Preparation method of high-capacity silicon-carbon negative electrode material

Abstract

The invention relates to the technical field of battery negative electrode materials, in particular to a preparation method of a high-capacity silicon-carbon negative electrode material. According to the invention, the problems of low battery capacity and poor cycling stability of a battery assembled by using a silicon-carbon negative electrode material as a negative electrode material are solved. The preparation method comprises the following steps: controlling the particle size of iron nanoparticles, carrying out heating reaction to prepare pretreated silicon powder, cleaning, and modifying with a silane coupling agent to obtain nano silicon powder; carrying out microwave-assisted high-temperature calcination on the phenolic resin to obtain porous carbon; adding nano silicon powder and lithium carbonate into porous carbon, performing ball milling, adding titanium dioxide, performing ball milling again, and performing aluminum phosphate coating; then phenolic resin is used as a carbon source for carbon layer coating and high-temperature sintering, and the prepared silicon-carbon material is used for manufacturing a negative pole piece and assembling a battery; the battery capacity is improved by controlling the particle size of the nano micro powder and cooperating with porous carbon loading; and through microwave-assisted high-temperature calcination and the synergistic effect of the carbon coating layer and lithium carbonate, the cycle stability of the battery is improved, and the comprehensive performance of the battery is effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of battery anode materials, and particularly to a preparation method of a high-capacity silicon-carbon anode material. Background Art

[0002] With the rapid development of electronic devices and the rise of the new energy vehicle industry, higher requirements are put forward for battery performance. Among many battery anode materials, silicon-carbon materials have become a very promising research object due to their high theoretical specific capacity. The theoretical specific capacity of silicon is as high as 4200 mAh / g, far higher than that of traditional graphite anode materials (the theoretical specific capacity is about 372 mAh / g), which makes silicon-carbon materials have great advantages in improving the energy density of batteries.

[0003] However, there are still many problems with the silicon-carbon materials in the current existing technologies. On the one hand, its actual specific capacitance is much lower than the theoretical value. During the charge and discharge process, silicon undergoes a huge volume change during lithium insertion and extraction, which will cause the destruction of the material structure, electrode pulverization, and then make the electrical contact between the active material and the current collector worse, the electron transport is blocked, seriously affecting the specific capacitance of the material and unable to fully exert its advantage of high theoretical capacity.

[0004] On the other hand, when the battery undergoes charge and discharge cycles, the volume change of silicon will accumulate continuously, resulting in continuous damage to the electrode structure. At the same time, under the condition of high-rate charge and discharge, the volume change of silicon intensifies, the electrode polarization phenomenon is serious, and the internal resistance of the battery increases rapidly. This will not only greatly reduce the charge and discharge efficiency of the battery, but also cause the cycle life of the battery to be shortened sharply, making it difficult to meet the requirements of fast charge and discharge and long cycle life in practical applications.

[0005] In summary, in the existing technologies, the improvement of the comprehensive performance of silicon-carbon anode materials is solved by various methods such as optimizing the material structure and surface coating modification, but the problems of low capacitance and poor cycle stability of silicon-carbon anode materials have not been solved yet.

[0006] Therefore, a preparation method of a high-capacity silicon-carbon anode material is proposed. Summary of the Invention

[0007] The object of the present invention is to provide a preparation method of a high-capacity silicon-carbon anode material; by controlling the particle size of iron nanoparticles, pretreated silicon powder is obtained through a temperature-rising reaction, and then nanosilicon powder is obtained through cleaning and modification with a silane coupling agent; phenolic resin is calcined at high temperature with microwave assistance to obtain porous carbon; nanosilicon powder and lithium carbonate are added to the porous carbon for ball milling, and titanium dioxide is added for further ball milling, followed by coating with aluminum phosphate; then, using phenolic resin as a carbon source for carbon layer coating and high-temperature sintering, the prepared silicon-carbon material is used for the production of anode sheets and battery assembly; by controlling the particle size of nanometer micropowders and the load of porous carbon, the battery capacity is increased; through microwave-assisted high-temperature calcination and the synergistic effect of the carbon coating layer and lithium carbonate, the cycle stability of the battery is improved, effectively enhancing the comprehensive performance of the battery.

