A negative electrode porous carbon material and preparation method thereof

Abstract

The present invention discloses a negative electrode porous carbon material and a preparation method thereof, belonging to the technical field of negative electrode materials for sodium ion batteries. The carboxyl groups of acrylic acid react with the carboxyl groups of 2-hydroxyaniline, and the remaining hydroxyl groups combine with silanol groups generated by hydrolysis of 3-mercaptopropyltrimethoxysilane. Sulfonic acid-modified acrylic acid / aniline is obtained under the action of hydrogen peroxide. After calcination, sulfur- and nitrogen-doped conductive hollow carbon spheres are formed. Sulfur doping can participate in the formation of the SEI film, generate a stable interface layer, reduce electrolyte decomposition and irreversible consumption of active lithium, and improve the initial coulombic efficiency. Nitrogen doping can construct an electron high-speed channel and improve conductivity. The conductive hollow carbon spheres are coated with MXene nanosheets and deposited on the surface of foamed carbon. Through the three-level synergy of layered, hollow, and foamed forms, a rigid-flexible effect can be achieved while alleviating volume expansion.

Description

Technical Field

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

[0002] Lithium battery is a common rechargeable secondary battery, which structurally includes positive electrode materials, negative electrode materials, electrolytes and separators. The separator is used to separate the positive and negative electrodes to prevent short circuits. The electrolyte is a conductive medium between the positive and negative electrodes, and its main function is to allow lithium ions to be transferred between the positive and negative electrodes. 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 charging, lithium ions move from the positive electrode to the negative electrode and embed into the negative electrode material. During discharging, 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 operating voltage, low self-discharge rate, small size, light weight, and long cycle life. They 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 ongoing. The energy density of lithium batteries is affected by multiple factors. In addition to the limitations of the battery's size and shape, as well as the influence of the battery's operating temperature, the energy density of the positive and negative electrode materials is a key factor in determining the energy density of lithium-ion batteries. Existing negative electrode materials have a large shrinkage and expansion rate. Due to the change in volume during the battery's charge and discharge process, the negative electrode material may crack or peel, ultimately affecting the battery's service life.

[0004] Chinese patent CN109256541B discloses a hard carbon negative electrode material. The battery negative electrode material with nano-ribbon V3O7 and crystalline water is synthesized by oil-water mixing method. It has a typical layered crystal structure and a large interlayer spacing, which is conducive to the free movement of lithium ions between layers. The negative electrode material has a soft one-dimensional nano-shaped morphology, which can shorten the diffusion distance of lithium ions and alleviate the volume change caused by lithium ion insertion and extraction. However, the mitigation ability of the nanoribbons in this scheme is low, and it is not enough to effectively alleviate the volume change after multiple cycles. Summary of the Invention

[0005] The purpose of the present invention is to provide a negative electrode porous carbon material and a preparation method thereof, in which conductive hollow carbon spheres are coated with MXene nanosheets and deposited on the surface of foamed carbon. Through the three-level synergy of layered, hollow and foamed forms, the effect of both rigidity and flexibility can be achieved while alleviating volume expansion.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] A method for preparing a negative electrode porous carbon material comprises the following steps:

[0008] Add 30-40% formaldehyde solution, ammonium dihydrogen phosphate, phenol, MXene nanosheet-coated conductive hollow carbon spheres and deionized water A into the reactor, stir at 55-60°C and 500-600r / min for 1-2h, then add 1-2% sodium hydroxide solution, continue to react for 1-2h, heat at 95-100°C for 1-2h, cool the product to 60-70°C, and adjust the pH to 0. The product is neutralized and distilled under reduced pressure at a vacuum degree of 0.092-0.098 MPa, dehydrated, and placed in a mixed solution of Tween 80, n-pentane, concentrated sulfuric acid and deionized water B, stirred at 3000-3500 r / min for 20-25 min, transferred to a mold, foamed and cured at 60-70 ° C for 20-22 h, and transferred to a muffle furnace. Under nitrogen protection, calcined at 550-600 ° C for 2-3 h to obtain a negative electrode porous carbon material.

[0009] Furthermore, the dosage ratio of 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.

