Hard carbon negative electrode material and preparation method thereof

Abstract

The application discloses a kind of hard carbon negative electrode material and preparation method thereof, belong to battery material technical field.The preparation method of the hard carbon negative electrode material includes the following steps: epoxy resin is uniformly mixed with phthalic anhydride, is heated and solidified, and is made into powder;Powder is pre-carbonized and high-temperature carbonization treatment is obtained hard carbon material;Modified siloxane is reacted with hard carbon material to obtain negative electrode active material;N-methyl pyrrolidone, negative electrode active material, conductive agent, binder are mixed uniformly after being coated on copper foil, and are dried after being rolled to obtain hard carbon negative electrode material;The modified siloxane is obtained by 3,5-difluorocinnamic acid and diethanolamine reaction 3-(bis (2-hydroxyethyl) amino) -3-(3,5-difluorophenyl) propionic acid, and then reacts with 3-chloropropyl trimethoxysilane to prepare it.The hard carbon negative electrode material prepared by the application can effectively reduce the interface charge transfer impedance, has excellent initial coulomb efficiency and cycle stability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of battery materials, in particular to a hard carbon negative electrode material and a preparation method thereof. BACKGROUND

[0002] In the field of ion batteries, sodium ion batteries are gradually becoming a research hotspot due to their low cost and abundant resources. However, compared with lithium ion batteries, the performance of sodium ion batteries still needs to be improved. Among the many candidate materials, hard carbon has become one of the most promising negative electrode materials for sodium ion batteries due to its unique disordered carbon layer structure, wide voltage platform characteristics and industrial production feasibility. However, hard carbon materials have the problems of low reversible capacity and large specific surface area, which will result in low initial coulombic efficiency and affect the long cycle performance of sodium ion batteries. Therefore, through the synergistic innovation of advanced carbon source screening strategy and microstructure regulation technology, it is important to build hard carbon materials with fast ion diffusion dynamics and long cycle stability to improve the performance of sodium ion batteries.

[0003] The Chinese invention with the publication number CN119038524A discloses a preparation method of a hard carbon negative electrode material. The invention obtains a porous material by high-temperature carbonization of plant materials in an inert atmosphere, embeds or attaches organic pyrolytic carbon inside or on the surface of the porous material through one-step pyrolysis and two-step pyrolysis, and inserts high-conductive carbon nanotubes between the porous material and the pyrolytic carbon to form a good conductive network. Then, the high-conductive carbon nanotubes and the organic pyrolytic carbon form a part of parallel arranged graphite structure through calcination, thereby improving the rate performance of the hard carbon negative electrode material. The carbon negative electrode material obtained by the preparation method of the invention has high ion storage sites, good conductive performance, low internal resistance, and high rate performance, but its long-term cycle stability is poor. SUMMARY

[0004] In view of the deficiencies of the prior art, the purpose of the present application is to provide a hard carbon negative electrode material and a preparation method thereof.

[0005] To achieve the above-mentioned purpose, the present application realizes the following technical scheme:

[0006] A preparation method of a hard carbon negative electrode material, comprising the following steps:

[0007] (1) uniformly mixing epoxy resin and phthalic anhydride, and heating and curing to form a powder;

[0008] (2) performing pre-carbonization treatment and high-temperature carbonization treatment on the powder to obtain a hard carbon material;

[0009] (3) reacting modified siloxane with the hard carbon material to obtain a negative electrode active material;

[0010] (4) mixing N-methyl pyrrolidone, negative active material, conductive agent and binder uniformly, coating on copper foil, drying and rolling to obtain hard carbon negative electrode material;

[0011] The modified siloxane is prepared by the following method:

[0012] S1: 3,5-difluorocinnamic acid reacts with diethanolamine in methanol to generate 3-(bis(2-hydroxyethyl)amino)-3-(3,5-difluorophenyl)propionic acid; the reaction equation is as follows:

[0013]

[0014] S2: 3-(bis(2-hydroxyethyl)amino)-3-(3,5-difluorophenyl)propionic acid reacts with 3-chloropropyltrimethoxysilane to generate modified siloxane; the reaction equation is as follows:

[0015]

[0016] In step S1, the feeding molar ratio of 3,5-difluorocinnamic acid to diethanolamine is 1:(1.5-1.8); in step S2, the feeding molar ratio of 3-(bis(2-hydroxyethyl)amino)-3-(3,5-difluorophenyl)propionic acid to 3-chloropropyltrimethoxysilane is 1:(2.2-2.5).

