Method for preparing a solid electrolyte

Abstract

The present invention relates to a method for preparing a solid electrolyte, comprising the steps of: (a) mixing a solid electrolyte selected from among sulfides with at least a sulfur-containing agent; (b) adding the mixture obtained at the end of step (a) to an organic solvent; and (c) recovering the solid electrolyte obtained.

Description

[Technical field]

[0001] The present invention relates to the field of all-solid-state batteries. More particularly, the present invention relates to a specific method for preparing a solid electrolyte.

[0002] The present invention also relates to a method for preparing an all-solid-state battery cell. [Background technology]

[0003] Conventionally, an all-solid-state battery comprises one or more positive electrodes, one or more negative electrodes, a solid electrolyte forming a separator, an anode current collector and a cathode current collector.

[0004] The performance qualities of a battery depend on the transport properties of ions and electrons. In the case of solid-state batteries, ion transport at the electrode scale takes place through a network formed by the solid electrolyte. For such batteries to be in working condition, this network is percolated to form ion-conducting paths through the entire volume of the electrode, ensuring the transport of ions to and from all active material particles.

[0005] All-solid-state batteries use different types of materials as solid electrolytes, for example polymers such as poly(ethylene oxide) (PEO), oxides such as garnets, perovskites, Nasicon, or even sulfides (LGPS, LPSCL, etc.).

[0006] The use of all-solid-state batteries is generally limited to laboratory scale through the use of very small cells (button cells, small cells with a capacity of less than 2 Ah).

[0007] The production of solid-state batteries is a major challenge for all players in the field, but many problems remain to be solved before the technology can be developed on an industrial scale, as players in the field face various technological obstacles.

[0008] One problem is the high cost of the solid electrolyte materials, in particular, since certain operating conditions must be observed.

[0009] For example, the synthesis of oxide-based solid electrolyte materials must be carried out at high temperatures, and the forming of oxide- and sulfide-based solid electrolytes is difficult.

[0010] Moreover, the ionic conductivity of solid electrolyte materials is generally low.

[0011] Particularly for sulfide-based solid electrolyte materials, current processing involves a "dry" preparation process that does not involve a dissolution step. The use of these solid electrolyte materials via a "dry" process has many disadvantages.

[0012] Therefore, it is difficult to reduce the size of the solid electrolyte particles and therefore to reduce and / or eliminate porosity in the resulting electrode.

[0013] Furthermore, it is difficult to shape the solid electrolyte that forms the separator, which means that not only is it impossible to obtain thin films on the order of 10 to 25 μm in thickness, but it is also difficult to obtain uniform electrodes.

[0014] Due to these various disadvantages, the electrochemical performance quality is not satisfactory.

[0015] Furthermore, attempts have been made to use sulfide-based solid electrolyte materials in solution. Unfortunately, degradation of the chemical structure of the solid electrolyte and a decrease in ionic conductivity are observed.

[0016] There is therefore a need to develop new methods of preparing solid electrolytes, including the use of solid electrolytes chosen from the sulfides, that make it possible to overcome the above-mentioned disadvantages.

[0017] It has been surprisingly found that a method of preparing a solid electrolyte comprising the use of a solid electrolyte selected from the sulfides allows for improved ionic conductivity and a non-degrading chemical structure of said solid electrolyte.

[0018] Description of the Invention A subject of the present invention is therefore a method for preparing a solid electrolyte comprising the following steps: a) mixing a solid electrolyte selected from sulfides with at least a sulfur-containing agent; b) adding the mixture obtained at the end of step a) to an organic solvent; c) recovering the obtained solid electrolyte Includes.

[0019] Another subject of the invention is a method for the preparation of a battery cell, comprising the preparation of a solid electrolyte according to the method of the invention.

[0020] Other advantages and features of the present invention will become more clearly apparent by consideration of the detailed description and accompanying drawings. [Brief description of the drawings]

[0021] [Figure 1] FIG. 1 shows the diffractogram of argyrogenite involved in the implementation of the comparative method. [Diagram 2] FIG. 2 shows the diffraction diagram of the solid electrolyte involved in the implementation of the method according to the invention. [Diagram 3] FIG. 2 shows the diffraction diagram of the solid electrolyte involved in the implementation of the method according to the invention. [Figure 4] FIG. 1 is a graph showing the ionic conductivity of solid electrolytes obtained at the end of various methods. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] It is defined that the expression "from to" as used in this specification should be understood to include each of the limits referred to.

[0023] As indicated above, according to step a) of the method according to the invention, a solid electrolyte selected from sulfides is mixed with an agent containing at least sulfur.

[0024] Advantageously, the solid electrolyte chosen from the sulfides has the formula: A m+ 12-n-x B n+ Ch 2- 6-x X - x [In the formula, - A stands for Cu, Ag or Li, B stands for Ge, Si, Al or P, Ch stands for O, S, Se or Te, preferably Ch stands for S, and X stands for Cl, Br or I; - m equals 1; - n is equal to 3, 4 or 5; - x ranges from 0 to 2]; Li 4-y Ge 1-y P y S 4-y [where y ranges from 0 to 1]; Li 11-z M 2-z P 1+z S 12 [wherein M refers to Ge, Sn or Si, and z varies from 0 to 1.75]; Preferably Li 7-t P.S. 6-t X, where X denotes Cl, Br or I and t varies from 0 to 2, more preferentially Li6PS5X, where X denotes Cl, Br or I, and even more preferentially Li6PS5Cl.

