Solid electrolyte for lithium-based rechargeable batteries

Abstract

The present invention relates to a solid electrolyte for rechargeable batteries, and to rechargeable batteries including said solid electrolyte, in particular a solid electrolyte that has a suitable lithium salt content for introducing lithium ions as charge carriers. The electrolyte according to the invention forms, starting from a copolymer, a solid that is mechanically flexible and highly conductive in particular for lithium ions.

Description

[0001] Solid electrolyte for lithium-based rechargeable batteries

[0002] The present invention relates to a solid electrolyte for rechargeable batteries, as well as to rechargeable batteries comprising the solid electrolyte, in particular a solid electrolyte containing a suitable alkali metal salt, which is preferably a lithium salt, for introducing lithium ions as charge carriers, or which is a sodium salt for introducing sodium ions as charge carriers. The electrolyte according to the invention forms, with or from a copolymer, a solid that is mechanically flexible and has high conductivity, particularly for lithium ions. Furthermore, the invention relates to a process for producing rechargeable batteries using the solid electrolyte, wherein the solid electrolyte can be produced during battery production.

[0003] Gadjourova et al., Nature 412, 520-523 (2001) describe that ionic conduction in lithium-ion batteries occurs in a polyethylene oxide (PEO) electrolyte in its amorphous phase above the glass transition temperature through movement of the polymer chains. Xue et al., J. Mater. Chem. A 3, 19218-19253 (2015) describe polyethylene oxide (PEO) and its branched or linear derivatives as electrolytes for rechargeable lithium-ion batteries.

[0004] Quartarone et al., Solid State Ionics 110, 1-14 (1998) describe that ionic conduction in polyethylene oxide (PEO) electrolytes is greatly favored by their amorphous state and occurs through the movement of the polymer chains. While PEO exhibits high ionic conductivity at temperatures of 60-80°C, this decreases sharply at lower temperatures. However, high temperatures are unfavorable for battery operation and also lead to faster degradation of the polymer, thus limiting the service life of batteries based on them. It is proposed to obtain polymers with an increased stability range while maintaining the amorphous state from PEO, for example, by modifying PEO by forming cross-linked polymer matrixes or copolymers or by incorporating organic or inorganic filler particles.

[0005] While the improvement in ionic conductivity has been demonstrated in many studies, for example by Ben Youcev et al., Electrochim. Acta 220, 587-594 (2016), a strong temperature dependence is still described, which precludes use in batteries operating at room temperature.

[0006] The object of the invention is to provide a solid electrolyte and a rechargeable battery with a solid electrolyte which has a high conductivity for ions, preferably alkali metal ions, in particular lithium ions and / or sodium ions, even at room temperature and only slightly elevated temperatures and which is mechanically stable. A solid electrolyte is an electrolyte which is present as a solid at the operating temperature of the battery, e.g. up to 80°C, but at least at room temperature. The solid electrolyte should preferably be suitable for arrangement between the electrodes of a battery without the need for an additional separator such as a membrane between the electrodes. Accordingly, a battery according to the invention preferably does not contain an additional separator, which can be, for example, a film made of plastic, in particular polypropylene (PP) or polyimide (PI), a nonwoven fabric made of plastic, e.g. PET, or a nonwoven fabric made of glass fibers.Preferably, the solid electrolyte should also be able to be integrated into the cathode layer. The battery is preferably a lithium-based battery, in particular with one of the electrodes made of metallic lithium or a lithium alloy, more preferably a lithium-sulfur battery.

[0007] The invention solves the problem with the features of the claims and in particular by a solid electrolyte which comprises or consists of a copolymer produced by polymerizing a first component which has at least three, preferably four terminal, radically polymerizable radicals, and a second component which has at least one, preferably two, e.g. 2 to 12, to 11, to 10 or to 9 ethylene glycol units, preferably three to eight, to six or to five ethylene glycol units between two terminal, radically polymerizable radicals, wherein the copolymer contains distributed lithium ions, optionally particles distributed in the copolymer which preferably have side chains linked to the copolymer, in particular side chains linked to the copolymer by radical reaction.

[0008] The solid electrolyte has the advantage of not being liquid due to polymerization at temperatures between 0 and 80°C, for example, but rather of exhibiting high mechanical stability. This means that the solid electrolyte does not liquefy even upon heating and does not leak from a battery or between the electrodes. This minimizes the risk of fire, particularly significantly less than when using liquid electrolytes such as ethylene carbonate (EC), dimethyl carbonate (DMC), or diethyl carbonate (DEC). Due to its high plasticity, the solid electrolyte according to the invention results in low interfacial resistances to adjacent components of the battery after battery cell production, in particular to the anode, which is, for example, a lithium anode, and can also optionally be incorporated into particulate electrodes, preferably the cathode.

