LITHIUM-ION-CONDUCTING COMPOSITE MATERIAL AND PROCESS FOR PRODUCING

Abstract

A lithium-ion-conducting composite material and process of producing are provided. The composite material includes at least one polymer and lithium-ion-conducting particles. The particles have a sphericity ψ of at least 0.7. The composite material includes at least 20 vol % of the particles for a polydispersity index PI of the particle size distribution of <0.7 or are present in at least 30 vol % of the composite material for the polydispersity index in a range from 0.7 to <1.2, or are present in at least 40 vol % of the composite material for the polydispersity index of >1.2.

Claims

1. A lithium-ion-conducting composite material, comprising: a polymer; and lithium-ion-conducting particles having a sphericity ψ of at least 0.7, wherein the particles: (i) are present in at least 20 vol % of the composite material for a polydispersity index of particle size distribution of <0.7, or (ii) are present in at least 30 vol % of the composite material for the polydispersity index in a range from 0.7 to <1.2, or (iii) are present in at least 40 vol % of the composite material for the polydispersity index of >1.2.

2. The lithium-ion-conducting composite material of claim 1, wherein the polymer comprises a material selected from a group consisting of: polyacrylonitrile, polyester, polypropylene oxide, ethylene oxide/propylene oxide copolymer, polyethylene oxide crosslinked with trifunctional urethane, poly(bis(methoxy-ethoxy-ethoxide))phosphazene (MEEP), triol-like polyethylene oxide crosslinked with difunctional urethane, poly((oligo)oxethylene) methacrylate-co-alkali metal methacrylate, polymethyl methacrylate (PMMA), polymethylacrylonitrile (PMAN), polysiloxanes and copolymers and derivatives thereof, polyvinylidene fluoride or polyvinylidene chloride and copolymers and derivatives thereof, poly(chlorotrifluoroethylene), poly(ethylene-chlorotrifluoroethylene), poly(fluorinated ethylene-propylene), acrylate-based polymers, condensed or crosslinked combinations thereof, and/or physical mixtures thereof.

3. The lithium-ion-conducting composite material of claim 2, wherein the polymer comprises at least one lithium-ion-conducting compound.

4. The lithium-ion-conducting composite material of claim 3, wherein lithium-ion-conducting compound is bistrifluoromethanesulfonimidate.

5. The lithium-ion-conducting composite material of claim 1, wherein the polymer comprises at least one lithium-ion-conducting compound.

6. The lithium-ion-conducting composite material of claim 5, wherein lithium-ion-conducting compound is bistrifluoromethanesulfonimidate.

7. The lithium-ion-conducting composite material of claim 1, wherein the polymer comprises at least one ion conducting compound comprising conductive salts selected from the group consisting of: LiAsF.sub.6, LiClO.sub.4, LiSbF.sub.6, LiPtCl.sub.6, LiAlCl.sub.4, LiGaCl.sub.4, LiSCN, LiAlO.sub.4, LiCF.sub.3CF.sub.2SO.sub.3, Li(CF.sub.3)SO.sub.3 (LiTf), LiC(SO.sub.2CF.sub.3).sub.3, phosphate-based lithium salts, borate-based lithium salts, and/or lithium salts of sulfonylimides.

8. The lithium-ion-conducting composite material of claim 1, further comprising: a polyelectrolyte that carries Li.sup.+ as counter-ion, or polymerized imidazolium-, pyridinium-, phosphonium- or guanidinium-based ionic liquids that carry a discrete number of chemically bonded ionic groups.

