CN118263414A

CN118263414A - Preparation method of coated graphite anode material and solid-state battery

Info

Publication number: CN118263414A
Application number: CN202410250276.9A
Authority: CN
Inventors: 李浩东; 鞠宇航; 孙振; 罗明
Original assignee: High Energy Era Shenzhen New Energy Technology Co ltd
Current assignee: High Energy Era Shenzhen New Energy Technology Co ltd
Filing date: 2024-03-05
Publication date: 2024-06-28

Abstract

The invention belongs to the technical field of battery materials, and discloses a preparation method of a coated graphite anode material and a solid-state battery. The preparation method comprises the following steps: (1) Activating the carbon material by using acid liquor to obtain an activated carbon material; (2) Treating TiN with oxidant hydrogen peroxide and alkali ammonia water to obtain yellow liquid; (3) Adding activated carbon material into yellow liquid, adding dispersant and alkaline lithium-containing substance, stirring, adding hydrolysis initiator, stirring, and drying to obtain precursor; (4) Calcining the precursor in a protective atmosphere to obtain a coated graphite anode material; the dispersant does not include polyacrylic acid; the hydrolysis initiator includes ethanol and water. The coated graphite anode material prepared by the preparation method has low volume expansion rate and low interface resistance, and can obviously improve the cycle stability and the multiplying power performance of the battery when being applied to the battery.

Description

Preparation method of coated graphite anode material and solid-state battery

Technical Field

The invention belongs to the technical field of battery materials, and particularly relates to a preparation method of a coated graphite anode material and a solid-state battery.

Background

In recent years, with the development of new energy automobiles, electronic communication devices and large-scale energy storage grids, consumers have increasingly demanded lithium ion batteries which have high capacity, long life, high stability and rapid charge and discharge performance. Although the liquid lithium ion battery with the high-nickel positive electrode material matched with the high-capacity silicon-carbon negative electrode can achieve the energy density of 300Wh/kg, the unsafe performance of the liquid lithium ion battery seriously hinders the popularization and application of the technology, and particularly, the spontaneous combustion event of the new energy automobile which is endlessly layered in recent years is the first new energy for vigorous development, and the popularization and application of the new energy automobile are seriously hindered.

The use of stable solid state electrolytes instead of flammable organic liquid electrolytes is an important approach to overcome the challenges of lithium batteries and to construct lithium batteries with higher safety performance and energy density. Among the numerous solid electrolytes, sulfide electrolytes have ion conductivity comparable to that of liquid electrolytes, and sulfide electrolytes are soft in texture, can achieve close contact of electrodes by simple cold pressing, and exhibit high cold pressing ion conductivity. This is an incomparable advantage to other electrolytes, and sulfide solid state electrolytes are therefore important candidates for achieving all-solid state batteries.

The anode materials matched with sulfide solid electrolyte which are widely studied at present are lithium metal and silicon carbon anode materials, which respectively have the defects of lithium dendrite, serious interface reaction, huge volume expansion and the like, and are difficult to break through commercial application in a short time. The graphite negative electrode material is used as the most widely used liquid lithium ion battery negative electrode material at present, has the advantages of low cost, excellent structural stability and the like, and the graphite as the sulfide all-solid-state battery negative electrode is matched with the high-nickel ternary positive electrode material, so that the safety performance of the battery can be improved while the energy density is improved. The graphite is used as the cathode of the sulfide all-solid-state battery, firstly, the electrochemical window of the sulfide solid-state electrolyte is narrower, and the graphite can be continuously decomposed to generate a passivation film under the low potential of the graphite, so that the rate performance of the battery is poor; secondly, the contact property of the graphite and sulfide electrolyte in the composite negative electrode is poor, the void ratio of the pole piece is overlarge, and the void between the graphite and the sulfide electrolyte is gradually expanded along with the volume expansion and contraction caused by the lithium intercalation and deintercalation of the graphite, so that the negative electrode material is invalid, and the cycle performance is reduced.

