A graphite negative electrode material for lithium battery and preparation method thereof

Abstract

The present invention provides a graphite negative electrode material for lithium batteries and a preparation method thereof, the preparation method comprising the following steps: (1) preparing a modified phenolic resin; (2) adding natural graphite and modified phenolic resin to a reactor, continuing to add modified graphene, and stirring and heating coating under a nitrogen atmosphere, specifically: first heating to 150-200°C at 1-2°C / min, keeping warm for 100-120min, then heating to 550-600°C at 4-6°C / min, keeping warm for 180-200min, cooling, and obtaining coated graphite; (3) placing the coated graphite in an atmosphere furnace for carbonization, sieving, and obtaining a graphite negative electrode material for lithium batteries. When the negative electrode material of the present invention is used to prepare a lithium battery, the capacity retention rate is high, the rate performance is good, and the impedance is low and the lithium precipitation point of fast charging is high.

Description

Technical Field

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

[0002] Lithium-ion battery anode materials are a crucial component of the battery, storing lithium ions during charging and releasing them during discharge. Graphite, with its abundant resources, low price, high reversible capacity, low charge and discharge voltage plateau, no voltage hysteresis, and excellent conductivity, has rapidly attracted widespread attention, making it one of the primary materials for lithium battery anodes.

[0003] Although graphite is currently the most commonly used negative electrode material for lithium-ion batteries, its weak interlayer forces and interlayer spacing smaller than that of graphite intercalation compounds can lead to easy exfoliation and pulverization of graphite flakes during charge and discharge, thus affecting the battery's cycling performance, especially at low temperatures. Furthermore, due to structural defects in graphite itself, the presence of numerous active groups on its surface results in a large specific surface area, which results in relatively low initial charge and discharge efficiencies.

[0004] In order to overcome the above-mentioned shortcomings, the existing technology uses asphalt and phenolic resin to modify graphite to improve the specific capacity and circulation efficiency of graphite materials. However, the carbonization temperature of asphalt coating is high and the energy consumption is large; phenolic resin easily forms an adhesive system that is easy to settle during stirring or volatilization, resulting in uneven coating on the graphite surface. The surface of the graphite coated with phenolic resin will have holes, and contact with the electrolyte will cause the generation of irreversible capacity, thereby reducing the circulation performance of the graphite.

[0005] Therefore, there is an urgent need for a graphite negative electrode material for lithium batteries and a preparation method thereof. Summary of the Invention

[0006] The purpose of the present invention is to provide a graphite negative electrode material for lithium batteries and a preparation method thereof.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] A method for preparing a graphite negative electrode material for a lithium battery, the method comprising the following steps:

[0009] (1) 50-55 parts by weight of 3-hydroxymethyl-3-ethyloxetane (CAS: 3143-02-0), 43-45 parts by weight of epichlorohydrin and 23-25 ​​parts by weight of sodium hydroxide are mixed, and the mixture is reacted at 40-45° C. for 18-20 hours to obtain a reaction raw material; 65-70 parts by weight of the reaction raw material, 20-25 parts by weight of phenolic resin, 4-6 parts by weight of sodium hydroxide and 160-180 parts by weight of toluene are mixed, the mixture is stirred and heated to 80-85° C., the mixture is reacted for 10-14 hours, the pH is adjusted to neutral, and the toluene is evaporated under reduced pressure to obtain a modified phenolic resin;

[0010] (2) adding natural graphite and modified phenolic resin into a reaction kettle, continuing to add modified graphene, stirring and heating under a nitrogen atmosphere for coating, specifically: first heating to 150-200°C at 1-2°C / min, keeping warm for 100-120min, then heating to 550-600°C at 4-6°C / min, keeping warm for 180-200min, and cooling to obtain coated graphite;

[0011] (3) The coated graphite is placed in an atmosphere furnace for carbonization and passed through a 325-mesh sieve to obtain a graphite negative electrode material for lithium batteries.

[0012] Furthermore, the particle size D50 of the natural graphite in step (2) is 10-30 μm.

[0013] Furthermore, in step (2), the weight ratio of natural graphite, modified phenolic resin and modified graphene is 100:(3-5):(2-4).

