A negative electrode sheet for a solid-state battery, a method of manufacturing the same, and a battery

Abstract

The application provides a negative electrode sheet for a solid-state battery, a preparation method of the negative electrode sheet and a battery, and the negative electrode sheet for the solid-state battery comprises graphite, an electrolyte, a binder and an additive; the additive is lithium fluoride; the electrolyte comprises a sulfide electrolyte and / or an oxide electrolyte; the mass ratio of the graphite to the electrolyte, the binder and the additive is (50-90):(10-50):(0.5-5):(0.5-2); and the additive is coated on at least part of the surface of the graphite. The negative electrode sheet provided by the application can effectively improve the rate performance of a lithium ion battery.

Description

Technical Field

[0001] This invention relates to a negative electrode sheet for solid-state batteries, and more particularly to a negative electrode sheet for solid-state batteries, its preparation method, and the battery thereof, belonging to the field of lithium-ion battery technology. Background Technology

[0002] With the rapid development of the electric vehicle industry, people's requirements for driving range and safety performance are constantly increasing, making the development of high-energy-density and high-safety power batteries imperative. All-solid-state batteries, because they do not use flammable organic electrolytes, have become a key focus in the development of next-generation high-safety power batteries.

[0003] In existing technologies, compared with negative electrode active materials such as metallic lithium and lithium-indium alloy, graphite has been widely used as a negative electrode active material in the field of all-solid-state batteries due to its advantages of low cost, good conductivity, stable chemical properties, high specific capacity and low charge-discharge platform.

[0004] However, in the process of preparing all-solid-state ion batteries, the contact between the graphite anode sheet and the solid electrolyte is only point contact or line contact, which is not conducive to the transfer of lithium ions inside the graphite anode and limits the rate performance of the graphite anode active material in solid-state batteries.

[0005] Therefore, how to improve the rate performance of lithium-ion batteries is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] This invention provides a negative electrode for solid-state batteries to improve the rate performance and other electrochemical properties of the batteries.

[0007] The present invention provides a battery comprising the above-mentioned negative electrode sheet for solid-state batteries, which has advantages such as good rate performance.

[0008] This invention provides a negative electrode sheet for solid-state batteries, comprising graphite, electrolyte, binder, and additives; the additives include lithium fluoride; the electrolyte includes sulfide electrolyte and / or oxide electrolyte;

[0009] The mass ratio of the graphite to the electrolyte, the binder, and the additive is (50-90):(10-50):(0.5-5):(0.5-2); the additive coats at least a portion of the surface of the graphite.

[0010] The negative electrode for solid-state batteries as described above, wherein the sulfide electrolyte comprises Li6PS5Cl, Li3PS4, and Li7PS5Cl. 11 Li 10 GeP2S 12 Li 5.5 PS4.5 Cl 1.5 Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 At least one of them.

[0011] The negative electrode for solid-state batteries as described above, wherein the initial coulombic efficiency of the half-cell including the negative electrode for solid-state batteries is not less than 94%.

[0012] The present invention also provides a method for preparing a negative electrode sheet for a solid-state battery, comprising the following steps:

[0013] 1) Lithium fluoride and binder are respectively mixed with their corresponding organic solvents to prepare lithium fluoride solution and binder solution, and then the lithium fluoride solution and binder solution are mixed evenly to obtain lithium fluoride suspension solution.

[0014] 2) The lithium fluoride suspension is added to an active material system including graphite and electrolyte, and mixed evenly to obtain a negative electrode slurry;

[0015] 3) The negative electrode slurry is coated on the surface of the negative electrode current collector and dried to obtain the negative electrode sheet for solid-state batteries.

[0016] In the method for preparing the negative electrode sheet for solid-state batteries as described above, the molar concentration of the lithium fluoride solution is 0.05–0.2 mol / L.

[0017] In the method for preparing a negative electrode sheet for a solid-state battery as described above, the viscosity of the negative electrode slurry is controlled to be 100–1500 mPa·s.

[0018] In the method for preparing a negative electrode sheet for solid-state batteries as described above, the solid content of the negative electrode slurry is 50% to 65%.

[0019] The present invention also provides a battery comprising a negative electrode sheet for a solid-state battery as described above.