[0010] Furthermore, the preparation steps of MXene nanosheet-coated conductive hollow carbon spheres are as follows:

[0011] The suspension of conductive hollow carbon spheres, MXene nanosheets and N,N-dimethylformamide were added to a reactor, stirred at 20-25°C and 400 r / min for 4-5 hours, centrifuged at 5000-6000 r / min for 10-15 minutes, filtered, and the filter cake was washed with deionized water and ethanol 2-4 times, and vacuum dried at 60-70°C for 1-2 hours to obtain MXene nanosheet-coated conductive hollow carbon spheres.

[0012] Furthermore, the ratio of the conductive hollow carbon spheres, the MXene nanosheet suspension and N,N-dimethylformamide is 20-30 g: 40-50 g: 1-2 L.

[0013] Furthermore, the preparation steps of conductive hollow carbon spheres are as follows:

[0014] Polystyrene nanospheres with a particle size of 20-30 nm, sulfonic acid-modified acrylic acid / aniline and deionized water are added to a reactor, stirred at 20-25°C and 400 r / min for 20-30 minutes, then ammonium persulfate as an initiator is added, heated to 80-90°C, stirred for 4-5 hours, cooled to 0°C, and reacted for 12-14 hours. The reaction was filtered, and the filter cake was washed with N,N-dimethylformamide to remove the polystyrene template, and then washed with anhydrous ethanol 2-4 times, vacuum dried at 60-70°C for 1-2 hours, and the product was transferred to a muffle furnace and calcined at 550-600°C for 2-3 hours under nitrogen protection to obtain conductive hollow carbon spheres.

[0015] Furthermore, the usage 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:

[0016] Furthermore, the preparation steps of the MXene nanosheet suspension are as follows:

[0017] Lithium fluoride and a hydrochloric acid solution with a mass fraction of 35-40% were added to the reactor, stirred at 20-25 ° C and 400 r / min for 20-30 minutes, and then titanium aluminum carbide was added. Stirring was continued for 48-50 hours, centrifuged at 5000-6000 r / min for 3-5 minutes, filtered, and the filter cake was washed with deionized water and ethanol until the last washing liquid was neutral. Ultrasonic peeling was performed at an argon flow rate of 20-25 mL / min, and centrifuged at 5000-6000 r / min for 1-2 minutes to obtain a suspension of MXene nanosheets.

[0018] Furthermore, the usage ratio of lithium fluoride, hydrochloric acid solution and titanium aluminum carbide is 30-40 g: 500-600 mL: 12-15 g.

[0019] Furthermore, the preparation steps of sulfonic acid modified acrylic acid / aniline are as follows:

[0020] Acrylic acid-modified hydroxyaniline, 3-mercaptopropyltrimethoxysilane and an ethanol solution are added to a reactor, stirred at 60-70° C. and 500-600 r / min for 1-2 hours, filtered, and the filter cake is washed with deionized water 2-4 times and vacuum-dried at 60-70° C. for 1-2 hours to obtain mercapto-modified acrylic acid / aniline. Mercapto-modified acrylic acid / aniline and a 20-25 wt% hydrogen peroxide solution are added to a reactor in a ratio of 20-30 g:200-300 mL, stirred at 20-25° C. and 500-600 r / min for 1-2 hours, and then a 0.5 M sodium hydroxide solution is added to a pH value of 9, filtered, and the filter cake is washed with deionized water and ethanol 2-4 times and vacuum-dried at 60-70° C. for 1-2 hours to obtain sulfonic acid-modified acrylic acid / aniline.

[0021] Furthermore, the usage ratio of acrylic acid-modified hydroxyaniline, 3-mercaptopropyltrimethoxysilane and ethanol solution is 40-50 g: 100-200 mL: 500-600 mL.

[0022] Furthermore, the preparation steps of acrylic acid-modified hydroxyaniline are as follows:

[0023] Add 2-hydroxyaniline and deionized water into a reactor, stir at 80-85°C and 400-500 r / min for 1-2 hours, then add acrylic acid solution and polymerization inhibitor hydroquinone, continue to react for 1-2 hours, filter, wash the filter cake with deionized water 2-4 times, and vacuum dry at 60-70°C for 1-2 hours to obtain acrylic acid-modified hydroxyaniline.

[0024] Furthermore, the usage 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.

[0025] Beneficial effects of the present invention:

[0026] 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 coulombic efficiency of lithium batteries.

