Method for producing a solid electrolyte separator, as well as the solid electrolyte separator obtainable by the method and its use

Abstract

The invention relates to a method for producing a solid electrolyte separator (40), comprising the steps of: (1) providing a solvent-free solid electrolyte (20) in solid form; (2) compressing the solid electrolyte (20); (3) providing a binder (30) in liquid form; (4) allowing the solid electrolyte to infiltrate with the binder in liquid form from step (3); (5) allowing the binder (30) to set; and (6) obtaining a solid electrolyte separator (40). The invention also relates to the solid electrolyte separator (40) obtainable by the method and its use.The invention is characterized in that the solid electrolyte separator (40) obtainable according to the invention has improved electrochemical performance, resulting from the higher amount of solid electrolyte (20), the lower amount of binder (20), increased density, and higher mechanical stability, with better control of the morphology of the solid electrolyte separator (40). Furthermore, by sealing most of the pores (25a) with the binder (30), undesirable dendrite growth is avoided, thereby preventing short circuits.

Description

[0001] The invention relates to a method for producing a solid electrolyte separator, the solid electrolyte separator obtainable by the method, and its use.

[0002] In recent years, lithium-ion battery systems have become increasingly prevalent in battery technology. These are characterized in particular by their high energy density and expected long lifespan, enabling more efficient battery configurations. The high chemical reactivity and low mass of lithium ions, as well as their high mobility, play a key role in this.

[0003] A battery typically consists of three layers: anode, separator and cathode, with the anode and cathode storing the active energy via lithium ions and the separator, in the form of a solid electrolyte separator, providing insulation between the electrodes and the transport of charge carriers in the form of lithium ions between the cathode and anode during charging and discharging.

[0004] In all-solid-state batteries (ASSBs), short circuits due to dendrite growth are a common occurrence. Dendrite growth is a phenomenon that occurs in lithium-ion batteries, where lithium deposits form needle-like microstructures called dendrites during the charging process. Over the course of several charge and discharge cycles, these dendrites can form a network-like structure, known as mossy lithium. These dendrites can grow so large that they penetrate the separator and cause short circuits. This not only reduces the battery's efficiency and lifespan but also poses a significant safety risk, as short circuits can lead to overheating or fires. Therefore, there is a need to minimize or completely prevent dendrite growth.

[0005] One possible cause of dendrite growth is seen here in the presence of many pores in the solid electrolyte separator.

[0006] A typical manufacturing process for a solid electrolyte separator according to the state of the art will be described based on the Fig. 1a to 1e will be illustrated. First, a solution of a solid electrolyte ( Fig. 1a) is produced from a solvent 10 and one or more solid electrolytes 20. Furthermore, it is produced from a solvent 10 and a binder or binder mixture 30 ( Fig. 1b 7 cross-hatched filling) a separate solution was prepared. The solvent 10 can be the same solvent in both solutions. The solution is not necessarily a true solution, but can also be a dispersion of solid in solvent or an emulsion. The two solutions of Fig. 1a and Fig. 1b are then mixed together ( Fig. 1c), where the aim is essentially to coat the solid electrolyte with a thin binder layer. The resulting mixture of Fig. 1c subjected to drying ( Fig. 1d), whereby the solvent is removed. Then the dried mixture is pressed ( Fig. 1e) obtaining a solid electrolyte binder mixture which can be used as a solid electrolyte separator 40 in a solid-state battery.

[0007] However, this manufacturing process is disadvantageous because it creates numerous and randomly distributed open pores 25a into which lithium can grow, resulting in an undesirable short circuit in the solid-state battery. The resulting porosity cannot be influenced or controlled with this manufacturing process.

[0008] One such manufacturing process is disclosed, for example, in Nathalie Riphaus et al.: "Slurry-Based Processing of Solid Electrolytes: A Comparative Binder Study" in Journal of The Electrochemical Society, 165 (16) A3993-A3999 (2018) [DOI: 10.1149 / 2.0961816jes]. This article deals with slurry processes for the production of the sulfide solid electrolyte Li 10 SnP2S 12(LSPS), in which various polymers were investigated for their suitability as binders for thin, freestanding solid electrolyte (SE) films. The manufacturing process was carried out as follows: The process steps were performed in an argon-filled glovebox. The sulfide solid electrolyte LSPS was first homogenized using a mortar and pestle and then dispersed in toluene by stirring. The binder was dissolved in toluene, and the appropriate amount of the binder solution was added to the LSPS dispersion. After a stirring time of at least 12 hours, the viscosity of the slurry was adjusted, and the slurry was applied to a siliconized polyester film using a doctor blade. The SE films were dried at room temperature for 1 hour at ambient pressure and for a further 12 hours under dynamic vacuum.For compression, the plates were sealed in a bag made of aluminum foil and calendered at 60 °C outside the glove box.