[0020] The negative electrode sheet for solid-state batteries provided by this invention uses graphite as the negative electrode active material and conductive agent. This not only limits the selection of additives and electrolytes, but also limits the mass ratio between the various components in the negative electrode sheet, and controls the coating form of additives and negative electrode active materials, thereby improving the stability of the negative electrode sheet, increasing the ionic conductivity of the negative electrode sheet, and maintaining the efficient lithium ion insertion / extraction capability during battery charging and discharging. As a result, the battery including this electrode sheet exhibits excellent rate performance.

[0021] In the method for preparing a negative electrode sheet for solid-state batteries provided by the present invention, an additive solution and a binder solution are prepared separately, and the additive solution and the binder solution are mixed evenly to obtain an additive suspension. This solution blending method is beneficial to improving the dispersibility of lithium fluoride in the negative electrode sheet, and in particular, it can avoid the electrolyte from reacting negatively with the organic solvent during the preparation of the negative electrode sheet, thereby obtaining a battery with high rate performance.

[0022] The battery provided by this invention is prepared based on the negative electrode sheet for solid-state batteries as described above, and has good electrochemical performance such as good rate performance. Attached Figure Description

[0023] Figure 1 This is a graph showing the first charge-discharge curve of the battery prepared in Example 1 of the present invention;

[0024] Figure 2 This is a graph showing the first charge-discharge curve of the battery prepared in Comparative Example 1 of the present invention.

[0025] Figure 3 The diagram shows the rate capability and cycle performance of the battery prepared in Example 1 of this invention.

[0026] Figure 4 The diagram shows the rate capability and cycle performance of the battery prepared in Comparative Example 1 of this invention.

[0027] Figure 5 This is a SEM image of the negative electrode sheet for solid-state batteries prepared in Example 1 of the present invention.

[0028] Figure 6 This is an EDS image of the negative electrode sheet for solid-state batteries prepared in Example 1 of the present invention. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0030] This invention provides a negative electrode sheet for solid-state batteries, comprising graphite, electrolyte, binder, and additives; the additives include lithium fluoride; the electrolyte includes sulfide electrolyte and / or oxide electrolyte.

[0031] The mass ratio of graphite to electrolyte, binder and additive is (50-90):(10-50):(0.5-5):(0.5-2); the additive is coated on at least part of the surface of graphite.

[0032] The negative electrode sheet generally consists mainly of active material, electrolyte, conductive agent, and binder. The active material can be divided into two main categories: metal alloys such as lithium metal and lithium-indium alloys, and carbon materials such as graphite. Compared to metal alloys, graphite has advantages such as low cost, stable chemical properties, high specific capacity, and a lower charge-discharge platform. Therefore, this invention uses graphite as the active material of the negative electrode sheet to prepare an all-solid-state battery with excellent electrochemical performance. In addition, graphite also has high conductivity; therefore, in this invention, graphite is also used as a conductive agent, thereby reducing the production cost of the battery.

[0033] To further improve lithium-ion transport efficiency, the negative electrode of this invention also includes an electrolyte, which includes a sulfide electrolyte and / or an oxide electrolyte. Furthermore, a sulfide electrolyte is selected because it possesses advantages such as high room-temperature ionic conductivity, good mechanical ductility, and good interfacial contact with the electrode, thus contributing to further improvement in the battery's electrochemical performance.

[0034] The negative electrode sheet of this invention, prepared by adding specific additives and matching graphite, electrolyte, binder, and additives in a specific mass ratio, and controlling the coating form of the additives with the negative electrode active material, yields a negative electrode sheet with high chemical stability and good lithium-ion transport performance, thereby enabling the battery to exhibit excellent rate performance. The inventors analyzed this principle and believe the reason may be that, on the one hand, adding lithium fluoride and mixing graphite, electrolyte, binder, and lithium fluoride in a specific mass ratio can improve the overall stability of the negative electrode sheet, especially the interfacial stability, allowing for more sufficient contact between lithium fluoride and the active material in the negative electrode sheet, extending the lifespan of each component in the negative electrode sheet, and maintaining the lithium conductivity of the electrolyte, thus enabling the battery to exhibit excellent rate performance; on the other hand, coating the graphite with additives on at least a portion of its surface (through...) Figure 5 and Figure 6 The comparison shows that fluorine is distributed on the surface of the negative electrode, indicating that lithium fluoride is coated on at least part of the graphite surface, allowing lithium fluoride and graphite to come into full contact and form a coating structure with lithium fluoride as the shell and graphite as the core. This coating structure can further reduce the contact between the electrolyte and the active material, reduce the probability of negative reactions between the electrolyte and the active material, and thus improve the rate performance of the battery.