The particle size, morphology, specific surface area and the like of sulfide electrolyte in the graphite and the composite negative electrode can be controlled to effectively reduce the void ratio of the composite negative electrode and improve the contact between the graphite and the composite negative electrode, but the capacity of the battery still can be rapidly attenuated along with the progress of the lithiation and delithiation process of the graphite.

Specifically, the prior art has the problem that sulfide solid electrolyte is continuously decomposed due to the low potential of a graphite electrode; the lithium intercalation potential of the graphite is low (about 0.1V), and the electrochemical window of most sulfide solid electrolyte is narrow (1.6-1.7V), so that the sulfide solid electrolyte can be reduced on the surface of the low-potential graphite to generate Li ₂ S, liP with low ion conductivity and the like, thereby preventing the transmission of lithium ions and limiting the rate capability of the battery. The contact property of graphite and sulfide solid electrolyte is continuously deteriorated in the circulating process; the simple solid phase mixing is difficult to realize the excellent contact of sulfide and graphite, more gaps are generated in the cold pressing process, so that the electron and ion transmission between the sulfide and the graphite is poor, and along with the circulation, about 10 percent of volume expansion occurs in the lithium intercalation and deintercalation process of the graphite, so that the gaps are continuously expanded, the contact between the sulfide and the graphite is further damaged, and the circulation performance is rapidly attenuated.

Accordingly, it is desirable to provide a new anode material having a low volume expansion rate and a low interfacial resistance, thereby improving cycle performance and rate performance of the battery.

Disclosure of Invention

The present invention aims to solve at least one of the technical problems in the prior art described above. Therefore, the invention provides a preparation method of a coated graphite anode material and a solid-state battery. The coated graphite anode material prepared by the preparation method has low volume expansion rate and low interface resistance, and can obviously improve the cycle stability and rate capability of the battery when applied to the battery.

The first aspect of the invention provides a preparation method of a coated graphite anode material.

Specifically, the preparation method of the coated graphite anode material comprises the following steps:

(1) Activating the carbon material by using acid liquor to obtain an activated carbon material;

(2) Treating TiN with oxidant hydrogen peroxide and alkali ammonia water to obtain yellow liquid;

(3) Adding the activated carbon material into the yellow liquid, adding a dispersing agent and an alkaline lithium-containing substance, stirring, adding a hydrolysis initiator, stirring, and drying to obtain a precursor;

(4) Calcining the precursor in a protective atmosphere to obtain the coated graphite anode material;

the dispersant does not include polyacrylic acid;

the hydrolysis initiator includes ethanol and water.

Preferably, in the step (1), the carbon material includes at least one of mesophase carbon microspheres, activated carbon, charcoal, natural graphite, artificial graphite, and composite graphite, and more preferably mesophase carbon microspheres or graphite. The graphite may also be spherical natural graphite. The spheroidized graphite substrates with the appropriate particle size can achieve smaller void fraction control.

Preferably, in the step (1), the particle diameter D ₅₀ of the carbon material is 5 to 25 μm, and more preferably, the particle diameter D ₅₀ of the carbon material is 10 to 20 μm.

Preferably, in the step (1), the acid solution is at least one selected from sulfuric acid solution, nitric acid solution, hydrochloric acid solution, phosphoric acid solution and boric acid solution.

Preferably, in the step (1), the concentration of the acid solution is 0.1-1mol/L or 40-65% mass fraction.

Preferably, in step (1), the temperature of the activation treatment is 20 to 80 ℃, and more preferably 30 to 60 ℃.

Preferably, in step (1), the time of the activation treatment is 0.01 to 10 hours, more preferably 0.5 to 2 hours. the-OH and-COOH groups on the surface of the activated carbon material (such as graphite) are obviously increased, and the activated carbon material can be better combined with titanium-containing oxide.

