Surface-modified graphite negative electrode material, preparation method therefor, and use thereof

Abstract

The present application relates to the technical field of solid-state batteries, and discloses a surface-modified graphite negative electrode material, a preparation method therefor, and a use thereof. The surface-modified graphite negative electrode material comprises a graphite core, an inner coating layer, and an outer coating layer, the inner coating layer coats the surface of the graphite core, and the outer coating layer coats the surface of the inner coating layer; the inner coating layer is made of a LiX-doped binary sulfide electrolyte, and the outer coating layer is made of a ternary sulfide electrolyte; X is a halogen element; and the mass ratio of the graphite core to the inner coating layer to the outer coating layer is (85-99.5):(0.25-5):(0.25-10). In the present application, coating modification is performed on the graphite negative electrode material, so that the probability of side reactions between the graphite negative electrode material and an electrolyte material is reduced, thereby improving the ionic conductivity and the electronic conductivity of the negative electrode material, and improving the rate performance of the negative electrode material and a solid-state battery.

Description

Surface-modified graphite negative electrode material, preparation method and application thereof

[0001] This application claims priority to Chinese patent application 2024108914796 with a filing date of July 4, 2024. This application incorporates the entirety of the aforementioned Chinese patent application. TECHNICAL FIELD

[0002] The present application relates to the technical field of solid-state batteries, in particular to a surface-modified graphite negative electrode material, a preparation method and application thereof. BACKGROUND

[0003] Graphite has become an excellent negative electrode material due to its low cost, low lithium potential and high reversible lithium intercalation capacity, and it has great application prospects in the field of all-solid-state batteries. However, graphite negative electrodes still have the following problems that hinder their further industrial application in sulfide all-solid-state batteries:

[0004] 1. The lithium intercalation platform potential of graphite negative electrode is low, which is 0.1 V (vs. Li / Li + ), which easily leads to side reactions at the interface between the two, i.e., the sulfide electrolyte is partially reduced to obtain a side reaction product, and the side reaction product has poor ion and electron conductivity;

[0005] 2. The contact between the graphite end face and the sulfide electrolyte is random. If the contact area between the graphite end face and the electrolyte becomes smaller, it will lead to poor rate performance of the negative electrode. In addition, the low ion conductivity of the electrolyte coating layer is also not conducive to improving the rate performance.

[0006] In order to inhibit the side reaction between the sulfide electrolyte and the graphite negative electrode, it has been shown that when preparing a composite negative electrode containing graphite and electrolyte, a new electrolyte obtained by doping LiI into a binary sulfide electrolyte can replace the current thiophosphate-type electrolyte to inhibit the side reaction. Although this method inhibits the occurrence of side reactions, the ion conductivity of the LiI-doped binary sulfide electrolyte (1 mS / cm) is significantly lower than that of the thiophosphate-type electrolyte (> 5 mS / cm), which is not conducive to improving the rate performance. SUMMARY

[0007] The main purpose of the present application is to provide a surface-modified graphite negative electrode material, a preparation method and application thereof, to solve the problems of the existing technology that the graphite negative electrode is easy to generate harmful side reaction products with the sulfide electrolyte, the ion conductivity of the composite negative electrode is low, and the rate performance is poor.

[0008] In order to achieve the above-mentioned purpose, according to a first aspect of the present application, a surface-modified graphite negative electrode material is provided, which comprises a graphite inner core, an inner coating layer and an outer coating layer, the inner coating layer is located on the surface of the graphite inner core, and the outer coating layer is located on the surface of the inner coating layer; the material of the inner coating layer is a binary sulfide electrolyte doped with LiX, and the material of the outer coating layer is a ternary sulfide electrolyte; wherein X is a halogen element; in addition, the mass ratio of the graphite inner core, the inner coating layer and the outer coating layer is (85-99.5):(0.25-5):(0.25-10).

[0009] Further, in the material of the inner coating layer, the molar ratio of LiX to the binary sulfide electrolyte is 1:(0.5-5).

[0010] Further, the mass ratio of the graphite inner core, the inner coating layer and the outer coating layer is (95-97):(1-4):(1-4).