[0025] According to a preferred embodiment, the at least sulfur-containing agent is selected from P2S5, Li4P2S6, S8, Li3PS4, Li4P2S7 and mixtures thereof, preferably P2S5, Li4P2S7 and mixtures thereof.

[0026] Advantageously, the content of at least one agent comprising sulfur ranges from 1% to 30% by weight, preferably from 5% to 15% by weight and more preferentially from 8% to 12% by weight, relative to the total weight of the mixture comprising the solid electrolyte chosen from sulfides and the at least one agent comprising sulfur.

[0027] As indicated above, according to step b) of the process according to the invention, the mixture obtained at the end of step a) is added to an organic solvent.

[0028] Preferably, the organic solvent is selected from alcoholic solvents, ethers such as tetrahydrofuran (THF), aromatic solvents such as toluene, and nitriles such as acetonitrile. Preferably, the organic solvent is chosen from alcoholic solvents, more preferentially ethanol.

[0029] Preferably, the method according to the invention may further comprise a step d) of drying the solid electrolyte obtained at the end of step c) at a temperature in the range of from 40°C to 550°C, preferably from 40°C to 150°C.

[0030] Another subject of the present invention is a method for preparing a battery cell comprising a negative electrode, a positive electrode and a separator, comprising the following steps: - preparing a solid electrolyte by the method of the invention as described above to form a separator; - producing said negative electrode and said positive electrode, both present in the form of an ink; - coating the negative electrode ink and the positive electrode ink onto a separator and then drying the coating; The method includes:

[0031] Preferably, the coating is dried at a temperature in the range of 40°C to 150°C.

[0032] The invention is illustrated in a non-limiting manner by the following examples. EXAMPLES

[0033] Example 1: Comparison Method The germanite of formula Li6PS5Cl is used.

[0034] A diffraction pattern of the pristine material is generated, as shown in Figure 1 (Material 1a). The characteristic peaks of arginite can be identified in the diffraction pattern.

[0035] According to the first method, to obtain material 1b, argonite is added to ethanol and then dried at 40° C. Then, a diffraction pattern of material 1b is generated, as shown in FIG.

[0036] It is clearly evident that the structure of argonite is destroyed after dissolving in ethanol. The appearance of several peaks indicates that the material is decomposed into several phases.

[0037] According to the second method, to obtain material 1c, arginite is added to ethanol and then dried at 100° C. Then, the diffraction pattern of material 1c is generated, as shown in FIG.

[0038] It is again clearly evident that the structure of arginite is destroyed after dissolving in ethanol.

[0039] Example 1 shows that such materials are unstable in organic solvents. Therefore, during the preparation of battery cells, especially solid-state battery cells, such materials cannot be used in the electrode coating process, because the electrode coating process necessarily involves dissolving in organic solvents.

[0040] Example 2: Method according to the invention The germanite of formula Li6PS5Cl is used.

[0041] It is mixed with a material of formula P2S5. More specifically, 10% by weight of the material of formula P2S5 is used, relative to the total weight of the mixture including the argonite of formula Li6PS5Cl and the material of formula P2S5.

[0042] The resulting mixture is then added to ethanol.

[0043] Generate a diffraction diagram of the mixture of materials as shown in Figure 2 (Material 2a).

[0044] According to the first method, to obtain material 2b, the mixture is added to ethanol and then dried at 40° C. Then, the diffraction pattern of material 2b is generated, as shown in FIG.

[0045] It is clearly evident that the structure of the characterized materials is not degraded after dissolution in ethanol.

[0046] According to the second method, to obtain material 2c, the mixture is added to ethanol and then dried at 100° C. Then, the diffraction pattern of material 2c is generated, as shown in FIG.

[0047] It is again clearly evident that the structure of the characterized material is not degraded after dissolution in ethanol.

[0048] Example 2 clearly shows the beneficial effect of the presence of the material of formula P2S5 on the chemical stability of arginine. Arginine is chemically stable in organic solvents thanks to the presence of the material of formula P2S5. Therefore, arginine can be used in the coating process of electrodes during the preparation of battery cells, especially all-solid-state battery cells.

[0049] Example 3: Method according to the invention The germanite of formula Li6PS5Cl is used.

[0050] It is mixed with a material of formula Li4P2S7. More specifically, 10% by weight of the material of formula Li4P2S7 is used, relative to the total weight of the mixture including the argyrophile of formula Li6PS5Cl and the material of formula Li4P2S7.

[0051] The resulting mixture is then added to ethanol.

[0052] Generate a diffraction diagram of the mixture of materials as shown in Figure 3 (Material 3a).

[0053] According to the first method, to obtain material 3b, the mixture is added to ethanol and then dried at 40° C. Then, the diffraction pattern of material 3b is generated, as shown in FIG.