Preferably, in the step (1), after the activation treatment, washing and drying are performed to obtain the activated carbon material. For example, washing with deionized water or absolute ethanol, and vacuum drying at 60-80deg.C for 8-12 hr.

Preferably, in the step (2), the oxidizing agent is hydrogen peroxide, more preferably 15-35% by mass of hydrogen peroxide, and even more preferably 20-30% by mass of hydrogen peroxide.

Preferably, in the step (2), the alkali solution is ammonia water, more preferably 15-35% by mass of ammonia water, and still more preferably 20-30% by mass of ammonia water. The TiN can be better dissolved by adopting hydrogen peroxide and ammonia water.

Preferably, in the step (2), the mass ratio of the oxidant to the alkali liquor is (1-10): (1-10), preferably (5-10): (1-5).

Preferably, the mass ratio of TiN to carbon material is (1-6): (5-25), more preferably (1-5): (5-20), more preferably 1: (10-20).

Preferably, in the step (3), the alkaline lithium-containing substance is at least one selected from lithium hydroxide and lithium carbonate.

Preferably, in the step (3), the dispersant is at least one selected from polyvinylpyrrolidone, carboxymethyl cellulose, diisooctyl sodium sulfosuccinate (T-100) and citric acid, and more preferably polyvinylpyrrolidone.

Preferably, in step (3), the hydrolysis initiator includes ethanol and water.

Preferably, in the hydrolysis initiator, the volume ratio of water to ethanol is (1-10): (1-10), further preferably 1: (1.5-2). The volume ratio of water to ethanol is controlled to control the speed of hydrolysis reaction.

Preferably, in step (3), after the addition of the hydrolysis initiator, the stirring time is from 0.1 to 10 hours, preferably from 0.1 to 2 hours. This corresponds to the hydrolysis time.

Preferably, in the step (3), the addition amount of the alkaline lithium-containing substance is determined according to a molar ratio of Li/Ti, and the molar ratio of Li/Ti is (3.8-4.4): 5, more preferably (4-4.2): 5, more preferably 4.12:5.

Preferably, in the step (3), the addition amount of the dispersing agent is determined according to the mass of TiN, and the mass ratio of TiN to the dispersing agent is (1-12): 1, more preferably (1-10): 1, more preferably (1-5): 1.

Preferably, in the step (3), the drying method is at least one of evaporation drying, freeze drying and filtration, and more preferably freeze drying. The drying is aimed at removing the solvent (e.g. water, ethanol).

Preferably, in the step (4), the protective atmosphere is at least one selected from Ar, he and N ₂.

Preferably, in step (4), the calcination temperature is 300 to 1000 ℃, more preferably 500 to 1000 ℃, and even more preferably 700 to 800 ℃.

Preferably, in step (4), the calcination time is from 0.5 to 10 hours, preferably from 5 to 8 hours.

According to the preparation method, an acidic solution is utilized to pretreat a carbon material (such as graphite), the activity of the carbon material is improved, lithium titanate is conveniently combined on the surface of the graphite, then titanium nitride (TiN) is used as a raw material, the titanium nitride is dissolved in a mixture of hydrogen peroxide and ammonia water, a titanium peroxide complex formed by dissolving the TiN under the action of water and ethanol is hydrolyzed into a titanium-containing oxide, the titanium-containing oxide and lithium salt are uniformly distributed and coated on the surface of the graphite under the action of a polyvinylpyrrolidone dispersing agent, and a precursor obtained by removing the solution is annealed at a high temperature to obtain graphite@lithium titanate (@represents lithium titanate coated graphite). The uniformly coated lithium titanate can avoid the contact between graphite and sulfide solid electrolyte, and the high lithiation potential can effectively inhibit the decomposition of the sulfide electrolyte, reduce the generation of inert products and reduce the interface resistance so as to improve the rate capability of the graphite cathode in the sulfide solid battery; and secondly, the hard shell formed by the lithium titanate can relieve the volume expansion and contraction in the lithiation and delithiation process of the graphite, inhibit the contact failure between the graphite and the sulfide solid electrolyte, and effectively improve the cycling stability of the graphite cathode material in the sulfide solid battery. The TiN is used as a titanium source and the polypropylene pyrrolidone is used as a dispersing agent to realize uniform lithium titanate coating on the surface of the graphite, so that a plurality of defects of a graphite cathode in the sulfide solid-state battery are overcome, and the method has important significance for realizing commercialization of the sulfide solid-state battery.