[0009] Optionally, the solid electrolyte has been polymerized by polymerizing the first component and the second component in contact with at least one of the electrodes or both electrodes. Alternatively, the solid electrolyte is polymerized to form a layer and then bonded to one or both of the electrodes, e.g. by pressing. One of the electrodes can have a cathode layer and / or the other electrode can have an anode layer, which contain the solid electrolyte or a liquid electrolyte. The solid electrolyte has the further advantage of being mechanically flexible, particularly in embodiments without ceramic particles or with functionalized ceramic particles. Preferred ceramic particles comprise or consist of lithium-containing and / or sodium-containing metal oxides, preferably lithium-containing metal oxides if the alkali metal ion in the electrolyte is lithium.Sodium-containing metal oxides, if the alkali metal ion in the electrolyte is sodium. Furthermore, the solid electrolyte has the advantage of providing the battery with high operational stability.

[0010] A further advantage of the electrolyte is its high ionic conductivity, especially for lithium ions or sodium ions, especially at low temperatures close to room temperature, e.g. at 0 to 40°C, especially at 15 to 25°C or at 20°C. Preferably, the electrolyte with alkali metal ions contained therein has a conductivity of at least 10' 3 S / cm at 20°C.

[0011] The copolymer preferably has a three-dimensional network in which a first component has, at each of at least three, preferably four terminal residues, at least one or precisely one second component bonded to one of its ends by radical addition, to the opposite end of which a further first component is bonded. Preferably, particles are distributed throughout the copolymer, which preferably have surface-bonded side chains that are covalently bonded to the copolymer by radical addition. In general, molecules of the first component can also be covalently bonded to one another and / or molecules of the second component can be covalently bonded to one another in the copolymer.

[0012] The terminal, radically polymerizable residues of the first component are preferably ethylenically unsaturated double bonds, e.g., terminal vinyl residues, acrylic acid residues attached by an ester bond, or thiol groups. The molecules of the first component can each have the same terminal residues or combinations of at least two different terminal residues.

[0013] Preferably, neither the first component nor the second component contains any aromatic constituents, in particular no aromatic five-membered rings, no aromatic six-membered rings, no condensates of these, and preferably no aliphatic rings. The terminal, radically polymerizable radicals of the second component are preferably ethylenically unsaturated double bonds, e.g., terminal vinyl radicals, acrylic acid radicals attached via an ester bond, or thiol groups. The molecules of the second component can each have the same terminal radicals or combinations of at least two different terminal radicals. In general, the second component consists of unbranched or linear molecules.

[0014] The first component can be, for example, pentaerythritol tetraacrylate (PETEA), pentaerythritol triacrylate, trimethylolpropane triacrylate or pentaerythritol tetrakis-(3-mercaptopropionate) or a mixture of at least two of these.

[0015] The second component can be, for example, short-chain polyethylene oxide (PEO), also called polyethylene glycol (PEG), e.g. consisting of two to five, preferably three ethylene oxide units with radically polymerizable radicals, in particular vinyl groups or thio groups, identical or different, at both ends, in particular short-chain poly(ethylene glycol) divinyl ether, short-chain poly(ethylene glycol) diacrylate (PEGDA), short-chain poly(ethylene glycol) dithiol or short-chain poly(ethylene glycol) methyl ether thiol, in particular tri(ethylene glycol) divinyl ether (TEG), di(ethylene glycol) divinyl ether and tetra(ethylene glycol) dithiol. Generally preferred is a short-chain poly(ethylene glycol) with 1 to 5, preferably two, three or four ethylene oxide units.

