Negative electrode porous carbon material and preparation method thereof

Abstract

The invention discloses a negative electrode porous carbon material and a preparation method thereof, and belongs to the technical field of sodium ion battery negative electrode materials, carboxyl of acrylic acid reacts with carboxyl of 2-hydroxyaniline, residual hydroxyl groups are combined with silicon hydroxyl generated by hydrolysis of 3-mercaptopropyltrimethoxysilane, and the negative electrode porous carbon material is obtained. Sulfonic acid modified acrylic acid / aniline is obtained under the action of hydrogen peroxide, sulfur and nitrogen doped conductive hollow carbon spheres are formed after calcination, sulfur doping can participate in formation of an SEI film, a stable interface layer is generated, electrolyte decomposition and irreversible consumption of active lithium are reduced, the first coulombic efficiency is improved, and nitrogen doping can construct an electron high-speed channel and improve conductivity. The conductive hollow carbon spheres are coated with the MXene nanosheets and deposited on the surface of the foamy carbon, and the effect of combining rigidity and softness can be achieved while volume expansion is relieved through layered, hollow and foamy three-stage synergism.

Description

Technical Field

[0001] The present invention belongs to the technical field of anode materials for sodium-ion batteries, and specifically relates to a porous carbon anode material and a preparation method thereof. Background Art

[0002] Lithium batteries are a common type of rechargeable secondary battery, which structurally include a positive electrode material, a negative electrode material, an electrolyte, and a separator, etc. The separator is used to isolate the positive electrode and the negative electrode to prevent short circuits. The electrolyte is a conductive medium between the positive electrode and the negative electrode, and its main function is to allow lithium ions to be transmitted between the positive electrode and the negative electrode. The positive electrode material of a lithium-ion battery is generally a lithium-containing compound, and the negative electrode material is generally a carbon material. During the charging process, lithium ions move from the positive electrode to the negative electrode and are embedded in the negative electrode material. During the discharging process, lithium ions are deintercalated from the negative electrode and return to the positive electrode. Compared with lead-acid batteries, lithium batteries have the advantages of high energy density, high working voltage, low self-discharge rate, small size, light weight, and long cycle life, and are widely used in various portable electronic devices, electric vehicles, drones and other products.

[0003] With the development of the new energy vehicle industry, research on improving the energy density of lithium batteries is also continuously carried out. The energy density of lithium batteries is affected by multiple factors. In addition to the limitations of the size and shape of the battery itself, and the influence of battery operating temperature, etc., the energy densities of the positive electrode material and the negative electrode material are the key factors determining the energy density of lithium-ion batteries. Existing negative electrode materials have the problem of relatively large shrinkage and expansion rates. During the charge and discharge process of the battery, due to volume changes, cracks or peeling occur in the negative electrode material, ultimately affecting the service life of the battery.

[0004] Chinese Patent CN109256541B announced a hard carbon anode material, which synthesized a nano-ribbon-like V3O7 with crystal water as the anode material of the battery by an oil-water mixed heat method. It has a typical layered crystal structure and a relatively large interlayer spacing, which is beneficial to the free movement of lithium ions between the layers. The anode material has a soft one-dimensional nano-like morphology, which can shorten the diffusion distance of lithium ions and relieve the volume change generated by the deintercalation and intercalation of lithium ions. However, the mitigation ability of the nano-ribbons in this scheme is relatively low and is not sufficient to effectively relieve the volume change after multiple cycles. Summary of the Invention

[0005] The purpose of the present invention is to provide a porous carbon anode material and a preparation method thereof. By coating MXene nanosheets on conductive hollow carbon spheres and depositing them on the surface of carbon foam, through the three-level synergy of layered, hollow and foam-like structures, the effect of combining rigidity and flexibility can be achieved when relieving volume expansion.

[0006] The purpose of the present invention can be achieved through the following technical solutions: A preparation method of a porous carbon anode material includes the following steps: Add a formaldehyde solution with a mass fraction of 30 - 40%, ammonium dihydrogen phosphate, phenol, MXene nanosheet-coated conductive hollow carbon spheres, and deionized water A into a reaction kettle, stir at 55 - 60 °C and 500 - 600 r / min for 1 - 2 h, then add a sodium hydroxide solution with a mass fraction of 1 - 2%, continue to react for 1 - 2 h, heat at 95 - 100 °C for 1 - 2 h, cool the product to 60 - 70 °C, adjust the pH value to neutral with a hydrochloric acid solution with a concentration of 1 mol / L, and carry out vacuum distillation and dehydration under a vacuum degree of 0.092 - 0.098 MPa. Place the product in a mixed solution of Tween 80, n-pentane, concentrated sulfuric acid, and deionized water B, stir at 3000 - 3500 r / min for 20 - 25 min, transfer the mixture to a mold, foam and cure at 60 - 70 °C for 20 - 22 h, transfer the product to a muffle furnace, and calcine at 550 - 600 °C for 2 - 3 h under nitrogen protection to obtain a negative electrode porous carbon material.