[0014] Furthermore, the phenolic resin is a mixture of phenolic resin A, phenolic resin B, and phenolic resin C in a weight ratio of 1:(1.3-1.5):(0.1-0.3); phenolic resin A has a viscosity of 20-30 cp at 25°C, a free phenol content of 3-6 wt%, and a residual carbon content of 23-28 wt%; phenolic resin B has a viscosity of 500-800 cp at 25°C, a free phenol content of 3-7 wt%, and a residual carbon content of 35-40 wt%; and phenolic resin C has a viscosity of 10,000-14,000 cp at 25°C, a free phenol content of 10-12 wt%, and a residual carbon content of 43-47 wt%. All of the phenolic resins were purchased from Hebei Zetian Chemical Co., Ltd.

[0015] In the prior art, natural graphite is directly coated with phenolic resin, and the performance of the negative electrode material prepared is not ideal. The present invention modifies the phenolic resin to improve the discharge capacity of the prepared lithium ion battery. Moreover, when the phenolic resin with specific parameters is compounded, the capacity retention rate of the lithium ion battery can be improved. Analysis shows that the present invention obtains an epoxy-modified phenolic resin by chemically grafting the oxetane group at the end of the chain of the phenolic resin. The epoxy-modified phenolic resin contains an epoxy group that can form a covalent bond with the active group on the graphite surface, thereby improving the bonding force with the graphite substrate and forming a more uniform coating. The modified phenolic resin prepared by compounding in a specific ratio has better fluidity and forms a denser structure on the graphite surface, which can improve the capacity retention rate of the lithium ion battery.

[0016] Furthermore, the preparation method of the modified graphene in step (2) comprises the following steps:

[0017] (1) mixing 1 part by weight of graphene oxide, 7-9 parts by weight of p-phenylenediamine, 0.2-0.3 parts by weight of polyethylene glycol 600, and 15-20 parts by weight of water, and stirring under reflux at 80-85° C. for 4-5 hours to obtain a p-phenylenediamine-modified graphene oxide dispersion;

[0018] (2) Adding hydrazine hydrate to the p-phenylenediamine-modified graphene oxide dispersion, reacting at 80-85° C. for 26-28 hours; centrifuging and vacuum drying to obtain modified graphene.

[0019] Furthermore, the graphene oxide has a sheet diameter of 10-20 μm and a thickness of 1-5 nm.

[0020] Furthermore, the mass ratio of hydrazine hydrate to graphene oxide is (2-4):1.

[0021] To improve the high impedance and capacity loss during charge and discharge, as well as the irrational rate performance, of lithium batteries, the present invention attempted to add graphene oxide to the coating material, but the results were unsatisfactory. The present invention modifies graphene oxide to improve the impedance of lithium batteries. Analysis shows that graphite, modified phenolic resin, and modified graphene can form a stable composite structure, which can improve the diffusion path of lithium ions in the graphite, form a conductive network, reduce the resistance to lithium ion migration, and thus lower the interfacial impedance.

[0022] Furthermore, the stirring speed in step (2) is 15-25 r / min.

[0023] Furthermore, in step (3), the carbonization temperature is 700-900° C., and the carbonization time is 7-9 hours.

[0024] The present invention also provides a graphite negative electrode material for lithium batteries prepared by the above preparation method.

[0025] Compared with the prior art, the advantages and beneficial effects of the present invention are:

[0026] 1. When the negative electrode material of the present invention is prepared into a lithium battery, it has high capacity retention, good rate performance, low impedance, and a high lithium deposition point for fast charging.

[0027] 2. The present invention modifies the phenolic resin to improve the discharge capacity of the prepared lithium-ion battery. Furthermore, when compounded with a phenolic resin having specific parameters, the capacity retention rate of the lithium-ion battery can be improved.

[0028] 3. The present invention modifies graphene oxide to improve the impedance of lithium batteries and at the same time increases the lithium deposition point of LG fast charging. DETAILED DESCRIPTION

[0029] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0030] Example 1

[0031] This embodiment provides a graphite negative electrode material for a lithium battery, and a preparation method thereof comprises the following steps:

[0032] (1) 52 parts by weight of 3-hydroxymethyl-3-ethyloxetane (CAS: 3143-02-0), 44 parts by weight of epichlorohydrin and 24 parts by weight of sodium hydroxide were mixed and reacted at 42° C. for 19 hours to obtain a reaction raw material; 68 parts by weight of the reaction raw material, 23 parts by weight of phenolic resin, 5 parts by weight of sodium hydroxide and 170 parts by weight of toluene were mixed, stirred and heated to 82° C., reacted for 12 hours, adjusted the pH to neutral, and evaporated the toluene under reduced pressure to obtain a modified phenolic resin;