[0016] The copolymer preferably contains the first component, which is preferably PETEA, and the second component in a molar ratio of 1:3 to 1:14, preferably up to 1:12 or up to 1:10 or up to 1:8. The copolymer preferably contains the first component and the second component in a molar ratio in which the terminal, radically polymerizable groups of the first component to the terminal, radically polymerizable groups of the second component are in a molar ratio of 1:7 to 1:5, in particular 1:6, in each case ±50% or ±30% or ±10%, or the copolymer is produced therefrom. More preferably, the solid electrolyte contains, in particular if it does not contain particles of a cathode active material, e.g.consists only of polymerized first and second components and the alkali metal salt dissociated therein, preferably lithium salt or sodium salt, and is preferably not in contact with particles of a cathode active material, and is more preferably arranged in a battery, a maximum of 10% by weight, preferably a maximum of 5% by weight of solvent, more preferably no solvent, optionally after drying following the polymerization, wherein a solvent is, for example, an organic compound that is not covalently bonded to the copolymer and is preferably uncharged and / or not an ion. A solid electrolyte which contains a maximum of 10% by weight, preferably a maximum of 5% by weight.-% solvent, more preferably no solvent, optionally after drying following the polymerization, is preferably obtainable in that the mixture which contains the first and the second component and dissociated lithium ions and is polymerized without particles of a cathode active material contains a maximum of 10 wt.%, preferably a maximum of 5 wt.% solvent, or the mixture contains no solvent, so that the solid electrolyte is free of solvent without drying. More preferably, the solid electrolyte contains a maximum of 10 wt.%, preferably a maximum of 5 wt.%, preferably no solvent, e.g. after drying which has taken place following the polymerization. More preferably, the mixture from which the solid electrolyte is produced by polymerization and the solid electrolyte produced, in particular when it is polymerized to form a layer and then connected to the cathode and / or anode by pressing, contains no solvent.

[0017] In embodiments in which the copolymer contains at least one cathode active material and optionally ceramic particles, preferably functionalized ceramic particles, the mixture to be polymerized and the resulting copolymer may contain a solvent. Optionally, solvent can be at least partially removed from a solvent-containing copolymer by drying under reduced pressure and / or elevated temperature and / or by pressing.

[0018] In embodiments in which the solid electrolyte contains functionalized ceramic particles and / or non-functionalized ceramic particles and is free of cathode active material or anode active material, the mixture to be polymerized, comprising the first and second components and the ceramic particles, preferably contains no solvent. Accordingly, the solid electrolyte produced therefrom, which contains ceramic particles as particulate ingredients but no particles of a cathode active material or anode active material, is solvent-free without drying.

[0019] Lithium ions are converted into lithium by a suitable lithium salt, which may optionally be a mixture of several

[0020] Lithium salts can be used, e.g. lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and / or lithium bis(fluorosulfonyl)imide (LiFSI). In general, a suitable lithium salt is one that can be dissolved in the mixture of components and is dissociated in the solid electrolyte after polymerization. For this purpose, a mixture of the lithium salt with the first and second components, optionally additionally functionalized ceramic particles, is prepared before polymerization, so that the lithium salt, which can be a mixture of at least two lithium salts, is contained in the copolymer as a result of the polymerization. Lithium ions are contained in the mixture, e.g. in a molar ratio of (first component + second component) : lithium ions equal to 12 (number of oxygen atoms in the first and second components) : 1. The number of oxygen atoms in the second component can be correlated with its number of ethylene oxide units plus one.For PETEA and PEO3 with terminal vinyl groups in a molar mixing ratio of 1 : 12, for example, the molar ratio of PETEA : PEO3 : Li is 3:36 : 14.

[0021] Accordingly, sodium ions are introduced by means of a suitable sodium salt, which can optionally be a mixture of several sodium salts, e.g. sodium bis(trifluoromethanesulfonyl)imide (NaTFSI) and / or sodium bis(fluorosulfonyl)imide (NaFSI). In general, a suitable sodium salt is one that can be dissolved in the mixture of components and is dissociated in the solid electrolyte after polymerization. For this purpose, a mixture of the sodium salt with the first and second components, optionally additionally functionalized ceramic particles, is prepared before polymerization, so that the sodium salt, which can be a mixture of at least two sodium salts, is contained in the copolymer through polymerization. Sodium ions are contained in the mixture, e.g., at a molar ratio of (first component + second component) : sodium ions equal to 12 (number of oxygen atoms of the first and second components) : 1.The number of oxygen atoms in the second component can be correlated with its number of ethylene oxide units plus one. For PETEA and PEO3 with terminal vinyl groups in a molar mixing ratio of 1:12, for example, this results in a molar ratio of PETEA:PEO3:Na of 3:36:14.

[0022] The introduced particles can, for example, have a size of 20 nm to 1.2 pm. The particles are preferably ceramic particles and consist of a lithium-containing ceramic, in particular LiyLasZ^On (LLZO). Generally, the ceramic particles preferably have surface-bound organic side chains, which are bonded to the surface, for example, by a surface modification treatment.