[0017] In step (1), the feeding mass ratio of the epoxy resin to phthalic anhydride is 10:(6-8), the curing temperature is 130-140℃, and the curing time is 6-8h.

[0018] In step (2), the pre-carbonization treatment temperature is 400-500℃, and the holding time is 1-2h; the high-temperature carbonization treatment temperature is 1000-1300℃, and the holding time is 30-60min.

[0019] In step (3), the feeding mass ratio of the modified siloxane to the hard carbon material is (1-3):10.

[0020] In step (4), the conductive agent is one of conductive carbon black and conductive graphite.

[0021] In step (4), the binder is prepared by the following method:

[0022] N1: N-benzoyl-DL-homocysteine reacts in DMSO to generate 4,4'-dithiobis(2-benzamidobutyric acid); the reaction equation is as follows:

[0023]

[0024] N2: 4,4'-dithiobis(2-benzamidobutyric acid) reacts with sodium carboxymethyl cellulose to form a binder, in which the hydroxyl group in sodium carboxymethyl cellulose esterifies with the carboxylic acid in 4,4'-dithiobis(2-benzamidobutyric acid) to form a binder with a three-dimensional network structure.

[0025] In step N1, the mass ratio of the N-benzoyl-DL-homocysteine to DMSO is 1:6; in step N2, the mass ratio of the 4,4'-dithiobis(2-benzamidobutyric acid) to sodium carboxymethyl cellulose is 1:12.

[0026] In step (4), the mass ratio of the negative electrode active material, the conductive agent, and the binder is (70-80):10:(5-15).

[0027] A hard carbon negative electrode material is prepared by the above method.

[0028] Due to the above technical solutions, the present application has the following beneficial effects:

[0029] (1) The hard carbon negative electrode material prepared by the present application has modified siloxane loaded on the surface of the hard carbon material, which can effectively reduce the interface charge transfer impedance and enhance the cycle stability; the carboxyl group, the strong electronegative fluorine atom, and the benzene ring are introduced into the hard carbon negative electrode material through the modified siloxane, and the synergistic effect of the three improves the charge specific capacity, the first coulombic efficiency, and the cycle stability.

[0030] (2) The binder prepared by the present application forms hydrogen bonds or covalent bonds on the surface of the negative electrode active material and the conductive agent through the carboxyl group and the hydroxyl group, and increases the adhesion through the three-dimensional network structure; the dynamic bond effect of the disulfide bond in the binder can effectively alleviate the interface damage generated during the battery cycle. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 The high-resolution mass spectrum of the modified siloxane prepared in Example 1.

[0032] Figure 2 The high-resolution mass spectrum of 4,4'-dithiobis(2-benzamidobutyric acid) prepared in Example 4. DETAILED DESCRIPTION

[0033] The present application will be further described below in conjunction with examples, but the present application is not limited to these examples.

[0034] Example 1 Preparation of modified siloxane

[0035] S1: 600 ml of methanol and 1.5 mol of diethanolamine were placed in a reaction kettle under nitrogen protection, and 500 ml of a methanol solution containing 1 mol of 3,5-difluorocinnamic acid was added dropwise. After 2 h of dropwise addition, the reaction was allowed to proceed at room temperature for 18 h. The reaction mixture was distilled at 50°C under reduced pressure for 3 h to obtain 3-(bis(2-hydroxyethyl)amino)-3-(3,5-difluorophenyl)propionic acid. The nuclear magnetic resonance hydrogen spectrum data are as follows: 1 H NMR (300 MHz, Chloroform- d ) δ 10.80 (s, 1H), 7.01 - 6.82 (m, 3H), 4.17 (tt, J = 8.3, 0.7 Hz, 1H), 3.67 (qd, J = 5.8, 3.5 Hz, 4H), 3.08 - 2.95 (m, 3H), 2.88 (dt, J= 12.5, 5.7 Hz, 2H), 2.81 - 2.68 (m, 3H);