[0027] 2. The sulfonic acid-modified acrylic acid / aniline of the present invention is prepared by reacting the carboxyl group of acrylic acid with the carboxyl group of 2-hydroxyaniline to obtain acrylic acid-modified hydroxyaniline. The remaining hydroxyl group combines with the silanol group generated by hydrolysis of 3-mercaptopropyltrimethoxysilane to obtain mercapto-modified acrylic acid / aniline. The sulfonic acid-modified acrylic acid / aniline is then obtained under the action of hydrogen peroxide. After calcination, the polyaniline and the 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 electrolyte decomposition and irreversible consumption of active lithium, and improve the initial coulombic efficiency. Nitrogen doping can construct a high-speed electron channel and improve conductivity.

[0028] 3. The MXene nanosheets of the present invention are coated with conductive hollow carbon spheres. Free radicals are generated by the decomposition of acrylic acid in ammonium persulfate, which triggers the copolymerization of acrylic acid and aniline. A cross-linked shell is formed on the surface using polystyrene nanospheres as a template. The polystyrene template is removed by washing with N,N-dimethylformamide and then carbonized to obtain conductive hollow carbon spheres. Suspension of MXene nanosheets is 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 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, further alleviating the volume expansion of the lithium battery during charging and discharging. The conductive hollow carbon spheres and MXene nanosheets have excellent conductivity and can increase the conductivity of the lithium battery. The three-dimensional conductive network constructed by MXene nanosheets, conductive hollow carbon spheres and foamed carbon can increase the conductivity of the lithium battery and improve the high-rate performance of the lithium battery.

[0029] 4. Phenolic resin foam material is generated by formaldehyde and phenol and carbonized to obtain phenolic resin foam carbon, and the surface is loaded with MXene nanosheets coated with conductive hollow carbon spheres. The internal cavity reserves expansion space for lithium ion embedding, relieves the internal stress of the particles, and the layered structure is flexible, absorbs the mechanical stress caused by volume change, and prevents structural collapse. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a scanning electron microscope image of the negative electrode porous carbon material of Example 3.

[0031] Figure 2 This is the BET diagram data of Example 1.

[0032] Figure 3 This is the BET diagram data of Example 2.

[0033] Figure 4 This is the BET diagram data of Example 3.

[0034] Figure 5 This is the BET diagram data of Comparative Example 1.

[0035] Figure 6 This is the BET diagram data of Comparative Example 2.

[0036] Figure 7 This is the BET diagram data of Comparative Example 3. DETAILED DESCRIPTION

[0037] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0038] Example 1: A method for preparing a negative electrode porous carbon material, comprising the following steps:

[0039] S1: 40 g of 2-hydroxyaniline and 200 mL of deionized water were added to a reactor and stirred at 80°C and 400 rpm for 1 h. Then, 50 mL of acrylic acid solution and 0.5 g of polymerization inhibitor hydroquinone were added and the reaction was continued for 1 h. The mixture was filtered and the filter cake was washed twice with deionized water and dried under vacuum at 60°C for 1 h to obtain acrylic acid-modified hydroxyaniline.

[0040] S2: 40 g of acrylic acid-modified hydroxyaniline, 100 mL of 3-mercaptopropyltrimethoxysilane and 500 mL of ethanol solution were added to a reactor, stirred at 60°C and 500 r / min for 1 h, filtered, and the filter cake was washed twice with deionized water and dried in vacuum at 60°C for 1 h to obtain mercapto-modified acrylic acid / aniline; 20 g of mercapto-modified acrylic acid / aniline and 200 mL of 20 wt% hydrogen peroxide solution were added to a reactor, stirred at 20°C and 500 r / min for 1 h, and then a 0.5 M sodium hydroxide solution was added to a pH value of 9, filtered, and the filter cake was washed twice with deionized water and ethanol, and dried in vacuum at 60°C for 1 h to obtain sulfonic acid-modified acrylic acid / aniline.

[0041] S3: Add 20g of polystyrene nanospheres with a particle size of 20nm, 50g of sulfonic acid-modified acrylic acid / aniline and 1L of deionized water into the reactor, stir at 20℃ and 400r / min for 20min, then add 2g of initiator ammonium persulfate, heat to 80℃, continue stirring for 4h, cool to 0℃, continue to react for 12h, filter, wash the filter cake with N,N-dimethylformamide to remove the polystyrene template, then wash it twice with anhydrous ethanol, vacuum dry at 60℃ for 1h, transfer the product to a muffle furnace, and calcine at 550℃ for 2h under nitrogen protection to obtain conductive hollow carbon spheres.

