A negative electrode material, preparation method and application thereof

Abstract

The present invention provides a negative electrode material, a preparation method, and applications thereof. The negative electrode material includes pre-lithiated graphite and pre-lithiated graphene, wherein the pre-lithiated graphite and the pre-lithiated graphene are cross-linked with each other via a cross-linking agent to form a mutually cross-linked structure. By forming the mutually cross-linked pre-lithiated graphite and pre-lithiated graphene, the addition of graphene can increase the electron and ion conductivity of the graphite material. The cross-linked structure can increase the bonding strength between the negative electrode materials, reduce the risk of the negative electrode material being stripped during cycling, improve the capacity stability of the battery during cycling, and further, through pre-lithiation, significantly improve the battery's initial efficiency and cycle capacity retention rate.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium batteries, and in particular relates to a negative electrode material, a preparation method and applications thereof. Background Art

[0002] In recent years, with the development of electric vehicles and energy storage devices, people have placed higher demands on battery energy and volume density, charging rate, and capacity. Currently, the initial coulombic efficiency of positive electrode materials such as lithium iron phosphate and lithium cobalt oxide is greater than 95%, which is the main source of active lithium ions. However, the initial irreversible lithium consumption of negative electrode graphite is as high as 5% to 15%. This is because the initial charge and discharge process consumes active lithium ions, forming a layer of SEI film on the graphite surface, which reduces the battery's energy density. To improve the reversible cycle capacity of batteries, researchers have developed pre-lithiation technology. By introducing external active lithium ions, they offset the lithium consumed by SEI film formation. This reduces the consumption of lithium ions during the positive electrode's deintercalation and deintercalation, thereby increasing the battery's capacity.

[0003] The current pre-lithiation methods mainly use metallic lithium or lithium alloys as pre-lithiation reagents, but their chemical activity is high, and the production difficulty and cost are large; electrochemical pre-lithiation is in the presence of an electrolyte, in which the negative electrode reacts with metallic lithium to pre-deposit metallic lithium on the negative electrode. The negative electrode after electrochemical pre-lithiation has high chemical reactivity and cannot exist stably in the air, and the current density is low, which takes a long time. The high preparation requirements limit its application; the chemical pre-lithiation method is to transfer lithium-containing reagents with strong reducing properties to the negative electrode material through redox reactions. This reaction process is complex and inefficient.

[0004] CN113540448A discloses a pre-lithiated graphene and a preparation method thereof, wherein the pre-lithiated graphene comprises the following components: lithium oxide and lithium carbide, wherein the lithium carbide is Li2CO3, LiC x and R-Li, wherein R is reduced graphene, 1 / 6≤x≤1; the preparation method comprises: mixing a lithium source, graphene oxide, and an electron transfer carrier, adding a solvent, reacting, and drying to obtain pre-lithiated graphene, wherein the electron transfer carrier is at least one of tert-butylbenzene, tert-butylbenzo, and 4,4-di-tert-butylbenzo; by using the above-mentioned pre-lithiated graphene as the negative electrode, Li2CO3 will be generated due to the change in lithium content during the pre-lithiation process, thereby reducing the capacity and cycle capacity of the battery; and the cost of graphene as the negative electrode is relatively high, and it is not suitable for mass production. Summary of the Invention

[0005] In view of the shortcomings and defects of the existing technology, the present invention aims to provide a negative electrode material, preparation method and application thereof. First, by forming mutually cross-linked graphite and graphene, on the one hand, the addition of graphene can improve the electron and ion conductivity of the graphite material, and on the other hand, the formation of a mutually cross-linked structure can improve the bonding force between the negative electrode materials, reduce the risk of the negative electrode material being peeled off during the cycle, and improve the capacity stability of the battery during the cycle; secondly, by pre-lithiation of graphite and graphene, the first efficiency and cycle capacity retention rate of the battery can be greatly improved.

[0006] In order to achieve the above-mentioned object, the first aspect of the present invention provides a negative electrode material, which adopts the following technical solution:

[0007] A negative electrode material comprises: pre-lithiated graphite and pre-lithiated graphene, wherein the pre-lithiated graphite and the pre-lithiated graphene are cross-linked with each other through a cross-linking agent to form a cross-linked structure.