[0033] (2) Adding natural graphite with a particle size of D50 of 20 μm and modified phenolic resin into a reactor, and then adding modified graphene; the weight ratio of natural graphite, modified phenolic resin, and modified graphene is 100:4:3; stirring, heating, and coating are performed under a nitrogen atmosphere, and the stirring speed is 20 r / min, specifically: first heating to 170°C at 1°C / min, keeping warm for 110 minutes, then heating to 570°C at 5°C / min, keeping warm for 190 minutes, and cooling to obtain coated graphite;

[0034] The phenolic resins are a mixture of phenolic resin A, phenolic resin B, and phenolic resin C in a weight ratio of 1:1.4:0.2. Phenolic resin A has a viscosity (25°C) of 20-30 cp, a free phenol content of 3-6 wt%, and a residual carbon content of 23-28 wt%. Phenolic resin B has a viscosity (25°C) of 500-800 cp, a free phenol content of 3-7 wt%, and a residual carbon content of 35-40 wt%. Phenolic resin C has a viscosity (25°C) of 10,000-14,000 cp, a free phenol content of 10-12 wt%, and a residual carbon content of 43-47 wt%. All were purchased from Hebei Zetian Chemical Co., Ltd.

[0035] The preparation method of the modified graphene comprises the following steps:

[0036] S1: 1 part by weight of graphene oxide, 8 parts by weight of p-phenylenediamine, 0.25 parts by weight of polyethylene glycol 600, and 18 parts by weight of water were mixed, and the mixture was stirred under reflux at 82°C for 4.5 hours to obtain a p-phenylenediamine-modified graphene oxide dispersion; the graphene oxide flakes had a diameter of 10-20 μm and a thickness of 1-5 nm.

[0037] S2: adding hydrazine hydrate to the p-phenylenediamine-modified graphene oxide dispersion with a mass ratio of hydrazine hydrate to graphene oxide of 3:1; reacting at 82° C. for 27 h; centrifuging and vacuum drying to obtain modified graphene.

[0038] (3) The coated graphite is placed in an atmosphere furnace for carbonization at a temperature of 800°C for 8 hours; the carbonization temperature is sieved through a 325-mesh sieve to obtain a graphite negative electrode material for lithium batteries.

[0039] Example 2

[0040] This embodiment provides a graphite negative electrode material for a lithium battery, and a preparation method thereof comprises the following steps:

[0041] (1) 50 parts by weight of 3-hydroxymethyl-3-ethyloxetane (CAS: 3143-02-0), 43 parts by weight of epichlorohydrin and 23 parts by weight of sodium hydroxide were mixed and reacted at 40° C. for 18 hours to obtain a reaction raw material; 65 parts by weight of the reaction raw material, 20 parts by weight of phenolic resin, 4 parts by weight of sodium hydroxide and 160 parts by weight of toluene were mixed, stirred and heated to 80° C., reacted for 10 hours, adjusted the pH to neutral, and evaporated the toluene under reduced pressure to obtain a modified phenolic resin;

[0042] (2) adding natural graphite with a particle size D50 of 10-30 μm and modified phenolic resin into a reactor, and continuing to add modified graphene, the weight ratio of natural graphite, modified phenolic resin, and modified graphene is 100:3:2; stirring, heating, and coating are carried out under a nitrogen atmosphere, and the stirring speed is 15 r / min, specifically: first heating to 150°C at 1°C / min, keeping warm for 100 minutes, then heating to 550°C at 4°C / min, keeping warm for 180 minutes, and cooling to obtain coated graphite;

[0043] The phenolic resins are a mixture of phenolic resin A, phenolic resin B, and phenolic resin C in a weight ratio of 1:1.3:0.1. Phenolic resin A has a viscosity of 20-30 cp at 25°C, a free phenol content of 3-6 wt%, and a residual carbon content of 23-28 wt%. Phenolic resin B has a viscosity of 500-800 cp at 25°C, a free phenol content of 3-7 wt%, and a residual carbon content of 35-40 wt%. Phenolic resin C has a viscosity of 10,000-14,000 cp at 25°C, a free phenol content of 10-12 wt%, and a residual carbon content of 43-47 wt%. All were purchased from Hebei Zetian Chemical Co., Ltd.

[0044] The preparation method of the modified graphene comprises the following steps:

[0045] S1: 1 part by weight of graphene oxide, 7 parts by weight of p-phenylenediamine, 0.2 parts by weight of polyethylene glycol 600, and 15 parts by weight of water were mixed, and the mixture was stirred under reflux at 80°C for 4 hours to obtain a p-phenylenediamine-modified graphene oxide dispersion; the graphene oxide flakes had a diameter of 10-20 μm and a thickness of 1-5 nm.