[0009] Furthermore, Yong-Gun Lee et al. reveal in “High-energy long-cycling all-solid-state lithiummetal batteries enabled by silver-carbon composite anodes” in Nature energy, online publication on March 9, 2020; pages 1 to 10; https: / / doi.org / 10.1038 / s41560-020-0575-z ; that unwanted Li dendrite growth in a lithium solid-state battery is avoided by using an Ag-C nanocomposite anode. Here too, the preparation of the sulfide solid electrolyte (SSE) was carried out as is customary in the prior art: The Li3PS3Cl solid electrolyte and a non-aqueous acrylate binder in xylene and anhydrous isobutyl isobutyrate (50:50 wt / wt) were mixed with a 4 Å molecular sieve and ZrO2 beads in a planetary centrifugal mixer at 2,000 rpm for 6 minutes. The resulting mixture was applied to a polyethylene terephthalate film (75 µm) using a doctor blade.The film was then dried for a few minutes on a hot plate at 50 °C and dried overnight in a vacuum oven at 40 °C. The process was carried out in a drying room.

[0010] The manufacturing processes described above lead to the formation of numerous and randomly distributed pores in which dendrite growth can occur, resulting in a fatal short circuit in the solid-state battery.

[0011] Therefore, there is still a need to further improve the properties of solid electrolytes.

[0012] The present invention therefore aims to provide a manufacturing process that avoids the disadvantages of the prior art and to provide a solid electrolyte separator that has improved properties and thus also provides an improved solid-state battery.

[0013] According to the invention, the above problem is solved by a method for producing a solid electrolyte separator, comprising the steps of: (1) Providing a solvent-free solid electrolyte in solid form; (2) Compressing the solid electrolyte; (3) Providing a binder in liquid form; (4) Allow the solid electrolyte to infiltrate with the binder in liquid form from step (3); (5) Allow the binding agent to set; and (6) Obtaining a solid electrolyte separator.

[0014] The present invention therefore relates to a method for producing solid electrolyte separators in which the pores remaining after pressing are closed by binder infiltration, resulting in improved electrochemical performance.

[0015] In step (1), a solvent-free solid electrolyte is provided as a solid. This is provided as such in solid form, i.e., without solvent. The solid electrolyte can also be a mixture of several solid electrolytes, such as a composite or hybrid solid electrolyte. The solid electrolyte can be any solid electrolyte known to a person skilled in the art that is suitable for a solid-state battery. Solid electrolytes include, for example, the groups of solid polymer electrolytes, solid oxide electrolytes, solid sulfide electrolytes (also known as thiophosphate electrolytes), solid halide electrolytes, and closo-borate solid electrolytes. By way of example, one of the following can be used, or a composite or hybrid solid electrolyte can be used that has or consists of two or more of the following: 1. Polyether-based SPEs: e.g., poly(ethylene oxide) (PEO), propylene oxide (PPO), and the like; 2. Polycarbonate-based SPEs: e.g. polyethylene carbonate (PEC), polypropylene carbonate (PPC), polytrimethylene carbonate (PTMC) and the like; 3. Polysiloxane-based SPEs; and 4. SPEs based on polymer crystals.

[0016] Solid oxide electrolytes: 1. Perovskite conductors: e.g., Ln 1 / 3 NbO3 (Ln = La, Ce, Pr, Nd); 2. NASICON leader: e.g. Na 1+x Zr2P 3-x Si x O 12 with 0 < x < 3 3. Garnet-like conductors: e.g. Li5La3M2O 12 (M=Nb, Ta, Zr); and 4. Amorphous / glass: e.g. LiPON.

[0017] Solid sulfide electrolytes: 1. Thio-LISICONs: e.g. Li 4-x M 1-y M y S4 (M=Si, Ge, and M=P, Al, Zn, Ga 2. LGPS family: e.g. Li 10 GeP2S 12 ; and 3. Argyrodites: e.g. B. Li6PS5X (X =Cl, Br, I).