[0008] The negative electrode material of the present invention comprises pre-lithiated graphite and pre-lithiated graphene, wherein the pre-lithiated graphite and the pre-lithiated graphene are cross-linked with each other through a cross-linking agent to form a cross-linked structure, wherein the pre-lithiated graphite comprises: LiC x and R-Li, 1 / 6≤x≤1, R is graphite; the pre-lithiated graphene includes: LiC y and R'-Li, 1 / 6≤y≤1, R' is reduced graphene; pre-lithiated graphite is a composite of graphite and lithium, or graphite and a lithium-containing compound, in which part of the lithium and graphite are ionically bonded, and part of the lithium will form other lithium-containing compounds uniformly distributed on the surface of the graphite and graphene, which are cross-linked to form a mutually cross-linked structure; pre-lithiated graphene is a composite of graphene and lithium, or graphene and a lithium-containing compound, in which part of the lithium and graphene are ionically bonded, and part of the lithium will form other lithium-containing compounds uniformly distributed on the surface of the graphite and graphene, which are cross-linked to form a mutually cross-linked structure. By forming pre-lithiated graphite and pre-lithiated graphene with mutually cross-linked structures as negative electrode materials, the conduction rate of electrons and ions can be improved compared to single graphite materials, and the capacity stability of the battery during the cycle can be improved; secondly, by pre-lithiating graphite and graphene, the first efficiency and cycle capacity of the battery can be greatly improved; finally, due to the high cost of graphene preparation, the negative electrode material of the present invention is lower in cost than single graphene negative electrode materials and is suitable for industrial mass production; in particular, the pre-lithiated graphite and pre-lithiated graphene are cross-linked with each other to form a mutually cross-linked structure, which increases the electrode stability of the negative electrode material during the cycle, improves the cycle performance and rate performance of the battery, etc.

[0009] A second aspect of the present invention provides a method for preparing the above-mentioned negative electrode material, comprising:

[0010] S1. Using graphite as a raw material, sequentially performing pre-oxidation treatment, oxidation treatment, filtration treatment, washing treatment, and drying treatment to obtain graphene oxide;

[0011] S2, dispersing graphene oxide, graphite, and a cross-linking agent in a first solvent, and sequentially performing cross-linking treatment, filtering treatment, and drying treatment to obtain a mixed carbon source;

[0012] S3, dispersing the mixed carbon source and lithium source in a second solvent, adding an electron transfer carrier, performing pre-lithiation treatment, filtering treatment, and drying treatment to obtain a negative electrode material.

[0013] The present invention prepares graphene oxide by using Hummer's improved method, then disperses the graphene oxide, graphite and a cross-linking agent in a first solvent, performs a cross-linking treatment, so that the graphene oxide and the graphite are cross-linked, then disperses a mixed carbon source and a lithium source in a second solvent, and then adds an electron transfer carrier to complete the reduction and pre-lithiation of the graphene oxide and the pre-lithiation of the graphite to obtain a negative electrode material; by using a wet process, PVDF is dissolved in NMP, and then the prepared negative electrode material is added, stirred and dispersed, and the negative electrode slurry is obtained by discharging, and then coated. Drying is performed to obtain a negative electrode sheet; wherein, lithium metal is limited as a lithium source, which can reduce graphene oxide and pre-lithiate graphene; di-tert-butyl peroxide (DTBP) is limited as an electron transfer carrier, which can transfer electrons, pre-lithiate graphite and graphene, and simultaneously complete the reduction of graphene oxide; cassava flour is limited as a cross-linking agent, which can cause cross-linking between graphene oxide and graphite, on the one hand, which can reduce the aggregation of graphene, and on the other hand, can improve the bonding ability between negative electrode materials, thereby reducing the risk of negative electrode materials being stripped during the cycle.

[0014] In the above-mentioned method for preparing the negative electrode material, as a preferred embodiment, in step S1, the pre-oxidation treatment is to add graphite to a concentrated sulfuric acid solution under ice-water bath conditions, and pre-oxidize for 3-15 minutes to obtain pre-oxidized graphite;

[0015] Preferably, the mass fraction of the concentrated sulfuric acid solution is greater than 70%;

[0016] Preferably, the ratio of the volume mL of the concentrated sulfuric acid solution to the mass g of the graphite is (40-50):1.