9. The lithium-ion-conducting composite material of claim 1, wherein the lithium-ion-conducting particles comprise a lithium-ion-conducting compound selected from the group consisting of: lithium lanthanum zirconate (LLZO), lithium aluminium titanium phosphate (LATP) compounds with garnet-like crystal structure, compound composed of a material with a garnet-like crystal structure having the empirical formula Li.sub.7+x−y M.sub.x.sup.II M.sub.3−x.sup.III M.sub.2−y.sup.IV M.sub.y.sup.V O.sub.12 where: M.sup.II is a divalent cation, M.sup.ill is a trivalent cation, M.sup.I″ is a tetravalent cation, and M.sup.y is a pentavalent cation, where preferably 0≤x<3, or 0≤x≤2, 0≤y<2, or 0≤y≤1 or compounds derived therefrom, compounds doped with Al, Nb or Ta, compounds having a crystal structure isostructural with NaSICon, compounds having an empirical formula Li.sub.1+x−yM.sup.5+.sub.yM.sup.3+.sub.xM.sup.4+.sub.2−x−y(PO.sub.4).sub.3, where x and y are in the range from 0 to 1 and (1+x−y) >1 and M is a cation of valency +3, +4 or +5, or compounds derived therefrom.

10. The lithium-ion-conducting composite material of claim 1, wherein the lithium-ion-conducting particles have an average particle diameter of 0.02 μm to 100 μm.

11. The lithium-ion-conducting composite material of claim 10, wherein the lithium-ion-conducting particles have an average particle diameter of 0.2 μm to 2 μm.

12. The lithium-ion-conducting composite material of claim 10, wherein the lithium-ion-conducting particles have an average particle diameter of 5 μm to 70 μm.

13. The lithium-ion-conducting composite material of claim 1, further comprising: a surface modification of the lithium-ion-conducting particles, wherein the surface modification provides an interfacial resistance of lithium-ion conductivity between the polymer and the lithium-ion-conducting particles that is reduced so that the lithium-ion conductivity is greater than for a composite material without the surface modification.

14. The lithium-ion-conducting composite material of claim 1, wherein the lithium-ion-conducting particles are spray calcination particles.

15. The lithium-ion-conducting composite material of claim 14, wherein the lithium-ion-conducting particles are pulsation reactor particles.

16. A process for producing a lithium ion conductor, comprising: providing a lithium-ion-conducting composite material, the lithium-ion-conducting composite material comprising a polymer and lithium-ion-conducting particles having a sphericity ψ of at least 0.7, wherein the lithium-ion-conducting particles: (i) are present in at least 20 vol % of the lithium-ion-conducting composite material for a polydispersity index of particle size distribution of <0.7 or (ii) are present in at least 30 vol % of the lithium-ion-conducting composite material for the polydispersity index in a range from 0.7 to <1.2, or (iii) are present in at least 40 vol % of the lithium-ion-conducting composite material for the polydispersity index of >1.2; and sintering the lithium-ion-conducting composite material.

17. The process of claim 16, wherein the sintering comprises sintering under elevated temperature and/or elevated pressure.

18. The process of claim 16, wherein the lithium-ion-conducting particles are produced by a method selected from the group consisting of: spray calcinating, pulsation reactor spray calcinating, filamentization from a salt melt, droplet formation, and glass sphere production.

19. The lithium-ion-conducting composite material of claim 7, wherein the phosphate-based lithium salts are selected from the group consisting of: LiPF6, LiPF3(CF3)3 (LiFAP) and LiPF4(C2O4) (LiTFOB), the borate-based lithium salts are selected from the group consisting of: LiBF4, LiB(C2O4)2 (LiBOB), LiBF2(C2O4) (LiDFOB), LiB(C2O4)(C3O4) (LiMOB), Li(C2F5BF3) (LiFAB) and Li2B12F12 (LiDFB), and/or the lithium salts of sulfonylimides are selected from the group consisting of: LiN(FSO2)2 (LiFSI), LiN(SO2CF3)2 (LiTFSI) and/or LiN(SO2C2F5)2 (LiBETI).

