Powder of a solid electrolyte for producing a separator for a battery cell

Abstract

The invention relates to a powder (10) of a solid electrolyte (F) for producing a separator (S) for a battery cell, in particular a solid electrolyte battery cell (1), wherein the powder (10) of the solid electrolyte (F) is coated with a protective agent (12) having a boiling point of at most 400°C and / or a melting point of at least 20°C and / or at most 100°C. The invention also relates to a method for producing a green film (G) as a semi-finished product of a separator (S) for a battery cell (1), wherein such a powder (10) of a solid electrolyte (F) coated with a protective agent (12) is used, and wherein green film (G) is produced using this coated powder (10) of the solid electrolyte (F).

Description

[0001] Description

[0002] Powder of a solid electrolyte for the production of a separator for a battery cell

[0003] The invention relates to a powder of a solid electrolyte for the production of a separator for a battery cell, as well as a method for producing a semi-finished product of a corresponding separator for a battery cell.

[0004] In the production of rechargeable batteries (accumulators), one of the main challenges is to achieve the highest possible energy density, i.e. the highest possible storage capacity per unit volume (in kWh / dm 3This is particularly important for applications in electric vehicles, where, due to the limited space for battery cells, this space must be used optimally in terms of storage capacity to achieve the longest possible range. However, this is also fundamentally important for portable / mobile battery applications.

[0005] A promising approach here is the use of so-called lithium (Li)-ion batteries. In these batteries, the anode is negatively charged and the cathode is positively charged in each individual battery cell. This charge can supply an electrical load with electrical current by transferring an excess of electrons to the load as electricity. An electrolyte is arranged between the anode and cathode, which enables the movement of positive Li ions as charge carriers from the anode to the cathode (when charging the battery, this movement is reversed). To prevent a short circuit, a separator is arranged between the anode and the cathode, which is permeable to the charge carriers (in this case, the Li ions).

[0006] While Li-ion batteries with liquid electrolytes in the individual cells are already widely used, these have the obvious disadvantage that if the battery casing is damaged, the electrolyte can leak out, potentially causing irreparable damage to the affected battery cells. Furthermore, in such a case, environmental impact from the electrolyte cannot be ruled out. For this reason, there is increasing focus on batteries or battery cells with solid-state electrolytes. In these batteries, the separator is preferably formed directly by a crystal II structure of an electrolyte, in which the movement of the Li ions through defects in the crystal lattice is still sufficiently possible.Battery cells with solid-state electrolytes can also be constructed more compactly than those with liquid electrolytes, since the anode, separator, and cathode can be arranged in thin layers on top of each other. There are also hybrid battery cells that, in addition to the metallic lithium of the anode, also use a liquid or gel electrolyte on the cathode side. These also use a separator with a crystal structure as described above.

[0007] The separator plays a key role here. The materials typically used for such separators are sensitive to moisture and oxygen during storage and therefore oxidize easily.

[0008] The object of the invention is to provide a material for producing a separator for a solid electrolyte battery cell that is better protected against environmental influences, in particular moisture and carbon dioxide. Furthermore, the object of the invention is to provide a method for producing a semi-finished product of a separator for a battery cell, in which the solid electrolyte material used is as well protected as possible against environmental influences, in particular moisture and carbon dioxide.

[0009] The first-mentioned object is achieved according to the invention by a powder of a solid electrolyte for the production of a separator for a battery cell, in particular a solid electrolyte battery cell, wherein the powder of the solid electrolyte is coated with a protective agent which has a boiling point of at most 400°C, preferably at most 350°C, particularly preferably at most 300°C and / or a melting point of at least 20°C, preferably at least 30°C and / or at most 100°C, preferably at most 70°C, particularly preferably at most 50°C. Advantageous and partly inventive embodiments are the subject of the dependent claims and the following description.

[0010] The second object is achieved according to the invention by a method for producing a green film as a semi-finished product of a separator for a battery cell, wherein the above-described solid electrolyte powder coated with a protective agent is used to produce the green film. The method according to the invention for producing a green film as a semi-finished product of a separator for a battery cell shares the advantages of the solid electrolyte powder according to the invention for producing a separator for a battery cell. The advantages stated for the solid electrolyte powder and for its further developments can be applied analogously to the method for producing the green film and its further developments, and vice versa.