[0042] S4: Add 30 g of lithium fluoride and 500 mL of 35% hydrochloric acid solution into the reactor, stir at 20°C and 400 r / min for 20 min, then add 12 g of titanium aluminum carbide, continue stirring 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 liquid is neutral, ultrasonically peel at an argon flow rate of 20 mL / min, and centrifuge at 5000 r / min for 1 min to obtain a suspension of MXene nanosheets.

[0043] S5: 20 g of conductive hollow carbon spheres, 40 g of MXene nanosheet suspension and 1 L of N,N-dimethylformamide were added to the reactor, stirred at 20°C and 400 r / min for 4 h, centrifuged at 5000 r / min for 10 min, filtered, and the filter cake was washed twice with deionized water and ethanol, and vacuum dried at 60°C for 1 h to obtain MXene nanosheet-coated conductive hollow carbon spheres.

[0044] S6: 70 mL of 30% formaldehyde solution, 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 were added to a reactor and stirred at 55 ° C and 500 r / min for 1 hour. Then 10 mL of 1% mass fraction sodium hydroxide solution was added and the reaction was continued for 1 hour. The product was heated at 95 ° C for 1 hour, and the pH value was adjusted to neutral with a 1 mol / L hydrochloric acid solution. The product was distilled under reduced pressure at a vacuum degree of 0.092 MPa and dehydrated. The product was placed in a mixed solution of 1 mL Tween 80, 40 mL n-pentane, 4 mL concentrated sulfuric acid and 10 mL deionized water B, stirred at 3000 r / min for 20 minutes, and the mixture was transferred to a mold. Foaming and curing at 60 ° C for 20 hours, the product was transferred to a muffle furnace, and calcined at 550 ° C for 2 hours under nitrogen protection to obtain a negative electrode porous carbon material.

[0045] Example 2: A method for preparing a negative electrode porous carbon material, comprising the following steps:

[0046] S1: 45 g of 2-hydroxyaniline and 250 mL of deionized water were added to a reactor and stirred at 82.5°C and 450 r / min for 1.5 h. Then, 55 mL of acrylic acid solution and 0.65 g of polymerization inhibitor hydroquinone were added and the reaction was continued for 1.5 h. The mixture was filtered and the filter cake was washed three times with deionized water and dried in vacuo at 65°C for 1.5 h to obtain acrylic acid-modified hydroxyaniline.

[0047] S2: 45 g of acrylic acid-modified hydroxyaniline, 150 mL of 3-mercaptopropyltrimethoxysilane and 550 mL of ethanol solution were added to a reactor, stirred at 65°C and 550 r / min for 1.5 h, filtered, and the filter cake was washed with deionized water three times and dried in a vacuum at 65°C for 1.5 h to obtain mercapto-modified acrylic acid / aniline; 25 g of mercapto-modified acrylic acid / aniline and 250 mL of a 22.5 wt% hydrogen peroxide solution were added to a reactor, stirred at 22.5°C and 550 r / min for 1.5 h, and then a 0.5 M sodium hydroxide solution was added to a pH of 9, filtered, and the filter cake was washed with deionized water and ethanol three times, and dried in a vacuum at 65°C for 1.5 h to obtain sulfonic acid-modified acrylic acid / aniline.

[0048] 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 the reactor, stir at 22.5 ° C and 400 r / min for 25 minutes, then add 2.5 g of initiator ammonium persulfate, heat to 85 ° C, continue stirring for 4.5 hours, cool to 0 ° C, continue to react for 13 hours, filter, wash the filter cake with N, N-dimethylformamide to remove the polystyrene template, and then wash it with anhydrous ethanol three times, vacuum dry at 65 ° C for 1.5 hours, transfer the product to a muffle furnace, and calcine at 575 ° C for 2.5 hours under nitrogen protection to obtain conductive hollow carbon spheres.

[0049] S4: Add 35 g of lithium fluoride and 550 mL of 37.5% hydrochloric acid solution into the reactor, stir at 22.5 ° C and 400 r / min for 25 minutes, then add 13.5 g of titanium aluminum carbide, continue stirring for 49 hours, centrifuge at 5500 r / min for 4 minutes, filter, wash the filter cake with deionized water and ethanol until the last washing liquid is neutral, ultrasonically peel at an argon flow rate of 22.5 mL / min, and centrifuge at 5500 r / min for 1.5 minutes to obtain a suspension of MXene nanosheets.