[0017] In the above-mentioned method for preparing the negative electrode material, as a preferred embodiment, in step S1, the oxidation treatment is to add an oxidant to the pre-oxidized graphite in an ice-water bath, mix them evenly, then oxidize them at 40-60°C for 1-3h, and then add a terminator at 80-100°C to terminate the reaction;

[0018] Preferably, the oxidant is potassium permanganate, and the mass ratio of the graphite to the potassium permanganate is 2:(10-15);

[0019] Preferably, the terminator is deionized water and hydrogen peroxide, the hydrogen peroxide is added in the form of an aqueous hydrogen peroxide solution, and the mass ratio of the graphite to the aqueous hydrogen peroxide solution is 1:(5-20); preferably, the mass fraction of the aqueous hydrogen peroxide solution is 27%-30%;

[0020] More preferably, deionized water is added first, and then the aqueous hydrogen peroxide solution is added, and the mass ratio of the aqueous hydrogen peroxide solution to the deionized water is 3:7.

[0021] In the above-mentioned method for preparing the negative electrode material, as a preferred embodiment, in step S1, the washing treatment is first washing with a 5% volume fraction hydrochloric acid solution, and then washing with deionized water until neutral.

[0022] In the above-mentioned method for preparing the negative electrode material, as a preferred embodiment, in step S2, the cross-linking agent is cassava flour, and the mass ratio of the graphene oxide, the graphite and the cross-linking agent is 0.4:(90-100):(15-20);

[0023] Preferably, the first solvent is selected from one of deionized water, N-methylpyrrolidone, and ethanol; and the ratio of the volume mL of the first solvent to the mass mg of the graphene oxide is 100:(10-20).

[0024] The present invention limits the mass ratio of graphene oxide, graphite and cassava flour in the cross-linking treatment to 0.4:(90-100):(15-20). Within this mass ratio limit, graphene oxide and graphite are conducive to better forming a mutually cross-linked structure; if the mass of graphite is too much, it is easy to cause incomplete pre-lithiation, thereby reducing the initial coulombic efficiency of the battery; if the mass of graphite is too little, the degree of pre-lithiation is high, and the prepared negative electrode material is very easy to deposit lithium after being manufactured into a battery.

[0025] In the above-mentioned method for preparing the negative electrode material, as a preferred embodiment, in step S2, the cross-linking treatment is carried out in a water bath under heating and stirring conditions, the heating temperature is 80-100° C., and the holding time is 5-20 min.

[0026] Preferably, the drying process is carried out at 90-120° C. for 6-12 hours.

[0027] In the above-mentioned method for preparing the negative electrode material, as a preferred embodiment, in step S3, the lithium source is metallic lithium;

[0028] Preferably, the electron transfer carrier is di-tert-butyl peroxide (DTBP);

[0029] Preferably, the mass ratio of the mixed carbon source, the lithium source, and the electron transfer carrier is 100:(5-20):(5-60);

[0030] Preferably, the second organic solvent is N-methylpyrrolidone, and the ratio of the volume mL of the second solvent to the mass g of the mixed carbon source is (500-1000):25.

[0031] In the above-mentioned method for preparing the negative electrode material, as a preferred embodiment, in step S3, the pre-lithiation treatment is carried out under argon conditions at 60-100° C. for 0.5-2 h;

[0032] Preferably, the drying process is carried out under vacuum conditions, the drying temperature is 80-100° C., and the drying time is 6-12 hours.

[0033] The present invention limits the mass ratio of the mixed carbon source, lithium source, and electron transfer carrier in the pre-lithiation process to 100:(5-20):(5-60). This mass ratio range facilitates better pre-lithiation of graphene and graphite. If too little lithium source is added, pre-lithiation of the negative electrode material is incomplete; if too much lithium source is added, lithium deposition is likely to occur in the battery fabricated from the negative electrode material. The pre-lithiation process is performed under argon to prevent oxidation of the lithium metal and deterioration of the lithium metal.

[0034] A third aspect of the present invention provides a use of the above-mentioned negative electrode material or the negative electrode material prepared by the above-mentioned preparation method in a lithium-ion battery.