[0008] To achieve the above object, the present invention provides the following technical solutions:

[0009] The present invention provides a preparation method of a high-capacity silicon-carbon anode material, and the preparation of the silicon-carbon anode material includes the following steps:

[0010] S1 Using iron nanoparticles as a catalyst, silane gas is introduced, and a temperature-rising reaction is carried out to obtain pretreated silicon powder; the pretreated silicon powder is ultrasonically cleaned, centrifuged, and modified with a silane coupling agent to obtain nanosilicon powder;

[0011] S2 Phenol and formaldehyde are reacted under the action of dilute hydrochloric acid, and a curing agent is added to obtain phenolic resin; the phenolic resin is calcined in segments by microwave-assisted heating to obtain porous carbon;

[0012] S3 Nanosilicon powder, porous carbon, and lithium carbonate are ball milled in a dispersant to obtain a silicon-loaded matrix; the silicon-loaded matrix is ground with titanium dioxide and coated with aluminum dihydrogen phosphate to obtain a coated phosphorus-carbon-silicon matrix; the mass ratio of porous carbon, nanosilicon powder, and lithium carbonate is 18 - 20:8 - 10:1; the thickness of aluminum phosphate in the coated phosphorus-carbon-silicon matrix is 62 - 80 nm;

[0013] S4 Phenolic resin is obtained as a resin sol through the sol-gel method; the coated phosphorus-carbon-silicon matrix is dispersed in the resin sol, aged, dried, and sintered at high temperature to obtain a carbon-silicon material; the thickness of the carbon coating in the carbon-silicon material is 108 - 124 nm;

[0014] S5 The carbon-silicon material and an auxiliary agent are formulated into a slurry; the slurry is cast on a copper foil, cold-pressed, trimmed, and sliced to obtain the silicon-carbon anode material.

[0015] Preferably, the silane coupling agent is aminopropyltriethoxysilane; the curing agent is melamine; the dispersant is polyvinylpyrrolidone.

[0016] Preferably, the preparation of nanosilicon powder in S1 includes the following steps:

[0017] Place iron nanoparticles in the reaction chamber, repeat the gas replacement 3 times to normal pressure, introduce silane gas at a flow rate of 100 - 200 sccm, and simultaneously introduce argon as a carrier gas at a flow rate of 600 sccm to obtain a mixed system; rapidly raise the temperature of the mixed system to 600 - 700 °C, react for 15 - 25 min, then stop introducing silane gas, and use argon to quickly cool the reaction system to room temperature. The nano-silicon powder settles to the bottom of the reaction chamber and is collected by an electrostatic collector to obtain pre-treated silicon powder; add the pre-treated silicon powder to deionized water, and obtain treated silicon powder through ultrasonic cleaning and centrifugal separation; add ethanol to aminopropyltriethoxysilane to obtain a silane coupling agent solution; slowly add the treated silicon powder to the silane coupling agent solution, ultrasonicate, and vacuum dry to obtain nano-silicon powder with a particle size of 8 - 10 nm.

[0018] Preferably, the preparation of the porous carbon in S2 includes the following steps:

[0019] Mix phenol, an aqueous formaldehyde solution with a mass percentage concentration of 35%, and dilute hydrochloric acid with a mass concentration of 10%, heat to 80 - 100 °C, react for 3 h, and cool to obtain a first mixed solution; add melamine to the first mixed solution, heat to 70 - 90 °C to obtain a second mixed solution; sieve, wash, and dry the second mixed solution to obtain phenolic resin.

[0020] Put the phenolic resin powder into a quartz crucible, place it in the reaction chamber of a high-temperature furnace, and perform gas replacement treatment; through microwave-assisted heating, set the microwave power to 400 - 600 W, maintain the preheating temperature at 200 - 400 °C, and preheat for 30 min; then raise the temperature to 800 - 1000 °C and hold for 3 h to obtain a reaction system; stop heating the reaction system, and control the cooling rate to 5 - 8 °C / min with nitrogen and cool to room temperature to obtain porous carbon.

[0021] Preferably, the preparation of the phosphorus-carbon-silicon matrix coating in S3 includes the following steps:

[0022] Dissolve polyvinylpyrrolidone in ethanol and stir evenly to obtain a mixed solution; put the nano-silicon powder and lithium carbonate into a ball mill, add porous carbon, slowly add the mixed solution, and ball mill to obtain a silicon matrix support.

[0023] Add titanium dioxide to the silicon matrix support, put it into the ball mill again, and ball mill for 5 h to obtain a dispersed silicon matrix; dissolve aluminum dihydrogen phosphate in absolute ethanol to prepare a 1 mol / L solution, add deionized water, and then dropwise add concentrated hydrochloric acid to adjust the pH value of the solution to 3. Under the condition of a constant temperature water bath at 60 - 80 °C, ultrasonically assist stirring for 8 h to prepare a sol; add the dispersed silicon matrix to the sol and stir to obtain a mixed colloidal solution; age the mixed colloidal solution at room temperature and vacuum dry to obtain a dried product; calcine the dried product at 500 - 600 °C for 3 h to obtain the phosphorus-carbon-silicon matrix coating.