[0050] S5: 25 g of conductive hollow carbon spheres, 45 g of MXene nanosheet suspension and 1.5 L of N,N-dimethylformamide were added to the reactor, stirred at 22.5 ° C and 400 r / min for 4.5 h, centrifuged at 5500 r / min for 12.5 min, filtered, and the filter cake was washed three times with deionized water and ethanol, and vacuum dried at 65 ° C for 1.5 h to obtain MXene nanosheet-coated conductive hollow carbon spheres.

[0051] S6: 75 mL of 35% formaldehyde solution, 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 were added to a reactor and stirred at 57.5 ° C and 550 r / min for 1.5 h. Then 11 mL of 1.5% mass fraction sodium hydroxide solution was added and the reaction was continued for 1.5 h. The product was heated at 97.5 ° C for 1.5 h, cooled to 65 ° C, and the pH value was adjusted to neutral with a 1 mol / L hydrochloric acid solution. The product was dehydrated by reduced pressure distillation at a vacuum degree of 0.095 MPa. The product was placed in a mixed solution of 1.5 mL Tween 80, 50 mL n-pentane, 4.5 mL concentrated sulfuric acid and 11 mL deionized water B, stirred at 3250 r / min for 22.5 min, and the mixture was transferred to a mold. Foaming and curing at 65 ° C for 21 h, the product was transferred to a muffle furnace and calcined at 575 ° C for 2.5 h under nitrogen protection to obtain a negative electrode porous carbon material.

[0052] Example 3: A method for preparing a negative electrode porous carbon material, comprising the following steps:

[0053] S1: 50 g of 2-hydroxyaniline and 300 mL of deionized water were added to a reactor and stirred at 85°C and 500 rpm for 2 h. Then, 60 mL of acrylic acid solution and 0.8 g of polymerization inhibitor hydroquinone were added and the reaction was continued for 2 h. The mixture was filtered and the filter cake was washed four times with deionized water and dried under vacuum at 70°C for 2 h to obtain acrylic acid-modified hydroxyaniline.

[0054] S2: 50 g of acrylic acid-modified hydroxyaniline, 200 mL of 3-mercaptopropyltrimethoxysilane and 600 mL of ethanol solution were added to a reactor, stirred at 70°C and 600 r / min for 2 h, filtered, and the filter cake was washed with deionized water 4 times and dried in vacuum at 70°C for 2 h to obtain mercapto-modified acrylic acid / aniline; 30 g of mercapto-modified acrylic acid / aniline and 300 mL of 25 wt% hydrogen peroxide solution were added to a reactor, stirred at 25°C and 600 r / min for 2 h, and then a 0.5 M sodium hydroxide solution was added to a pH value of 9, filtered, and the filter cake was washed with deionized water and ethanol 4 times, and dried in vacuum at 70°C for 2 h to obtain sulfonic acid-modified acrylic acid / aniline.

[0055] S3: Add 30g of polystyrene nanospheres with a particle size of 30nm, 60g of sulfonic acid-modified acrylic acid / aniline and 2L of deionized water into the reactor, stir at 25℃ and 400r / min for 30min, then add 3g of initiator ammonium persulfate, heat to 90℃, continue stirring for 5h, cool to 0℃, continue to react for 14h, filter, wash the filter cake with N,N-dimethylformamide to remove the polystyrene template, then wash it with anhydrous ethanol 4 times, vacuum dry at 70℃ for 2h, transfer the product to a muffle furnace, and calcine at 600℃ for 3h under nitrogen protection to obtain conductive hollow carbon spheres.

[0056] S4: Add 40 g of lithium fluoride and 600 mL of 40% hydrochloric acid solution into the reactor, stir at 25 ° C and 400 r / min for 30 minutes, then add 15 g of titanium aluminum carbide, continue stirring for 50 hours, centrifuge at 6000 r / min for 5 minutes, filter, wash the filter cake with deionized water and ethanol until the last washing liquid is neutral, ultrasonically peel at an argon flow rate of 25 mL / min, and centrifuge at 6000 r / min for 2 minutes to obtain a suspension of MXene nanosheets.

[0057] S5: 30 g of conductive hollow carbon spheres, 50 g of MXene nanosheet suspension and 2 L of N,N-dimethylformamide were added to the reactor, stirred at 25 ° C and 400 r / min for 5 h, centrifuged at 6000 r / min for 15 min, filtered, and the filter cake was washed with deionized water and ethanol four times, and vacuum dried at 70 ° C for 2 h to obtain MXene nanosheet-coated conductive hollow carbon spheres.