[0011] Further, in the material of the inner coating layer, the molar ratio of LiX to the binary sulfide electrolyte is 1:(1-3).

[0012] Further, in the surface-modified graphite negative electrode material, X is one of Cl, Br and I.

[0013] Further, the binary sulfide electrolyte is at least one of Li3PS4, Li7P3S 11 , Li4SnS4.

[0014] Further, the ternary sulfide electrolyte is a argyrodite-type electrolyte, which is at least one of Li6PS5Cl, Li6PS5Br, Li6PS5I, Li 10 GeP2S 12 .

[0015] Further, X is I (iodine), the binary sulfide electrolyte is Li3PS4, and the ternary sulfide electrolyte is Li6PS5Cl.

[0016] According to a second aspect of the present application, a preparation method of a surface-modified graphite negative electrode material is provided, which comprises the following steps:

[0017] S1, coating a binary sulfide electrolyte doped with LiX on the surface of graphite to obtain a graphite negative electrode material with an inner coating layer;

[0018] S2, coating a ternary sulfide electrolyte on the surface of the graphite negative electrode material with the inner coating layer to obtain a surface-modified graphite negative electrode material.

[0019] Further, the coating method in S1 and S2 is at least one of a solid-phase ball milling method, a magnetron sputtering method, a liquid-phase coating method, and an atomic layer deposition (ALD) method.

[0020] Further, in S1, the coating method is a solid-phase ball milling method, specifically, graphite, lithium sulfide, phosphorus pentasulfide, and LiX are mixed, ball-milled, and then heat-treated at 180-250 DEG C in an inert atmosphere for 8-12 hours to obtain the graphite negative electrode material with an inner coating layer.

[0021] Further, in S2, the coating method is a solid-phase ball milling method, specifically, the ternary sulfide electrolyte is blended with the graphite negative electrode material with an inner coating layer, and then ball-milled to obtain the surface-modified graphite negative electrode material.

[0022] Further, in S2, the ternary sulfide electrolyte is prepared by mixing lithium sulfide, phosphorus pentasulfide, and lithium chloride in a certain proportion, and then heat-treated at 500-600 DEG C in an inert atmosphere for 8-12 hours.

[0023] Further, in S2, the D50 particle size of the ternary sulfide electrolyte is 0.5-1 microns.

[0024] According to a third aspect of the present application, a composite negative electrode material is provided, which comprises a surface-modified graphite negative electrode material and a sulfide electrolyte, wherein the mass ratio of the surface-modified graphite negative electrode material to the sulfide electrolyte is (50-100):(0-50); the surface-modified graphite negative electrode material is the surface-modified graphite negative electrode material of the first aspect of the present application or the surface-modified graphite negative electrode material prepared by the preparation method of the second aspect of the present application.

[0025] According to a fourth aspect of the present application, a full-solid-state lithium battery is also provided, which comprises the above-mentioned surface-modified graphite negative electrode material or the composite negative electrode material.

[0026] By modifying the graphite negative electrode and coating the LiX-doped binary sulfide electrolyte and ternary sulfide electrolyte on the surface of the graphite negative electrode from the inside to the outside, the problems of easy side reaction between the existing graphite negative electrode and the electrolyte, low ionic conductivity, and poor rate performance are solved. The modification method is simple, the prepared negative electrode material has good electrical performance, and is suitable for industrial application. BRIEF DESCRIPTION OF DRAWINGS

[0027] FIG. 1 is a first cycle 0.05C charge-discharge curve of a full-solid-state battery assembled with the composite negative electrode material of application example 1 and application comparative examples 1-2;

[0028] FIG. 2 is a first cycle 0.05C dQ / dV curve of a full-solid-state battery assembled with the composite negative electrode material of application comparative example 1;

[0029] Figure 3 is a dQ / dV curve of the first circle 0.05C of the full solid-state battery assembled with the composite negative electrode material of application example 1;

[0030] Figure 4 is a cycle performance test diagram of the full solid-state battery assembled with the composite negative electrode material of application example 1, application comparative example 1-2;

[0031] The following figure contains the following figure marks: 1, application example 1; 2, application comparative example 1; 3, application comparative example 2. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be described clearly and completely below. If the specific conditions are not specified in the embodiments, the conventional conditions or the conditions recommended by the manufacturer are used. If the reagents or instruments used are not specified by the manufacturer, they are all conventional products that can be purchased on the market.