[0011] The separator, for the production of which the powder is designed and configured, is intended to separate an anode from a cathode in a battery cell, in particular a solid electrolyte battery cell or a hybrid battery cell, in such a way that a short circuit between the anode and the cathode is prevented and, at the same time, the transport of charge carriers, in particular lithium ions as charge carriers, is enabled. The separator is preferably intended for arrangement between the anode and the cathode, wherein further layers can be applied between the separator and the anode or cathode to improve conductivity. Accordingly, both the above-described powder of the solid electrolyte and the said method for producing the green film as a semi-finished product of the separator are designed to ensure these required properties in the separator.

[0012] The protective agent used here is, in particular, an organic protective agent, preferably with a melting or boiling point in the aforementioned temperature ranges. Ethylene carbonate is used as a protective agent in particular.

[0013] The powder of a solid electrolyte forms a starting material for the separator manufacturing process, with the green film being produced in an intermediate step of said manufacturing process. The powder preferably has a grain size of 0.04 μm to 100 μm, particularly preferably 0.4 μm to 10 μm. Monomodal or multimodal distributions can be used. The solid electrolyte is in particular an inorganic solid electrolyte, in particular a sulfidic solid electrolyte and / or an oxide solid electrolyte. Particular preference is given to using an inorganic solid electrolyte with a NASICON structure, in particular LATP, LAPG, or LAGTP, an inorganic solid electrolyte with a garnet structure, in particular LLZO, or an inorganic solid electrolyte with a LISICON structure.An inorganic solid electrolyte with a perovskite or anti-perovskite structure is also conceivable. For the process for producing the green film, the powder is provided coated with the protective agent. In this case, the coating of the solid electrolyte powder with the protective agent can be carried out as a preparatory step prior to the process. However, the coating of the solid electrolyte powder can also be carried out separately from the production of the separator, so that the powder is stored in the coated state (and, if necessary, transported to a separator production facility).

[0014] For the process for producing the green film, the solid electrolyte powder prepared as described can be dispersed in a solvent. The solvent must be specifically matched to the protective agent. An organic solvent is preferably used. This causes the protective agent to dissolve in the solvent, and after the solvent has evaporated, it can be resolidified, crystallized, or settled.

[0015] After the dispersion process in the solvent, the solid electrolyte powder prepared and further processed as described is applied to a carrier, preferably in a thin layer of 1 μm to 500 μm, preferably 10 μm to 250 μm, particularly preferably 20 μm to 150 μm. This creates the green film, which can be further processed into the finished separator by further annealing and / or sintering.

[0016] The further processing of the solid electrolyte powder into the green film can preferably take place before the solvent has evaporated (or completely evaporated). In this case, the powder is dispersed in the solvent-protective agent solution and is applied to the substrate in this state. After the solvent has completely evaporated, the protective agent also redeposits onto the solid electrolyte powder (at least on the free surface) and can also act as a binder or additional "adhesive." This advantageously eliminates the need for an additional binder in the manufacturing process.

[0017] In an alternative embodiment of the process for producing the green film, the powder of the solid electrolyte coated with the protective agent is heated above the melting point of the protective agent, and the powder of the solid electrolyte with the molten protective agent is further processed into the green film, for example by spraying onto a carrier or pouring and subsequent rolling of the viscous mass.

[0018] When the green foil is baked out, preferably during a sintering process, to complete the separator, the protective agent is evaporated due to its boiling point, so that the finished separator no longer contains any significant amounts of the protective agent with which the solid electrolyte powder was coated.

[0019] Typically, a separator for a solid electrolyte battery is manufactured by first mixing the solid electrolyte powder with a (usually organic) binder and a solvent. A carrier material is coated with the dispersion (or the described slurry), and the solution is dried, creating the green film. This is then baked to evaporate the binder and then sintered to form the finished separator. However, the solid electrolytes commonly used for this purpose are significantly instable toward atmospheric humidity and, in particular, toward carbon dioxide. Reaction with air components (particularly with H2O and / or CO2) can reduce the permeability for charge carriers (e.g., lithium ions) of the finished battery cell and thus the conductivity, thereby reducing the performance of the finished separator membrane in the solid electrolyte battery cell.

[0020] One way to better protect the solid electrolyte powder against these atmospheric constituents would be to process and, preferably, store the powder in a protective atmosphere, minimizing contact with the atmospheric constituents that are problematic for the powder. However, processing the solid electrolyte powder in a protective atmosphere is particularly costly, which is why this solution would not be sufficiently efficient. It should be noted that the costly processing in a protective atmosphere would be necessary even if storing the solid electrolyte powder in a protective atmosphere were technically less demanding and therefore more cost-effective.