[0018] Solid halide electrolytes: e.g. Li a MX b(X = F, Cl, Br, I, M = metallic elements, such as the lanthanides (M = Sc, Y, La - Lu), elements of group 13 (M = Al, Ga, In) and various divalent metals (M = Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd, Mg, Pb) with a = e.g. 1.5 to 3 and b = e.g. 4 to 6.

[0019] Another group consists of closo-borate solid electrolytes.

[0020] Of course, other solid electrolytes known to experts can also be used.

[0021] In step (2), the solid electrolyte is compressed. This compression can be carried out, for example, using a calendering process. The calendering process can be performed at an elevated temperature above room temperature (25 °C), for example, in the range of 40–60 °C. Lower or higher temperatures are also possible in individual cases.

[0022] In step (3), a binder is provided, which is in liquid form. The binder can also be a mixture of several binders. The binder(s) are in liquid form and are therefore either one or more liquids or are dispersed or dissolved in one or more solvents. The liquid form is not further restricted and signifies flowability in the sense of fluidity, so that the binder can infiltrate, i.e., penetrate, the solid electrolyte in the subsequent step (4).

[0023] Within the scope of the invention, any binder known to those skilled in the art can be used that is suitable for a solid electrolyte separator used in a solid-state battery. The binder is, for example, a thermoplastic or thermosetting resin. Examples include polysiloxane, polyalkylene glycol, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyisobutene (PIB), polymethyl methacrylate (PMMA), polychlorotrifluoroethylene (PTFE), styrene-butadiene rubber (SBR), polyacrylonitrile butadiene, hydrogenated nitrile butadiene rubber (HNBR), polyethylene vinyl acetate (PEVA), tetrafluoroethylene-hexafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer (ETFE resin), and vinylidene fluoride-pentafluoropropylene copolymer.Propylene tetrafluoroethylene copolymer, ethylene chlorotrifluoroethylene copolymer (ECTFE), vinylidene fluoride hexafluoropropylene tetrafluoroethylene copolymer, vinylidene fluoride perfluoromethyl vinyl ether tetrafluoroethylene copolymer, ethylene acrylic acid copolymer, ethylene methacrylic acid copolymer, ethylene methyl acrylate copolymer and ethylene methyl methacrylate copolymer.

[0024] Preferred materials include polysiloxane, polyalkylene glycol, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyisobutene (PIB), poly(methyl methacrylate) (PMMA), polychlorotrifluoroethylene (PTFE), styrene-butadiene rubber (SBR), poly(acrylonitrile butadiene), hydrogenated nitrile butadiene rubber (HNBR) and poly(ethylene vinyl acetate) (PEVA).

[0025] Non-polar aprotic solvents are preferably used as solvents for dispersing the binder(s) to create a slurry. These include, for example, hydrocarbons such as hexane, heptane, octane, nonane, decane, decalin, dichloroethane, toluene, xylene, tetrahydrofuran, and methylene chloride. Since sulfide-based solid electrolytes are readily hydrolyzed, solvents with a low water content are preferably used. The water content in the solvents is preferably < 30 ppm, more preferably < 10 ppm, and particularly preferably < 1 ppm.

[0026] In step (4), the solid electrolyte is infiltrated with a liquid binder. The term "infiltration" refers to the penetration of the liquid binder from the outside into the open pores that remain after the solid electrolyte has been compressed, and the complete filling of these pores with the liquid binder. For this purpose, the liquid binder is applied to the surface of the solid electrolyte and penetrates through the open pores in the compressed electrolyte. It is then absorbed into the pores by capillary action, similar to a sponge, and remains there due to capillary forces. Alternatively, the solid electrolyte is immersed in the liquid binder and thus completely saturated.

[0027] After the binder has been allowed to infiltrate, any remaining binder on the surface that has not penetrated the compressed solid electrolyte can be removed.

[0028] According to step (5), the liquid binder now present in the pores of the compressed solid electrolyte is allowed to set, thereby transforming the previously open pores into binder-filled pores. The binder is thus solidified within the pores. This setting can be carried out with or without external influence, for example, by applying a suitable temperature and / or pressure. It can also be achieved, for example, by hardening and / or drying the binder. This can be accomplished, for example, by evaporating the solvent. An elevated temperature and / or a vacuum can be used for this purpose. Step (5) can also be carried out by allowing the solid electrolyte containing the binder to stand at room temperature, for example, and solidify. Any solvent present can evaporate at room temperature, thus causing the binder to set.The specific conditions depend on the individual case and the materials selected.