[0046] S2: adding hydrazine hydrate to the p-phenylenediamine-modified graphene oxide dispersion with a mass ratio of hydrazine hydrate to graphene oxide of 2:1; reacting at 80° C. for 26 h; centrifuging and vacuum drying to obtain modified graphene.

[0047] (3) The coated graphite was placed in an atmosphere furnace for carbonization at a temperature of 700°C for 7 hours; the graphite was sieved through a 325-mesh sieve to obtain a graphite negative electrode material for lithium batteries.

[0048] Example 3

[0049] This embodiment provides a graphite negative electrode material for a lithium battery, and a preparation method thereof comprises the following steps:

[0050] (1) 55 parts by weight of 3-hydroxymethyl-3-ethyloxetane (CAS: 3143-02-0), 45 parts by weight of epichlorohydrin and 25 parts by weight of sodium hydroxide were mixed and reacted at 45° C. for 20 hours to obtain a reaction raw material; 70 parts by weight of the reaction raw material, 25 parts by weight of phenolic resin, 6 parts by weight of sodium hydroxide and 180 parts by weight of toluene were mixed, stirred and heated to 85° C., reacted for 14 hours, adjusted the pH to neutral, and evaporated the toluene under reduced pressure to obtain a modified phenolic resin;

[0051] (2) adding natural graphite with a particle size D50 of 10-30 μm and modified phenolic resin into a reactor, and continuing to add modified graphene, the weight ratio of natural graphite, modified phenolic resin, and modified graphene is 100:5:4; stirring, heating, and coating are carried out under a nitrogen atmosphere, and the stirring speed is 25 r / min, specifically: first heating to 200°C at 2°C / min, keeping warm for 120 minutes, then heating to 600°C at 6°C / min, keeping warm for 200 minutes, and cooling to obtain coated graphite;

[0052] The phenolic resins are a mixture of phenolic resin A, phenolic resin B, and phenolic resin C in a weight ratio of 1:1.5:0.3. Phenolic resin A has a viscosity of 20-30 cp at 25°C, a free phenol content of 3-6 wt%, and a residual carbon content of 23-28 wt%. Phenolic resin B has a viscosity of 500-800 cp at 25°C, a free phenol content of 3-7 wt%, and a residual carbon content of 35-40 wt%. Phenolic resin C has a viscosity of 10,000-14,000 cp at 25°C, a free phenol content of 10-12 wt%, and a residual carbon content of 43-47 wt%. All were purchased from Hebei Zetian Chemical Co., Ltd.

[0053] The preparation method of the modified graphene comprises the following steps:

[0054] S1: 1 part by weight of graphene oxide, 9 parts by weight of p-phenylenediamine, 0.3 parts by weight of polyethylene glycol 600, and 20 parts by weight of water were mixed, and the mixture was stirred under reflux at 85°C for 5 hours to obtain a p-phenylenediamine-modified graphene oxide dispersion; the graphene oxide flakes had a diameter of 10-20 μm and a thickness of 1-5 nm.

[0055] S2: adding hydrazine hydrate to the p-phenylenediamine-modified graphene oxide dispersion with a mass ratio of hydrazine hydrate to graphene oxide being 4:1; reacting at 85° C. for 28 h; centrifuging and vacuum drying to obtain modified graphene.

[0056] (3) The coated graphite was placed in an atmosphere furnace for carbonization at a temperature of 900°C for 9 hours; the graphite was sieved through a 325-mesh sieve to obtain a graphite negative electrode material for lithium batteries.

[0057] Comparative Example 1

[0058] The difference between this comparative example and Example 1 is that the modified phenolic resin is replaced by phenolic resin.

[0059] The phenolic resins are a mixture of phenolic resin A, phenolic resin B, and phenolic resin C in a weight ratio of 1:1.5:0.3. Phenolic resin A has a viscosity of 20-30 cp at 25°C, a free phenol content of 3-6 wt%, and a residual carbon content of 23-28 wt%. Phenolic resin B has a viscosity of 500-800 cp at 25°C, a free phenol content of 3-7 wt%, and a residual carbon content of 35-40 wt%. Phenolic resin C has a viscosity of 10,000-14,000 cp at 25°C, a free phenol content of 10-12 wt%, and a residual carbon content of 43-47 wt%. All were purchased from Hebei Zetian Chemical Co., Ltd.