[0036] S2: 500 ml of toluene was added to the reaction kettle, and the temperature was raised to 100°C. After 2 h of water removal, the reaction mixture was cooled to room temperature. 0.1 mol of 3-(bis(2-hydroxyethyl)amino)-3-(3,5-difluorophenyl)propionic acid and 0.2 mol of KOH were added and stirred for 10 min. The mixture was mixed uniformly, and 0.22 mol of 3-chloropropyltrimethoxysilane was added. The reaction was carried out at 60°C for 12 h. After cooling to room temperature, the reaction mixture was filtered, and the filtrate was distilled at 60°C under reduced pressure for 2 h to obtain a modified siloxane. The nuclear magnetic resonance hydrogen spectrum data are as follows: 1 H NMR (300 MHz, Chloroform- d ) δ 10.80 (s, 1H), 7.01 - 6.82 (m, 3H), 4.13 (tt, J = 8.2, 0.7 Hz, 1H), 3.59 (s, 18H), 3.52 (d, J = 3.6 Hz, 4H), 3.40 (t, J = 7.3 Hz, 4H), 3.01 (dd, J = 16.0, 8.2 Hz, 1H), 2.92 - 2.64 (m, 5H), 1.68 - 1.51 (m, 4H), 0.75 (t, J = 9.8 Hz, 4H);HRMS(m / z)=613.2674。

[0037] Example 2 Preparation of modified siloxane

[0038] S1: 600 ml of methanol and 1.6 mol of diethanolamine were placed in a reaction kettle under ice water bath, 500 ml of methanol solution containing 1 mol of 3,5-difluorocinnamic acid was added dropwise under nitrogen protection, 2 h after dropping, it was raised to room temperature for reaction for 20 h, 3-(bis(2-hydroxyethyl)amino)-3-(3,5-difluorophenyl)propionic acid was obtained by distillation at 50 ℃ under reduced pressure for 3 h;

[0039] S2: 500 ml of toluene was added into the reaction kettle, and it was heated to 100 ℃, water was removed for 2 h, and then it was cooled to room temperature, 0.1 mol of 3-(bis(2-hydroxyethyl)amino)-3-(3,5-difluorophenyl)propionic acid and 0.2 mol of KOH were added and stirred for 10 min, and then 0.24 mol of 3-chloropropyltrimethoxysilane was added, and the mixture was reacted at 70 ℃ for 8 h, and then it was cooled to room temperature, filtered, and then 2 h of distillation at 60 ℃ under reduced pressure to obtain modified siloxane.

[0040] Example 3: Preparation of modified siloxane

[0041] S1: 600 ml of methanol and 1.6 mol of diethanolamine were placed in a reaction kettle under ice water bath, 500 ml of methanol solution containing 1 mol of 3,5-difluorocinnamic acid was added dropwise under nitrogen protection, 2 h after dropping, it was raised to room temperature for reaction for 20 h, 3-(bis(2-hydroxyethyl)amino)-3-(3,5-difluorophenyl)propionic acid was obtained by distillation at 50 ℃ under reduced pressure for 3 h;

[0042] S2: 500 ml of toluene was added into the reaction kettle, and it was heated to 100 ℃, water was removed for 2 h, and then it was cooled to room temperature, 0.1 mol of 3-(bis(2-hydroxyethyl)amino)-3-(3,5-difluorophenyl)propionic acid and 0.2 mol of KOH were added and stirred for 10 min, and then 0.24 mol of 3-chloropropyltrimethoxysilane was added, and the mixture was reacted at 70 ℃ for 8 h, and then it was cooled to room temperature, filtered, and then 2 h of distillation at 60 ℃ under reduced pressure to obtain modified siloxane.

[0043] Example 4: Preparation of adhesive

[0044] N1: 300 g of DMSO and 50 g of N-benzoyl-DL-homocysteine were sequentially added into a reaction kettle, stirred and uniformly mixed, heated to 80 ℃ for reaction for 12 h, distilled at 80 ℃ under reduced pressure for 2 h, and then purified by using a silica gel chromatographic column (the eluent was a mixed solvent of methanol and dichloromethane, and the volume ratio of methanol to dichloromethane was = 10:1) to obtain 4,4'-dithiobis(2-benzamidobutyric acid); the nuclear magnetic resonance hydrogen spectrum data are as follows: 1 H NMR (300 MHz, Chloroform- d) δ 10.94 (s, 2H), 7.94 (d, J = 8.5 Hz, 2H), 7.86-7.75 (m, 4H), 7.57-7.39 (m, 6H), 4.40 (dt, J = 8.6, 5.0 Hz, 2H), 2.87 (dt, J = 13.7, 5.2 Hz, 2H), 2.73 (dt, J = 13.7, 5.3 Hz, 2H), 2.23 (dq, J = 13.3, 5.2 Hz, 2H), 2.05-1.91 (m, 2H); HRMS (m / z) = 476.1143.