20. The lithium-ion-conducting composite material of claim 8, wherein the polyelectrolyte is polystyrenesulfonate (PSS).

Description

DETAILED DESCRIPTION

[0068] According to requirements and field of use, both the lithium-ion-conducting composite material of the invention and a lithium-ion conductor produced from the lithium-ion-conducting composite material may be used as a lithium-ion-conducting component or constituent of such a component.

[0069] Further described are formulations for producing composite precursors for hybrid electrolytes or ceramic slips for producing sintered, purely inorganic, solid-state lithium-ion conductor components, in which, at the same volume fill levels, the viscosity of the particle-filled formulation when using non-spherical particles is significantly higher than when using the particles of high sphericity W used in accordance with the invention, provided that particle size and/or particle-size distribution are the same in both cases.

[0070] Moreover, formulations for producing composite precursors for hybrid electrolytes or ceramic slips for producing sintered, purely inorganic, solid-state lithium-ion conductor components are described in which the corresponding formulations, without substantial change in the viscosity, can be provided with significantly higher fill levels in the case of the spherical variant than in the case of the non-spherical embodiment. The proviso in this case again is that in both cases there are no substantial differences in particle size and particle-size distribution.

[0071] The lithium-ion-conducting material produced in accordance with the invention in the form of spherical particles with size in the μm- or sub-μm range may be incorporated as filler into a polymer electrolyte or into polyelectrolytes, in which case the resulting composite is popularly referred to as a hybrid electrolyte. Alternatively to this, it may be compressed to a compact using suitable tooling, or incorporated into a ceramic slip (with or without the addition of a binder), and subjected to a suitable shaping process (e.g. tape casting), and in both cases may be sintered at temperature to form a purely inorganic, ion-conducting moulding. Both forms of presentation—hybrid electrolyte and purely inorganic, ceramic, solid-state ion conductor—may be used as solid-state electrolytes in next-generation rechargeable lithium or lithium-ion batteries, as for example in solid-state lithium batteries (all-solid-state batteries (ASSB)) or lithium-air batteries. One possibility is the use thereof as a separator: introduced between the electrodes, it preserves them from unwanted short-circuiting and so ensures the functional capacity of the system as a whole. For this purpose, the corresponding composite may either be applied as a layer to one or both electrodes or integrated as a self-standing membrane, in the form of a solid-state electrolyte, into the battery. An alternative possibility is that of compounding with the active electrode materials—in the case of the hybrid electrolyte, by incorporation on the active electrode material into the hybrid electrolyte formulation; in the case of the purely inorganically ceramic electrolyte, by co-sintering with that electrolyte. In this case, the solid-state electrolyte brings about the transport of the relevant charge carriers (lithium ions and electrons) to the electrode materials and to or away from the conducting electrodes, according to whether the battery is being discharged or charged.

Working Examples:

[0072] Examples of production of lithium-ion-conducting particles of high sphericity W of at least 0.7 from a lithium-ion-conducting material:

[0073] Production of spherical LAGP particles

[0074] Shaping directly from the green glass melt

[0075] A starting glass for an eventually lithium-ion-conducting, phosphate-based glass-ceramic of the composition 5.7 wt % Li.sub.2O, 6.1 wt % Al.sub.2O.sub.3, 37.4 wt % GeO.sub.2 and 50.8 wt % P.sub.2O.sub.5 was melted in a discharge crucible at a temperature of 1650° C.

[0076] In the melting assembly selected, the glass melt was held at a temperature of 1600° C. It was discharged from a nozzle with a diameter of 2 mm, positioned on the base of the crucible. The glass jet thus produced was dropped onto a 53-toothed striking wheel 8 mm thick and with an outer diameter of 135 mm, this wheel rotating at a frequency of 5000 rpm about its own axis. In this way, the glass stream was filamentized into individual sub-strands, and accelerated with an angle of inclination of between 20 to 30° as measured with respect to the horizontal. It was subsequently passed through a tubular furnace 3 m long, constructed in a curved shape and heated to 1550° C. with two gas burners, this furnace mimicking the flight path of the filamentized glass stream. As a result of the tendency to minimize the surface energy, the filaments in elongate form underwent a change in shape to spheres. Following emergence from the tubular furnace, the glass spheres were cooled by further flight in air until sufficient dimensional stability was achieved, and were finally captured in a collecting vessel.