[0029] In step (6) the solid electrolyte separator is then obtained.

[0030] The term "solid electrolyte" refers to one or more solid electrolytes used as starting material in the manufacture of the separator. The "solid electrolyte separator" is the separator produced from the solid electrolyte as starting material, used in a solid-state battery, and may contain one or more binders and optionally other additives in addition to the solid electrolyte(s). Examples of additives used include fillers, particularly inorganic fillers, dispersing agents, or other additives, provided they are suitable for use in a solid electrolyte separator.

[0031] In the process according to the invention, the solid electrolyte is first compressed, and the resulting open pores are infiltrated with binder and thereby closed by filling them with binder as much as possible. This increases the amount of solid electrolyte in the solid electrolyte separator, reduces the amount of binder required, and results in a solid electrolyte separator with fewer pores overall.

[0032] A solid electrolyte separator obtainable with the method according to the invention enables higher electrochemical performance, while avoiding the occurrence of short circuits.

[0033] Furthermore, it is advantageous that a much smaller amount of solvent is required compared to a known manufacturing process in which solvent is provided separately for dissolving the solid electrolyte and the binder. The amount of solvent required only for the binder to form a slurry is therefore sufficient.

[0034] Furthermore, the invention provides a solid electrolyte separator that achieves improved conductivity. The solid electrolyte separator allows for increased density, higher mechanical stability, and better control of its morphology.

[0035] Finally, by closing most of the pores with the binder, unwanted dendrite growth is avoided or significantly reduced, and a short circuit caused by dendrite growth can be prevented.

[0036] The invention also relates to the solid electrolyte separator obtainable with the method according to the invention.

[0037] The invention also relates to the use of the described solid electrolyte separator in a solid-state battery.

[0038] The invention also relates to a solid-state battery comprising the solid electrolyte separator according to the present invention. According to a preferred embodiment, the solid-state battery is in pouch cell format and is also referred to as a 'pouch cell'. Pouch cells are particularly advantageous for certain applications. They can be manufactured with small thicknesses, low weight, and application-specific dimensions, and their flat outer shape provides good heat dissipation.

[0039] For example, the solid-state battery according to the invention can be used in a smartphone, a drone, a laptop, or an electric vehicle. Preferably, the solid-state battery of the present invention is a high-power battery; that is, a solid-state battery of the present invention is used in particular in an electric vehicle (BEV, battery electric vehicle).

[0040] The invention therefore also discloses an electrically powered vehicle (BEV) with one or more solid-state batteries comprising the solid electrolyte separator according to the invention.

[0041] The solid-state battery of the present invention can be an anode-free solid-state battery. Furthermore, the solid-state battery can be a secondary battery that can be repeatedly charged and discharged. Primary batteries can only be discharged once and cannot be recharged afterward. Secondary batteries, also known as accumulators, are rechargeable.

[0042] The present invention is explained in more detail with reference to the following embodiment, wherein the accompanying figures are drawn schematically and not to scale, so that no assumptions can be made about exact geometric values ​​in relation to the original size. The figures of this disclosure form part of the description and constitute a portion thereof, with the embodiment shown illustrating the present invention without limiting the invention thereto.

[0043] This shows: Fig. 1a to 1e: a schematically simplified representation of a manufacturing process for a solid electrolyte separator from the prior art; and Fig. 2a to 2c: a schematically simplified representation of a manufacturing process for a solid electrolyte separator according to an embodiment of the invention.

[0044] The Fig. Items 1a to 1e have already been described.

[0045] In Fig. 2a A solid electrolyte 20 is provided in solid form, i.e., solvent-free, according to step (1). A mixture of several solid electrolytes may also be present.

[0046] In Fig. Figure 2b shows the solid electrolyte 20 already compressed according to step (2) of the method according to the invention. The compression can be carried out in a known manner, for example by a calendering process. Open pores 25a are formed.