[0045] N2: Put 700 ml of DMF, 800 ml of formamide, 8 g of p-toluene sulfonic acid into the reaction kettle, stir and mix, add 10 g of 4,4'-dithiobis(2-benzamidobutyric acid), 15 g of 4-dimethylaminopyridine, 12 g of N,N-dicyclohexyl carbodiimide, stir, warm up to 60°C, stir for 30 min, add 120 g of sodium carboxymethyl cellulose, react for 10 h, add 1500 ml of anhydrous ethanol, stir to precipitate, filter, wash with anhydrous ethanol three times (300 ml each time), and vacuum dry at 50°C for 12 h to obtain the binder.

[0046] Example 5 Preparation of hard carbon negative electrode material

[0047] (1) Mix 100 g of epoxy resin with 60 g of phthalic anhydride uniformly, heat to 130°C for 8 h for curing, cool to room temperature, and use a vibration mill to make a powder with a particle size of 200 mesh;

[0048] (2) Under nitrogen protection, transfer 50 g of the powder into a tube furnace, perform pre-carbonization treatment, warm up to 400°C at a rate of 5°C / min, after holding for 2 h, perform high-temperature carbonization treatment, warm up to 1000°C at a rate of 4°C / min, hold for 60 min, and naturally cool to room temperature to obtain the hard carbon material;

[0049] (3) Add 100 ml of methanol, 10 ml of deionized water, and 1 g of modified siloxane (prepared in Example 1) into the reaction kettle in sequence, stir and mix uniformly, adjust the pH to 4 using acetic acid, warm up to 40°C, add 10 g of the hard carbon material, react for 2 h, filter, and vacuum dry at 80°C for 6 h to obtain the negative electrode active material;

[0050] (4) Mix 15 g of N-methyl pyrrolidone, 7 g of the negative electrode active material, 1 g of the conductive agent (conductive graphite), and 0.5 g of the binder (prepared in Example 4) uniformly, coat on a copper foil with a coating thickness of 75 μm, vacuum dry at 100°C for 5 h, roll at 10 MPa, and obtain the hard carbon negative electrode material.

[0051] Example 6 Preparation of hard carbon negative electrode material

[0052] (1) 100 g of epoxy resin was mixed with 70 g of phthalic anhydride, heated to 135°C for 7 h for curing, and cooled to room temperature. A vibration mill was used to prepare a powder with a particle size of 200 mesh;

[0053] (2) Under nitrogen protection, 50 g of the powder was transferred to a tube furnace for pre-carbonization treatment, heated to 450°C at a heating rate of 5°C / min, and kept for 1.5 h. Then high-temperature carbonization treatment was carried out, heated to 1200°C at a heating rate of 4°C / min, and kept for 45 min. The hard carbon material was obtained by natural cooling to room temperature;

[0054] (3) 100 ml of methanol, 10 ml of deionized water, and 2 g of modified siloxane (prepared in Example 2) were sequentially added to a reaction kettle and stirred uniformly. Acetic acid was used to adjust the pH to 4, and the temperature was raised to 45°C. 10 g of hard carbon material was added and reacted for 2 h. Filtration and vacuum drying at 80°C for 6 h obtained the negative electrode active material;

[0055] (4) 15 g of N-methyl pyrrolidone, 7.5 g of negative electrode active material, 1 g of conductive agent (conductive carbon black), and 1.0 g of binder (prepared in Example 4) were mixed uniformly and coated on a copper foil with a coating thickness of 75 μm. Vacuum drying at 100°C for 5 h and rolling at 10 MPa obtained the hard carbon negative electrode material.