[0021] The proposed solid electrolyte powder for the production of a separator for a battery cell and the proposed method for producing a green film as a semi-finished product of a separator for a solid electrolyte battery cell solve this problem by coating the solid electrolyte powder with the protective agent or by appropriately preparing the powder coated in this way. Coating the powder with the protective agent protects the solid electrolyte powder from environmental influences, particularly from the aforementioned atmospheric constituents. The powder can be coated with the protective agent according to the preparation method and then either directly processed into a separator or stored in the coated state for an extended period.In the case of Li-ions as charge carriers, the separator manufactured as described also enables the in-situ formation of a Li anode in the finished solid electrolyte battery cell during the first charging cycle. This requires specific surface properties of the separator to allow efficient Li deposition. These surface properties can be ensured by the separator manufactured according to the process described above.

[0022] In the green film manufacturing process, the solvent is preferably evaporated after the solid electrolyte powder is applied to the carrier to form the green film. Thus, the solvent can facilitate further processing of the powder into the green film. In particular, the solvent can already be partially evaporated before the powder is applied to the carrier, so that a partially moist mass of powder, preservative, and solvent is applied to the carrier, and the remaining solvent is then evaporated.

[0023] According to the invention, a protective agent is used with a boiling point of at most 400°C, preferably at most 350°C, particularly preferably at most 300°C and / or a melting point of at least 20°C, preferably at least 30°C and / or at most 100°C, preferably at most 70°C, particularly preferably at most 50°C. This choice of protective agent allows the protective agent to be heated only slightly above normal room temperatures for coating the powder, and to be in a solid state at said room temperatures (and accordingly the coating adheres to the powder). The not too high boiling point leads to the protective agent essentially completely evaporating during baking before the actual sintering process begins, which is advantageous for the structural integrity of the separator.

[0024] An organic compound, particularly preferably ethylene carbonate (EC), is used as the preservative. EC is already widely used in the manufacture of battery cells for accumulators, so its material properties (and possible interactions with other materials and, where appropriate, systems) are already sufficiently known.

[0025] The solvent used is preferably a polar, non-protic solvent. The solvent can be, in particular, an ether, an organic carbonate, an acetate, a ketone such as acetonitrile, chloroform, ethyl acetate, ethyl methyl ether, or dimethyl carbonate. Preferably, a solvent is used that is also used for the liquid electrolytes of a lithium-ion battery, such as an organic carbonate (e.g., dimethyl carbonate). This is particularly advantageous for an organic preservative such as EC.

[0026] The invention further mentions a method for providing a powder of a solid electrolyte for producing a separator for a battery cell. According to the method, the powder of the solid electrolyte is coated with a protective agent, wherein a protective agent having a boiling point of at most 400°C, preferably at most 350°C, particularly preferably at most 300°C and / or a melting point of at least 20°C, preferably at least 30°C and / or at most 100°C, preferably at most 70°C, particularly preferably at most 50°C is used.

[0027] Preferably, the protective agent is melted, whereby the powder of the solid electrolyte for the coating is wetted with the molten protective agent, and the protective agent is subsequently cured, in particular crystallizing. This allows a largely seamless coating of the individual powder grains with the protective agent to be achieved. In an alternative embodiment, the protective agent is dispersed in a solvent, the powder of the solid electrolyte is added to the solvent with the protective agent dispersed therein, and the solvent is then evaporated.

[0028] The invention further mentions a method for producing a separator for a battery cell, wherein a green film is produced as a semi-finished product of the separator according to the method described above, wherein said green film is heated to complete the separator, and thereby the protective agent is caused to evaporate.

[0029] The method according to the invention for producing the separator and the method according to the invention for providing the powder of the solid electrolyte share the advantages of the corresponding powder of the solid electrolyte according to the invention and of the method according to the invention for producing the green film, wherein the advantages stated for said methods or said powder and for their further developments can be transferred to one another in a corresponding manner.

[0030] An embodiment of the invention is explained in more detail below with reference to the accompanying drawings, each of which shows schematically:

[0031] Fig. 1 shows a block diagram of a solid electrolyte battery cell, and Fig. 2 shows a block diagram of a method for producing a separator for the solid electrolyte battery cell according to Fig. 1.

[0032] Corresponding parts and sizes are provided with the same reference numerals in all figures.