[0035] In addition, the addition of lithium fluoride is beneficial to the formation of a SEI film with better performance, which can passivate the negative electrode, reduce the resistance to lithium ion transport, thereby enhancing the lithium conduction capability of the negative electrode, and thus reducing the growth of lithium dendrites during charging and discharging, thereby improving the first coulombic efficiency of the battery.

[0036] In one specific embodiment, the sulfide electrolyte includes Li6PS5Cl, Li3PS4, and Li7PS5Cl. 11 Li 10 GeP2S 12 Li 5.5 PS 4.5 Cl 1.5 Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 At least one of the following. Further, the sulfide electrolyte is preferably Li6PS5Cl or Li 5.5 PS 4.5 Cl 1.5 These two sulfide electrolytes have better chemical stability and superior lithium stability compared to other sulfide electrolytes, thus greatly improving the electrochemical performance of the battery.

[0037] In one specific embodiment, the initial coulombic efficiency of the half-cell including the negative electrode for a solid-state battery is not less than 94%. Specifically, in this invention, the negative electrode is used as both the positive electrode and the reference electrode, a lithium indium alloy is used as the negative electrode, and Li6PS5Cl is used as the electrolyte to assemble a coin cell half-cell. A charge-discharge tester is used to perform a charge-discharge test under 0.1C discharge / 0.1C charge conditions, and the initial coulombic efficiency of this half-cell is not less than 94%. Therefore, according to the solution provided by the present invention, after the negative electrode sheet is applied to a lithium-ion battery, the synergistic effect of graphite, sulfide electrolyte, binder and lithium fluoride in a specific mass ratio results in excellent initial coulombic efficiency performance of the battery. For example, when the mass ratio of graphite, electrolyte, binder and lithium fluoride in the negative electrode sheet is (50-90):(10-50):(0.5-5):(0.5-2), the initial coulombic efficiency can be achieved by further limiting the mass ratio of each component; for example, the initial coulombic efficiency can be achieved by uniformly coating the entire surface of graphite with lithium fluoride; for example, the initial coulombic efficiency can be achieved by using a special sulfide electrolyte as the electrolyte.

[0038] The present invention also provides a method for preparing a negative electrode sheet for a solid-state battery, comprising the following steps:

[0039] 1) Mix lithium fluoride and binder with their respective organic solvents to prepare lithium fluoride solution and binder solution, and then mix the lithium fluoride solution and binder solution evenly to obtain lithium fluoride suspension solution.

[0040] 2) Add the lithium fluoride suspension to the active material system including graphite and electrolyte, mix evenly, and obtain the negative electrode slurry;

[0041] 3) The negative electrode slurry is coated on the surface of the negative electrode current collector and dried to obtain the negative electrode sheet for solid-state batteries.

[0042] Specifically, in step 1), the lithium fluoride solution in this invention is prepared by dispersing lithium fluoride in an organic solvent such as dibutyl ether and then ultrasonically treating it. This invention does not limit the specific parameters of the ultrasonic treatment; for example, it can be performed at an ultrasonic power of 10 to 1000 kW for 30 min to 3 h.

[0043] The adhesive solution is a solution obtained by uniformly mixing an adhesive with an organic solvent. The adhesive and matching organic solvent provided by this invention are conventional materials in the art. Those skilled in the art can select the adhesive and organic solvent as needed. For example, the adhesive can be styrene-butadiene rubber or nitrile rubber. In one specific embodiment, the mass percentage of the adhesive in the adhesive solution is 0.5% to 10%, that is, 0.5 to 10g of adhesive is included in every 100g of adhesive solution, specifically selected from the range of 0.5%, 2%, 4%, 6%, 8%, 10%, or any combination thereof.