[0033] The full solid-state battery uses solid electrolyte and does not contain flammable and volatile components, avoiding the safety hazards such as battery smoking and fire caused by liquid leakage, having a wider working temperature range and being safer. However, the interface impedance between the solid electrolyte and the electrode is large, the interface compatibility is poor, and the volume expansion and shrinkage of the material during the charging and discharging process easily lead to interface separation, which limits the further application of the full solid-state battery.

[0034] The application of graphite as a negative electrode material has been relatively mature. Compared with other negative electrode materials, the volume expansion rate of graphite is only 10% when it is fully embedded with lithium ions, so it is suitable for application in full solid-state batteries. Sulfide electrolyte has the advantages of wide potential window, high voltage, fast transmission rate, non-oxidation at high temperature, and non-solidification at low temperature, and has a wide application in full solid-state batteries. However, the graphite negative electrode and the high ionic conductivity sulfide electrolyte are easy to react to generate byproducts, hindering the transmission of ions.

[0035] In order to solve the above problems, in a typical embodiment of the present application, a surface modified graphite negative electrode material is provided, which comprises a graphite core, an inner coating layer and an outer coating layer. The inner coating layer is located on the surface of the graphite core, and the outer coating layer is located on the surface of the inner coating layer. The material of the inner coating layer is a binary sulfide electrolyte doped with LiX, and the material of the outer coating layer is a ternary sulfide electrolyte; wherein X is a halogen element; in addition, the mass ratio of the graphite core, the inner coating layer and the outer coating layer is (85-99.5):(0.25-5):(0.25-10).

[0036] The binary sulfide electrolyte has good chemical stability and certain ion conductivity. By coating the graphite surface with the LiX-doped binary sulfide electrolyte as the inner coating layer, the reaction between the graphite and the ternary sulfide electrolyte with high ion conductivity can be inhibited, and the interface impedance caused by the byproduct of the side reaction can be reduced. The coating of the ternary sulfide electrolyte outer coating layer on the surface of the inner coating layer can improve the lithium ion transmission rate. By the above double-layer coating, the inner coating layer is arranged between the ternary sulfide electrolyte outer coating layer and the graphite inner core, and the mass ratio of the graphite inner core, the inner coating layer and the outer coating layer is controlled, so that the generation of the byproduct is inhibited, and the rate performance of the surface-modified graphite negative electrode material is not obviously affected.

[0037] As a preferred embodiment of the present application, in the material of the inner coating layer, the mass ratio of LiX to the binary sulfide electrolyte is 1:(0.5-5).

[0038] The limitation of the mass ratio of LiX to the binary sulfide electrolyte in the material of the inner coating layer can reduce the probability of the side reaction between the graphite inner core and the sulfide electrolyte with high ion conductivity, and is beneficial to improve the ion transmission rate and the electron transmission rate.

[0039] As a preferred embodiment of the present application, the mass ratio of the graphite inner core, the inner coating layer and the outer coating layer is (95-97):(1-4):(1-4); and / or, in the material of the inner coating layer, the mass ratio of LiX to the binary sulfide electrolyte is 1:(1-3).

[0040] The above limitation of the mass ratio of LiX to the binary sulfide electrolyte is to improve the stability of the negative electrode material, and further improve the rate performance of the negative electrode material.

[0041] As a preferred embodiment of the present application, X is one of Cl, Br and I; and / or, the binary sulfide electrolyte is at least one of Li3PS4, Li7P3S 11 4 and Li4SnS4; and / or, the ternary sulfide electrolyte is a argyrodite-type electrolyte, and the argyrodite-type electrolyte is at least one of Li6PS5Cl, Li6PS5Br, Li6PS5I, Li 10 GeP2S 12 4.