[0007] Furthermore, the dosage ratio of the formaldehyde solution, ammonium dihydrogen phosphate, phenol, MXene nanosheet-coated conductive hollow carbon spheres, deionized water A, sodium hydroxide solution, Tween 80, n-pentane, concentrated sulfuric acid, and deionized water B is 70 - 80 mL : 12 - 14 g : 80 - 100 g : 15 - 20 g : 500 - 600 mL : 10 - 12 mL : 1 - 2 mL : 40 - 60 mL : 4 - 5 mL : 10 - 12 mL.

[0008] Furthermore, the preparation steps of the MXene nanosheet-coated conductive hollow carbon spheres are as follows: Add the conductive hollow carbon spheres, the suspension of MXene nanosheets, and N,N-dimethylformamide into a reaction kettle, stir at 20 - 25 °C and 400 r / min for 4 - 5 h, centrifuge at 5000 - 6000 r / min for 10 - 15 min, filter, wash the filter cake with deionized water and ethanol 2 - 4 times, and vacuum dry at 60 - 70 °C for 1 - 2 h to obtain the MXene nanosheet-coated conductive hollow carbon spheres.

[0009] Furthermore, the dosage ratio of the conductive hollow carbon spheres, the suspension of MXene nanosheets, and N,N-dimethylformamide is 20 - 30 g : 40 - 50 g : 1 - 2 L.

[0010] Furthermore, the preparation steps of the conductive hollow carbon spheres are as follows: Add polystyrene nanospheres with a particle size of 20 - 30 nm, sulfonic acid - modified acrylic acid / aniline, and deionized water into a reaction kettle. Stir at 20 - 25 °C and 400 r / min for 20 - 30 min, then add ammonium persulfate as an initiator, heat to 80 - 90 °C, continue stirring for 4 - 5 h, cool down to 0 °C, and continue reacting for 12 - 14 h. Filter, wash the filter cake with N,N - dimethylformamide to remove the polystyrene template, then wash with absolute ethanol 2 - 4 times, and vacuum - dry at 60 - 70 °C for 1 - 2 h. Transfer the product to a muffle furnace, and calcine at 550 - 600 °C for 2 - 3 h under nitrogen protection to obtain conductive hollow carbon spheres.

[0011] Further, the dosage ratio of polystyrene nanospheres, sulfonic acid - modified acrylic acid / aniline, deionized water, and ammonium persulfate is 20 - 30 g : 50 - 60 g : 1 - 2 L : 2 - 3 g Further, the preparation steps of the suspension of MXene nanosheets are as follows: Add lithium fluoride and a hydrochloric acid solution with a mass fraction of 35 - 40% into a reaction kettle. Stir at 20 - 25 °C and 400 r / min for 20 - 30 min, then add aluminum titanium carbide, continue stirring for 48 - 50 h, centrifuge at 5000 - 6000 r / min for 3 - 5 min, filter, wash the filter cake with deionized water and ethanol until the last washing liquid is neutral, perform ultrasonic exfoliation at an argon flow rate of 20 - 25 mL / min, and centrifuge at 5000 - 6000 r / min for 1 - 2 min to obtain a suspension of MXene nanosheets.

[0012] Further, the dosage ratio of lithium fluoride, hydrochloric acid solution, and aluminum titanium carbide is 30 - 40 g : 500 - 600 mL : 12 - 15 g.

[0013] Further, the preparation steps of sulfonic acid - modified acrylic acid / aniline are as follows: Add acrylic acid - modified hydroxyaniline, 3 - mercaptopropyltrimethoxysilane, and an ethanol solution into a reaction kettle. Stir at 60 - 70 °C and 500 - 600 r / min for 1 - 2 h, filter, wash the filter cake with deionized water 2 - 4 times, and vacuum - dry at 60 - 70 °C for 1 - 2 h to obtain mercapto - modified acrylic acid / aniline; add mercapto - modified acrylic acid / aniline and a hydrogen peroxide solution with a mass fraction of 20 - 25 wt% into the reaction kettle according to the dosage ratio of 20 - 30 g : 200 - 300 mL, stir and react at 20 - 25 °C and 500 - 600 r / min for 1 - 2 h, then add a 0.5 M sodium hydroxide solution until the pH value reaches 9, filter, wash the filter cake with deionized water and ethanol 2 - 4 times, and vacuum - dry at 60 - 70 °C for 1 - 2 h to obtain sulfonic acid - modified acrylic acid / aniline.