[0044] By mixing the aforementioned lithium fluoride solution with the adhesive solution, the lithium fluoride solution and the adhesive solution are fused together and uniformly dispersed, thereby obtaining a lithium fluoride suspension. This invention is not limited to the mixing method; it can be any means that can achieve uniform mixing, such as ultrasonic treatment, magnetic stirring, or mechanical stirring.

[0045] In step 2), the active material, which includes graphite and electrolyte, is prepared by mixing graphite and electrolyte powders thoroughly and evenly. This invention does not impose many limitations on the mixing method; for example, the active material can be obtained by mixing graphite and electrolyte and then manually grinding them.

[0046] The lithium fluoride suspension described above is added to the active material comprising graphite and electrolyte, and after thorough mixing, a negative electrode slurry is obtained. This invention does not limit the specific parameters of the stirring process; for example, stirring can be performed at a stirring speed of 300–1000 r / min for 24–48 h.

[0047] By combining lithium fluoride solution with binder solution using a blending method, lithium fluoride is uniformly dispersed in the binder solution. This suspended binder solution is then mixed with active materials. This process facilitates uniform dispersion of lithium fluoride and binder in the negative electrode slurry, allowing for full interaction between lithium fluoride and the active materials. It also makes it easier for lithium fluoride to coat the graphite surface, reducing the contact between the electrolyte and organic solvents during the negative electrode preparation process. This inhibits negative reactions between the electrolyte and organic solvents, preventing decomposition and deactivation, thus resulting in a battery with superior rate performance.

[0048] In step 3), the aforementioned negative electrode slurry is uniformly coated onto the surface of the negative electrode current collector using a coating method. Then, the negative electrode current collector with the negative electrode slurry is dried to obtain the negative electrode sheet. This invention does not impose excessive limitations on the selection of the negative electrode current collector; for example, the negative electrode current collector can be any type of copper foil. The drying process in this invention is a conventional electrode sheet preparation method in the art, and those skilled in the art can select appropriate preparation methods as needed.

[0049] In one specific embodiment, the molar concentration of the lithium fluoride solution is 0.05–0.2 mol / L, meaning that each liter of solution contains 0.05–0.2 mol of lithium fluoride, specifically selected from a range of 0.05 mol / L, 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, or any combination thereof. Within this molar concentration range, the negative electrode slurry prepared according to the method of this application exhibits higher uniformity, and the dispersion of lithium fluoride in the negative electrode slurry is better. This allows lithium fluoride to better enhance the interfacial stability of the negative electrode sheet, reduce lithium-ion transport resistance, and thus obtain a battery with superior rate performance and initial coulombic efficiency.

[0050] In one specific embodiment, the viscosity of the negative electrode slurry is controlled to be 100–1500 mPa·s. It is worth noting that a suspension is prepared by a solvent blending method and then stirred uniformly with the active material to obtain the negative electrode slurry. The viscosity of the slurry is controlled by adjusting the stirring rate and stirring time. By controlling the viscosity of the negative electrode slurry within this range, graphite at least partially coated with lithium fluoride can be prepared, thereby improving the hydrophobic properties of the negative electrode and passivating the graphite, further improving the rate performance of the battery.

[0051] In one specific embodiment, the solid content of the negative electrode slurry is 50% to 65%, meaning that every 100 grams of negative electrode slurry includes 50g to 65g of solid material composed of graphite, electrolyte, binder, and lithium fluoride. Specifically, it can be selected from a range of 50%, 55%, 60%, 65%, or any combination thereof. With a solid content within this range, a negative electrode sheet with a convenient preparation process, uniform thickness, and smooth surface can be prepared. This avoids problems such as poor lithium-ion transport caused by unstable surface structure of the negative electrode sheet, resulting in a battery with excellent rate performance. Furthermore, it facilitates the preparation and production of the negative electrode sheet and reduces waste of the negative electrode slurry.

[0052] The present invention also provides a battery comprising the aforementioned negative electrode for a solid-state battery. Based on the negative electrode for a solid-state battery provided by the present invention, the battery provided by the present invention exhibits better initial coulombic efficiency and rate performance.