[0054] It is clearly evident that the structure of the characterized materials is not degraded after dissolving in ethanol.

[0055] According to the second method, to obtain material 3c, the mixture is added to ethanol and then dried at 100° C. Then, the diffraction pattern of material 3c is generated, as shown in FIG.

[0056] It is again clearly evident that the structure of the characterized material is not degraded after dissolution in ethanol.

[0057] Example 3 clearly shows the beneficial effect of the presence of a material of formula Li4P2S7 on the chemical stability of arginine. Arginine is chemically stable in organic solvents thanks to the presence of a material of formula Li4P2S7. Therefore, arginine can be used in the coating process of electrodes during the preparation of battery cells, especially all-solid-state battery cells.

[0058] Ionic Conductivity The ionic conductivity was measured at 25° C. for each of the materials 1a through 3c. All of the ionic conductivity measurements can be found in FIG.

[0059] Thus, a significant decrease in the ionic conductivity values ​​for materials 1b and 1c can be observed compared to material 1a.

[0060] These measurements therefore indicate that during the preparation of battery cells, in particular all-solid-state battery cells, this material cannot be used in the electrode coating process, a process which necessarily involves dissolving it in an organic solvent.

[0061] This is because the final ionic conductivity value of this solid electrolyte in the electrode composition is very low, which makes it impossible to obtain good electrochemical performance quality of the battery cell and battery.

[0062] On the contrary, for materials 2a to 2c, it is quite noticeable that, even if a decrease in the ionic conductivity values ​​for materials 2b and 2c could be observed, it is more moderate compared to material 2a.

[0063] In any case, the ionic conductivity of material 2b is much greater than that of material 1b. Similarly, the ionic conductivity of material 2c is much greater than that of material 1c.

[0064] This clearly demonstrates the beneficial effect of the presence of materials of formula P2S5 on the ionic conductivity of arginite.

[0065] Similar observations can be made for materials 3a through 3c.

[0066] It is quite noticeable that, even though a decrease in the ionic conductivity values ​​for materials 3b and 3c could be observed in comparison with material 3a, it is more moderate.

[0067] In any case, the ionic conductivity of material 3b is much greater than that of material 1b. Similarly, the ionic conductivity of material 3c is much greater than that of material 1c.

[0068] This clearly demonstrates the beneficial effect of the presence of material of formula Li4P2S7 on the ionic conductivity of argyrogenite.

Claims

1. A method for preparing a solid electrolyte comprising the steps of: a) mixing a solid electrolyte selected from sulfides with at least a sulfur-containing agent; b) adding the mixture obtained at the end of step a) to an organic solvent; c) recovering the resulting solid electrolyte A method comprising:

2. The solid electrolyte selected from sulfides has the formula: A ｍ＋ １２－ｎ－ｘ B ｎ＋ Ch ２－ ６－ｘ X － ｘ [Where, A refers to Cu, Ag or Li, B refers to Ge, Si, Al or P, Ch refers to O, S, Se or Te, preferably Ch refers to S, and X refers to Cl, Br or I; m is equal to 1; n is equal to 3, 4 or 5; x ranges from 0 to 2]; Li ４－ｙ Ge １－ｙ P ｙ S ４－ｙ [wherein y ranges from 0 to 1]; Li １１－ｚ M ２－ｚ P １＋ｚ S １２ where M refers to Ge, Sn or Si and z varies from 0 to 1.75; Preferably Li ７－ｔ P.S. ６－ｔ X, where X denotes Cl, Br or I and t varies from 0 to 2, more preferentially Li ６ P.S. ５ X, where X denotes Cl, Br or I, and even more preferentially Li ６ P.S. ５ 2. The method according to claim 1, characterized in that the material is selected from Cl.

3. The agent containing at least sulfur is P ２ S ５ , Li ４ P ２ S ６ , S ８ , Li ３ P.S. ４ , Li ４ P ２ S ７ and mixtures thereof.

4. 2. The method according to claim 1, characterized in that the content of said agent comprising at least sulfur ranges from 1% to 30% by weight, preferably from 5% to 15% by weight and more preferentially from 8% to 12% by weight, relative to the total weight of the mixture comprising a solid electrolyte chosen from sulfides and said agent comprising at least sulfur.

5. 2. The process according to claim 1, characterized in that the organic solvent is selected from alcoholic solvents, ethers, aromatic solvents and nitriles, preferably alcoholic solvents, more preferentially ethanol.

6. 2. A method according to claim 1, characterized in that it comprises a step d) of drying the solid electrolyte obtained at the end of step c) at a temperature ranging from 40° C. to 550° C., preferably from 40° C. to 150° C.

7. 1. A method for preparing a battery cell comprising a negative electrode, a positive electrode, and a separator, comprising the steps of: preparing a solid electrolyte by the method of any one of claims 1 to 6 and forming a separator; producing said negative electrode and said positive electrode, both present in the form of an ink; Coating the negative electrode ink and the positive electrode ink onto the separator and then drying the coating. A method comprising:

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