[0014] Furthermore, the dosage ratio of acrylic acid modified hydroxyaniline, 3-mercaptopropyltrimethoxysilane and ethanol solution is 40 - 50 g : 100 - 200 mL : 500 - 600 mL.

[0015] Furthermore, the preparation steps of acrylic acid modified hydroxyaniline are as follows: Add 2-hydroxyaniline and deionized water into the reaction kettle, stir at 80 - 85 °C and 400 - 500 r / min for 1 - 2 h, then add acrylic acid solution and inhibitor hydroquinone, continue to react for 1 - 2 h, filter, wash the filter cake with deionized water for 2 - 4 times, and vacuum dry at 60 - 70 °C for 1 - 2 h to obtain acrylic acid modified hydroxyaniline.

[0016] Furthermore, the dosage ratio of 2-hydroxyaniline, deionized water, acrylic acid solution and hydroquinone is 40 - 50 g : 200 - 300 mL : 50 - 60 mL : 0.5 - 0.8 g.

[0017] The beneficial effects of the present invention: 1. The present invention can significantly increase the conductivity of lithium batteries, promote the rapid transmission of lithium ions, alleviate the problem of volume expansion during the charge and discharge process of lithium batteries, and increase the cycle capacity, first discharge capacity and first Coulomb efficiency of lithium batteries.

[0018] 2. In the sulfonic acid modified acrylic acid / aniline of the present invention, acrylic acid modified hydroxyaniline is obtained by the reaction of the carboxyl group of acrylic acid with the carboxyl group of 2-hydroxyaniline. The remaining hydroxyl groups combine with the silanol groups generated by the hydrolysis of 3-mercaptopropyltrimethoxysilane to obtain mercapto modified acrylic acid / aniline, and sulfonic acid modified acrylic acid / aniline is obtained under the action of hydrogen peroxide. After calcination, polyaniline and sulfonic acid groups can form sulfur and nitrogen doped conductive hollow carbon spheres. Sulfur doping can participate in the formation of the SEI film, generate a stable interface layer, reduce the decomposition of the electrolyte and the irreversible consumption of active lithium, and improve the first Coulomb efficiency. Nitrogen doping can construct an electron high-speed channel and improve the conductivity.

[0019] 3. The MXene nanosheet-coated conductive hollow carbon spheres of the present invention are prepared by generating free radicals through the decomposition of ammonium persulfate with acrylic acid, initiating the copolymerization reaction of acrylic acid and aniline, forming a cross-linked shell layer on the surface using polystyrene nanospheres as a template, carbonizing after washing away the polystyrene template with N,N-dimethylformamide to obtain conductive hollow carbon spheres, and self-assembling the suspension of MXene nanosheets on the surface of the conductive hollow carbon spheres through hydrogen bonding to obtain MXene nanosheet-coated conductive hollow carbon spheres. The layered structure of the MXene nanosheets is coated on the surface of the hollow carbon spheres to form a core-shell structure. The nanosheets can rely on the layered structure and the hollow carbon spheres can rely on the hollow structure to further alleviate the volume expansion during the charge and discharge process of lithium batteries. The conductive hollow carbon spheres and MXene nanosheets have excellent electrical conductivity, which can increase the electrical conductivity of lithium batteries. The three-dimensional conductive network constructed by MXene nanosheets, conductive hollow carbon spheres and foam carbon can increase the electrical conductivity of lithium batteries and improve the high-rate performance of lithium batteries.

[0020] 4. Phenolic resin foam carbon is obtained by generating a phenolic resin foam material from formaldehyde and phenol and carbonizing it, and the surface is loaded with MXene nanosheet-coated conductive hollow carbon spheres. The internal cavity reserves expansion space for the insertion of lithium ions, alleviating the internal stress of the particles. The layered structure is flexible and can absorb the mechanical stress generated by volume changes to prevent the structure from collapsing. Brief Description of the Drawings

[0021] Figure 1 Scanning electron microscope image of the negative electrode porous carbon material of Example 3.

[0022] Figure 2 BET diagram data of Example 1.

[0023] Figure 3 BET diagram data of Example 2.

[0024] Figure 4 BET diagram data of Example 3.

[0025] Figure 5 BET diagram data of Comparative Example 1.

[0026] Figure 6 BET diagram data of Comparative Example 2.

[0027] Figure 7 BET diagram data of Comparative Example 3. Detailed Description of the Embodiments

[0028] Next, in combination with the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0029] Embodiment 1: A preparation method of a negative electrode porous carbon material, comprising the following steps: S1: Add 40 g of 2-hydroxyaniline and 200 mL of deionized water into a reaction kettle, stir at 80 °C and 400 r / min for 1 h, then add 50 mL of acrylic acid solution and 0.5 g of inhibitor hydroquinone, continue to react for 1 h, filter, wash the filter cake with deionized water twice, and dry it in vacuum at 60 °C for 1 h to obtain acrylic acid-modified hydroxyaniline.