[0053] In one specific embodiment, the battery is an all-solid-state battery, which, in addition to the negative electrode sheet for solid-state batteries provided by this invention, also includes a positive electrode sheet and an inorganic solid-state electrolyte layer, specifically:

[0054] The positive electrode includes a positive current collector and a positive active material layer disposed on the surface of the positive current collector. The positive active material layer includes a positive active material, a conductive agent, and a binder. The positive current collector is typically aluminum foil, and the positive active material is selected from lithium transition metal oxides, such as LiCoO2, LiMn2O4, LiMnO2, Li2MnO4, LiFePO4, and Li... 1+a Mn 1-x M x O2, LiCo 1-x M x O2, LiFe 1-x M x PO4, Li2Mn 1-x O4, M is selected from one or more of Ni, Co, Mn, Al, Cr, Mg, Zr, Mo, V, Ti, B, and F, 0≤a<0.2, 0≤x<1.

[0055] The inorganic solid electrolyte layer comprises an inorganic solid electrolyte and a binder; the inorganic solid electrolyte in the inorganic solid electrolyte layer is the same as the sulfide solid electrolyte in the negative electrode. This invention does not have special requirements for the binder; any binder conventional in the art is acceptable. The ratio of the inorganic solid electrolyte to the binder is well known to those skilled in the art, and this invention does not impose any special limitations.

[0056] The negative electrode sheet for solid-state batteries provided by the present invention will be described below with reference to specific embodiments:

[0057] Example 1

[0058] The negative electrode sheet for solid-state batteries provided in this embodiment includes graphite, electrolyte, binder and additives. The electrolyte includes Li6PS5Cl sulfide electrolyte, the binder includes styrene-butadiene rubber (SBR), and the additive is lithium fluoride (LiF). The mass ratio of graphite to Li6PS5Cl, SBR and LiF is 70:30:2:1.

[0059] The method for preparing the negative electrode sheet for solid-state batteries in this embodiment includes:

[0060] 1) Disperse LiF in dibutyl ether, stir evenly and then ultrasonically disperse to obtain a LiF solution with a molar concentration of 0.1 mol / L; dissolve SBR in isobutanol to obtain an SBR gel; mix the LiF solution and the SBR gel thoroughly to obtain a LiF suspension.

[0061] 2) Graphite and Li6PS5Cl sulfide electrolyte are mixed and ground, and then LiF suspension is stirred and mixed with it to obtain a uniformly mixed negative electrode slurry with a solid content of 61% and a viscosity of 630 mPa·s.

[0062] 3) The negative electrode slurry is coated onto a clean copper foil with a scraper, and then dried at 60°C to obtain the negative electrode sheet.

[0063] Example 2

[0064] The preparation method in this embodiment is basically the same as that in Example 1, and the specific parameters are shown in Table 1.

[0065] Example 3

[0066] The preparation method in this embodiment is basically the same as that in Example 1, and the specific parameters are shown in Table 1.

[0067] Example 4

[0068] The preparation method in this embodiment is basically the same as that in Example 1, and the specific parameters are shown in Table 1.

[0069] Example 5

[0070] The preparation method in this embodiment is basically the same as that in Example 1, and the specific parameters are shown in Table 1.

[0071] Example 6

[0072] The preparation method in this embodiment is basically the same as that in Example 1, and the specific parameters are shown in Table 1.

[0073] Example 7

[0074] The preparation method in this embodiment is basically the same as that in Example 1, and the specific parameters are shown in Table 1.

[0075] Example 8

[0076] The preparation method in this embodiment is basically the same as that in Example 1, and the specific parameters are shown in Table 1.

[0077] Example 9

[0078] The negative electrode sheet for solid-state batteries provided in this embodiment includes graphite, electrolyte, binder and additives. The electrolyte includes Li6PS5Cl sulfide electrolyte, the binder includes styrene-butadiene rubber (SBR), and the additives include lithium fluoride (LiF). The mass ratio of graphite to Li6PS5Cl, SBR and LiF is 70:30:2:1.

[0079] The method for preparing the negative electrode sheet for solid-state batteries in this embodiment includes:

[0080] 1) Graphite and Li6PS5Cl sulfide electrolyte are mixed and ground, and then LiF and SBR are mixed with it. The solid components are dispersed in dibutyl ether, stirred evenly and then ultrasonically dispersed to obtain a negative electrode slurry. The solid content of the negative electrode slurry is 60% and the viscosity is 855 mPa·s.