[0042] Compared with other lithium halide materials, the binary sulfide electrolyte doped with LiCl, LiBr and Lil as the inner coating layer has a better effect of preventing the reaction of graphite and high ionic conductivity sulfide electrolyte, which is conducive to improving the rate performance and cycle performance of the battery. The binary sulfide electrolyte is a commonly used binary sulfide electrolyte, which has relatively high ionic conductivity and chemical stability, is easy to prepare, and is widely used in solid-state batteries; the ternary sulfide electrolyte has better ionic conductivity.

[0043] As a preferred embodiment of the present application, X is I, the binary sulfide electrolyte is Li3PS4, and the ternary sulfide electrolyte is Li6PS5Cl. The negative electrode material prepared from the above materials has the best electrical performance.

[0044] In another typical embodiment of the present application, a preparation method of a surface-modified graphite negative electrode material is provided, which comprises the following steps:

[0045] S1, coating a binary sulfide electrolyte doped with LiX on the surface of graphite to obtain a graphite negative electrode material with an inner coating layer;

[0046] S2, coating a ternary sulfide electrolyte on the surface of the graphite negative electrode material with the inner coating layer to obtain a surface-modified graphite negative electrode material;

[0047] Typically but not limitedly, the coating method in S1 and S2 is at least one of solid-phase ball milling, magnetron sputtering, liquid-phase coating and atomic layer deposition (ALD).

[0048] As a preferred embodiment of the present application, in S1, the coating method is solid-phase ball milling, which is specifically as follows: mixing graphite, lithium sulfide, phosphorus pentasulfide and LiX, ball milling, and then heat treating in an inert atmosphere at 180-250°C for 8-12h to obtain a graphite negative electrode material with an inner coating layer.

[0049] As a preferred embodiment of the present application, in S2, the coating method is solid-phase ball milling, which is specifically as follows: blending the ternary sulfide electrolyte with the graphite negative electrode material with the inner coating layer, and then ball milling to obtain a surface-modified graphite negative electrode material. The solid-phase ball milling is to put solid materials into a container, then add a certain amount of ball milling medium, and the container is rotated at the same time, so that the ball milling medium impacts, extrudes and rubs the solid materials, so that the solid materials are crushed and mixed; the solid-phase ball milling is widely used in the fields of nanomaterials, alloy powders, ceramic powders, metal abrasives and catalysts, and has the advantages of simple operation, low cost and good controllability of the reaction process.

[0050] As a preferred embodiment of the present application, in S2, the preparation method of the ternary sulfide electrolyte is: mixing lithium sulfide, diphosphorus pentasulfide and lithium chloride in proportion, and heat treating in an inert atmosphere at 500-600°C for 8-12h, with a heating rate of 5-15°C / min. The ternary sulfide electrolyte prepared by the above method has good structural stability and good ionic conductivity.

[0051] As a preferred embodiment of the present application, in S2, the D50 particle size of the ternary sulfide electrolyte is 0.5-1μm. The above limitation on the D50 particle size of the ternary sulfide electrolyte is to make the ternary sulfide electrolyte uniformly coated on the surface of the graphite negative electrode material with an inner coating layer, and to improve the ionic conductivity of the surface-modified graphite negative electrode material.

[0052] In a typical embodiment of the present application, a composite negative electrode material is provided, which comprises the above surface-modified graphite negative electrode material and a sulfide electrolyte, and the mass ratio of the surface-modified graphite negative electrode material and the sulfide electrolyte is (50-100):(0-50). The composite negative electrode material prepared by mixing the surface-modified graphite negative electrode material and the sulfide electrolyte has higher ionic conductivity, and by limiting the mass ratio of the two, the ionic conductivity can be improved without affecting the lithium ion insertion into the graphite negative electrode and the lithium ion extraction from the graphite negative electrode.

[0053] In another typical embodiment of the present application, a full-solid-state lithium battery is provided, which comprises the above surface-modified graphite negative electrode material or the above composite negative electrode material. The above full-solid-state lithium battery significantly improves the lithium ion transport capacity while suppressing the side reaction of graphite and electrolyte, and has excellent rate performance and cycle performance.

