide (NCA), lithium nickel manganese cobalt oxide (NMC), lithium- and manganese-rich lithium nickel manganese cobalt oxide or lithium nickel manganese oxide (LMR), lithium manganese oxide (LMO), lithium iron phosphate (LFP), lithium manganese iron phosphate (LMFP), lithium nickel manganese oxide spinel (LNMO), and derivatives, as well as combinations thereof. The cathode active material 20 is designed to reversibly absorb and release lithium ions.

[0139] The first fluorine-containing polymer 22 has a partially fluorinated or perfluorinated backbone and contains at least one ionic group of the general formula (I): wherein, M is a cation selected from the group consisting of protons and alkali metals; n is an integer from 1 to 4; Z is a central ion selected from the group consisting of aluminum and boron; and R is a monovalent, optionally fluorine-substituted hydrocarbon residue selected from the group consisting of C1-C8 alkyl, C2-C10 alkenyl, C2-C10 alkynyl, C6-C12 cycloalkyl, and C6-C12 aryl; wherein the ionic group is connected to the backbone of the first fluorine-containing polymer via at least one bridging oxygen atom of the ionic group.

[0140] Preferably, in the general formula (I), M is lithium, n equals 1, and Z is aluminum. The hydrocarbon residue R is particularly preferably a trifluoromethyl residue and / or a perfluoro-tert-butyl residue. Thus, the first fluorine-containing polymer is a lithium ion conductor.

[0141] Furthermore, the cathode layer 25 can comprise at least one binder (not shown here), wherein the binder is selected from the group consisting of polyvinylidene fluoride (PVDF), hydrogenated acrylonitrile butadiene rubber (HNBR), carboxymethylcellulose (CMC), styrene butadiene rubber (SBR), polyacrylate (PAA), lithium polyacrylate (LiPAA) and polyvinyl alcohol (PVA), as well as combinations thereof.

[0142] The cathode layer 25 can also contain a conductive additive (not shown here), wherein the conductive additive is selected from the group consisting of conductive carbon black, carbon nanotubes, graphene, graphite and carbon nanofibers, as well as combinations thereof.

[0143] The solid separator 18 is arranged between the anode 16 and the cathode 26 and comprises at least one ceramic, polymer-based or gel-based solid electrolyte or combinations thereof.

[0144] The following compositions, in particular, can be used as solid electrolytes: a lithium phosphorus sulfide and / or a lithium boron sulfide with the general formula Li c T y S z R q , where T means boron or phosphorus, and R means a halogen, and where 2≤ c ≤7, 1≤y≤7, 3≤ z ≤13, 0≤ q≤1; a compound of the general formula Li 1-abcd P a T b A c X d , where 0 ≤ a ≤ 0.129, 0 ≤ b ≤ 0.096, 0.316 ≤ c ≤ 0.484, 0.012 ≤ d ≤ 0.125 and where T is an element from the group consisting of As, Si, Ge, Al and B, X is one or more halogens or N, and A is one or more of S and Se; a composition based on lithium (Li), boron (B) and sulfur (S) characterized by an a:b:c molar ratio of Li:B:S, where c / b is in a range of about 1 to about 3; a lithium-containing garnet of the general formula Li n La m M' p M" q Zr s O t , wherein 4< n <8.5 , 1.5 <m< 4, 0≤ p ≤2, 0≤ q ≤2, 0≤ s ≤2.5 and 10< t≤13, and wherein M' and M" are independently selected from the group consisting of aluminium, molybdenum, tungsten, niobium, antimony, calcium, barium, strontium, cerium, hafnium, rubidium, gallium and tantalum; a lithium-containing garnet with the general formula Li w La v Zr k O h ·gAl 2 O 3 , wherein 5≤ w ≤8, 2≤ v ≤5, 0≤ k ≤3, 10≤ h ≤13 and 0≤g≤1 is; a lithium-containing garnet with the general formula Li j La 3 Zr b O 12 ·gAl 2 O 3 , wherein 5≤ j ≤8, 0< b≤2.5, and 0≤g≤1; an ion-conducting lithium yttrium halide of the general formula Li 6-3z Y z X 6 , wherein 0 <z<2 ist und X Cl oder Br bedeutet; ein ionenleitendes Polymer auf der Basis von Polyethylenoxid, Flüssigkristallpolymeren, Polyetheretherketon (PEEK), Polyphenylensulfid (PPS) und semikristallinen Polymeren mit einer Kristallinität von mehr als 30%, zusammen mit einem Lithiumsalz, bevorzugt Li 2 O, LiTFSI (Lithium-bis-trifluoromethansulfonimid), LiBOB (Lithium-bis(oxalat)borat) oder Kombinationen davon; und Polylithiumacrylat zusammen mit einem hydrophilen Polymer, einem Lithiumsalz und einer Lewissäure.