[0023] The particles preferably have, as a bonded organic side chain, at least one vinyl group bonded via a silane group, which is, for example, an acrylate or methacrylate group, e.g., silylalkyl methacrylate as a bonded side chain. Particles having such a side chain are also referred to as functionalized particles. Preferably, one or at least two silanes, such as 3-(trimethoxysilyl)alkyl methacrylate, 3-(triethoxysilyl)alkyl methacrylate, 3-(trimethoxysilyl)alkyl acrylate, or 3-(triethoxysilyl)alkyl acrylate, are used for the surface modification treatment, where the alkyl is generally a C1- to C8-alkyl, e.g., methyl, ethyl, n-propyl, or n-butyl.

[0024] Preferably, all radically polymerizable residues have a vinyl group.

[0025] The radical initiator can be, for example, azobisisobutyronitrile (AIBN).

[0026] In the process for producing the solid electrolyte, the copolymer can be produced in one step by radical polymerization of the first and second components, preferably functionalized particles, and a lithium salt. The particles, which preferably have radically polymerizable side chains, are mixed with the first and second components and a lithium salt and polymerized together.

[0027] To produce a rechargeable battery, the solid electrolyte can be prepared and then applied to an electrode, e.g. as a moldable mass or as a layer preformed from the solid electrolyte.

[0028] Alternatively, the solid electrolyte can be produced by polymerizing the first and second components, preferably in a mixture with particles, on one electrode or between both electrodes. For this purpose, a mixture containing or consisting of the first and second components, preferably nanoparticles, a lithium salt and a free radical initiator can be applied to one or both electrodes and polymerized there, e.g. by initiating polymerization through irradiation or heating. The mixture containing the first and second components is preferably free of solvent. Optionally, the solid electrolyte can contain aramid particles or aramid oligomers. Aramid particles can have the form of fibers, spherical or irregular particles or a fibrous material. Aramid oligomers, for example, have a length of 5 to 20 monomer units.Furthermore, aramid particles or aramid oligomers can optionally contain functional groups that are reactive and polymerizable with the components of the solid electrolyte. For example, the aramid particles can be functionalized with terminal vinyl groups or acrylate groups. Aramid oligomers or aramid particles are preferably contained in the electrolyte and / or in the cathode; optionally, aramid oligomers or aramid particles are only contained in the solid electrolyte, which is a component of the cathode.

[0029] Aramid particles in the form of fibers, polymer powder, and fiber material are preferably dispersed or dissolved in a composition containing the monomers according to the invention for producing the copolymer of the solid electrolyte. The resulting mixture can then be subjected to a coating process. The ideal thickness of the aramid fibers in this embodiment is 0.25 mm ±10%. When using aramid oligomers with a molecular weight of less than 5000 g / mol and polymerizable functional groups, PETEA and PEG and modified aramid monomers or oligomers, e.g., modified with polymerizable groups, e.g., radically polymerizable groups, can be crosslinked and copolymerized to form robust solid electrolytes.

[0030] Aramid particles may be contained in the electrode layer.

[0031] Particles contained in the electrolyte, in particular ceramic particles, aramid oligomers and / or aramid particles, can promote the long-term stability of the capacity of a battery with the electrolyte, e.g. over at least 500, preferably over at least 800 or over at least 1000 charging and discharging cycles.

[0032] Alternatively or additionally, the solid electrolyte can be integrated directly into an electrode and form a component of an electrode, in particular by polymerizing the first and second components, preferably in a mixture with functionalized particles, in a mixture with particles of the active material of this electrode and optionally additionally particles of a conductivity additive. For this purpose, a mixture which contains or consists of a particulate active material and optionally additionally particulate conductivity additive, the first and second components, preferably functionalized particles, and a free radical initiator is applied to a carrier which forms a metallic current collector foil and then polymerized, e.g. by initiating the polymerization through irradiation or heating. A particulate conductivity additive is, for example, particulate carbon.The particulate active material, also referred to as cathode active material, can be, for example, lithium iron phosphate (LiFePCU), a lithium metal oxide LiMCL, where M is Mn, Co or Ni or a mixture thereof, or a lithium metal oxide LiM2C>4, where M is Mn, Co or Ni or a mixture thereof, or a mixture of at least two of LiFePCU, LiMCL, LiM2O4, or elemental sulfur.

[0033] A first electrode, also referred to as the negative electrode, which forms the anode when the battery is discharged, preferably has a first carrier, e.g., metallic copper (Cu°), as a current collector, and preferably metallic lithium (Li°) thereon. Generally, the Li° can be applied to the first carrier by electrodeposition.