[0030] S2: Add 40 g of acrylic acid-modified hydroxyaniline, 100 mL of 3-mercaptopropyltrimethoxysilane and 500 mL of ethanol solution into a reaction kettle, stir at 60 °C and 500 r / min for 1 h, filter, wash the filter cake with deionized water twice, and dry it in vacuum at 60 °C for 1 h to obtain mercapto-modified acrylic acid / aniline; add 20 g of mercapto-modified acrylic acid / aniline and 200 mL of hydrogen peroxide solution with a mass fraction of 20 wt% into a reaction kettle, stir and react at 20 °C and 500 r / min for 1 h, then add a sodium hydroxide solution with a concentration of 0.5 M until the pH value reaches 9, filter, wash the filter cake with deionized water and ethanol twice, and dry it in vacuum at 60 °C for 1 h to obtain sulfonic acid-modified acrylic acid / aniline.

[0031] S3: Add 20 g of polystyrene nanospheres with a particle size of 20 nm, 50 g of sulfonic acid-modified acrylic acid / aniline and 1 L of deionized water into a reaction kettle, stir at 20 °C and 400 r / min for 20 min, then add 2 g of initiator ammonium persulfate, heat to 80 °C, continue to stir for 4 h, cool to 0 °C, continue to react for 12 h, filter, wash the filter cake with N,N-dimethylformamide to remove the polystyrene template, then wash it with anhydrous ethanol twice, dry it in vacuum at 60 °C for 1 h, transfer the product to a muffle furnace, and calcine it at 550 °C for 2 h under nitrogen protection to obtain conductive hollow carbon spheres.

[0032] S4: Add 30 g of lithium fluoride and 500 mL of hydrochloric acid solution with a mass fraction of 35% into the reaction kettle, stir at 20 °C and 400 r / min for 20 min, then add 12 g of aluminum titanium carbide, continue to stir for 48 h, centrifuge at 5000 r / min for 3 min, filter, wash the filter cake with deionized water and ethanol until the last washing solution is neutral, perform ultrasonic exfoliation under an argon flow rate of 20 mL / min, and centrifuge at 5000 r / min for 1 min to obtain a suspension of MXene nanosheets.

[0033] S5: Add 20 g of conductive hollow carbon spheres, 40 g of the suspension of MXene nanosheets and 1 L of N,N-dimethylformamide into the reaction kettle, stir at 20 °C and 400 r / min for 4 h, centrifuge at 5000 r / min for 10 min, filter, wash the filter cake with deionized water and ethanol twice, and dry in vacuum at 60 °C for 1 h to obtain MXene nanosheets coated with conductive hollow carbon spheres.

[0034] S6: Add 70 mL of formaldehyde solution with a mass fraction of 30%, 12 g of ammonium dihydrogen phosphate, 80 g of phenol, 15 g of MXene nanosheets coated with conductive hollow carbon spheres and 500 mL of deionized water A into the reaction kettle, stir at 55 °C and 500 r / min for 1 h, then add 10 mL of sodium hydroxide solution with a mass fraction of 1%, continue to react for 1 h, heat at 95 °C for 1 h, cool the product to 60 °C, adjust the pH value to neutral with a hydrochloric acid solution with a concentration of 1 mol / L, and perform vacuum distillation and dehydration under a vacuum of 0.092 MPa. Place the product in a mixed solution of 1 mL of Tween 80, 40 mL of n-pentane, 4 mL of concentrated sulfuric acid and 10 mL of deionized water B, stir at 3000 r / min for 20 min, transfer the mixture to a mold, foam and cure at 60 °C for 20 h, transfer the product to a muffle furnace, and calcine at 550 °C for 2 h under nitrogen protection to obtain a negative electrode porous carbon material.

[0035] Example 2: A preparation method of a negative electrode porous carbon material, comprising the following steps: S1: Add 45 g of 2-hydroxyaniline and 250 mL of deionized water into the reaction kettle, stir at 82.5 °C and 450 r / min for 1.5 h, then add 55 mL of acrylic acid solution and 0.65 g of inhibitor hydroquinone, continue to react for 1.5 h, filter, wash the filter cake with deionized water three times, and dry in vacuum at 65 °C for 1.5 h to obtain acrylic acid-modified hydroxyaniline.