[0145] The solid-state separator 18 conductively connects the cathode 26 to the anode 16. In particular, the solid-state separator 18 forms a protective layer between the anode layer 14 of the anode 16 and the cathode layer 25 of the cathode 26.

[0146] The solid separator 18 can be configured as a single layer or in multiple layers. In particular, several layers with different solid separators can be present. The composition of the layers can vary in steps or gradually.

[0147] According to one embodiment, the solid-state separator 18 can comprise an anode-side region that exhibits higher resistance to lithium metal than a cathode-side region of the solid-state separator. The anode-side region preferably comprises an oxide solid electrolyte, particularly preferably a lithium-containing garnet such as lithium lanthanum zirconate (LLZO). The lithium-ion solid-state battery 10 shown here exhibits a particularly good ionic bond between the cathode 26 and the solid-state separator 18. It is especially advantageous that the first fluorine-containing polymer 22 is mechanically flexible and can adapt to the rigid and inflexible shape of the solid-state separator 18 and reliably compensate for volume changes.

[0148] Figure 2 The lithium-ion solid-state battery shows 10 from Figure 1 with a modified composition of the cathode 26.

[0149] The cathode 26 in Figure 2 comprises a cathode layer 25, which is a composite and includes a mixture of a cathode active material 20, a first fluorine-containing polymer 22 and a solvent component 28.

[0150] Furthermore, the lithium-ion solid-state battery 10 can contain the same components as described above.

[0151] Unlike Figure 1 , the cathode in Figure 2 a solvent component 28.

[0152] The solvent component 28 is preferably selected from the group consisting of perfluorocarbonates, perfluoroaromatics, perfluoroethers and perfluoroesters, as well as combinations and derivatives thereof.

[0153] The solvent component 28 reacts with the first fluorine-containing polymer to form a gel electrolyte. Preferably, the gel electrolyte has a gel-like consistency. The gel electrolyte is therefore dimensionally stable, yet also mechanically flexible and extensible.

[0154] Due to the gel-like consistency, good ionic bonding between the cathode active material 20 and the gel electrolyte is ensured.

[0155] Furthermore, an ionic bond exists between the gel electrolyte and the solid separator 18.

[0156] Furthermore, the presence of a gel electrolyte with a gel-like consistency makes it possible to compensate for the volume expansion of the cathode active material 20 during the regular operation of the lithium-ion solid-state battery 10.

[0157] Figure 3 The lithium-ion solid-state battery shows 10 from Figure 2 with a different composition of the cathode 26.

[0158] The cathode 26 in Figure 3comprises a cathode layer 25, which includes a mixture of a solvent component 28, a cathode active material 20, a first fluorine-containing polymer 22 and a second fluorine-containing polymer 30.

[0159] The difference between Figure 2 and Figure 3 This therefore consists in the presence of a second fluorine-containing polymer in the cathode 26.

[0160] Furthermore, the lithium-ion solid-state battery 10 can contain the same components as described above.

[0161] The second fluorine-containing polymer 30 is preferably selected from the group of sulfonated perfluorinated polymers with SO₃Li-containing and / or SO₂C(CN)₂Li-containing perfluoroalkyl side chains, preferably a polytetrafluoroethylene (PTFE) such as Nafion®, or polymers derived from Nafion®. Other possible side chains are SO₂-N-Li+-SO₂CF₃-containing perfluoroalkyl side chains.

[0162] Thus, the second fluorine-containing polymer 30 contains perfluorinated side chains saturated with lithium ions. The second fluorine-containing polymer 30 is therefore also a lithium ion conductor.

[0163] Preferably, the second fluorine-containing polymer 30 forms a gel with the first fluorine-containing polymer 22 and the solvent component 28.

[0164] In other words, the cathode active material 20 is in a gel consisting of the first fluorine-containing polymer 22, the second fluorine-containing polymer 30 and the solvent component 28.

[0165] The gel enables an ionic bonding of the cathode active material 20 to the solid-state separator 18 and the cathode current collector 24.