[0034] During battery production, the solid electrolyte, in particular its first and second components, optionally particles, preferably functionalized particles, as well as lithium ions and radical initiators, can be polymerized into a layer and then applied to the first carrier or a cathode layer or anode layer, preferably subsequently brought into contact therewith by pressing. In this embodiment, the solid electrolyte is applied as a preformed layer to the first carrier or an anode layer made of Li° applied thereto and brought into contact therewith by pressing.

[0035] A second electrode, also referred to as the positive electrode, which forms the cathode when the battery is discharged, preferably has a second metal carrier, preferably metallic aluminum (Al°), as a current collector, onto which a cathode layer is applied directly, which contains or consists of particulate cathode active material, particulate conductivity additive, and the solid electrolyte. Alternatively, the cathode layer applied to the second carrier can contain or consist of particulate cathode active material, particulate conductivity additive, an organic binder material, and a liquid electrolyte material. In general, a cathode layer, particularly when formed with the solid electrolyte containing a cathode active material, can have a high proportion of cathode active material, which can be greater than the gravimetric content of solid electrolyte or liquid electrolyte material.Preferably, the cathode layer, which rests on the carrier forming the current collector, contains lithium iron phosphate, lithium metal oxide LiMCL, lithium metal oxide LiNLCU or a mixture of at least two of these, or sulfur, in particular elemental sulfur, e.g. Ss, as cathode active material.

[0036] The battery has a layer containing the solid electrolyte between the electrodes, also referred to as the electrolyte layer, in which the first and second components, preferably with particles contained therein, preferably functionalized particles, in particular particles bound by radical polymerization of their side chains, and lithium ions, or consist of them. Optionally, a porous membrane or support structure (separator) can be arranged within the electrolyte layer or between the electrolyte layer and the conductivity layer and / or between the electrolyte layer and the carbon layer. Preferably, the battery does not have a porous membrane or support structure in or adjacent to the electrolyte layer.

[0037] The battery preferably has, or consists of, as electrochemically active components, in particular within a gas-tight housing, a first carrier, metallic lithium lying directly thereon, an electrolyte layer lying directly thereon, a cathode layer lying directly thereon and a second carrier directly thereon and opposite the first carrier.

[0038] In general, the battery components only refer to their electrochemically active components, so that the battery has these electrochemically active components or its electrochemically active components consist of them. Accordingly, in addition to the electrochemically active components on the carriers opposite the electrolyte, the battery can have, for example, a gas-tight housing, incorporated protective layers, e.g., polymer layers made of PEO or ceramic layers of the type NASICON or Lii.5Alo.5Gei.5(PO4)3 (LAGP), to stabilize the lithium anode or cathode, and structural components such as a porous membrane or support structure. The polymer layers consist, for example, of long-chain PEO (poly(ethylene oxide)) with molecular weights M w > 100,000 g mol' 1 .

[0039] During battery production, each layer containing the solid electrolyte, in particular the electrolyte layer and the cathode layer, can be prefabricated as a separate layer by polymerization. The polymerization can proceed completely or, optionally, only until a strength sufficient for handling is reached, and the layer still has reactive residues of the first and / or second component, optionally functionalized particles, on its surface. Such prefabricated layers with still reactive residues can react when arranged on another prefabricated layer, so that adjacent layers bond to one another through polymerization.

[0040] Alternatively, during battery production, the components of one layer can be applied as a reactive mixture and subsequently polymerized by initiating polymerization. The components of the next adjacent layer can then be applied as a reactive mixture and subsequently polymerized by initiating polymerization. It is preferred that polymerization only proceed until a strength is reached at which a mixture subsequently applied to this layer does not penetrate, so that the polymerized layer still has reactive residues of the first and / or second component, optionally functionalized particles, on its surface, which polymerize with the mixture subsequently applied thereto.

[0041] The invention will now be described by way of example with reference to the figures, which show in Fig. 1 the ionic conductivity of electrolytes for lithium ions,

[0042] - Fig. 2 the result of the voltammetric measurement,

[0043] - Fig. 3 the ionic conductivity for different contents of functionalized particles,

[0044] - Fig. 4 Specific capacity measurements over 50 charge / discharge cycles, varying the charge and discharge rate in the first 20 cycles,

[0045] - Fig. 5 the voltage curve during charge / discharge cycles over the capacity and

[0046] - Fig. 6 shows the voltage curve during charge / discharge cycles over the capacity.