[0036] S2: Add 45 g of acrylic acid modified hydroxyaniline, 150 mL of 3-mercaptopropyltrimethoxysilane, and 550 mL of ethanol solution into a reaction kettle, stir at 65 °C and 550 r / min for 1.5 h, filter, wash the filter cake with deionized water three times, and vacuum dry at 65 °C for 1.5 h to obtain mercapto-modified acrylic acid / aniline; Add 25 g of mercapto-modified acrylic acid / aniline and 250 mL of hydrogen peroxide solution with a mass fraction of 22.5 wt% into the reaction kettle, stir and react at 22.5 °C and 550 r / min for 1.5 h, then add a sodium hydroxide solution with a concentration of 0.5 M until the pH value reaches 9, filter, wash the filter cake with deionized water and ethanol three times, and vacuum dry at 65 °C for 1.5 h to obtain sulfonic acid-modified acrylic acid / aniline.

[0037] S3: Add 25 g of polystyrene nanospheres with a particle size of 25 nm, 55 g of sulfonic acid-modified acrylic acid / aniline, and 1.5 L of deionized water into a reaction kettle, stir at 22.5 °C and 400 r / min for 25 min, then add 2.5 g of initiator ammonium persulfate, heat to 85 °C, continue stirring for 4.5 h, cool to 0 °C, and continue reacting for 13 h, filter, wash the filter cake with N,N-dimethylformamide to remove the polystyrene template, then wash with absolute ethanol three times, vacuum dry at 65 °C for 1.5 h, transfer the product to a muffle furnace, and calcine at 575 °C for 2.5 h under nitrogen protection to obtain conductive hollow carbon spheres.

[0038] S4: Add 35 g of lithium fluoride and 550 mL of hydrochloric acid solution with a mass fraction of 37.5% into a reaction kettle, stir at 22.5 °C and 400 r / min for 25 min, then add 13.5 g of aluminum titanium carbide, continue stirring for 49 h, centrifuge at 5500 r / min for 4 min, filter, wash the filter cake with deionized water and ethanol until the last washing liquid is neutral, perform ultrasonic exfoliation at an argon flow rate of 22.5 mL / min, and centrifuge at 5500 r / min for 1.5 min to obtain a suspension of MXene nanosheets.

[0039] S5: Add 25 g of conductive hollow carbon spheres, 45 g of the suspension of MXene nanosheets, and 1.5 L of N,N-dimethylformamide into a reaction kettle, stir at 22.5 °C and 400 r / min for 4.5 h, centrifuge at 5500 r / min for 12.5 min, filter, wash the filter cake with deionized water and ethanol three times, and vacuum dry at 65 °C for 1.5 h to obtain MXene nanosheet-coated conductive hollow carbon spheres.

[0040] S6: Add 75 mL of formaldehyde solution with a mass fraction of 35%, 13 g of ammonium dihydrogen phosphate, 90 g of phenol, 17.5 g of MXene nanosheet-coated conductive hollow carbon spheres, and 550 mL of deionized water A into a reaction kettle, stir at 57.5 °C and 550 r / min for 1.5 h, then add 11 mL of sodium hydroxide solution with a mass fraction of 1.5%, continue to react for 1.5 h, heat at 97.5 °C for 1.5 h, cool the product to 65 °C, adjust the pH value to neutral with a hydrochloric acid solution with a concentration of 1 mol / L, and perform vacuum distillation and dehydration under a vacuum of 0.095 MPa. Place the product in a mixed solution of 1.5 mL of Tween 80, 50 mL of n-pentane, 4.5 mL of concentrated sulfuric acid, and 11 mL of deionized water B, stir at 3250 r / min for 22.5 min, transfer the mixture to a mold, foam and cure at 65 °C for 21 h, transfer the product to a muffle furnace, and calcine at 575 °C for 2.5 h under nitrogen protection to obtain a negative electrode porous carbon material.

[0041] Example 3: A method for preparing a negative electrode porous carbon material, comprising the following steps: S1: Add 50 g of 2-hydroxyaniline and 300 mL of deionized water into a reaction kettle, stir at 85 °C and 500 r / min for 2 h, then add 60 mL of acrylic acid solution and 0.8 g of inhibitor hydroquinone, continue to react for 2 h, filter, wash the filter cake 4 times with deionized water, and dry in vacuum at 70 °C for 2 h to obtain acrylic acid-modified hydroxyaniline.

[0042] S2: Add 50 g of acrylic acid-modified hydroxyaniline, 200 mL of 3-mercaptopropyltrimethoxysilane, and 600 mL of ethanol solution into a reaction kettle, stir at 70 °C and 600 r / min for 2 h, filter, wash the filter cake 4 times with deionized water, and dry in vacuum at 70 °C for 2 h to obtain mercapto-modified acrylic acid / aniline; add 30 g of mercapto-modified acrylic acid / aniline and 300 mL of hydrogen peroxide solution with a mass fraction of 25 wt% into a reaction kettle, stir and react at 25 °C and 600 r / min for 2 h, then add sodium hydroxide solution with a concentration of 0.5 M until the pH value is 9, filter, wash the filter cake 4 times with deionized water and ethanol, and dry in vacuum at 70 °C for 2 h to obtain sulfonic acid-modified acrylic acid / aniline.