[0035] Compared with the prior art, the present invention has the following advantages:

[0036] First, graphene and graphite are cross-linked, increasing the conduction rate of electrons and ions in the negative electrode graphite, improving the capacity stability during cycling. Second, the graphene and graphite are pre-lithiated, significantly improving the battery's initial efficiency and cycle capacity. Because graphene preparation is relatively complex, this method saves a lot of resources compared to graphene negative electrodes and can be widely applied. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention.

[0038] The embodiments of the present invention are implemented on the premise of the technical solution of the present invention, and detailed implementation methods and processes are given. However, the protection scope of the present invention is not limited to the following embodiments. The process parameters in the following embodiments that do not specify specific conditions are generally based on conventional conditions.

[0039] The endpoints of the ranges and any values disclosed herein are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values can be combined with each other to form one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed in the present invention.

[0040] Throughout the present invention, unless otherwise specified and / or explained, all references to component amounts are in parts by weight. Process parameters in the following examples, where specific conditions are not specified, generally follow conventional conditions. The raw materials described in the following examples were all obtained from publicly available commercial sources.

[0041] A specific embodiment of the present invention provides a method for preparing a negative electrode material, comprising:

[0042] (1) Graphene oxide is prepared by using Hummer's improved method, comprising: adding graphite to a concentrated sulfuric acid solution under ice-water bath conditions, pre-oxidizing for 3-15 minutes to obtain pre-oxidized graphite, wherein the ratio of the volume mL of the concentrated sulfuric acid solution to the mass g of the graphite is (40-50):1; then adding potassium permanganate to the pre-oxidized graphite under ice-water bath conditions, mixing evenly, and then oxidizing for 1-3 hours at 40-60°C, then adding deionized water at 80-100°C and then adding hydrogen peroxide to terminate the reaction, wherein the mass ratio of the graphite to potassium permanganate is 2:(10-15), the mass ratio of the graphite to hydrogen peroxide is 1:(5-20), and the mass ratio of hydrogen peroxide to deionized water is 3:7; then centrifuging, washing, and drying to obtain graphene oxide, wherein the washing treatment is ultrasonic cleaning, first washing with a 5% volume fraction hydrochloric acid solution, and then washing with deionized water until neutral.

[0043] (2) dispersing graphene oxide, graphite, and tapioca flour in a first solvent (one of deionized water, N-methylpyrrolidone, and ethanol), wherein the mass ratio of graphene oxide, graphite, and tapioca flour is 0.4:(90-100):(15-20), and the ratio of the volume mL of the first solvent to the mass mg of graphene oxide is 100:(10-20); then cross-linking treatment is performed in a water bath under heating and stirring conditions, the heating temperature is 80-100°C, and the holding time is 5-20min; then filtering treatment is performed, and finally drying at 90-120°C for 6-12h to obtain a mixed carbon source;

[0044] (3) The mixed carbon source and metallic lithium are dispersed in N-methylpyrrolidone, and then di-tert-butyl peroxide (DTBP) is added, and the mixture is reacted at 60-100°C for 0.5-2h under argon conditions for pre-lithiation treatment, wherein the mass ratio of the mixed carbon source, metallic lithium, and DTBP is 100:(5-20):(5-60), and the ratio of the volume mL of N-methylpyrrolidone to the mass g of the mixed carbon source is (500-1000):25. Then, the mixture is filtered and vacuum dried under vacuum conditions at a drying temperature of 80-100°C and a drying time of 6-12 to obtain a negative electrode material.

[0045] The present invention will be further described in detail below with reference to specific embodiments.

[0046] Example 1 Preparation of a negative electrode material, comprising:

[0047] (1) Preparation of graphene oxide: First, 3 g of graphite was added to 120 mL of concentrated H2SO4 solution (mass fraction 98%) in an ice-water bath for pre-oxidation reaction for 10 min to obtain pre-oxidized graphite, and then 15 g of potassium permanganate was added to the pre-oxidized graphite in an ice-water bath and mixed evenly, and then oxidation reaction was carried out at 45°C for 1.5 h, and then 72.8 g of deionized water was added at 95°C, and then 30 mL of a 30% mass fraction hydrogen peroxide aqueous solution was added to terminate the reaction, and then filtered, washed, and dried to obtain graphene oxide, wherein the washing treatment was first ultrasonically cleaned with a 5% volume fraction hydrochloric acid solution, and then ultrasonically cleaned with deionized water until neutral;

[0048] (2) Preparation of mixed carbon source: First, 250 mg of graphene oxide, 60 g of graphite, and 10 g of cassava flour were dispersed in 1600 mL of deionized water, and then heated and stirred in a water bath to produce crosslinking. The heating temperature was 90 ° C. and the temperature was kept for 10 min. After that, the mixture was filtered and dried at 100 ° C. for 10 h to obtain a mixed carbon source.