[0033] Figure 1 shows a schematic block diagram of a solid electrolyte battery cell 1 of a solid electrolyte accumulator (not shown in detail). The layer thicknesses are not drawn to scale. An anode A (solid line), to which a voltage tap 2 for a negative voltage (-) is attached, comprises, during normal operation of the accumulator, a layer 4 (dashed line) of metallic Li. A cathode K (solid line), to which a voltage tap 6 for a positive voltage (+) is attached, comprises a layer 8 (dashed line) of a crystalline material suitable for storing Li ions. This material can in particular be a positive electrode active material, such as lithium nickel manganese cobalt oxide (LNMC), lithium nickel manganese oxide (LNMO), LiCoPO4, LiNiPO4, LiFePO4 or lithium cobalt oxide (LOO).When manufacturing the cathode, an aluminum foil is preferably used as a current collector.

[0034] A separator S is arranged between the anode A and the cathode K. The separator is to be manufactured according to the present invention using a method to be described in more detail below. The separator S comprises a solid electrolyte material, such as LLZO or LATP, and serves both to spatially separate the anode A and the cathode K to prevent short circuits and as an electrolyte for charge transport. Additional layers (not shown) can be arranged between the anode A and the separator S and / or between the cathode K and the separator S to improve contact and thus the conductivity of the Li ions (e.g., layers made of polymers or polymer-ceramic mixtures or similar). The layer 4 made of metallic Li can comprise the entire anode A or only a portion adjacent to the separator (or to one of the additional layers made of polymer-ceramic or similar adjacent to the separator).Likewise, layer 8 may comprise the entire cathode K, or only a part adjacent to the separator (or to one of the said additional layers adjacent to the separator).

[0035] Typically, to produce the separator, a solid electrolyte powder is mixed with a (usually organic) binder and a solvent, and a substrate is (thinly) coated with the mixture, thus creating the so-called green film. As the green film layer dries, the solvent evaporates. The green film is then sintered, with the binder first being heated out, and then (at higher temperatures) the actual sintering process begins. The end product of the sintering process is the finished separator.

[0036] However, in order to better protect the powder of the solid electrolyte from environmental influences such as moisture, oxidation, and carbonization, the invention proposes an alternative manufacturing process for the separator S according to Figure 1. This process is schematically illustrated in a block diagram in Figure 2.

[0037] In a step S10, a powder 10 of a solid electrolyte F coated with EC is first provided, which, as already described in relation to Figure 1, can be provided in particular by LLZO or LATP. EC serves as a protective agent 12 for the powder against the aforementioned environmental influences. In alternative embodiments of the method (not shown), another protective agent can also be used, which particularly preferably has a melting point between 35°C and 50°C and a boiling point below 300°C.

[0038] In a next step S20, the EC-coated powder 10 is dispersed in a preferably organic solvent L. The EC dissolves in the solvent. In an (optional) step S25, the dispersion of the solvent L, the powder 10, and the EC is brought to the viscosity required for the subsequent processing steps, which may include partially evaporating the solvent L from said solution (or partially drying the dissolved powder 10), so that a residually moist mass 14 of powder 10 wetted with the solvent L remains, with the EC still dissolved. It should be noted that the residually moist mass 14 is still sufficiently liquid to ensure the said solution of the EC in the solvent and the subsequent further processing.

[0039] In a next step S30, the said residually moist mass, which comprises the powder 10 of the solid electrolyte F, is applied to a carrier material 16, thereby producing the green film G as a semi-finished product 18 of the separator. During or after this step, in a step S35, the remaining solvent L is evaporated from the green film G. As a result, the EC, which was previously dissolved in the solvent L, crystallizes again on the surface of the grains of the powder (10), thereby further protecting the solid electrolyte (F), and serves as an additional binder in the green film G, thus eliminating the need for a separate binder during production.

[0040] Finally, in a process step S40, the green film G is sintered to form the finished separator S. In a sub-step S41, the EC, which has a boiling point of 248°C, is first annealed from the green film G, so that the actual sintering process only begins in a subsequent sub-step S42 at even higher temperatures.

[0041] The provision of the EC-coated powder 10 of the solid electrolyte F can, in turn, comprise further sub-steps. For example, in a first sub-step S11, the EC can be melted by gently heating it above ambient temperature (melting point 36°C), in a sub-step S12, the powder 10 of the solid electrolyte F can be wetted with the molten EC, and in a further sub-step S13, the EC can be cured again by cooling to ambient temperature, so that the powder 10 is coated with a coating of EC. The powder 10 coated in this way can then be stored accordingly (care must be taken to ensure that the melting point of EC is not exceeded during storage) and also transported (for example, to a production facility for the separator S, which can be spatially separate from the location where the coated powder 10 is provided).