[0024] The molar ratio of deionized water to aluminum dihydrogen phosphate is 5 - 10:1; the frequency of ultrasonic assistance is 20 - 40 kHz, and the power of ultrasonic assistance is 100 - 200 W.

[0025] Preferably, the preparation of the carbon-silicon material in S4 includes the following steps:

[0026] Dissolve phenolic resin in absolute ethanol to prepare a solution with a mass fraction of 20%, add ammonia water, and adjust the pH value to 9 to obtain a resin solution; react the resin solution in a water bath at 60 - 90 °C for 6 h to obtain a resin sol; disperse the coated phosphorus-carbon-silicon matrix in the resin sol, stir for 3 h, transfer it to a sealed container, age at room temperature for 12 - 18 h, and vacuum dry to obtain the material to be calcined; put the material to be calcined into a high-temperature furnace, carry out high-temperature sintering at 600 - 800 °C, with a heating rate of 15 - 20 °C / min, and sinter for 3 h to obtain the carbon-silicon material.

[0027] Preferably, the preparation of the silicon-carbon anode material in S5 includes the following steps:

[0028] Mix the carbon-silicon material and additives, disperse them in deionized water to form a slurry; cast the slurry onto a copper foil by the doctor blade method, bake at 85 °C for 3 h, carry out cold pressing, edge cutting, and slicing, and then dry in a vacuum at 90 °C for 18 hours to obtain the silicon-carbon anode material;

[0029] The additives are graphite, carbon black, and polyvinylidene fluoride; the mass ratio of graphite, carbon-silicon material, carbon black, and polyvinylidene fluoride is 65:30:1.5:3.5.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] 1. The present invention controls iron nanoparticles to obtain nanosilicon powder with a particle size of 8 - 10 nm, and utilizes the synergistic effect of silane modification of nanosilicon powder and porous carbon loading to improve the dispersion uniformity of nanosilicon powder in the anode material; the improvement of dispersion uniformity increases the contact area between silicon powder and other electrode materials and electrolyte, enabling more silicon atoms to participate in the electrochemical reaction, thereby significantly improving the capacitance of the battery material.

[0032] 2. The present invention adjusts the preparation sequence of the aluminum phosphate coating layer, uses ultrasonic-assisted gelation technology for aluminum phosphate coating and controls the coating layer thickness, combines porous carbon loading of nanosilicon powder and surface treatment of nanosilicon powder and other technologies to synergistically improve the rate retention of the battery material.

[0033] 3. The present invention reduces the structural damage of the battery during the cycling process and significantly enhances the cycling performance of the battery material by using porous carbon to load nano-silicon powder, synergistically with microwave-assisted heating and a segmented calcination process, and by means of the synergistic effect of the carbon coating layer and lithium carbonate; the three-dimensional porous structure of the porous carbon accommodates the volume expansion of silicon, increases the buffering performance and the dispersion effect on silicon, and the uniform structure is conducive to the transmission of electrons and ions, ensuring the performance stability of the material during multiple cycles.

[0034] 4. The present invention introduces a porous carbon structure to load nano-silicon powder, controls the dispersion uniformity of nano-silicon powder by adding lithium carbonate during the loading process, uses the carbon dioxide generated by lithium carbonate at high temperature to create pores, forms a lithium-silicon alloy by compounding to inhibit the volume expansion of silicon, and then combines phenolic resin as a carbon source to coat a carbon layer on the surface of the structure, effectively reducing the expansion rate of the negative electrode material. The porous carbon buffers the expansion of silicon, and lithium carbonate and the carbon coating layer synergistically inhibit silicon expansion from the inside and outside, reducing the expansion of the negative electrode of the battery material and extending the service life of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a flow chart of the preparation method of the high-capacity silicon-carbon negative electrode material prepared in Example 1 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0036] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. 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.