The lithium titanate shell layer formed by the preparation method is taken as a typical zero-strain negative electrode material, has excellent multiplying power performance, is taken as a coating material to be coated on the surface of a graphite material, on one hand, inhibits the volume expansion of graphite, and reduces the damage of the volume change of an active material in the lithiation and delithiation process to the contact property of the active material and sulfide solid electrolyte; on the other hand, the lithium titanate with the lithium potential of up to 1.55V can slow down the decomposition of sulfide solid electrolyte on the surface of active substances, reduce the formation of inert intermediate layers and improve the cycle stability and the rate capability of the material.

The second aspect of the invention provides a coated graphite anode material.

Specifically, the coated graphite anode material is prepared by the preparation method, and comprises a core and a shell layer, wherein the core comprises graphite, and the shell layer is lithium titanate containing amorphous carbon.

Preferably, the thickness of the shell layer is 5 to 100nm, more preferably 10 to 80nm.

Preferably, the mass of the graphite accounts for 10-95% of the total mass of the coated graphite anode material, and more preferably 80-95%.

The third aspect of the invention provides an application of the coated graphite anode material.

A solid-state battery comprises a positive electrode, a solid electrolyte and a negative electrode, wherein the negative electrode comprises the coated graphite negative electrode material.

Preferably, the solid electrolyte is a sulfide solid electrolyte.

Compared with the prior art, the invention has the following beneficial effects:

(1) According to the preparation method, tiN is used as a titanium source, a specific hydrolysis initiator, a dispersing agent and an alkaline lithium-containing substance are decomposed to generate a titanium peroxide complex which is uniformly combined on the surface of graphite, so that the uniform coating of graphite is realized, the contact between the graphite and a sulfide solid electrolyte is avoided, the decomposition of the sulfide solid electrolyte can be effectively inhibited by high lithiation potential, the generation of inert products is reduced, and the interface resistance is reduced, so that the multiplying power performance of a graphite cathode in the sulfide solid battery is improved. In addition, the hard shell formed by the lithium titanate can relieve the volume expansion and contraction in the lithiation and delithiation process of the graphite, inhibit the contact failure between the graphite and the sulfide solid electrolyte and effectively improve the circulation stability of the graphite cathode material in the sulfide solid battery.

(2) The key point of the preparation method is that TiN is decomposed under the catalysis of a hydrolysis initiator to generate a titanium peroxide complex which is uniformly combined on the surface of graphite, and the preparation method realizes uniform coating by a liquid phase method; if titanium oxide is used instead of TiN, it is difficult to dissolve and dissociate titanium oxide in the solution, and in practice, titanium oxide is still in solid contact with graphite, and dispersion is not uniform.

(3) The lithium titanate uniformly distributed on the surface of the coated graphite anode material can be in excellent contact with the sulfide solid electrolyte, so that the contact between graphite and the sulfide solid electrolyte is reduced, the decomposition of the sulfide solid electrolyte under low potential is inhibited, the interface resistance is reduced, and the three-dimensional conductive network of the lithium titanate can realize the rapid transmission of lithium ions and improve the multiplying power performance of the sulfide solid battery. The lithium titanate material has zero strain in the lithiation and delithiation process, and can be used as a shell to reduce the influence of volume expansion of graphite on an electrode structure, inhibit the increase of void ratio in a composite negative electrode, reduce the contact failure of the negative electrode material and sulfide solid electrolyte, and improve the capacity attenuation acceleration problem of the material in the long-term circulation process.