[0058] S6: 80 mL of 40% formaldehyde solution, 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 were added to a reactor and stirred at 60°C and 600 r / min for 2 h. Then, 12 mL of 2% sodium hydroxide solution was added and the reaction was continued for 2 h. The product was heated at 100°C for 2 h, cooled to 70°C, and the pH value was adjusted to neutral with 1 mol / L hydrochloric acid solution. The product was then distilled under reduced pressure at a vacuum degree of 0.098 MPa for dehydration. The product was placed 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, stirred at 3500 r / min for 25 min, and the mixture was transferred to a mold. The mixture was foamed and cured at 70°C for 22 h. The product was transferred to a muffle furnace and calcined at 600°C for 3 h under nitrogen protection to obtain a negative electrode porous carbon material.

[0059] Comparative Example 1: Based on Example 3, without the treatment in step S2, the sulfonic acid-modified acrylic acid / aniline in step S3 is replaced by acrylic acid-modified hydroxyaniline in step S1.

[0060] Comparative Example 2: Based on Example 3, the MXene nanosheet-coated conductive hollow carbon spheres in step S6 were replaced by the conductive hollow carbon spheres in step S3.

[0061] Comparative Example 3: Based on Example 3, the MXene nanosheet-coated conductive hollow carbon spheres in step S6 are replaced by the suspension of MXene nanosheets in step S4.

[0062] The negative electrode porous carbon materials obtained in Examples 1-3 and Comparative Examples 1-3 were prepared into lithium battery negative electrodes and then into lithium battery samples, and performance tests were performed: the negative electrode porous carbon material, acetylene black, and polyvinylidene fluoride were dispersed in N-methylpyrrolidone at a mass ratio of 8:1:1, then coated on the surface of copper foil. After drying, a negative electrode sheet was formed using a sheet press. A metal lithium sheet was used as the counter electrode, and a 1 mol / L LiPF6 solution of ethylene carbonate + diethyl carbonate was used as the electrolyte. The battery was assembled with a Celgard 2500 diaphragm in a glove box to form a button cell. The battery's charge and discharge performance was tested using a battery tester. The voltage range was 0.01-3V, and the results are shown in Table 1:

[0063] Table 1 Performance test table of negative electrode porous carbon materials

[0064]

[0065] As can be seen from Table 1, the negative electrode porous carbon materials obtained in Examples 1-3 have significantly better first discharge specific capacity, first charge specific capacity, first coulombic efficiency and conductivity than the comparative example, indicating that the negative electrode porous carbon material prepared by the present invention can significantly increase the conductivity of the lithium battery, promote the rapid transmission of lithium ions, alleviate the volume expansion of the lithium battery during charging and discharging, and increase the cycle capacity, first discharge capacity and first coulombic efficiency of the lithium battery.

[0066] In Comparative Example 1, sulfonic acid-modified acrylic acid / aniline is replaced with acrylic acid-modified hydroxyaniline. The carboxyl group of acrylic acid reacts with the carboxyl group of 2-hydroxyaniline to obtain acrylic acid-modified hydroxyaniline. The remaining hydroxyl group combines with the silanol group generated by 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-nitrogen-doped conductive hollow carbon spheres. Sulfur doping can participate in the formation of the SEI film, generate a stable interface layer, reduce electrolyte decomposition and irreversible consumption of active lithium, and improve the first coulomb efficiency. Nitrogen doping can construct an electron high-speed channel and improve conductivity.

[0067] In Comparative Example 2, the MXene nanosheet-coated conductive hollow carbon spheres are replaced with conductive hollow carbon spheres. The suspension of MXene nanosheets is 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 is coated on the surface of the hollow carbon spheres, which can further alleviate the volume expansion of the lithium battery during charging and discharging. The hollow carbon spheres and MXene nanosheets have excellent conductivity and can increase the conductivity of the lithium battery. The three-dimensional conductive network constructed by MXene nanosheets, hollow carbon spheres and foam carbon can increase the conductivity of the lithium battery and improve the high-rate performance of the lithium battery.

[0068] In Comparative Example 3, the MXene nanosheet-coated conductive hollow carbon spheres are replaced with a suspension of MXene nanosheets. The layered structure of the MXene nanosheets is coated on the surface of the hollow carbon spheres to form 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 conductivity will decrease.

[0069] While the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations can be made to the embodiments without departing from the principles and spirit of the invention.