[0047] Fig. Figure 2c illustrates the infiltration of a previously compressed solid electrolyte 20 with a binder 30 provided in liquid form in step (3) according to step (4) of the process. The binder 30 can be a binder mixture. The binder 30 is used in liquid form, for example, dissolved or dispersed in one or more solvents. Fig.In step 2c, the open pores 25a of the compressed solid electrolyte 20 are already filled with binder 30, resulting in closed pores 25b. Infiltration into the open pores 25a is achieved, for example, by applying the liquid binder 30 to the surface of the solid electrolyte 20 or by immersing the solid electrolyte 20 in the liquid binder 30. Subsequently, in step (5), the binder is allowed to set, i.e., solidify. This is achieved, for example, by hardening and / or drying the binder. For example, a solvent can be evaporated or vaporized, possibly using a suitable temperature and / or pressure. Thus, the solid electrolyte separator 40 is obtained in step (6). QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited non-patent literature

[0000] Nathalie Riphaus et al.: "Slurry-Based Processing of Solid Electrolytes: A Comparative Binder Study" in Journal of The Electrochemical Society, 165 (16) A3993-A3999 (2018) [DOI: 10.1149 / 2.0961816jes

[0008] Yong-Gun Lee et al.: “High-energy long-cycling all-solid-state lithiummetal batteries enabled by silver-carbon composite anodes” in Nature energy, online publication on March 9, 2020; pages 1 to 10; https: / / doi.org / 10.1038 / s41560-020-0575-z

[0009]

Claims

[1] Method for producing a solid electrolyte separator (40) comprising the steps: (1) Providing a solvent-free solid electrolyte (20) in solid form; (2) Pressing the solid electrolyte (20); (3) Providing a binder (30) in liquid form; (4) Allow the solid electrolyte to infiltrate with the binder in liquid form from step (3); (5) Allow the binder to set (30); and (6) Obtaining a solid electrolyte separator (40). [2] Method according to claim 1, characterized by , that the compression of the solid electrolyte (20) in step (2) is carried out using a calendering process. [3] Method according to claim 1 or 2, characterized by, that the solid electrolyte (20) is selected from the group consisting of solid polymer electrolytes, solid oxide electrolytes, solid sulfide electrolytes, solid halide electrolytes and closo borate solid electrolytes or a mixture thereof. [4] Method according to any one of claims 1 to 3, characterized by that the binder (30) is used in step (3) as a liquid or dissolved or dispersed in one or more solvents (10). [5] Method according to any one of claims 1 to 4, characterized by , that the binder (30) is selected from the group consisting of polysiloxane, polyalkylene glycol, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyisobutene (PIB), poly(methyl methacrylate) (PMMA), polychlorotrifluoroethylene (PTFE), styrene-butadiene rubber (SBR), poly(acrylonitrile butadiene), hydrogenated nitrile butadiene rubber (HNBR), poly(ethylene vinyl acetate) (PEVA), tetrafluoroethylene-hexafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer (ETFE resin), vinylidene fluoride-pentafluoropropylene copolymer, Propylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer (ECTFE), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene copolymer,Ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, ethylene-methyl acrylate copolymer, ethylene-methyl methacrylate copolymer or mixtures thereof; the binder (30) is preferably selected from polysiloxane, polyalkylene glycol, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyisobutene (PIB), poly(methyl methacrylate) (PMMA), polychlorotrifluoroethylene (PTFE), styrene-butadiene rubber (SBR), poly(acrylonitrile butadiene), hydrogenated nitrile butadiene rubber (HNBR), poly(ethylene vinyl acetate) (PEVA) or mixtures thereof. [6] Method according to any one of claims 1 to 5, characterized by , that a non-polar aprotic solvent (10) is used as the solvent for the binder (30), in particular a hydrocarbon selected from the group consisting of hexane, heptane, octane, nonane, decane, decalin, dichloroethane, toluene, xylene, tetrahydrofuran and methylene chloride or mixtures thereof. [7] Method according to any one of claims 1 to 6, characterized by , that the infiltration of the solid electrolyte (20) with a binder (30) in liquid form is carried out: - by applying the liquid binder (30) to the surface of the compressed solid electrolyte (20) and allowing the liquid binder (30) to penetrate the pores (25a) of the solid electrolyte (20) remaining after compression in order to completely fill them; or - by immersing the solid electrolyte (20) in the liquid binder (30) and allowing the liquid binder (30) to penetrate the pores (25a) of the solid electrolyte (20) that remain after compression, in order to fill them completely. [8] Solid electrolyte separator (40) obtainable by the method according to any one of claims 1 to 7. [9] Use of the solid electrolyte separator according to claim 8 in a solid-state battery. [10] Solid-state battery comprising the solid electrolyte separator (40) according to claim 8, characterized by that the solid-state battery is a secondary battery. [11] Solid-state battery according to claim 10, characterized by that the solid-state battery is in pouch cell format.

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