Drawings

Fig. 1 is a schematic structural diagram of a coated graphite anode material prepared in example 1;

FIG. 2 is a Scanning Electron Microscope (SEM) image and an energy spectrum (EDS) image of the coated graphite anode material prepared in example 1;

FIG. 3 is a Scanning Electron Microscope (SEM) of comparative sample 1 prepared in comparative example 1;

FIG. 4 is an electrochemical impedance spectrum of a half cell composed of the coated graphite anode material prepared in example 1;

FIG. 5 is a graph showing the results of a first coulombic efficiency test for half-cells composed of the coated graphite negative electrode material prepared in example 1;

Fig. 6 is a graph showing the rate performance results of half cells composed of the coated graphite negative electrode material prepared in example 1.

Detailed Description

In order to make the technical solutions of the present invention more apparent to those skilled in the art, the following examples will be presented. It should be noted that the following examples do not limit the scope of the invention.

The starting materials, reagents or apparatus used in the following examples are all available from conventional commercial sources or may be obtained by methods known in the art unless otherwise specified.

Example 1

The preparation method of the coated graphite anode material comprises the following steps:

(1) Adding 10g D ₅₀ =15 μm graphite into 100mL of 0.5mol/L sulfuric acid solution, treating at 50 ℃ for 30min at 600rpm, filtering, washing with deionized water and absolute ethyl alcohol, and drying in a vacuum oven at 80 ℃ for 12h to obtain activated graphite;

(2) Adding 1g of TiN powder into 50mL of deionized water, adding 30mL of hydrogen peroxide with mass fraction of 30% and 10mL of ammonia water with mass fraction of 25%, and stirring at 600rpm for 1h to obtain yellow transparent solution;

(3) 10g of activated graphite is added into the yellow transparent solution, stirred for 2 hours at 600rpm, then 0.3g of lithium hydroxide and 0.2g of polyvinylpyrrolidone are added, and stirred for 2 hours at 600rpm and mixed uniformly; mixing 50mL of deionized water and 100mL of absolute ethyl alcohol to obtain a hydrolysis initiator, slowly adding the hydrolysis initiator at a constant stirring speed of 600rpm, stirring for 1h, freezing the obtained mixture by liquid nitrogen, and freeze-drying in a freeze dryer to remove the solvent to obtain a precursor;

(4) Finally, calcining the obtained precursor to obtain a coated graphite anode material (marked as sample 1 or graphite@lithium titanate), wherein the specific calcining procedure is as follows: the temperature was maintained at 300℃for 1h in an N ₂ atmosphere, followed by heating to 750℃at a heating rate of 5℃per minute and maintaining for 6h.

Example 2

The difference in example 2 compared with example 1 is that the amount of TiN in example 1 was adjusted to 0.5g, and the other steps were unchanged, and the obtained coated graphite anode material was designated as sample 2.

Example 3

Example 3 was different from example 1 only in that the amount of TiN used in example 1 was adjusted to 2g, and the other steps were unchanged, and the obtained coated graphite anode material was designated as sample 3.

Example 4

Example 4 differs from example 1 only in that the polyvinylpyrrolidone dispersing agent in example 1 was replaced with sodium carboxymethyl cellulose, and the other steps were unchanged, and the obtained coated graphite negative electrode material was designated as sample 4.

Example 5

Example 5 was different from example 1 only in that the amount of the polyvinylpyrrolidone dispersing agent in example 1 was adjusted to 0.4g, and the other steps were unchanged, and the obtained coated graphite anode material was designated as sample 5.

Comparative example 1

In comparison with example 1, comparative example 1 was different only in that TiN in example 1 was replaced with titanium oxide, the other steps were unchanged, and the obtained sample was designated as comparative sample 1.