[0049] (3) Preparation of negative electrode material: 50 g of mixed carbon source and 5 g of metallic lithium were dispersed in 1600 mL of N-methylpyrrolidone, and 15 g of DTBP was added. The mixture was ultrasonicated at 80°C for 1 h under argon atmosphere, and then centrifuged to obtain a filter cake, which was then dried at 80°C for 10 h under vacuum conditions to obtain the negative electrode material.

[0050] Example 2

[0051] The difference between Example 2 and Example 1 is that in step (2), the amount of graphene oxide is 250 mg and the amount of graphite is 56.25 g, and the rest are the same as in Example 1.

[0052] Example 3

[0053] The difference between Example 3 and Example 1 is that in step (2), the amount of graphene oxide is 250 mg and the amount of graphite is 62.5 g, and the rest are the same as in Example 1.

[0054] Example 4

[0055] The difference between Example 4 and Example 1 is that in step (3), 50 g of carbon source and 2.5 g of metallic lithium are mixed, and the rest are the same as in Example 1.

[0056] Example 5

[0057] The difference between Example 5 and Example 1 is that in step (3), 50 g of carbon source and 10 g of metallic lithium are mixed, and the rest are the same as in Example 1.

[0058] Comparative Example 1

[0059] The negative electrode material of Comparative Example 1 is the graphite in step (2) of Example 1;

[0060] Comparative Example 2 A method for preparing a negative electrode material comprises:

[0061] (1) Preparation of graphene oxide: First, 3 g of graphite was added to 120 mL of concentrated H2SO4 solution (mass fraction 98%) in an ice-water bath for pre-oxidation reaction for 10 min to obtain pre-oxidized graphite. Then, 15 g of potassium permanganate was added to the pre-oxidized graphite in an ice-water bath and mixed evenly. The mixture was oxidized at 45°C for 1.5 h. Then, 72.8 g of deionized water was added at 95°C, and then 30 mL of a 30% mass fraction hydrogen peroxide aqueous solution was added to terminate the reaction. The mixture was then filtered, washed, and dried to obtain graphene oxide. The washing treatment was first ultrasonically cleaned with a 5% volume fraction hydrochloric acid solution, and then ultrasonically cleaned with deionized water until neutral.

[0062] (2) Preparation of negative electrode material: 250 mg of graphene oxide and 25 mg of metallic lithium were dispersed in 500 mL of N-methylpyrrolidone, and 75 mg of DTBP was added. The mixture was ultrasonicated at 80°C for 1 h under argon atmosphere, and then centrifuged to obtain a filter cake, which was then dried at 80°C for 10 h under vacuum conditions to obtain the negative electrode material.

[0063] Comparative Example 3: A method for preparing a negative electrode material, comprising:

[0064] (1) Preparation of graphene oxide: First, 3 g of graphite was added to 120 mL of concentrated H2SO4 solution (mass fraction 98%) in an ice-water bath, and pre-oxidized for 10 min to obtain pre-oxidized graphite. Then, 15 g of potassium permanganate was added to the pre-oxidized graphite in an ice-water bath, mixed evenly, and oxidized at 45°C for 1.5 h. Then, 72.8 g of deionized water was added at 95°C, and then 30 mL of a 30% aqueous hydrogen peroxide solution was added to terminate the reaction. The graphene oxide was then centrifuged, washed, and dried to obtain graphene oxide, wherein the washing process used deionized water and HCl (5% by volume) to wash until neutral.

[0065] (2) Preparation of negative electrode material: 49.79 g of graphite, 210 mg of graphene oxide, and 5 g of metallic lithium were dispersed in 1600 mL of N-methylpyrrolidone, and 15 g of DTBP was added. The mixture was ultrasonicated at 80°C for 1 h under argon atmosphere, and then centrifuged to obtain a filter cake, which was then dried at 80°C for 10 h under vacuum conditions to obtain the negative electrode material.