[0077] The cooled, very largely X-ray-amorphous green glass spheres produced by the hot shaping process described were ceramicized and so converted into the eventual, lithium-ion-conducting glass-ceramic in the course of a further temperature treatment after nucleation in the temperature range between 500 and 600° C. for 2 to 4 hours with a maximum temperature of 850° C. and a hold time of 12 hours.

Shaping By Rounding of Non-Spherical Green Glass Particles

[0078] A starting glass for an eventually lithium-ion-conducting, phosphate-based glass-ceramic of the composition 5.7 wt % Li.sub.2O, 6.1 wt % Al.sub.2O.sub.3, 37.4 wt % GeO.sub.2 and 50.8 wt % P.sub.2O.sub.5 was melted in a discharge crucible at a temperature of 1650° C.

[0079] In the melting assembly selected, the glass melt was held at a temperature of 1600° C. It was discharged from a nozzle with a diameter of 2 mm, positioned on the base of the crucible into a nip between two contra-rotating, water-cooled rolls, where it was quenched to form a green glass ribbon. The green glass ribbon was singularized into small splinters mechanically, using a hammer.

[0080] The glass splinters were roughly comminuted by preliminary grinding in a bead mill, and the powder fraction having a particle size d.sub.100<100 μm was removed by sieving from this roughly comminuted material. This green glass powder isolated by sieving was comminuted further in an additional downstream step of dry grinding in an opposed-jet mill to a particle size with a distribution of d.sub.10=0.9 μm, d.sub.50=5 μm, d.sub.90=13 μm and d.sub.99=18 μm.

[0081] By introduction of the powder into an oxyhydrogen gas flame, the glass particles are melted again, and experience rounding in the process, owing to the tendency for minimization of the surface energy. On emergence from the flame, the particles are allowed to cool and are captured in a collecting vessel.

[0082] The cooled, very largely X-ray-amorphous green glass spheres produced by the hot shaping process described were ceramicized and so converted into the eventual, lithium-ion-conducting glass-ceramic in the course of a further temperature treatment after nucleation in the temperature range between 500 and 600° C. for 2 to 4 hours with a maximum temperature of 850° C. and a hold time of 12 hours.

Filamentization of Salt Melts

[0083] In a first step, a zirconium-containing precursor powder was produced as follows: 23.4 kg (50.0 mol) of zirconium n-propoxide (70% solution) are admixed dropwise with 5.0 kg (50.0 mol) of acetylacetone with stirring in a round-bottomed flask. The resulting reaction mixture is stirred at room temperature for 60 minutes. Then 2.7 kg (150.0 mol) of distilled water were added for hydrolysis. After a reaction time of about 1 hour, the resulting prehydrolysate was dried completely on a rotary evaporator. A sample of the resultant powder is then heated to determine the oxide content (900° C./5 hours).

[0084] 1.77 kg (5.0 mol) ZrO.sub.2 equivalent of the zirconium-containing precursor powder (oxide content: 35 wt %) produced in the preceding step were introduced together with 2.5 kg (7.5 mol) of lanthanum acetate sesquihydrate, 1.95 kg (19.2 mol) of lithium acetate dihydrate and 0.15 kg (0.61 mol) of aluminium chloride hexahydrate into a ball mill, where they were ground for 4 hours to produce an ideally homogeneous powder mixture. The grinding balls used for this purpose were Al.sub.2O.sub.3 balls with a diameter of 40 mm.