[0043] S3: Add 30 g of polystyrene nanospheres with a particle size of 30 nm, 60 g of sulfonic acid-modified acrylic acid / aniline, and 2 L of deionized water into a reaction kettle, stir at 25 °C and 400 r / min for 30 min, then add 3 g of initiator ammonium persulfate, heat to 90 °C, continue stirring for 5 h, cool to 0 °C, continue reacting for 14 h, filter, wash the filter cake with N,N-dimethylformamide to remove the polystyrene template, then wash with absolute ethanol 4 times, dry in vacuum at 70 °C for 2 h, transfer the product to a muffle furnace, calcine at 600 °C for 3 h under nitrogen protection to obtain conductive hollow carbon spheres.

[0044] S4: Add 40 g of lithium fluoride and 600 mL of hydrochloric acid solution with a mass fraction of 40% into a reaction kettle, stir at 25 °C and 400 r / min for 30 min, then add 15 g of aluminum titanium carbide, continue stirring for 50 h, centrifuge at 6000 r / min for 5 min, filter, wash the filter cake with deionized water and ethanol until the last washing liquid is neutral, perform ultrasonic exfoliation at an argon flow rate of 25 mL / min, centrifuge at 6000 r / min for 2 min to obtain a suspension of MXene nanosheets.

[0045] S5: Add 30 g of conductive hollow carbon spheres, 50 g of the suspension of MXene nanosheets, and 2 L of N,N-dimethylformamide into a reaction kettle, stir at 25 °C and 400 r / min for 5 h, centrifuge at 6000 r / min for 15 min, filter, wash the filter cake with deionized water and ethanol 4 times, dry in vacuum at 70 °C for 2 h to obtain MXene nanosheet-coated conductive hollow carbon spheres.

[0046] S6: Add 80 mL of formaldehyde solution with a mass fraction of 40%, 14 g of ammonium dihydrogen phosphate, 100 g of phenol, 20 g of MXene nanosheet-coated conductive hollow carbon spheres, and 600 mL of deionized water A into a reaction kettle, stir at 60 °C and 600 r / min for 2 h, then add 12 mL of sodium hydroxide solution with a mass fraction of 2%, continue reacting for 2 h, heat at 100 °C for 2 h, cool the product to 70 °C, adjust the pH value to neutral with a hydrochloric acid solution with a concentration of 1 mol / L, and perform vacuum distillation at a vacuum degree of 0.098 MPa to dehydrate. Place the product in a mixed solution of 2 mL of Tween 80, 60 mL of n-pentane, 5 mL of concentrated sulfuric acid, and 12 mL of deionized water B, stir at 3500 r / min for 25 min, transfer the mixture to a mold, foam and cure at 70 °C for 22 h, transfer the product to a muffle furnace, calcine at 600 °C for 3 h under nitrogen protection to obtain a porous carbon material for the negative electrode.

[0047] Comparative Example 1: On the basis of Example 3, without undergoing the treatment of step S2, replace the sulfonic acid-modified acrylic acid / aniline in step S3 with the acrylic acid-modified hydroxyaniline in step S1.

[0048] Comparative Example 2: On the basis of Example 3, the MXene nanosheet-coated conductive hollow carbon spheres in step S6 were replaced with the conductive hollow carbon spheres in step S3.

[0049] Comparative Example 3: On the basis of Example 3, the MXene nanosheet-coated conductive hollow carbon spheres in step S6 were replaced with the suspension of MXene nanosheets in step S4.

[0050] The anode porous carbon materials obtained in Examples 1-3 and Comparative Examples 1-3 were made into lithium battery anodes and then into lithium battery specimens for performance testing: The anode porous carbon materials, acetylene black, and polyvinylidene fluoride were dispersed in N-methylpyrrolidone according to a mass ratio of 8:1:1, and then coated on the surface of copper foil. After drying, an anode sheet was made with a tablet press. Using a lithium metal sheet as the counter electrode and a solution of 1 mol / L LiPF6 in ethylene carbonate + diethyl carbonate as the electrolyte, a button battery was assembled with a Celgard 2500 separator in a glove box, and a battery tester was used to test the charge and discharge performance of the battery. The voltage range was 0.01-3V, and the results are shown in Table 1: Table 1 Performance test table of anode porous carbon materials

[0051] As can be seen from Table 1, the anode porous carbon materials obtained in Examples 1-3 have significantly better initial discharge specific capacity, initial charge specific capacity, initial Coulomb efficiency, and conductivity than the comparative examples, indicating that the anode porous carbon materials prepared by the present invention can significantly increase the conductivity of lithium batteries, promote the rapid transmission of lithium ions, alleviate the volume expansion during the charge and discharge process of lithium batteries, and increase the cycle capacity, initial discharge capacity, and initial Coulomb efficiency of lithium batteries.