Comparative example 2

Comparative example 2 differs from example 1 only in that lithium hydroxide in example 1 was replaced with lithium acetate, and the other steps were performed, and the obtained sample was designated as comparative sample 2.

Comparative example 3

In comparison with example 1, comparative example 3 differs only in that the polyvinylpyrrolidone in example 1 was replaced with polyacrylic acid, the other steps were unchanged, and the obtained sample was designated as comparative sample 3.

Product effect test

1. Structural characterization

Fig. 1 is a schematic structural diagram of a coated graphite anode material prepared in example 1; namely, the core of the coated graphite anode material prepared in example 1 is graphite, and the shell is amorphous carbon-containing lithium titanate.

FIG. 2 is a Scanning Electron Microscope (SEM) image and an energy spectrum (EDS) image of the coated graphite anode material prepared in example 1; as can be seen from SEM, the coated graphite anode material prepared in the embodiment 1 consists of core graphite and shell lithium titanate, wherein small lithium titanate particles are uniformly distributed on the surface of the graphite, so that the graphite is firmly coated, the contact between the graphite and sulfide solid electrolyte can be effectively reduced, and the lithium guiding performance of the material is improved.

FIG. 3 is a Scanning Electron Microscope (SEM) of comparative sample 1 prepared in comparative example 1; the comparative sample 1 has obvious uneven surface distribution, bare graphite leakage and no obvious lithium titanate coating layer on the surface. This is due to the difficulty in uniformly distributing the titanium oxide solids on the graphite surface and producing a uniform coating of lithium titanate. Compared with titanium oxide, tiN can be dissolved in the solution to realize uniform liquid phase cladding, and the contact between a titanium source and graphite is effectively improved.

2. Electrochemical performance test

Samples 1-5 prepared in the examples and comparative samples 1-3 prepared in the comparative examples were used as active materials, respectively, and the active materials were mixed with LiP ₆S₅ Cl, PTFE (polytetrafluoroethylene) according to 60:40: and mixing the materials according to the mass ratio of 1 to form a composite negative electrode, and obtaining a negative electrode plate through a rolling and slicing process. The negative electrode sheet was put into a polyetheretherketone tube having a diameter of 10mm, then 100mg of LiP ₆S₅ Cl was weighed into the tube, press-molded using a pressure of 12MPa and brought into close contact with the negative electrode sheet, finally a sheet of Li-In alloy was added to the other side of the solid electrolyte, and press-molded using a pressure of 360MPa, to prepare a half cell having a three-layer structure (composite negative electrode/solid electrolyte/Li-In alloy).

Electrochemical impedance testing: the internal resistance of the half cell was measured by electrochemical impedance test (EIS) to determine the contact and lithium conductivity of the obtained anode material with the sulfide solid electrolyte, the electrochemical impedance spectrum of sample 1 is shown in fig. 4 (the abscissa "im-enhancement'" in fig. 4 represents the real part of the impedance, and the ordinate "-im-enhancement" "the imaginary part of the impedance), and the internal resistances of the half cells composed of the anode materials obtained in samples 1 to 5 and comparative samples 1 to 3 are shown in table 1.

TABLE 1

By comparing the internal resistances of the half batteries consisting of the samples 1-5 and the comparative samples 1-3, the contact between the sample 1 and the sulfide solid electrolyte is found to be best, and the combination of the sample 1 and the sulfide solid electrolyte realizes the better and lowest internal resistance, which is beneficial to the conduction of lithium ions and electrons in the composite negative electrode and is convenient for realizing better multiplying power performance. The sample 1 well realizes the coating of lithium titanate on graphite, effectively inhibits the contact between graphite and sulfide solid electrolyte, and simultaneously, lithium titanate can be used as an intermediate layer to rapidly transfer lithium ions and electrons. If the TiN is replaced by titanium oxide or the lithium hydroxide is replaced by lithium acetate and the polyvinylpyrrolidone is replaced by polyacrylic acid, the internal resistance of the prepared sample is obviously improved. Therefore, in the preparation process of the anode material, other substances can not be replaced at will, and the anode material has selectivity to the types of raw materials.