[0085] After sieving to remove the balls, the powder mixture was placed into an Al.sub.2O.sub.3 discharge crucible where it was brought to a temperature of 300° C., just above the melting point of anhydrous lithium acetate, which is 280-285° C. A salt melt is formed which was discharged via a nozzle with a diameter of 2 mm that was positioned on the base of the crucible. The jet generated in this way and consisting of the salt melt was dropped onto a 53-toothed striking wheel 8 mm thick with an outer diameter of 135 mm, this wheel rotating at a frequency of 5000 rpm about its own axis. In this way, the jet consisting of the salt melt was filamentized into individual strands and accelerated with an angle of inclination of between 20 to 30° as measured with respect to the horizontal. It was subsequently passed through a tubular furnace 3 m long and of curved construction that mimicked the flight path of the filamentized jet consisting of the salt melt. The furnace was heated electrically so as to be maintained in the entry zone at moderate temperatures of 300-320° C., so that the salt melt was retained and the filaments, initially still of elongate form, underwent a change in shape, owing to the tendency for minimization of the surface energy, into spheres which are still liquid. In the downstream zones, the temperature selected was then significantly higher—temperatures of around 900° C. were achieved here. Here, therefore, there was a first step of calcination of the liquid spheres, forming porous, preceramic particles as an intermediate. Following emergence from the tubular furnace, these spheres were allowed to cool by further flight in air and were finally captured in a collecting vessel.

[0086] The porous, preceramic particles were compacted in a further calcination step in an oven at 1050° C. with a hold time of 7-8 hours to give the final spheres consisting of the lithium-ion-conducting LLZO material.

Production of Spherical LLZO Particles Via Spray Calcination Using the Pulsation Reactor Method

[0087] 2.3 kg (4.7 mol) of zirconium acetylacetonate were dissolved in at least 10.0 kg (556 mol) of distilled water in a suitable reaction vessel. 2.4 kg (7 mol) of lanthanum acetate sesquihydrate were dissolved in a further reaction vessel in 10 kg (556 mol) of distilled water. 1.8 kg (18 mol) of lithium acetate dihydrate and 0.14 kg (0.58 mol) of aluminium chloride hexahydrate were dissolved in a third reaction vessel in 5.0 kg (278 mol) of distilled water. After complete dissolution of the components, the solutions were combined and the resulting reaction mixture was stirred at room temperature for 12 hours.

[0088] The solution is conveyed with the aid of a peristaltic pump into a pulsation reactor at a volume flow rate of 3 kg/h, where via a 1.8 mm titanium nozzle it is finely atomized into the reactor interior, where it is subjected to thermal treatment. The temperature of the combustion chamber here is maintained at 1030° C., and that of the resonance tube at 1136° C. The ratio of the quantity of combustion air to the quantity of fuel (natural gas) is 10:1 (air:gas).

[0089] The powder is introduced into a cuboidal alpha-alumina crucible and placed in a chamber kiln. The material for calcining is brought to a temperature of 1050° C. in the kiln, in an air atmosphere, for the complete compaction of the spherical microscale particles consisting of the LLZO.

Production of Spherical LLZO Particles Via the Droplet Formation Process

[0090] The LLZO material was first of all melted in a so-called skull crucible, as described in DE 199 39 782 C1, for instance. Employed for this purpose was a water-cooled crucible in which, during melting, a cooler protective layer of the material to be melted is formed. Accordingly, no crucible material is dissolved during the melting operation. The input of energy into the melt is accomplished by means of radio-frequency coupling via the surrounding induction coil into the molten material. A condition here is the sufficient conductivity of the melt, which in the case of lithium garnet melts is assured by the high lithium content. During the melting process, evaporation of lithium occurs, and can easily be corrected by an excess of lithium. For this purpose it is normal to operate with a 1.1- to 2-fold lithium excess.