[0054] The present application will be further described in detail below in conjunction with specific examples, which should not be construed as limiting the scope of the present application.

[0055] Examples 1-5

[0056] The preparation method of the surface-modified graphite negative electrode material of the present application, examples 1-5, comprises the following steps:

[0057] S1, mixing graphite, lithium sulfide, diphosphorus pentasulfide and LiI in a molar ratio of 3:1:1, ball milling at a speed of 400r / min for 10h, and heat treating in an argon atmosphere at 200°C for 10h to obtain a graphite negative electrode material with a LiI-doped binary sulfide Li3PS4 electrolyte inner coating layer;

[0058] S2, lithium sulfide, phosphorus pentasulfide and lithium chloride were added in a ball mill in a mass ratio of 5:1:2, and ball milling was performed to obtain a uniform powder, then the powder was kept at 550℃ in an argon atmosphere for 10h, and the heating rate was 10℃ / min, to obtain a argyrodite-type electrolyte Li6PS5Cl, the argyrodite-type electrolyte was refined to a D50 particle size of 1μm, and then mixed with the graphite negative electrode with the inner coating layer, and ball milling was performed by a solid-phase ball milling method to obtain a surface-modified graphite negative electrode material with a ternary sulfide electrolyte outer coating layer on the surface of the inner coating layer.

[0059] The mass ratio of the graphite core, the inner coating layer and the outer coating layer in Examples 1-5 is shown in Table 1.

[0060] Table 1

[0061] Examples 6-9

[0062] The difference between the examples of the surface-modified graphite negative electrode material of the present application, Examples 6-9, and Example 1 is that in S1, the mass ratio of lithium sulfide, phosphorus pentasulfide and LiI is different, in Example 6, the mass ratio of lithium sulfide, phosphorus pentasulfide and LiI is 4.5:1.5:1, in Example 7, the mass ratio of lithium sulfide, phosphorus pentasulfide and LiI is 1.5:0.5:1, in Example 8, the mass ratio of lithium sulfide, phosphorus pentasulfide and LiI is 1.5:0.5:2, and in Example 9, the mass ratio of lithium sulfide, phosphorus pentasulfide and LiI is 7.5:2.5:1.

[0063] The mass ratio of lithium sulfide, phosphorus pentasulfide and LiI in the inner coating layer of Examples 6-9 is shown in Table 2.

[0064] Table 2

[0065] Comparative Example 1

[0066] A surface-modified graphite negative electrode material, which is different from Example 1 in that only a LiI-doped binary sulfide electrolyte inner coating layer is coated on the surface of the natural graphite by step S1, and the operation in step S2 is not performed, and the obtained is a surface-modified graphite negative electrode material with an inner coating layer.

[0067] Application Examples 1-9 and Application Comparative Example 1

[0068] The application examples 1-9 and the application comparative example 1 are composite negative electrode materials. The surface modified graphite negative electrode materials in the application examples 1-9 and the application comparative example 1 are mixed with the ternary sulfide electrolyte Li6PS5Cl respectively, and are mechanically ground at 300 r / min for 30 minutes to obtain the composite negative electrode materials of the application examples 1-9 and the application comparative example 1, wherein the mass ratio of the surface modified graphite negative electrode material to the ternary sulfide electrolyte is 6:4.

[0069] The application comparative example 2

[0070] The application comparative example 2 is a composite negative electrode material, and the preparation method thereof is as follows: the natural graphite is mixed with the ternary sulfide electrolyte Li6PS5Cl, and is ground to obtain the composite negative electrode material.

[0071] The application examples and the application comparative examples are prepared into half batteries in the following manner: 100 mg of Li6PS5Cl electrolyte is weighed in a PEEK with a diameter of 10 mm, is pressurized at 1 t and is kept for 1 min, then 13 mg of the composite negative electrode material is weighed on one side of the electrolyte, is pressurized at 3.6 t and is kept for 3 min, then an indium foil with a diameter of 10 mm and a thickness of 100 μm and a lithium foil with a diameter of 9 mm and a thickness of 50 μm are sequentially placed on the other side of the electrolyte as a lithium-indium negative electrode, finally the whole battery is pressurized at 2 t and is kept for 3 min, is tightly screwed to apply a test pressure of 15 NM, and then is subjected to electrochemical performance test.