[0056] Example 7 Preparation of hard carbon negative electrode material

[0057] (1) 100 g of epoxy resin was mixed with 40 g of phthalic anhydride, heated to 140°C for 6 h for curing, and cooled to room temperature. A vibration mill was used to prepare a powder with a particle size of 200 mesh;

[0058] (2) Under nitrogen protection, 50 g of the powder was transferred to a tube furnace for pre-carbonization treatment, heated to 500°C at a heating rate of 5°C / min, and kept for 1 h. Then high-temperature carbonization treatment was carried out, heated to 1300°C at a heating rate of 4°C / min, and kept for 30 min. The hard carbon material was obtained by natural cooling to room temperature;

[0059] (3) 100 ml of methanol, 10 ml of deionized water, and 3 g of modified siloxane (prepared in Example 3) were sequentially added to a reaction kettle and stirred uniformly. Acetic acid was used to adjust the pH to 4, and the temperature was raised to 50°C. 10 g of hard carbon material was added and reacted for 2 h. Filtration and vacuum drying at 80°C for 6 h obtained the negative electrode active material;

[0060] (4) 15 g of N-methylpyrrolidone, 8 g of negative active material, 1 g of conductive agent (conductive carbon black), and 1.5 g of binder (prepared in Example 4) were mixed uniformly and coated on a copper foil, the coating thickness was 75 μm, vacuum dried at 100°C for 5 h, and roll-pressed at 10 MPa to obtain a hard carbon negative electrode material.

[0061] Comparative Example 1

[0062] (1) 100 g of epoxy resin was mixed uniformly with 70 g of phthalic anhydride, heated to 135°C and reacted for 7 h for curing, and then cooled to room temperature, and a powder having a particle size of 200 mesh was prepared using a vibration mill;

[0063] (2) 50 g of the powder was transferred to a tube furnace under nitrogen protection, heated to 450°C at a heating rate of 5°C / min, kept at 450°C for 1.5 h, heated to 1200°C at a heating rate of 4°C / min, kept at 1200°C for 45 min, and then naturally cooled to room temperature to obtain a hard carbon material;

[0064] (3) 15 g of N-methylpyrrolidone, 7.5 g of hard carbon material, 1 g of conductive agent (conductive carbon black), and 1.0 g of binder (prepared in Example 4) were mixed uniformly and coated on a copper foil, the coating thickness was 75 μm, vacuum dried at 100°C for 5 h, and roll-pressed at 10 MPa to obtain a hard carbon negative electrode material.

[0065] Comparative Example 2

[0066] The raw material composition and process of the hard carbon negative electrode material were basically the same as those of Example 6, except that the modified siloxane (prepared in Example 2) used in step (3) was replaced with an equal amount of modified siloxane prepared by the following method:

[0067] The preparation method of the modified siloxane was basically the same as that of Example 2, except that 3,5-difluorocinnamic acid in step S1 was replaced with an equal molar amount of cinnamic acid.

[0068] Comparative Example 3

[0069] The raw material composition and process of the hard carbon negative electrode material were basically the same as those of Example 6, except that the modified siloxane (prepared in Example 2) used in step (3) was replaced with an equal amount of modified siloxane prepared by the following method:

[0070] The preparation method of the modified siloxane was basically the same as that of Example 2, except that 3,5-difluorocinnamic acid in step S1 was replaced with an equal molar amount of 4,4-difluorobut-2-enoic acid.

[0071] Comparative Example 4

[0072] The raw material composition and process of the hard carbon negative electrode material are basically the same as those of Example 6, except that the modified siloxane used in step (3) (prepared in Example 2) is replaced with an equal weight of modified siloxane prepared by the following method:

[0073] The preparation method of the modified siloxane is basically the same as that of Example 2, except that the 3,5-difluorocinnamic acid in step S1 is replaced with an equal molar amount of 3,5-difluorostyrene.

[0074] Comparative Example 5

[0075] The raw material composition and process of the hard carbon negative electrode material are basically the same as those of Example 6, except that the modified siloxane used in step (3) (prepared in Example 2) is replaced with an equal weight of modified siloxane prepared by the following method:

[0076] The preparation method of the modified siloxane is basically the same as that of Example 2, except that the 3,5-difluorocinnamic acid in step S1 is replaced with an equal molar amount of 2,4-difluorocinnamic acid.