Claims

1. Cathode (26) for a solid-state battery (10), wherein the cathode (26) comprises the following components: (A) at least one active cathode material (20); (B) at least one first fluorine-containing polymer (22) having an at least partly fluorinated or perfluorinated base skeleton, where the first fluorine-containing polymer (22) contains at least one ionic group of the following formula (I): in which - M is a cation selected from the group consisting of proton and alkali metals; - n is an integer from 1 to 4; - Z denotes a central ion selected from the group consisting of aluminum and boron; and - R represents a monovalent, optionally fluorine-substituted hydrocarbyl radical and is selected from the group consisting of C1-C8-alkyl, C2-C10-alkenyl, C2-C10-alkynyl, C6-C12-cycloalkyl and C6-C12-aryl; where the ionic group is bonded to the base skeleton of the first fluorine-containing polymer (22) via at least one bridging oxygen atom in the ionic group.

2. Cathode (26) according to Claim 1, characterized in that the hydrocarbyl radical R is at least partly fluorine-substituted, preferably fully fluorine-substituted.

3. Cathode (26) according to either of the preceding claims, characterized in that the first fluorine-containing polymer (22) contains at least one ionic end group of the general formula (I) in which n = 1 and / or at least one ionic crosslinking group of the general formula (I) in which n = 2, 3 or 4.

4. Cathode (26) according to any of the preceding claims, characterized in that the general formula (I) has one or more of the following features: - Z denotes aluminum - M denotes lithium; and - R represents a linear, branched or cyclic C1-C10 perfluoroalkyl radical, preferably a trifluoromethyl radical, more preferably a perfluoro-tert-butyl radical.

5. Cathode (26) according to any of the preceding claims, characterized in that the base skeleton of the first fluorine-containing polymer (22) has repeat units of tetrafluoroethylene (-C2F4-) .

6. Cathode (26) according to any of the preceding claims, characterized in that the base skeleton of the first fluorine-containing polymer (22) includes at least one side chain of the general formula (VII) in which - Y denotes a fluorine atom or a linear, branched or cyclic C1-C10 perfluoroalkyl radical; - m is 0, 1 or 2; - v is 0 or 1; and where the ionic group of the general formula (I) is bonded to the base skeleton via the CY2 radical of the side chain.

7. Cathode (26) according to any of the preceding claims, characterized in that the cathode (26) comprises a second fluorine-containing polymer (30), where the second fluorine-containing polymer (30) is selected from the group of the sulfonated perfluorinated polymers, preferably the derivatives of polytetrafluoroethylene (PTFE) having SO3Li-containing, SO2-N-Li+-SO2CF3-containing and / or SO2C(CN)2Li-containing perfluoroalkyl side chains.

8. Cathode (26) according to any of the preceding claims, characterized in that the cathode (26) comprises at least one solvent component (28), where the solvent component (28) is selected from the group consisting of perfluorocarbonates, perfluoroaromatics, perfluoroethers and perfluoroesters, and combinations and derivatives thereof, more preferably in that the solvent component (28) forms a gel with the first and / or second fluorine-containing polymer (22, 30).

9. Cathode (26) for a solid-state battery (10) according to any of the preceding claims, characterized in that the cathode (26) comprises the following components, based in each case on the total weight of the cathode (26): (A) 40-98% by weight of at least one active cathode material (20); (B) 0.1-30% by weight of at least one first fluorine-containing polymer (22); (C) 0-30% by weight of at least one second fluorine-containing polymer (30), preferably selected from the group of the sulfonated perfluorinated polymers, preferably from the derivatives of polytetrafluoroethylene (PTFE) having SO3Li-containing, SO2-N-Li+-SO2CF3-containing and / or SO2C(CN)2Li-containing perfluoroalkyl side chains; (D) 0-70% by weight, preferably 0.1-70% by weight, of at least one solvent component (28) consisting of perfluorocarbonate, perfluoroaromatic, perfluoroether and perfluoroester, and combinations and derivatives thereof; where the proportions of components (A) to (D) add up to 100 percent.

10. Solid-state battery (10) having a cathode (26) according to any of the preceding claims, an anode (16) and a solid-state separator (18) that spatially separates the cathode (26) from the anode (16) and is in ion-conducting contact with the cathode (26) and the anode (16), where the solid-state separator (18) comprises at least one ceramic polymer-based or gel-based solid-state electrolyte or combinations thereof.