[0072] The 0.05C first circle test results are shown in Table 3, and the rate performance and cycle performance test results are shown in Table 4, wherein the rate performance test steps respectively test the performance of 0.05C / 0.05C one circle, 0.1C / 0.1C three circles, 0.2C / 0.2C three circles, 0.5C / 0.5C three circles and 1C / 1C three circles.

[0073] Table 3

[0074] As shown in Table 3, the 0.05C lithium deintercalation specific capacity of the full solid-state battery prepared from the application example 1 is similar to that of the full solid-state battery prepared from the application comparative example 1, and the first efficiency is obviously higher, while the 0.05C lithium deintercalation specific capacity of the full solid-state battery prepared from the application comparative example 2 is significantly attenuated, and the first efficiency is also lower; the above test results show that the composite negative electrode material exhibits more excellent electrochemical performance after double-layer coating.

[0075] Fig. 1 is a first circle 0.05C charge-discharge curve diagram of the full solid-state battery assembled with the composite negative electrode material of the application example 1, the application comparative examples 1-2, which is the same as the above results.

[0076] Fig. 2 and Fig. 3 are dQ / dV curves of the first circle 0.05C of the full solid-state batteries assembled with the composite negative electrode material of application comparative example 1 and application example 1, respectively, and it can be seen that there are three groups of obvious redox peaks, i.e. the four-order intercalation reaction: oxidation / reduction potential: -0.39 / -0.41V (vs. Li-In), the two-order and three-order intercalation reaction: oxidation / reduction potential: -0.45 / -0.49V (vs. Li-In) and the one-order intercalation reaction: oxidation / reduction potential: -0.51 / -0.54V (vs. Li-In), the peak positions in the dQ / dV curves of the three are the same, but the intensities of the three pairs of redox peaks are different, and the intensity relationship is as follows: application example 1>application comparative example 1, under the condition of the same peak position, the greater the intensity of the curve, the greater the peak area corresponding, i.e. the higher the capacity in the charge-discharge curve, which is also the same as the foregoing result.

[0077] Table 4

[0078] As can be seen from Table 4, the composite negative electrode materials described in application examples 1-9 all have good rate performance and cycle performance. The rate performance of application comparative example 1 is poor, and the rate performance and cycle performance of application comparative example 2 are both poor.

[0079] By comparing the test results of application examples 1-5 in Table 4, it can be found that when the mass ratio of the graphite core, the inner coating layer and the outer coating layer is (90-99):(0.5-5):(0.5-5), the electrochemical performance is better; when the ratio of the three does not meet the above limitation, either the rate of lithium ions entering the graphite core will be affected, or the contact resistance between the negative electrode material and the electrode material will be increased, resulting in a certain degree of decay of the electrochemical performance.

[0080] By comparing the test results of application examples 6-9 and application example 1 in Table 4, it can be found that with the change of the composition of the inner coating layer, the half-cell performance changes obviously, and when the amount-of-substance ratio of LiX and binary sulfide electrolyte is 1:(1-3), the rate performance and cycle performance are best.

[0081] Fig. 4 is a cycle performance test diagram of the full solid-state batteries assembled with the composite negative electrode material of application example 1 and application comparative examples 1-2, and it can be seen from the figure that the cycle performance of application example 1 and application comparative example 1 is obviously better than that of application comparative example 2, which indicates that the stability is improved by coating the graphite; in addition, by comparing the test results of application example 1 and application comparative example 1, it can be found that the transmission rate of lithium ions is effectively improved by double coating.

[0082] The above descriptions are only the preferred embodiments of the present application, and are not intended to limit the present application. The present application can have various modifications and changes for those skilled in the art. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A surface-modified graphite negative electrode material, characterized by, The surface modified graphite negative electrode material comprises a graphite core, an inner coating layer and an outer coating layer, the inner coating layer is located on the surface of the graphite core, and the outer coating layer is located on the surface of the inner coating layer; the material of the inner coating layer is a LiX doped binary sulfide electrolyte, and the material of the outer coating layer is a ternary sulfide electrolyte; X is a halogen element; the mass ratio of the graphite core, the inner coating layer and the outer coating layer is (85-99.5):(0.25-5):(0.25-10).