Claims

1. A method for preparing a negative electrode porous carbon material, characterized in that: The steps include: Add 30-40wt% formaldehyde solution, ammonium dihydrogen phosphate, phenol, MXene nanosheet-coated conductive hollow carbon spheres and deionized water A into a reactor, stir at 55-60℃ and 500-600r / min for 1-2h, then add 1-2wt% sodium hydroxide solution, continue the reaction for 1-2h, heat at 95-100℃ for 1-2h, cool the product to 60-70℃, and adjust the pH value to neutral with 1mol / L hydrochloric acid solution. The product was distilled under reduced pressure and dehydrated at a vacuum degree of 0.092-0.098 MPa, and placed in a mixed solution of Tween 80, n-pentane, concentrated sulfuric acid and deionized water B, stirred at 3000-3500 r / min for 20-25 minutes, and the mixture was transferred to a mold, foamed and cured at 60-70°C for 20-22 hours, and the product was transferred to a muffle furnace and calcined at 550-600°C for 2-3 hours under nitrogen protection to obtain a negative electrode porous carbon material.

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

4. The method for preparing a negative electrode porous carbon material according to claim 3, wherein: The preparation steps of the conductive hollow carbon spheres are as follows: Polystyrene nanospheres with a particle size of 20-30 nm, sulfonic acid-modified acrylic acid / aniline and deionized water are added to a reactor, stirred at 20-25°C and 400 r / min for 20-30 minutes, then ammonium persulfate as an initiator is added, heated to 80-90°C, stirred for 4-5 hours, cooled to 0°C, and reacted for 12-14 hours. The reaction was filtered, and the filter cake was washed with N,N-dimethylformamide to remove the polystyrene template, and then washed with anhydrous ethanol for 2-4 times. The product was vacuum dried and transferred to a muffle furnace. Under nitrogen protection, it was calcined at 550-600°C for 2-3 hours to obtain conductive hollow carbon spheres.

5. The method for preparing a negative electrode porous carbon material according to claim 4, wherein: The usage 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 method for preparing a negative electrode porous carbon material according to claim 3, wherein: The preparation steps of the MXene nanosheet suspension are as follows: Lithium fluoride and 35-40 wt% hydrochloric acid solution were added to a reactor, stirred at 20-25°C and 400 r / min for 20-30 min, and then titanium aluminum carbide was added. The mixture was stirred for 48-50 h, centrifuged at 5000-6000 r / min for 3-5 min, filtered, and washed until the washing liquid was neutral. Ultrasonic exfoliation was performed at an argon flow rate of 20-25 mL / min, and centrifuged at 5000-6000 r / min for 1-2 min to obtain a suspension of MXene nanosheets. The usage ratio of the lithium fluoride, the hydrochloric acid solution and the titanium aluminum carbide is 30-40 g: 500-600 mL: 12-15 g.

7. The method for preparing a negative electrode porous carbon material according to claim 4, wherein: The preparation steps of the sulfonic acid modified acrylic acid / aniline are as follows: Adding acrylic acid-modified hydroxyaniline, 3-mercaptopropyltrimethoxysilane, and an ethanol solution to a reactor, stirring at 60-70° C. and 500-600 r / min for 1-2 hours, filtering, washing, and vacuum drying to obtain mercapto-modified acrylic acid / aniline; adding mercapto-modified acrylic acid / aniline and a 20-25 wt% hydrogen peroxide solution at a ratio of 20-30 g:200-300 mL to a reactor, stirring at 20-25° C. and 500-600 r / min for 1-2 hours, then adding a 0.5 M sodium hydroxide solution to a pH of 9, filtering, washing, and vacuum drying to obtain sulfonic acid-modified acrylic acid / aniline; The usage ratio of the acrylic acid-modified hydroxyaniline, 3-mercaptopropyltrimethoxysilane and ethanol solution is 40-50 g: 100-200 mL: 500-600 mL.

8. The method for preparing 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 reactor, stir at 80-85°C and 400-500 r / min for 1-2 hours, then add acrylic acid solution and polymerization inhibitor hydroquinone, continue to react for 1-2 hours, filter, wash the filter cake with deionized water 2-4 times, and vacuum dry at 60-70°C for 1-2 hours to obtain acrylic acid-modified hydroxyaniline.

9. The method for preparing a negative electrode porous carbon material according to claim 8, wherein: The usage ratio of the 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 to 9.

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