[0042] In an alternative embodiment of the process, not shown in Fig. 2, no solvent is used to produce the green film G. Instead, the EC-coated solid electrolyte powder is heated above the melting point of EC, and the resulting liquid mass of EC and the solid electrolyte powder is processed into a thin layer and then cooled. During this process, the EC crystallizes and solidifies around the created mold structure of the solid electrolyte, and the EC-protected green film is obtained. The green film can then be further processed into the finished separator as described in Fig. 2.

[0043] Although the invention has been illustrated and described in detail by the preferred embodiment, the invention is not limited by the disclosed examples, and other variations may be derived therefrom by those skilled in the art without departing from the scope of the invention.

[0044] 1 solid electrolyte battery cell

[0045] 2 voltage tap

[0046] 4 layer (made of metallic Li)

[0047] 6 Voltage tap

[0048] 8 layer (made of crystalline material)

[0049] 10 powder (of the solid electrolyte)

[0050] 12 protective agents

[0051] 14 residual moisture mass

[0052] 16 Carrier material

[0053] 18 semi-finished products

[0054] A Anode

[0055] EC ethylene carbonate

[0056] F Solid electrolyte

[0057] G Green film

[0058] K cathode

[0059] L Solvent

[0060] 5 Separator

Claims

Patent claims. Powder (10) of a solid electrolyte (F) for producing a separator (S) for a battery cell (1), wherein the powder (10) of the solid electrolyte (F) is coated with a protective agent (12) having a boiling point of at most 400°C and / or a melting point of at least 20°C and / or at most 100°C. Powder of a solid electrolyte (F) according to claim 1, wherein the protective agent (12) is an organic compound, in particular ethylene carbonate. Powder (10) of a solid electrolyte (F) according to claim 1 or claim 2, wherein the solid electrolyte (F) is an inorganic solid electrolyte, in particular / or a sulfidic solid electrolyte and / or an oxidic solid electrolyte.A method for providing a powder (10) of a solid electrolyte (F) for producing a separator (S) for a solid electrolyte battery cell (1), wherein the powder (10) of the solid electrolyte (F) is coated with a protective agent (12), wherein a protective agent (12) with a boiling point of at most 400°C and / or a melting point of at least 20°C and / or at most 100°C is used. The method according to claim 4, wherein the protective agent (12) is melted, wherein the powder (10) of the solid electrolyte (10) is wetted with the molten protective agent (12) for the coating, and wherein the protective agent (12) is subsequently solidified. The method according to claim 4, wherein the protective agent (12) is dispersed in a solvent (L). wherein the powder (10) of the solid electrolyte (10) is added to the solvent (L) with the protective agent (12) dispersed therein, and wherein the solvent (L) is subsequently evaporated. Method according to one of claims 4 to 6, wherein ethylene carbonate (EC) is used as the protective agent (12), and / or wherein an inorganic solid electrolyte and / or a sulfidic solid electrolyte and / or an oxidic solid electrolyte is used as the solid electrolyte (F). Method for producing a green film (G) as a semi-finished product of a separator (S) for a battery cell (1), wherein a powder (10) of a solid electrolyte (F) according to one of claims 1 to 3 coated with a protective agent (12) is used, and wherein the green film (G) is produced using this coated powder (10) of the solid electrolyte (F).The method according to claim 8, wherein the powder (10) of the solid electrolyte (F) coated with the protective agent (12) is dispersed in a solvent (L), and wherein the powder (10) of the solid electrolyte (F) coated with the protective agent (12) is applied to a carrier (16) after the process of dispersing in the solvent (L), thus producing the green film (G). The method according to claim 8, wherein the powder (10) of the solid electrolyte (F) coated with the protective agent (12) is heated above the melting point of the protective agent (S), and wherein the powder (10) of the solid electrolyte (F) is further processed with the molten protective agent (S) to form the green film.Method for producing a separator (S) for a battery cell (1), wherein a green film (G) is produced as a semi-finished product of the separator (S) according to a method according to one of claims 8 to 10, and wherein said green film (G) is baked to complete the separator (S), and thereby the protective agent (S) is caused to evaporate.

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