[0037] Please refer to Figure 1 , the present invention provides a preparation method of a high-capacity silicon-carbon negative electrode material, Figure 1 It is a flow chart of the preparation method of the high-capacity silicon-carbon negative electrode material prepared in Example 1 of the present invention, and the technical solution is as follows:

[0038] Example 1

[0039] Place iron nanoparticles with a particle size of 8 nm in the reaction chamber, and reduce the air pressure in the reaction chamber to 1×10 -3Below Pa, then introduce high-purity argon into the reaction chamber to restore the air pressure to normal pressure, and repeat this operation 3 times; introduce silane gas at a flow rate of 200 sccm (standard cubic centimeters per minute), and at the same time introduce argon as a carrier gas at a flow rate of 600 sccm to obtain a mixed system; rapidly raise the temperature of the mixed system to 700 °C and react for 20 min, and a reaction product gradually aggregates and grows on the surface of the iron particles; after the reaction ends, stop introducing silane gas, continue to introduce argon, and keep the flow rate at 800 sccm, and use argon to rapidly cool the reaction system to room temperature. The nano-silicon micropowder settles to the bottom of the reaction chamber and is collected by an electrostatic collector to obtain pretreated silicon powder; add the pretreated silicon micropowder to deionized water, and use ultrasonic cleaning. The ultrasonic frequency is set to 50 kHz and the ultrasonic time is 60 min. By centrifugal separation, centrifuge at 10,000 r / min for 15 min, remove the supernatant, and repeat the cleaning and centrifugation operations 3 times to obtain treated silicon powder; add aminopropyltriethoxysilane to ethanol, and at room temperature, use a magnetic stirrer to stir at 300 r / min for 1 h to obtain a silane coupling agent solution; slowly add 100 parts of the treated silicon powder to the silane coupling agent solution, with an ultrasonic frequency of 60 kHz and an ultrasonic power of 200 W, treat at 60 °C for 2 h, and place it in a vacuum drying oven, dry at 80 °C for 10 h to obtain nano-silicon powder with a particle size of 8-10 nm.

[0040] Mix phenol, an aqueous formaldehyde solution with a mass percentage concentration of 35%, and dilute hydrochloric acid with a mass concentration of 10% in a mass ratio of 1:0.8:0.3, heat it to 100 °C, stir for 3 h, and the stirring speed is 800 rpm, and cool to obtain mixture one; add 8 parts of melamine to 100 parts of the mixed solution, heat to 80 °C, and stir at 500 rpm for 2 h to obtain mixture two; sieve, wash, and dry the mixture two to obtain phenolic resin.

[0041] Put the phenolic resin powder into a quartz crucible, place it in the reaction chamber of a high-temperature furnace, close the furnace door, start the vacuum pump, and reduce the air pressure in the reaction chamber to 1×10 -3 Below Pa, slowly introduce nitrogen, and repeat the operations of evacuating and filling inert gas; set the microwave power to 500 W, and at a heating rate of 10 °C / min, raise the temperature in the reaction chamber from room temperature to 300 °C, preheat for 30 min, turn off the microwave generator, and switch to the conventional heating mode of the high-temperature furnace. At a heating rate of 15 °C / min, raise the temperature to 800 °C and keep it warm for 3 h to obtain a reaction system; stop heating the reaction system, and control the cooling rate to 5 °C / min through nitrogen and cool to room temperature to obtain porous carbon.

[0042] Dissolve 4 parts of polyvinylpyrrolidone in 5 ml of ethanol and stir evenly to obtain a mixed solution; add 40 parts of nano-silicon powder and 5 parts of lithium carbonate into a ball mill, add 100 parts of porous carbon, slowly add the mixed solution, keep the ball-to-material ratio at 6:1, the rotation speed of the ball mill at 500 r / min, and the ball milling time at 3 h to obtain a silicon-supported matrix;

[0043] Add 10 parts of titanium dioxide to 100 parts of the silicon-supported matrix, put it into the ball mill again, and ball mill at a rotation speed of 400 r / min for 5 h to make it evenly mixed to obtain a dispersed silicon matrix; dissolve aluminum dihydrogen phosphate in 5 ml of absolute ethanol to prepare a 1 mol / L solution, add deionized water, keep the molar ratio of water to aluminum dihydrogen phosphate at 8:1, then add concentrated hydrochloric acid to adjust the pH value of the solution to 3, and under the condition of a constant temperature water bath at 80 °C, stir at a stirring speed of 200 r / min for 8 h with an ultrasonic frequency of 30 kHz and an ultrasonic power of 150 W to prepare a sol; add the dispersed silicon matrix into the sol and continue to stir for 2 h to obtain a mixed glue solution; transfer the mixed glue solution to a sealed container, age at room temperature for 24 h, place it in a vacuum drying oven, dry at 100 °C for 10 h to obtain a dried product; put the dried product into a high-temperature furnace and calcine at 600 °C for 3 h to obtain a phosphorus-carbon-silicon-coated matrix;

[0044] Dissolve the prepared phenolic resin in absolute ethanol to prepare a solution with a mass fraction of 20%, add ammonia water, and adjust the pH value to 9 to obtain a resin solution; react the resin solution at a constant temperature water bath at 80 °C with a stirring speed of 200 r / min for 6 h to obtain a resin sol; disperse the phosphorus-carbon-silicon-coated matrix in the resin sol, stir for 3 h, transfer it to a sealed container, age at room temperature for 15 h, place it in a vacuum drying oven and dry at 80 °C for 8 h to obtain a product to be calcined; put the product to be calcined into a high-temperature furnace and carry out high-temperature sintering at 800 °C with a heating rate of 20 °C / min and a holding time of 3 h to prepare a carbon-silicon material.