[0060] Comparative Example 2

[0061] This comparative example differs from Example 1 in that the phenolic resins are a mixture of phenolic resin A, phenolic resin B, and phenolic resin C in a weight ratio of 1:1:1. Phenolic resin A has a viscosity of 20-30 cp at 25°C, a free phenol content of 3-6 wt%, and a residual carbon content of 23-28 wt%. Phenolic resin B has a viscosity of 500-800 cp at 25°C, a free phenol content of 3-7 wt%, and a residual carbon content of 35-40 wt%. Phenolic resin C has a viscosity of 10,000-14,000 cp at 25°C, a free phenol content of 10-12 wt%, and a residual carbon content of 43-47 wt%. All are purchased from Hebei Zetian Chemical Co., Ltd.

[0062] Comparative Example 3

[0063] The difference between this comparative example and Example 1 is that the modified graphene is replaced by graphene oxide. The graphene oxide has a sheet diameter of 10-20 μm and a thickness of 1-5 nm.

[0064] Comparative Example 4

[0065] The difference between this comparative example and Example 1 is that the preparation method of the modified graphene is different.

[0066] The modified graphene preparation method comprises the following steps: mixing 1 part of graphene oxide and 10 parts of water by weight, adding sodium carbonate to adjust the pH value to 10, and stirring at 60° C. for 3 hours to form a suspension; adding 0.2 parts of hexadecyltrimethylammonium bromide to the 10 parts of the suspension, stirring evenly, stirring at 64° C. for 4 hours, filtering, washing, drying, and grinding through an 80-mesh sieve to obtain the modified graphene.

[0067] Comparative Example 5

[0068] The difference between this comparative example and Example 1 is that in step (2), the weight ratio of natural graphite, modified phenolic resin and modified graphene is 100:2:5.

[0069] Comparative Example 6

[0070] The difference between this comparative example and Example 1 is that the stirring heating coating is carried out, the stirring speed is 20 r / min, specifically: the temperature is increased to 570° C. at 5° C. / min, and the temperature is kept for 300 min.

[0071] Performance Testing

[0072] 1. The graphite negative electrode materials prepared in Examples 1-3 and Comparative Examples 1-6 were used to prepare half-cells according to the following method:

[0073] Graphite anode material, conductive carbon black SP, CMC, and SBR were weighed in a mass ratio of 95:1:2:2 and stirred in water to form a negative electrode slurry. This was then evenly coated onto copper foil using an applicator. The coated electrode was then placed in a vacuum drying oven at 110°C for 4 hours and pressed into a sheet to form the negative electrode. The compaction density is calculated as the electrode mass divided by the thickness of the pressed electrode - the thickness of the current collector. CR-2430 button cells were assembled in an argon-filled Braun glove box in Germany. The electrolyte consisted of 1M LiPF6 + EC:EMC:DMC = 1:1:1 (volume ratio). A lithium metal sheet served as the counter electrode.

[0074] The prepared half-cell was tested for discharge capacity and first discharge efficiency on an American Arbin BT2000 battery tester. The discharge capacity and first discharge efficiency were measured according to conventional test methods in the field under the conditions of a charge and discharge voltage range of 0.005 V to 1.0 V and a charge and discharge rate of 0.1 C.

[0075] 2. Impedance and fast lithium deposition point

[0076] Impedance (DCIR) refers to the direct current resistance under a specific load and discharge current. It is calculated by charging the half-cells prepared in Examples 1-3 and Comparative Examples 1-6 to 50% SOC and dividing the voltage drop of the graphite negative electrode material by the charging current.

[0077] Quickly Charge Teat (QCT-3C): refers to a fast charge test with an input current of 3C (the current required to fully charge the battery in 1 / 3 hour).

[0078] Table 1 Performance test results

[0079]

[0080] From the above performance test results, it can be seen that the performance of the lithium batteries prepared with the negative electrode materials of Examples 1-3 is excellent, especially the comprehensive performance of Example 1 is the most outstanding.

[0081] However, the comparative examples were significantly inferior to the embodiments in the corresponding performance tests because they did not adopt the necessary technical solutions. In comparative example 1, the phenolic resin was not modified, and the discharge capacity decreased. In comparative example 2, the phenolic resin ratio scheme was not used, and it can be seen from the results that the capacity retention effect decreased. In comparative example 3, the graphene oxide was not modified, and the preparation method of the modified graphene in comparative example 4 was different, which increased the impedance of the lithium battery. In comparative example 5, the ratio of modified phenolic resin and modified graphene was different, and the coating conditions in comparative example 6 were different, all of which led to a decrease in the performance of the lithium battery. The above experimental results further demonstrate the importance of the technical solution defined in the present invention for its technical effects.