[0081] 2) The negative electrode slurry is coated onto a clean copper foil with a scraper, and then dried at 60°C to obtain the negative electrode sheet.

[0082] Comparative Example 1

[0083] The negative electrode sheet for solid-state batteries provided in this comparative example includes graphite, an electrolyte, and a binder. The electrolyte comprises a Li6PS5Cl sulfide electrolyte, and the binder comprises styrene-butadiene rubber (SBR). The mass ratio of graphite to Li6PS5Cl and SBR is 70:30:2. In the following preparation process, the SBR solution has a mass percentage of 5%; the solid content of the negative electrode slurry is 61%, and the viscosity is 832 mPa·s.

[0084] The preparation method of the negative electrode sheet in this comparative example includes: mixing and grinding graphite with Li6PS5Cl sulfide electrolyte, then stirring and mixing SBR adhesive with it to obtain a uniformly mixed negative electrode slurry; coating the negative electrode slurry onto a clean copper foil with a scraper, and then drying it at 60°C to obtain the negative electrode sheet.

[0085] Comparative Example 2

[0086] The preparation method in this embodiment is basically the same as that in Example 1, and the specific parameters are shown in Table 1.

[0087] Comparative Example 3

[0088] The negative electrode sheet for solid-state batteries provided in this comparative example includes metal fluoride InF3 and binder PVDF, and the mass ratio of InF3 to PVDF is 95:5.

[0089] The method for preparing the negative electrode sheet for solid-state batteries in this comparative example includes: adding InF3 and PVDF to NMP solvent to prepare a slurry, and coating the slurry onto stainless steel to form a coating to prepare the negative electrode sheet.

[0090] Comparative Example 4

[0091] The negative electrode sheet for solid-state batteries provided in this comparative example includes graphite, electrolyte Li6PS5Cl, metal fluoride InF3, and binder PVDF, and the mass ratio of graphite, Li6PS5Cl, PVDF and InF3 is 70:30:2:1.

[0092] The method for preparing the negative electrode sheet for solid-state batteries in this comparative example includes: adding graphite, Li6PS5Cl, InF3 and PVDF to NMP solvent to prepare a slurry, and coating the slurry onto stainless steel to form a coating to prepare the negative electrode sheet.

[0093] Table 1 shows the preparation parameters of the negative electrode sheets for solid-state batteries provided in Examples 1-9 and Comparative Examples 1-4.

[0094]

[0095] Using the negative electrode sheets for solid-state batteries provided in Examples 1-9 and Comparative Examples 1-4 as counter electrodes and reference electrodes, and combining them with lithium indium alloy as the negative electrode and Li6PS5Cl sulfide electrolyte, half-cells were prepared.

[0096] The all-solid-state batteries prepared in Examples 1-9 and Comparative Examples 1-4 were subjected to the following battery performance tests, and the test methods are as follows:

[0097] First Coulombic Efficiency Test: The prepared battery was placed in a normal environment at 25°C and charged and discharged using a Newway tester. Constant current charge and discharge measurements were performed in the range of -0.62V to 2V, with a charge and discharge rate of 0.1C. The charge and discharge performance and first coulombic efficiency of the battery were tested. The first week's charge specific capacity was recorded as C1, and the first week's discharge specific capacity was recorded as C2. The first coulombic efficiency η1 = C1 / C2*100%, as shown in Table 2.

[0098] Rate performance testing: The prepared batteries were placed in a standard environment at 25℃ and charged / discharged using a Newway tester. Constant current charge / discharge measurements were performed within the range of -0.62V to 2V, with the charging rate increasing sequentially to test the battery's rate performance. Charge / discharge cycles were performed at 0.1C discharge / 0.1C charge, 0.1C discharge / 0.2C charge, 0.1C discharge / 0.5C charge, and 0.1C discharge / 1C charge, with the capacities recorded as C1, C3, C4, and C5, respectively. Finally, a charge / discharge cycle test was performed at 0.1C discharge / 0.5C charge. The capacity retention rate η2 after 50 cycles was the capacity C at the 50th cycle. 50 The percentage of the first week's 0.5C capacity C4, i.e., η2 = C 50 / C4*100%, see Table 2.