[0091] The raw materials were mixed in accordance with the following composition and introduced into the skull crucible, which is open at the top: 14.65 wt % Li.sub.2O, 56.37 wt % La.sub.2O.sub.3, 21.32 wt % ZrO.sub.2 and 7.66 wt % Nb.sub.2O.sub.5. It was necessary first of all to preheat the batch in order to achieve a certain minimum conductivity. This was done using a burner heating system. When the coupling temperature was reached, further heating and homogenization of the melt were achieved via radio-frequency coupling via the induction coil. In order to improve the homogenization of the melts, stirring took place with a water-cooled stirrer.

[0092] The material produced in this way may in principle be converted, either by direct solidification from the melt or by quenching, followed by a temperature treatment (ceramicization) into a glass-ceramic material with a garnet-like main crystal phase. In the example described here, the variant selected was that of direct quenching.

[0093] In this case, the material was obtained as a monolithic block, which was converted into a powder having a particle size d1.sub.00 <100 μm via a variety of rough comminution processes—such as processing with hammer and chisel in the first step, comminution of the fragments obtainable in that case, using a jaw crusher in the second step, and further preliminary grinding of the resultant coarse powder in the planetary mill, with subsequent sieving, in the third step. In a further downstream step, this powder was comminuted further by grinding in water, this being carried out in an attritor, to a particle size having a distribution of d.sub.10=0.14 μm, d.sub.50=0.42 μm, d.sub.90=1.87 μm and d.sub.99=2.92 μm. The content of LLZO solids in the grinding slip used in this case was around 30%. To stabilize the particles, a dispersant (Dolapix CE 64 or Dolapix A88 from Zschimmer & Schwarz GmbH & Co. KG) was added to the slip prior to grinding, with a fraction of 1.0%, based on the LLZO fraction in the suspension, proving to be highly practicable.

[0094] For further processing, the solids content of the grinding slip was increased to a level of 60% by partial evaporation of the water on the rotary evaporator, to obtain a suitable mixing ratio in respect of the viscosity.

[0095] Then ammonium alginate was added as a binder in an amount of 1.0%.

[0096] By means of a droplet formation process involving nozzles and/or hollow needles, dimensionally stable green bodies with sizes of 0.3 to 2.5 mm were obtained from the slip by immersion and also reaction in an aluminium lactate solution or an inorganic acid solution or an organic acid solution.

[0097] These green bodies were subsequently shaped to form sintered beads by a sintering process. Sintering took place in an air atmosphere under standard pressure at temperatures of 1150° C.

[0098] Examples for the production of formulations of lithium-ion-conducting composite materials filled with at least 20 vol % of lithium-ion-conducting particles with high sphericity ψ of at least 0.7 from a lithium-ion-conducting material with a polydispersity index PI of the particle size distribution of <0.7, or at least 30 vol % of corresponding particles at a polydispersity index PI of the particle size distribution of 0.7<PI<1.2, or at least 40 vol % of corresponding particles at a polydispersity index PI of the particle size distribution of >1.2.

[0099] Production of a composite material of the invention (production of a hybrid electrolyte membrane based on a polyethylene oxide (PEO) filled with LLZO particles/lithium bis(trifluoromethanesulfonyl)imide (LiTSFI) polymer electrolyte).

[0100] 1.4 g of polyethylene oxide (PEO, Dow Chemical) having a molar weight of 4×10.sup.6 g/mol were dried under reduced pressure at 50° C. for 48 hours. Added to the polymer under dry room conditions (dew point <−70° C.) were 8.5 g of lithium lanthanum zirconium oxide powder, consisting of particles having a sphericity of 0.92 and a particle size distribution as follows: d.sub.10=1.22 μm, d.sub.50=2.77 μm, d.sub.90=5.85 μm d.sub.99=9.01 μm. Correspondingly, in accordance with the invention, the polydispersity index PI of the particle size distribution is 0.681. The mixture was subjected to intensive grinding in a mortar. It was then admixed with 0.6 g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI, 3M) having a purity of >99% (suitable for battery applications), which had been dried beforehand under reduced pressure (10′ bar) at 120° C. for 24 hours. All of the components were further mixed intensely in the mortar, to form, finally, a homogeneous paste. This resulted in a PEO/LiTSFI polymer electrolyte matrix having a ratio of lithium ions to ethylene oxide monomer units (Li:EO) of 1:15, in which the inorganic solid-state lithium-ion conductor was embedded in a volume fraction of 50 vol %. The hybrid electrolyte thus produced was vacuum-welded into a pouch, heat-treated overnight at 100° C. and then subjected to hot pressing at 100° C. with an applied force of 50 kN (50—750 kg/cm.sup.2) (Servitec Polystat 200 T press). This gave a composite membrane having a thickness of around 100 μm.