2. The surface-modified graphite anode material of claim 1, wherein, In the material of the inner coating layer, the mass ratio of LiX to the binary sulfide electrolyte is 1:(0.5-5).

3. The surface modified graphite negative electrode material according to claim 2, characterized in that, the mass ratio of the graphite core, the inner coating layer and the outer coating layer is (95-97):(1-4):(1-4); and / or, in the material of the inner coating layer, the mass ratio of LiX to the binary sulfide electrolyte is 1:(1-3).

4. The surface modified graphite negative electrode material according to any one of claims 1 to 3, characterized in that, X is one of Cl, Br and I; and / or, at least one of Li3PS4, Li7P3S 11 Li4SnS4; and / or, The ternary sulfide electrolyte is argyrodite electrolyte, the argyrodite electrolyte is at least one of Li6PS5Cl, Li6PS5Br, Li6PS5I, Li 10 GeP2S 12 Br, Li6PS5I, Li 5. The surface-modified graphite anode material of claim 4, wherein the surface-modified graphite anode material has a specific surface area of 0.1 to 10 m2 / g. X is I, the binary sulfide electrolyte is Li3PS4, and the ternary sulfide electrolyte is Li6PS5Cl.

6. A method for producing the surface-modified graphite negative electrode material according to any one of claims 1 to 5, characterized by, comprising the following steps: S1, coating a LiX doped binary sulfide electrolyte on the surface of graphite to obtain a graphite negative electrode material with an inner coating layer; S2, coating a ternary sulfide electrolyte on the surface of the graphite negative electrode material with an inner coating layer to obtain the surface modified graphite negative electrode material.

7. The method of producing a surface-modified graphite negative electrode material according to claim 6, characterized by, In the S1 and the S2, the coating method is at least one of a solid phase ball milling method, a magnetron sputtering method, a liquid phase coating method and an atomic layer deposition method.

8. The preparation method of the surface modified graphite negative electrode material according to claim 7, characterized in that, in the S1, the coating method is a solid phase ball milling method, and the solid phase ball milling method is specifically as follows: graphite, lithium sulfide, phosphorus pentasulfide and LiX are mixed, ball milling is performed, and then the mixture is kept in an inert atmosphere at 180-250 DEG C for 8-12 h to obtain the graphite negative electrode material with an inner coating layer; and / or, in the S2, the coating method is a solid phase ball milling method, and the solid phase ball milling method is specifically as follows: a ternary sulfide electrolyte is blended with the graphite negative electrode material with an inner coating layer, and then ball milling is performed to obtain the surface modified graphite negative electrode material; and / or, in the S2, the preparation method of the ternary sulfide electrolyte is as follows: lithium sulfide, phosphorus pentasulfide and lithium chloride are mixed in a certain proportion, and then kept in an inert atmosphere at 500-600 DEG C for 8-12 h; and / or, in the S2, the D50 particle size of the ternary sulfide electrolyte is 0.5-1 μm.

9. A composite negative material, characterized by, The composite negative electrode material comprises a surface-modified graphite negative electrode material and a sulfide electrolyte, and the mass ratio of the surface-modified graphite negative electrode material to the sulfide electrolyte is (50-100):(0-50); the surface-modified graphite negative electrode material is the surface-modified graphite negative electrode material described in any one of claims 1 to 5 or prepared by the preparation method described in any one of claims 6 to 8.

10. An all-solid-state lithium battery, characterized by comprising: The composite negative electrode material comprises a surface-modified graphite negative electrode material and a sulfide electrolyte, and the mass ratio of the surface-modified graphite negative electrode material to the sulfide electrolyte is (50-100):(0-50); the surface-modified graphite negative electrode material is the surface-modified graphite negative electrode material described in any one of claims 1 to 5 or prepared by the preparation method described in any one of claims 6 to 8.

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