[0099] The test results are shown in Table 2.

[0100] Table 2. Performance test results of the batteries prepared in Examples 1-9 and Comparative Examples 1-4

[0101]

[0102] Table 2 shows that, based on the comparison between Examples 1-9 and Comparative Examples 1-4, the first charge-discharge curves of the batteries prepared in Examples 1 and Comparative Example 1 are shown in Table 2. Figure 1 and Figure 2 The rate and cycle performance diagrams of the batteries prepared in Example 1 and Comparative Example 1 are shown in Figure 1. Figure 3 and Figure 4 A comparison of the samples revealed that a mass ratio of graphite to electrolyte, binder, and LiF of (50-90):(10-50):(0.5-5):(0.5-2) helps improve the initial coulombic efficiency, rate performance, and cycle performance of the battery. Examples 1, 6, and 7 show that a lithium fluoride molar concentration of 0.05–0.2 mol / L is beneficial for improving the initial coulombic efficiency, rate performance, and cycle performance. Examples 1 and 8 show that a negative electrode slurry viscosity of 100–1500 mPa·s allows lithium fluoride to coat at least a portion of the graphite surface, improving the interfacial stability of the negative electrode and enhancing both the rate performance and cycle performance of the battery. A comparison of Examples 1, 6, and 9 shows that the negative electrode prepared by the method of this invention for solid-state batteries improves the initial coulombic efficiency, rate performance, and cycle performance of the battery. In summary, the negative electrode sheet for solid-state batteries and its preparation method provided by this invention are beneficial for improving the initial coulombic efficiency, rate performance, and cycle performance of batteries.

[0103] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A negative electrode sheet for solid-state batteries, characterized in that, It includes graphite, electrolyte, binder, and additives, which function as both negative electrode active material and conductive agent; the additives include lithium fluoride; the electrolyte includes sulfide electrolyte; The mass ratio of the graphite to the electrolyte, the binder, and the additive is (50-90):(10-50):(0.5-5):(0.5-2); the additive coats at least a portion of the surface of the graphite. The negative electrode sheet for solid-state batteries is obtained by coating a negative electrode slurry onto the surface of a negative electrode current collector and then drying it. The negative electrode slurry is obtained by mixing a lithium fluoride suspension into an active material system including graphite and electrolyte. The lithium fluoride suspension is obtained by mixing a lithium fluoride solution with a binder solution. The lithium fluoride solution and the binder solution are obtained by mixing the lithium fluoride and the binder with their respective organic solvents.

2. The negative electrode sheet for solid-state batteries according to claim 1, characterized in that, The sulfide electrolyte includes Li6PS5Cl, Li3PS4, and Li7PS5Cl. 11 Li 10 GeP2S 12 Li 5.5 PS 4.5 Cl 1.5 Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 At least one of them.

3. The negative electrode sheet for solid-state batteries according to claim 1 or 2, characterized in that, The initial coulombic efficiency of the half-cell including the negative electrode for the solid-state battery is not less than 94%.

4. A method for preparing a negative electrode sheet for a solid-state battery according to any one of claims 1-3, characterized in that, Includes the following steps: 1) Lithium fluoride and binder are mixed with their respective organic solvents to prepare lithium fluoride solution and binder solution, and then the lithium fluoride solution and binder solution are mixed evenly to obtain lithium fluoride suspension solution. 2) The lithium fluoride suspension is added to an active material system including graphite and electrolyte, and mixed evenly to obtain a negative electrode slurry; 3) The negative electrode slurry is coated on the surface of the negative electrode current collector and dried to obtain the negative electrode sheet for solid-state batteries.

5. The method for preparing a negative electrode sheet for a solid-state battery according to claim 4, characterized in that, The molar concentration of the lithium fluoride solution is 0.05~0.2 mol / L.

6. The method for preparing a negative electrode sheet for a solid-state battery according to claim 4, characterized in that, The viscosity of the negative electrode slurry is controlled to be 100~1500 mPa•s.

7. The method for preparing a negative electrode sheet for a solid-state battery according to claim 4, characterized in that, The solid content of the negative electrode slurry is 50%~65%.

8. A battery, characterized in that, Includes the negative electrode sheet for solid-state batteries as described in any one of claims 1-3.

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