[0101] The same procedure was used to produce hybrid electrolyte membranes, using an LLZO powder consisting of non-spherical particles (ψ=0.48), the particle size distribution being as follows: d.sub.10=0.44 μm, d.sub.50=1.24 μm, d.sub.90=3.50 μm, d.sub.99=6.94 μm. The polydispersity index of the particle size distribution, PI, was in this case, in accordance with the invention, 0.900. In these cases, however, only 4.6 g of LLZO powder could be incorporated practicably into the pEO/LiTSFI polymer electrolyte matrix; in these cases, in other words, the hybrid electrolyte was producible only with a maximum volume content of 29 vol %.

[0102] Production of a lithium-ion conductor of the invention from the composite material of the invention (production of a purely inorganic, sintered solid-state electrolyte membrane by means of a tapecasting process, based on a casting slip filled with LATP particles)

[0103] 11.4 g of polyvinyl butyral (PVB) having a molar weight of 35 000 g/mol, containing the vinyl butyral units and also 1.7 wt % of vinyl acetate and 18.9 wt % of vinyl alcohol units, were dissolved in 68.4 g of a solvent mixture consisting of ethanol and toluene (4:6). The viscosity of the solution was between 200 and 450 mPa s. The mixture was admixed with 5.7 g of dioctyl phthalate, which functioned as a plasticizer. Introduced finally into the mixture by dispersion, using a dissolver, were 200 g of a lithium aluminium titanium phosphate (LATP) glass-ceramic powder, which consisted of particles having a sphericity of 0.94 and a particle size distribution as follows: d.sub.10=0.81 μm, d.sub.50=2.23 μm, d.sub.90=5.17 μm, d.sub.99=8.46 μm. In accordance with the invention, the polydispersity index PI of the particle size distribution in this case was 0.805. The resulting casting compound had a viscosity of 4000-5000 mPa s. The glass-ceramic powder content was around 43 vol %.

[0104] The homogenized compound produced in this way was subsequently freed from gas bubbles (i.e. deaerated) by means of vacuum technology. This deaerated material was supplied to the customary tapecasting process on a film-drawing apparatus, and in that way was cast into a tape with a thickness (measured after drying) of around 0.3 mm. The green tape produced in this way was thereafter cut to the desired format and so singularized.

[0105] The singularized tape sections were finally sintered at 1000° C. for 4 hours to form dense LATP membranes. Tape shrinkage in this process was around 9%.

[0106] In accordance with the same procedure, a purely inorganic solid-state lithium-ion conductor membrane was produced, using an LATP powder which consisted of non-spherical particles (IP 0.46) and had a particle size distribution as follows: d.sub.10=0.68 μm, d.sub.50=1.74 μm, d.sub.90=3.86 μm, d.sub.99=7.21 μm. The polydispersity index of the particle size distribution, PI, was in this case 0.754, in accordance with the invention. In these cases, however, it was possible for only 90 g of LATP powder to be incorporated practicably into the binder solution consisting of PVB, dioctyl phthalate and ethanol/toluene, meaning that in these cases the tapecasting slip could only be produced with a volume content of max. 28 vol % without significantly exceeding the target viscosity of 4000-5000 mPa s. On account of the significantly reduced solids content, the contraction during sintering was around 15%.