[0077] Comparative Example 6

[0078] The raw material composition and process of the hard carbon negative electrode material are basically the same as those of Example 6, except that the binder used in step (4) (prepared in Example 4) is replaced with an equal weight of binder prepared by the following method:

[0079] Into a reaction kettle, 700 ml of DMF, 800 ml of formamide, and 8 g of p-toluene sulfonic acid were added and stirred to mix, 10 g of N-benzoyl-DL-homocysteine, 15 g of 4-dimethylaminopyridine, and 12 g of N,N-dicyclohexyl carbodiimide were added and stirred, the temperature was raised to 60°C, and stirred for 30 min, 15 g of 4-dimethylaminopyridine, 12 g of N,N-dicyclohexyl carbodiimide, and 120 g of sodium carboxymethyl cellulose were added in sequence, and reacted for 10 h, 1500 ml of anhydrous ethanol was added and stirred to precipitate, filtered, washed with anhydrous ethanol three times (300 ml each time), and vacuum dried at 50°C for 12 h to obtain the binder.

[0080] Comparative Example 7

[0081] The raw material composition and process of the hard carbon negative electrode material are basically the same as those of Example 6, except that the binder used in step (4) (prepared in Example 4) is replaced with an equal weight of binder prepared by the following method:

[0082] The preparation method of the binder is basically the same as that of Example 4, except that the N-benzoyl-DL-homocysteine in step N1 is replaced with an equal weight of L-homocysteine.

[0083] The epoxy resin used in the present application is bisphenol A type epoxy resin, model E-51; the conductive carbon black is model Super P; the conductive graphite is 1000 mesh graphite powder produced by Qingdao Dongkai Graphite Co., Ltd.; the sodium carboxymethyl cellulose is model FVH6-5, with a degree of substitution of 0.7DS, produced by Changzhou Guoyu Environmental Protection Technology Co., Ltd.

[0084] The hard carbon negative electrode materials prepared in Examples 5-7 and Comparative Examples were used as working electrodes, sodium metal sheets were used as counter electrodes, ester electrolyte was 1.0M NaPF6 in EC / DMC (1:1 vol / vol), where EC and DMC were ethylene carbonate and dimethyl carbonate respectively, and the separator was Celgard 2325. C2032 type button cells were assembled in an argon-filled glove box, and after assembly, they were left to stand for 24h, and then electrochemical performance tests were carried out at a constant temperature of 25℃. The first charge-discharge test was carried out at a current density of 0.1C, and the charge-discharge cut-off voltages were 2V and 0V respectively; the cycle stability test was carried out at a current density of 1C, and the cycle period was 1000 times. The test results are shown in Table 1.

[0085] Table 1 Electrochemical performance test data of battery materials assembled with hard carbon negative electrodes

[0086]

[0087] As can be seen from Examples 5, 6 and 7 in Table 1, the battery assembled with the hard carbon negative electrode material prepared in the present application has excellent charge specific capacity, first coulombic efficiency and cycle stability performance.

[0088] In the present application, the modified siloxane is covalently connected to the oxygen-containing functional groups of the hard carbon material under the action of acetic acid, forming an organic / inorganic hybrid solid electrolyte interface, which can effectively reduce the interface charge transfer impedance and enhance the cycle stability. The carboxyl groups in the modified siloxane prepared in the present application can provide additional active sites to promote the adsorption and intercalation of sodium ions, thereby increasing the charge specific capacity; the conjugated structure of the benzene ring can enhance the charge transport capacity and provide π electron storage sites to increase the charge specific capacity; the F atom has strong electronegativity, which can reduce the diffusion barrier of sodium ions, improve the intercalation and deintercalation efficiency of sodium ions, and the fluorocarbon bond has high bond energy, which can enhance the structural stability. The 3,5-difluoro-substituted symmetrical structure makes the benzene ring more stable, and the uniform electron cloud distribution is more conducive to the combination with sodium ions, so that the charge specific capacity is increased.