[0066] Comparative Example 4

[0067] The difference between Comparative Example 4 and Example 1 is that in step (2), the amount of graphene oxide is 250 mg and the amount of graphite is 51.25 g, and the rest are the same as in Example 1.

[0068] Comparative Example 5

[0069] The difference between Comparative Example 5 and Example 1 is that in step (2), the amount of graphene oxide is 250 mg and the amount of graphite is 65.625 g, and the rest are the same as in Example 1.

[0070] Performance Testing

[0071] The negative electrode materials prepared in Examples 1-5 and Comparative Examples 1-5 were mixed with the binder PVDF in a mass ratio of 90:10 to obtain a raw material for the negative electrode active material layer. The specific preparation method is as follows:

[0072] First, PVDF is dissolved in NMP solvent and mixed and stirred to form a glue. The mixing and stirring includes high-speed stirring and vacuum inversion defoaming in sequence. The high-speed stirring time is 2h, the revolution speed is 35rpm, and the dispersion speed is 8-11m / s to completely dissolve the glue. Then the dispersion speed is turned off and vacuum inversion defoaming is performed. The vacuum degree of vacuum inversion defoaming is -95KPa, the defoaming time is 30min, and the revolution speed is 15rpm. Then, the negative electrode active material is added and fully dispersed (first stirring and dispersing) to obtain a first mixture. The revolution speed of each full dispersion is 25rpm and the dispersion speed is 5-8m / s. Finally, NMP solvent is added to the first mixture to adjust the slurry viscosity to 3000-6000mPa.s and the solid content to 48%-58%. The slurry is sieved with a 120-mesh screen to obtain a negative electrode slurry. The negative electrode slurry is then coated on copper foil and dried to obtain a negative electrode sheet. The coating surface density is 152g / m2 on both sides. 2 ;

[0073] The positive electrode active material is lithium iron phosphate, the binder is PVDF, and the conductive agent is SP. They are dissolved in NMP at a mass ratio of 90:6:4 and mechanically stirred for 3 hours to form a stable slurry. The slurry is then evenly coated on a metal aluminum foil with a coating surface density of 330g / m 2 , and then dried in vacuum at 80°C for 2h to obtain the positive electrode sheet;

[0074] The diaphragm is a 9+3 single-sided ceramic diaphragm, and the electrolyte is LiPF6 dissolved in a 1:1 mixed solvent of EC and DMC, with a LiPF6 concentration of 1 mol / L and an N / P ratio of 1.15. A battery cell is prepared by stacking the diaphragm, negative electrode, diaphragm, positive electrode, and diaphragm. The battery cell is then hot-pressed and the tabs are welded, and then placed in an aluminum-plastic film to obtain a battery. After the battery is dried, the electrolyte is injected. After standing at room temperature for 24 hours, vacuum exhaust, heat sealing, formation, and sorting, a soft-pack battery with a capacity of 3Ah is obtained. At room temperature (25°C±1), the voltage is 0.01-3V, and the first discharge specific capacity is tested at 0.2C / 0.2C, and the cycle performance is tested at 0.5C / 0.5C. The test results are shown in Table 1.

[0075] Table 1

[0076]

[0077] By comparing Examples 1-5 and Comparative Examples 1-3, it can be seen that for batteries made with pre-lithiated graphite and pre-lithiated graphene that form mutually cross-linked structures as negative electrode materials, the cross-linked structure can improve the adhesion between the negative electrode materials, reduce the risk of the negative electrode materials being peeled off during the cycle, and improve the capacity stability of the battery during the cycle. In addition, through pre-lithiation, the first efficiency and cycle capacity retention rate of the battery can be greatly improved.

[0078] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention are within the scope of protection of the pending claims of the present invention.

Claims

1. A method for preparing a negative electrode material, wherein the negative electrode material comprises pre-lithiated graphite and pre-lithiated graphene, wherein the pre-lithiated graphite and the pre-lithiated graphene are cross-linked with each other by a cross-linking agent to form a mutually cross-linked structure, wherein the preparation method is characterized by comprising: S1. Using graphite as a raw material, sequentially performing pre-oxidation treatment, oxidation treatment, filtration treatment, washing treatment, and drying treatment to obtain graphene oxide; S2. Dispersing graphene oxide, graphite, and a cross-linking agent in a first solvent, and sequentially performing cross-linking treatment, filtering treatment, and drying treatment to obtain a mixed carbon source, wherein the mass ratio of the graphene oxide, the graphite, and the cross-linking agent is 0.4:(90-100):(15-20); S3, dispersing the mixed carbon source and lithium source in a second solvent, adding an electron transfer carrier, performing pre-lithiation treatment, filtering treatment, and drying treatment to obtain a negative electrode material.