[0052] In Comparative Example 1, sulfonic acid-modified acrylic acid / aniline was replaced with acrylic acid-modified hydroxyaniline. Through the reaction of the carboxyl group of acrylic acid with the carboxyl group of 2-hydroxyaniline, acrylic acid-modified hydroxyaniline was obtained. The remaining hydroxyl groups were combined with the silanol groups generated by the hydrolysis of 3-mercaptopropyltrimethoxysilane to obtain mercapto-modified acrylic acid / aniline, and sulfonic acid-modified acrylic acid / aniline was obtained under the action of hydrogen peroxide. After calcination, polystyrene and sulfonic acid groups can form sulfur and nitrogen-doped conductive hollow carbon spheres. Sulfur doping can participate in the formation of the SEI film, generate a stable interface layer, reduce the decomposition of the electrolyte and the irreversible consumption of active lithium, and improve the initial Coulomb efficiency. Nitrogen doping can construct an electron high-speed channel and improve the conductivity.

[0053] In Comparative Example 2, the MXene nanosheet-coated conductive hollow carbon spheres were replaced with conductive hollow carbon spheres. The suspension of MXene nanosheets was self-assembled on the surface of the conductive hollow carbon spheres through hydrogen bonds to obtain MXene nanosheet-coated conductive hollow carbon spheres. The layered structure of the MXene nanosheets coated on the surface of the hollow carbon spheres can further alleviate the volume expansion during the charge and discharge process of lithium batteries. The hollow carbon spheres and MXene nanosheets have excellent electrical conductivity and can increase the electrical conductivity of lithium batteries. The three-dimensional conductive network constructed by MXene nanosheets, hollow carbon spheres and foam carbon can increase the electrical conductivity of lithium batteries and improve the high-rate performance of lithium batteries.

[0054] In Comparative Example 3, the MXene nanosheet-coated conductive hollow carbon spheres were replaced with a suspension of MXene nanosheets. The layered structure of the MXene nanosheets coated on the surface of the hollow carbon spheres forms a core-shell structure. The core-shell structure can further alleviate the volume expansion. The loss of the conductive hollow carbon spheres will reduce the ability to alleviate the volume expansion and the electrical conductivity will decrease.

[0055] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made in these embodiments without departing from the principles and spirit of the present invention.

Claims

1. A method for preparing a porous carbon material for a negative electrode, characterized in that, It includes the following steps: Add 30 - 40 wt% formaldehyde solution, ammonium dihydrogen phosphate, phenol, MXene nanosheet-coated conductive hollow carbon spheres and deionized water A into a reaction kettle, stir at 55 - 60 °C and 500 - 600 r / min for 1 - 2 h, then add 1 - 2 wt% sodium hydroxide solution, continue to react for 1 - 2 h, heat at 95 - 100 °C for 1 - 2 h, cool the product to 60 - 70 °C, adjust the pH value to neutral with a 1 mol / L hydrochloric acid solution, and carry out vacuum distillation and dehydration under a vacuum of 0.092 - 0.098 MPa. Place the product in a mixed solution of Tween 80, n-pentane, concentrated sulfuric acid and deionized water B, stir at 3000 - 3500 r / min for 20 - 25 min, transfer the mixture to a mold, foam and cure at 60 - 70 °C for 20 - 22 h, transfer the product to a muffle furnace, and calcine at 550 - 600 °C for 2 - 3 h under nitrogen protection to obtain a negative electrode porous carbon material.

2. The preparation method of a negative electrode porous carbon material according to claim 1, characterized in that, The dosage ratio of the formaldehyde solution, ammonium dihydrogen phosphate, phenol, MXene nanosheet-coated conductive hollow carbon spheres, deionized water A, sodium hydroxide solution, Tween 80, n-pentane, concentrated sulfuric acid and deionized water B is 70 - 80 mL: 12 - 14 g: 80 - 100 g: 15 - 20 g: 500 - 600 mL: 10 - 12 mL: 1 - 2 mL: 40 - 60 mL: 4 - 5 mL: 10 - 12 mL.