[0082] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing a graphite negative electrode material for a lithium battery, characterized in that: The preparation method comprises the following steps: (1) 50-55 parts by weight of 3-hydroxymethyl-3-ethyloxetane, 43-45 parts by weight of epichlorohydrin and 23-25 ​​parts by weight of sodium hydroxide are mixed, and the mixture is reacted at 40-45° C. for 18-20 hours to obtain a reaction raw material; 65-70 parts by weight of the reaction raw material, 20-25 parts by weight of phenolic resin, 4-6 parts by weight of sodium hydroxide and 160-180 parts by weight of toluene are mixed, the mixture is stirred and heated to 80-85° C., and the mixture is reacted for 10-14 hours, the pH is adjusted to neutral, and the toluene is evaporated under reduced pressure to obtain a modified phenolic resin; the phenolic resin is Mix phenolic resin A, phenolic resin B and phenolic resin C in a ratio of 1: (1.3-1.5): (0.1-0.3); phenolic resin A has a viscosity of 20-30 cp at 25°C, a free phenol content of 3-6 wt%, and a residual carbon content of 23-28 wt%; phenolic resin B has a viscosity of 500-800 cp at 25°C, a free phenol content of 3-7 wt%, and a residual carbon content of 35-40 wt%; phenolic resin C has a viscosity of 10,000-14,000 cp at 25°C, a free phenol content of 10-12 wt%, and a residual carbon content of 43-47 wt%; (2) Adding natural graphite and modified phenolic resin into a reactor, and then adding modified graphene, stirring and heating the reactor under nitrogen atmosphere for coating, specifically: first heating to 150-200°C at 1-2°C / min, keeping the temperature for 100-120min, then heating to 550-600°C at 4-6°C / min, keeping the temperature for 180-200min, and cooling to obtain coated graphite; the weight ratio of the natural graphite, modified phenolic resin, and modified graphene is 100: (3-5): (2-4); the modified graphene is heated to 150-200°C at 1-2°C / min, keeping the temperature for 100-120min, and ... cooling to obtain coated graphite; the weight ratio of the natural graphite, modified phenolic resin, and modified graphene is 100: (3-5): (2-4); the modified graphene is heated to 150-200°C at 1-2°C / min, keeping the temperature for 100-120min, and then cooling to obtain coated graphite; the weight ratio of the natural graphite, modified phenolic resin, and modified graphene is 100: (3-5): (2-4); the modified graphene is heated to 150-200°C at 1-2°C / min, and keeping the temperature for 100-120min. The preparation method of graphene comprises the following steps: mixing 1 part by weight of graphene oxide, 7-9 parts by weight of p-phenylenediamine, 0.2-0.3 parts by weight of polyethylene glycol 600 and 15-20 parts by weight of water, and reacting the mixture under reflux and stirring at 80-85° C. for 4-5 hours to obtain a p-phenylenediamine-modified graphene oxide dispersion; adding hydrazine hydrate to the p-phenylenediamine-modified graphene oxide dispersion, and reacting the mixture at 80-85° C. for 26-28 hours; centrifuging and vacuum drying to obtain modified graphene; the mass ratio of hydrazine hydrate to graphene oxide is (2-4):1; (3) The coated graphite is placed in an atmosphere furnace for carbonization and sieved to obtain a graphite negative electrode material for lithium batteries.

2. The method for preparing a graphite negative electrode material for a lithium battery according to claim 1, wherein The particle size D50 of the natural graphite in step (2) is 10-30 μm.

3. The method for preparing a graphite negative electrode material for a lithium battery according to claim 1, wherein The sheet diameter of graphene oxide is 10-20 μm and the thickness is 1-5 nm.

4. The method for preparing a graphite negative electrode material for a lithium battery according to claim 1, wherein The stirring speed in step (2) is 15-25 r / min.

5. The method for preparing a graphite negative electrode material for a lithium battery according to claim 1, wherein In step (3), the carbonization temperature is 700-900° C., and the carbonization time is 7-9 hours.

6. A graphite negative electrode material for a lithium battery prepared by the preparation method according to any one of claims 1 to 5.

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