[0089] The binder prepared by the application contains a large number of carboxyl (-COOH) and hydroxyl (-OH) functional groups, which can form hydrogen bonds or covalent bonds with oxygen-containing functional groups or silicon hydroxyl groups on the surface of the negative active material, thereby providing a bonding effect. The binder prepared by the application contains a disulfide bond, and the dynamic bonding effect endows the interface with self-adjusting and self-repairing ability, effectively relieving the interface damage generated during the battery cycle process; the rigid skeleton of the benzene ring can relieve volume expansion and improve cycle stability.

[0090] The above is only the preferred embodiment of the application and is not used to limit the application; but for ordinary skilled in the art without departing from the scope of the technical solutions of the application, some changes, modifications and equivalent changes of the above disclosed technical content can be made, which are equivalent embodiments of the application; at the same time, any equivalent changes, modifications and evolution of the above embodiments according to the essential technology of the application are still within the protection scope of the technical solutions of the application.

Claims

1. A method for preparing a hard carbon negative electrode material, characterized by, The method comprises the following steps: (1) uniformly mixing epoxy resin and phthalic anhydride, heating and curing to form a powder; (2) performing pre-carbonization treatment and high-temperature carbonization treatment on the powder to obtain a hard carbon material; (3) reacting the modified siloxane with the hard carbon material to obtain a negative electrode active material; (4) uniformly mixing N-methyl pyrrolidone, the negative electrode active material, a conductive agent and a binder, coating the mixture on a copper foil, drying and then rolling to obtain a hard carbon negative electrode material; The modified siloxane is prepared by the following method: S1: reacting 3,5-difluorocinnamic acid with diethanolamine in methanol to form 3-(bis(2-hydroxyethyl)amino)-3-(3,5-difluorophenyl)propionic acid, S2: reacting 3-(bis(2-hydroxyethyl)amino)-3-(3,5-difluorophenyl)propionic acid with 3-chloropropyltrimethoxysilane to obtain the modified siloxane; In step S1, the molar ratio of 3,5-difluorocinnamic acid to diethanolamine is 1:(1.5-1.8); in step S2, the molar ratio of 3-(bis(2-hydroxyethyl)amino)-3-(3,5-difluorophenyl)propionic acid to 3-chloropropyltrimethoxysilane is 1:(2.2-2.5).

2. The method for preparing a hard carbon anode material according to claim 1, characterized in that, In step (1), the mass ratio of the epoxy resin to phthalic anhydride is 10:(6-8), the curing temperature is 130-140°C, and the curing time is 6-8h.

3. The method for preparing a hard carbon anode material according to claim 1, characterized in that, In step (2), the pre-carbonization treatment temperature is 400-500°C, and the holding time is 1-2h; the high-temperature carbonization treatment temperature is 1000-1300°C, and the holding time is 30-60min.

4. The method of claim 1, wherein the hard carbon negative electrode material is prepared by the steps of: preparing a mixture of a carbon source and a polymer; and heating the mixture to form the hard carbon negative electrode material. In step (3), the mass ratio of the modified siloxane to the hard carbon material is (1-3):

10.

5. The method of claim 1, wherein the hard carbon negative electrode material is prepared by the steps of: preparing a mixture of a carbon source and a polymer; and heating the mixture to form the hard carbon negative electrode material. In step (4), the conductive agent is one of conductive graphite and conductive carbon black.

6. The method for preparing a hard carbon anode material according to claim 1, characterized in that, In step (4), the binder is prepared by the following method: N1: reacting N-benzoyl-DL-homocysteine in DMSO to form 4,4'-dithiobis(2-benzamidobutyric acid); N2: reacting 4,4'-dithiobis(2-benzamidobutyric acid) with sodium carboxymethyl cellulose to form the binder.

7. The method for preparing a hard carbon anode material according to claim 6, characterized in that, In step N1, the mass ratio of N-benzoyl-DL-homocysteine to DMSO is 1:6; in step N2, the mass ratio of 4,4'-dithiobis(2-benzamidobutyric acid) to sodium carboxymethyl cellulose is 1:

12. 8.The method of claim 1, wherein the hard carbon negative electrode material is prepared by the following steps: mixing a carbon source and a solvent to obtain a mixture; and heating the mixture to obtain the hard carbon negative electrode material. In step (4), the mass ratio of the negative electrode active material, the conductive agent and the binder is (70-80):10:(5-15).

9. A hard carbon negative electrode material, characterized in that, The method is prepared by any one of claims 1-8.

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