[0047] Example 1: Preparation of a solid electrolyte

[0048] A solid electrolyte according to the invention, consisting of a copolymer of pentaerythritol tetraacrylate (PETEA) and tri(ethylene glycol) divinyl ether (TEG) with incorporated lithium ions, was prepared by radical polymerization of PETEA (TCI Chemicals, purity >80%) and TEG (Sigma-Aldrich, purity >98%) in the presence of LiTFSI in a molar ratio of 3:36:14. 0.1 wt.% azobisisobutyronitrile was added as a radical initiator. The mixture was coated onto a polyester film support (PPI Adhesive Products), polymerized at 60°C for 2 h, and then peeled off the support. The preparation was carried out under an argon atmosphere (O2 < 0.1 ppm, H2O < 0.1 ppm) until polymerization was complete.

[0049] As the preferred solid electrolyte, the same starting mixture was mixed with an additional 15 wt. % of functionalized ceramic particles made of LiyLasZ^On (LLZO), which had previously been functionalized by reaction with 3-(trimethoxysilyl)propyl methacrylate (A-LLZO) or l-vinyl-3-trimethoxysilaneimidazolium bis(trifluoromethanesulfonyl)imide (IL-LLZO) and thus contained chains with terminal polymerizable groups bonded via the silyl group. Polymerization was carried out under otherwise identical conditions. These particles had an average size of 100 nm and also contained agglomerates with a size of approximately 2 pm, determined by measuring a suspension of the particles in ethanol after 30 min of ultrasonication for fine dispersion using a particle size analyzer (Horiba LA-960, Retsch Technology, Japan). The shape of the particles was essentially cubic, determined by scanning electron microscopy (Helios G4 CX, FEI, Hillsboro, OR, USA).

[0050] The content of attached side chains in the particles was determined by thermogravimetric analysis (TGA / DSC1, STARe System, Mettler Toledo, Switzerland) at a heating rate of 10°C / min from 20°C to 900°C in a nitrogen atmosphere. At 900°C, the 3-(trimethoxysilyl)propyl methacrylate-functionalized nanoparticles (A-LLZO) retained a mass of 90.4%, the l-vinyl-3-trimethoxysilane-imidazolium-bis(trifluoromethanesulfonyl)imide-functionalized nanoparticles (IL-LLZO) retained a mass of 85.7%, and the unfunctionalized and otherwise identical nanoparticles retained a mass of 93.3%. This resulted in a ligand content of 3 wt.% for A-LLZO (side chain MW 248.35 g / mol) and 6 wt.% for IL-LLZO (side chain MW 537.52 g / mol). Due to the different molecular weights of the side chains, the contents are interpreted as approximately equal bond density of the side chains on the particles.

[0051] The electrolytes according to the invention were solvent-free and formed elastic layers that were flexible at a thickness of 0.5 to 1 mm, e.g., manually at 15 to 25°C to a radius of 3 to 5 mm. Analysis of platinum-sputtered samples of the functionalized particles using X-ray spectroscopy (4 nm, EM ACE600, Leica Microsystems, Wetzlar, Germany) showed that functionalization by the side chains did not alter the crystallinity of the ceramic nanoparticles made of LLZO.

[0052] The ionic conductivity measured at 20°C to 80°C is shown in Fig. 1, where for comparison pure PETEA (PETEA) crosslinked with the same radical initiator under the same conditions, or pure high molecular weight polyethylene oxide (PEO) (POLYOX WSR 205, DOW Chemical) with an average molecular weight of M w = 600,000 g mol' 1, was used. In both cases, LiTFSI was added at a concentration corresponding to the molar ratio of the oxygen atoms contained in the polymer to LiTFSI of 12:1. The electrolyte according to the invention made of PETEA and TEG with LiTFSI (PETEA:PEG 1:12, referred to as copolymer solid electrolyte) and the electrolyte according to the invention made of PETEA and TEG with LiTFSI and the functionalized particles (PETEA:PEG 1:12 + A-LLZO with 15 wt. %, referred to as hybrid solid electrolyte 1 due to the content of ceramic particles, and PETEA:PEG 1:12 + IL-LLZO with 15 wt. %, referred to as hybrid solid electrolyte 2) have higher ionic conductivities at 20°C and 40°C than the comparison electrolytes (PETEA and PEO, respectively) and a significantly flatter increase in conductivity with increasing temperature than the comparison electrolytes, which show a significantly steeper increase in ionic conductivity with increasing temperature.

[0053] For the preferred embodiment of the solid electrolyte with functionalized particles, a conductivity of 1.1 x 10' was measured at 20°C. 3 S / cm, for the solid electrolyte without the functionalized particles of approx. 10' 4 S / cm, a factor of about 10 higher than PEO.