2. The preparation method according to claim 1, characterized in that In step S1, the pre-oxidation treatment is to add graphite to a concentrated sulfuric acid solution under ice-water bath conditions, and perform a pre-oxidation reaction for 3-15 minutes to obtain pre-oxidized graphite.

3. The preparation method according to claim 2, characterized in that The mass fraction of the concentrated sulfuric acid solution is greater than 70%.

4. The preparation method according to claim 2, characterized in that The ratio of the volume mL of the concentrated sulfuric acid solution to the mass g of the graphite is (40-50):

1.

5. The preparation method according to any one of claims 1 to 4, characterized in that In step S1, the oxidation treatment is to add an oxidant to the pre-oxidized graphite in an ice-water bath and mix them evenly, then perform an oxidation reaction at 40-60° C. for 1-3 hours, and then add a terminator at 80-100° C. to terminate the reaction.

6. The preparation method according to claim 5, characterized in that The oxidant is potassium permanganate, and the mass ratio of the graphite to the potassium permanganate is 2:(10-15).

7. The preparation method according to claim 5, characterized in that The terminator is deionized water and hydrogen peroxide, the hydrogen peroxide is added in the form of an aqueous hydrogen peroxide solution, and the mass ratio of the graphite to the aqueous hydrogen peroxide solution is 1:(5-20).

8. The preparation method according to claim 7, characterized in that The mass fraction of the hydrogen peroxide aqueous solution is 27%-30%.

9. The preparation method according to claim 7, characterized in that Adding the terminator includes first adding deionized water and then adding the hydrogen peroxide aqueous solution, and the mass ratio of the hydrogen peroxide aqueous solution to the deionized water is 3:

7.

10. The preparation method according to claim 5, characterized in that In step S1 , the washing treatment is to first use a 5% volume fraction hydrochloric acid solution for washing, and then use deionized water for washing until neutrality.

11. The preparation method according to any one of claims 1 to 4, characterized in that In step S2, the cross-linking agent is cassava flour.

12. The preparation method according to any one of claims 1 to 4, characterized in that In step S2, the first solvent is selected from one of deionized water, N-methylpyrrolidone, and ethanol; the ratio of the volume mL of the first solvent to the mass mg of the graphene oxide is 100:(10-20).

13. The preparation method according to any one of claims 1 to 4, characterized in that In step S2, the cross-linking treatment is carried out in a water bath under heating and stirring conditions, the heating temperature is 80-100°C, and the insulation time is 5-20 minutes.

14. The preparation method according to any one of claims 1 to 4, characterized in that In step S2, the drying process is carried out at 90-120° C. for 6-12 hours.

15. The preparation method according to any one of claims 1 to 4, characterized in that In step S3, the lithium source is metallic lithium.

16. The preparation method according to any one of claims 1 to 4, characterized in that In step S3, the electron transfer carrier is di-tert-butyl peroxide.

17. The preparation method according to any one of claims 1 to 4, characterized in that In step S3, the mass ratio of the mixed carbon source, the lithium source, and the electron transfer carrier is 100:(5-20):(5-60).

18. The preparation method according to any one of claims 1 to 4, characterized in that In step S3, the second solvent is N-methylpyrrolidone, and the ratio of the volume mL of the second solvent to the mass g of the mixed carbon source is (500-1000):

25.

19. The preparation method according to any one of claims 1 to 4, characterized in that In step S3, the pre-lithiation treatment is carried out under argon at 60-100° C. for 0.5-2 h.

20. The preparation method according to any one of claims 1 to 4, characterized in that In step S3, the drying process is carried out under vacuum conditions, the drying temperature is 80-100°C, and the drying time is 6-12 hours.

21. Use of a negative electrode material prepared by the preparation method according to any one of claims 1 to 20 in a lithium ion battery.

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