3. The preparation method of a negative electrode porous carbon material according to claim 1, wherein, The preparation steps of the MXene nanosheet-coated conductive hollow carbon spheres are as follows: Add conductive hollow carbon spheres, a suspension of MXene nanosheets and N,N-dimethylformamide into a reaction kettle, stir at 20 - 25 °C and 400 r / min for 4 - 5 h, centrifuge at 5000 - 6000 r / min for 10 - 15 min, filter, wash the filter cake with deionized water and ethanol for 2 - 4 times, and vacuum dry at 60 - 70 °C for 1 - 2 h to obtain MXene nanosheet-coated conductive hollow carbon spheres; The dosage ratio of the conductive hollow carbon spheres, the suspension of MXene nanosheets and N,N-dimethylformamide is 20 - 30 g: 40 - 50 g: 1 - 2 L.

4. The preparation method of a negative electrode porous carbon material according to claim 3, characterized in that, The preparation steps of the conductive hollow carbon spheres are as follows: Add polystyrene nanospheres with a particle size of 20 - 30 nm, sulfonic acid-modified acrylic acid / aniline and deionized water into a reaction kettle, stir at 20 - 25 °C and 400 r / min for 20 - 30 min, then add the initiator ammonium persulfate, heat to 80 - 90 °C, continue to stir for 4 - 5 h, cool to 0 °C, continue to react for 12 - 14 h, filter, wash the filter cake with N,N-dimethylformamide to remove the polystyrene template, then wash with absolute ethanol for 2 - 4 times, vacuum dry, transfer the product to a muffle furnace, and calcine at 550 - 600 °C for 2 - 3 h under nitrogen protection to obtain conductive hollow carbon spheres.

5. The preparation method of a negative electrode porous carbon material according to claim 4, characterized in that, The dosage ratio of the polystyrene nanospheres, sulfonic acid-modified acrylic acid / aniline, deionized water and ammonium persulfate is 20 - 30 g: 50 - 60 g: 1 - 2 L: 2 - 3 g.

6. The preparation method of a negative electrode porous carbon material according to claim 3, characterized in that, The preparation steps of the suspension of MXene nanosheets are as follows: Add lithium fluoride and 35 - 40wt% hydrochloric acid solution into a reaction kettle, stir at 20 - 25°C and 400 r / min for 20 - 30 min, then add aluminum titanium carbide, continue to stir for 48 - 50 h, centrifuge at 5000 - 6000 r / min for 3 - 5 min, filter, wash until the washing liquid is neutral, ultrasonically exfoliate under an argon flow rate of 20 - 25 mL / min, and centrifuge at 5000 - 6000 r / min for 1 - 2 min to obtain the suspension of MXene nanosheets; The dosage ratio of lithium fluoride, hydrochloric acid solution and aluminum titanium carbide is 30 - 40 g : 500 - 600 mL : 12 - 15 g.

7. The preparation method of a negative electrode porous carbon material according to claim 4, characterized in that The preparation steps of the sulfonic acid - modified acrylic acid / aniline are as follows: Add acrylic acid - modified hydroxyaniline, 3 - mercaptopropyltrimethoxysilane and ethanol solution into a reaction kettle, stir at 60 - 70°C and 500 - 600 r / min for 1 - 2 h, filter, wash, and vacuum - dry to obtain mercapto - modified acrylic acid / aniline; Add mercapto - modified acrylic acid / aniline and 20 - 25wt% hydrogen peroxide solution into the reaction kettle according to the dosage ratio of 20 - 30 g : 200 - 300 mL, stir and react at 20 - 25°C and 500 - 600 r / min for 1 - 2 h, then add 0.5 M sodium hydroxide solution until the pH value reaches 9, filter, wash, and vacuum - dry to obtain sulfonic acid - modified acrylic acid / aniline; The dosage ratio of acrylic acid - modified hydroxyaniline, 3 - mercaptopropyltrimethoxysilane and ethanol solution is 40 - 50 g : 100 - 200 mL : 500 - 600 mL.

8. The preparation method of a negative electrode porous carbon material according to claim 7, wherein, The preparation steps of the acrylic acid - modified hydroxyaniline are as follows: Add 2 - hydroxyaniline and deionized water into a reaction kettle, stir at 80 - 85°C and 400 - 500 r / min for 1 - 2 h, then add acrylic acid solution and inhibitor hydroquinone, continue to react for 1 - 2 h, filter, wash the filter cake with deionized water 2 - 4 times, and vacuum - dry at 60 - 70°C for 1 - 2 h to obtain acrylic acid - modified hydroxyaniline.

9. The preparation method of a negative electrode porous carbon material according to claim 8, characterized in that, The dosage ratio of 2 - hydroxyaniline, deionized water, acrylic acid solution and hydroquinone is 40 - 50 g : 200 - 300 mL : 50 - 60 mL : 0.5 - 0.8 g.

10. A negative electrode porous carbon material, characterized in that, Prepared by the preparation method according to any one of claims 1 - 9.

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