[0054] The measurements further show, using the example of the different functionalization of the particles, that 3-(trimethoxysilyl)-propyl methacrylate-functionalized particles (A-LLZO) result in a higher conductivity of the electrolyte at the same temperature than particles functionalized with l-vinyl-3-trimethoxysilane-imidazolium-bis(trifluoromethanesulfonyl)imide (IL-LLZO).

[0055] Electrochemical measurements with the electrolyte were performed on button cells containing a first electrode made of copper foil (20 μm thick, Furukawa Electric Co.) as the first carrier, metallic lithium (500 μm thick, Goodfellow) on top, and an identically constructed second electrode in a gas-tight housing. Between them, the electrolyte had been polymerized as a separate layer. These symmetrical Cu / electrolyte / Cu cells were subjected to electrochemical impedance measurements (VSP-300 potentiostat, Biologie, Seyssinet-Pariset, France) at frequencies ranging from 4 MHz to 100 MHz at 20°C, 40°C, 60°C, or 80°C. Using the measured resistance values ​​R, the measured thickness 1 of the electrolyte layer, and its area A, the ionic conductivity was calculated as ia = -

[0056] AXR

[0057] For the linear voltage measurements, a cell made of Cu / electrolyte / Li 0with a sampling rate of 0.2 mV / s in the range from 0 to 6 V at 60°C. The copper electrode was used as the working electrode and the lithium foil (Li°) as the reference and counter electrode. To determine the electrolyte's transfer number, the polarization currents were recorded in symmetrical Li° / electrolyte / Li° cells at a low polarization potential (AV) of 10 mV at 60°C. The lithium ion transfer number was determined using the Bruce-Vincent equation: with the initial current / °, the equilibrium current I ss , the initial Mas sewi der stand R , the equilibrium resistance R b ss and the applied potential AF.

[0058] Figure 2 shows the results of the voltammetric measurement at 60°C for the solid electrolyte made of the copolymer (copolymer solid electrolyte), and for the solid electrolyte with 3-(trimethoxysilyl)propyl methacrylate-functionalized particles (A-LLZO), also referred to as hybrid solid electrolyte 1, as well as for the solid electrolyte with l-vinyl-3-trimethoxysilane-imidazolium-bis(trifluoromethanesulfonyl)imide-functionalized particles (IL-LLZO), also referred to as hybrid solid electrolyte 2. The solid electrolytes each contained equal amounts of LiTFSI at 13 wt.%. The result demonstrates high electrochemical stability over the voltage range from 0 to at least 5.2 V, e.g., up to 5.4 V. In comparison, electrolytes made of PEO tolerate a maximum of 4.0 V.

[0059] Figure 3 shows the ionic conductivity for solid electrolytes with different contents of functionalized particles, which are present in the copolymer at 3 to 35 wt.%. Particles functionalized with 3-(trimethoxysilyl)propyl methacrylate (A-LLZO) were used as representative functionalized particles. For these functionalized particles, the highest conductivity in the temperature range of the measurement was observed for 15 wt.%, at 3.2 x 10' 3 S / cm at 80°C, and 1.1 x 10' 3 S / cm at 20°C, which is sufficient for use in lithium-based batteries at room temperature. Computer-assisted X-ray tomography showed that the particles were evenly distributed throughout the copolymer up to a concentration of 15 wt.% and had not formed any large agglomerates.

[0060] The high conductivity for lithium ions of the exemplary electrolyte made of PETEA:TEG (1:12) with 15 wt.% A-LLZO as functionalized nanoparticles was also demonstrated by a transfer number of 0.69 at 60°C.

[0061] Example 2: Lithium-sulfur battery with solid electrolyte

[0062] For the cycling test, Li° / electrolyte / S° cells encased in button cells were used and cycled at 1.7–2.7 V at 20°C (Maccor Battery Cycler Series 4000, Maccor). The sulfur cathode was obtained by polymerizing a mixture of 46.6 wt% finely divided sulfur, 23.3 wt% carbon black as a conductivity additive (C65, Imerlys, >99.5%), and 30 wt% of a PETEA:TEG mixture (molar ratio 1:12) with AIBN as the initiator and LiTFSI as the lithium salt layer. Either a layer of the copolymer (copolymer solid electrolyte with PETE A :TEG ratio of 1 : 12 as described in Example 1) or a hybrid electrolyte layer (hybrid electrolyte 1 containing 15 wt.% A-LLZO as described in Example 1) was applied to the cathode layer.