First coulombic efficiency test: the half cells prepared according to the above method were subjected to a first coulombic efficiency (first effect) test, the first coulombic efficiency (ICE) of sample 1 was 96.48% (as shown in fig. 5), and the half cells assembled respectively with samples 1 to 5 and comparative samples 1 to 3 were subjected to the first coulombic efficiency test, the results of which are shown in table 2.

TABLE 2

By comparing the first coulombic efficiencies of the half cells of samples 1-5 and comparative samples 1-3, it can be seen that the first coulombic efficiency of sample 1 is highest, which means that the surface lithium titanate is coated most uniformly, and the uniformly coated lithium titanate effectively reduces the contact between graphite and sulfide solid electrolyte, so that the side reaction of graphite and sulfide solid electrolyte is correspondingly reduced, and the first effect is improved. While the first coulomb efficiency of the comparative samples 1 to 3 prepared in comparative examples 1 to 3 was remarkably reduced, it was found that the negative electrode material of the present invention was not optionally replaced with other kinds of substances during the preparation process, and the present invention was selective in the kinds of raw materials.

Rate performance test conditions: the half cell of the above sample 1 composition was subjected to charge and discharge tests at 60℃at currents of 0.5C, 1C, 2C and 3C and cut-off voltages of-0.61 to 1.8V, and the half cell was subjected to test at a pressure of 15MPa, and the results are shown in FIG. 6.

As can be seen from fig. 6, sample 1 exhibited excellent rate performance, which was able to maintain a specific capacity of 309.2mAh/g even at a rate of 4C. This fully demonstrates that the coated graphite anode material prepared by the invention has excellent rate capability and commercial potential.

Claims

1. The preparation method of the coated graphite anode material is characterized by comprising the following steps of:

the dispersant does not include polyacrylic acid;

the hydrolysis initiator includes ethanol and water.

2. The method of claim 1, wherein in step (1), the carbon material comprises at least one of mesophase carbon microspheres, activated carbon, charcoal, natural graphite, and artificial graphite.

3. The preparation method according to claim 1, wherein the mass ratio of TiN to carbon material is (1-6): (5-25).

4. The method according to claim 1, wherein in the step (3), the alkaline lithium-containing substance is at least one selected from lithium hydroxide and lithium carbonate.

5. The method according to claim 1, wherein in the step (3), the dispersant is at least one selected from polyvinylpyrrolidone, carboxymethyl cellulose, T-100, and citric acid, and more preferably polyvinylpyrrolidone.

6. The process according to any one of claims 1 to 5, wherein the volume ratio of water to ethanol in the hydrolysis initiator is (1 to 10): (1-10); and/or, the addition amount of the alkaline lithium-containing substance is determined according to a Li/Ti molar ratio of (3.8-4.4): 5, a step of; and/or the addition amount of the dispersing agent is determined according to the mass of TiN, and the mass ratio of the TiN to the dispersing agent is (1-12): 1, a step of; and/or in step (4), the temperature of the calcination is 300 to 1000 ℃, further preferably 500 to 1000 ℃, more preferably 700 to 800 ℃.

7. A coated graphite negative electrode material prepared by the preparation method of any one of claims 1 to 6, and comprising a core comprising graphite and a shell layer of amorphous carbon-containing lithium titanate.

8. The coated graphite anode material of claim 7, wherein the shell layer has a thickness of 5-100nm.

9. The coated graphite anode material of claim 7 or 8, wherein the mass of graphite is 10-95% of the total mass of the coated graphite anode material.

10. A solid-state battery comprising a positive electrode, a solid-state electrolyte, and a negative electrode comprising the coated graphite negative electrode material of any one of claims 7-9.