[0063] In the cycle tests, the first 5 cycles were not considered due to the formation of the solid-electrolyte interface (SEI). The Li hybrid electrolyte 1 (HE) sulfur-soot batteries (Li|HE|S / C) with the inventive electrolyte containing incorporated A-LLZO particles showed an initial specific capacity of 688 mAh / g at 0.05 C (1 C = 34 mA / g), whereas an otherwise identical comparison battery (Li|PE|S / C) using the copolymer solid electrolyte (PE) showed an initial capacity of only 270 mAh / g. After 20 cycles, the battery capacity was approximately 400 mAh / g at 0.1 C. The results are shown in Fig. 4 for the battery with hybrid solid electrolyte 1 (Li|HE|S / C) and for the copolymer solid electrolyte (Li|PE|S / C). The performance over 50 cycles with a constant charge-discharge rate of 0.1C, shown in Fig. 4, shows an earlier decrease in capacity for the hybrid solid electrolyte 1 compared to the copolymer solid electrolyte.This is attributed to the irreversible transfer of polysulfides to the anode (the so-called polysulfide shuttle mechanism). The voltage profile of the reference battery (Li|PE|S / C) with the copolymer solid electrolyte is shown in Fig. 5, and the voltage profile of the battery with hybrid electrolyte 1 (Li|HE|S / C) is shown in Fig. 6.

Claims

Claims: Solid electrolyte for a rechargeable battery, characterized in that the electrolyte is a copolymer produced by polymerization of a first component having three or four terminal, radically polymerizable residues and a second component having two to eight ethylene glycol units between two terminal, radically polymerizable residues, and containing lithium ions. Solid electrolyte according to claim 1, characterized in that the copolymer contains functionalized ceramic particles having surface-bound side chains that are covalently linked to the copolymer. Solid electrolyte according to claim 1, characterized in that the copolymer contains ceramic particles that do not have organic side chains.A solid electrolyte according to any one of the preceding claims, characterized in that it is polymerized from a solvent-free mixture comprising a first and a second component, optionally ceramic particles, aramid particles, and / or aramid oligomers. A solid electrolyte according to any one of the preceding claims, characterized in that the radically polymerizable residues of the first and second components are vinyl groups. A solid electrolyte according to any one of the preceding claims, characterized by a content of aramid particles and / or aramid oligomers having functional groups that are radically polymerizable with the first and / or the second component.Solid electrolyte according to one of claims 1, 2, 4, 5 and 6, characterized in that organic side chains of the ceramic particles or the aramid are bound to the ceramic particles or the aramid via a silane group and are covalently linked to the first component and / or the second component by polymerization. Solid electrolyte according to any one of the preceding claims, characterized in that it is present in a mixture with a cathode active material and the polymerized mixture thereof forms a cathode layer. Solid electrolyte according to any one of the preceding claims, characterized in that the first component is pentaerythritol tetraacrylate and the second component is tri(ethylene glycol) divinyl ether. Solid electrolyte according to any one of claims 2 to 9, characterized in that the ceramic particles are made of LiyLasZ^On. Rechargeable battery with a first electrode comprising metallic lithium on a first metal support, thereon a layer containing the solid electrolyte according to any one of the preceding claims, thereon a cathode layer containing particles of an active material, and a second metal support.Rechargeable battery according to claim 11, characterized in that the cathode layer comprises the solid electrolyte according to any one of claims 1 to 9. Rechargeable battery according to any one of claims 11 to 12, characterized in that the cathode layer contains particles of LiyLasZβOn. Rechargeable battery according to claim 13, characterized in that the particles of LiyLasZβOn have functionalized side chains that are covalently linked to the copolymer. Rechargeable battery according to any one of claims 11 to 14, characterized in that the cathode layer contains sulfur. Rechargeable battery according to any one of claims 11 to 15, characterized in that, in addition to the solid electrolyte, it does not contain a porous membrane or support structure (separator) between the first and second carriers. Rechargeable battery according to any one of claims 11 to 16, characterized in that it is housed in a gas-tight casing comprising a first carrier.A process for producing a battery according to any one of claims 11 to 17, characterized in that an electrolyte layer is produced by polymerizing a first component having three or four terminal, radically polymerizable residues, and a second component having two to eight ethylene glycol units between two terminal, radically polymerizable residues, as well as at least one lithium salt, to form a copolymer. A process according to claim 18, characterized by distributing ceramic particles in the mixture containing the first component and the second component, or distributing ceramic nanoparticles in the polymerized copolymer.The method according to claim 19, characterized in that the ceramic particles are functionalized in such a way that they have side chains that can be bonded to the copolymer.

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