[0045] Mix graphite, carbon-silicon material, carbon black and binder polyvinylidene fluoride (PVDF) in a mass ratio of 65:30:1.5:3.5, disperse them in deionized water to form a uniform slurry; cast the slurry on a copper foil by the doctor blade method, bake at 85 °C for 3.5 h, then carry out cold pressing, trimming and slicing, and then dry in a vacuum at 90 °C for 18 h to obtain a high-capacity silicon-carbon negative electrode material; assemble the high-capacity silicon-carbon negative electrode material, separator and electrolyte (the components of the electrolyte are 1 mol / L LiPF6 + EC / DMC (1∶4) + 2% FEC) into a lithium-ion button battery.

[0046] Examples 2-6 refer to the preparation method and parameter conditions of Example 1, and the differences are shown in Table 1.

[0047] Table 1 Parameter Changes in Examples 1 - 6

[0048]

[0049]

[0050] Comparative Example 1 Refer to Example 1, the difference is that porous carbon - supported nano - silicon powder is not added.

[0051] Comparative Example 2 Refer to Example 1, the difference is that polyvinylpyrrolidone is not used for dispersion during the process of porous carbon - supported nano - silicon powder.

[0052] Comparative Example 3 Refer to Example 1, the difference is that lithium carbonate is not added;

[0053] Comparative Example 4 Refer to Example 1, the difference is that titanium dioxide is not added;

[0054] Comparative Example 5 Refer to Example 1, the difference is that the added iron nanoparticles are 10 - 15 nm;

[0055] Comparative Example 6 Refer to Example 1, the difference is that commercially available nanoparticles with a particle size of 20 - 50 nm are used;

[0056] Comparative Example 7 Refer to Example 1, the difference is that the post - treatment operations of ultrasonic cleaning and centrifugal separation are not carried out;

[0057] Comparative Example 8 Refer to Example 1, the difference is that nano - silicon powder is not modified with aminopropyltriethoxysilane;

[0058] Experimental Example 1 Capacitance Test

[0059] The performance of the lithium - ion button batteries prepared in Examples 1 - 6 and Comparative Examples 1 - 8 was tested by an electrochemical test system; the capacity was determined through the first - efficiency test and the first - charge specific capacity;

[0060] First - efficiency test: The discharge capacity of discharging at 0.2 C to 2.5 V is divided by the charge capacity of the first charge at 0.1 C to 1.5 V × 100%;

[0061] First - charge specific capacity: In an environment of 25 °C, charge at 0.1 C to 1.5 V and record the charge capacity. The test results are shown in Table 2.

[0062] Table 2 Specific Capacity Tests of Examples 1 - 6 and Comparative Examples 1 - 8

[0063]

[0064]

[0065] It can be seen from the results in Table 2 that the particle size of the catalyst iron nanoparticles used in Comparative Example 5 is 10-15 nm, and the particle size range of the prepared nano-silicon powder is 15-30 nm. Compared with the 8-10 nm nano-silicon powder prepared in Examples 1-6, the particle size of the silicon powder has increased significantly. Combining the results of Comparative Example 6, it can be seen that by using large-particle-size silicon powder, the capacity of the prepared silicon-carbon negative electrode material has decreased significantly compared with Examples 1-8. Since nano-silicon powder with a small particle size has a larger specific surface area, it can provide more lithium-ion insertion sites, thereby increasing the capacitance; in Comparative Example 7, through post-treatment operations, dust impurities are avoided from being introduced during the preparation of nano-silicon powder, ensuring the purity of nano-silicon powder. High-purity nano-silicon powder can reduce the hindrance of impurities to lithium-ion transmission and improve the first efficiency; if the particle size of nano-silicon powder is too large, the lithium-ion insertion path will increase, resulting in a decrease in specific capacitance, and the increase in impurities will consume lithium ions and reduce the first efficiency; in Comparative Examples 1-2, without loading nano-silicon powder through the introduction of porous carbon or without using a dispersant for dispersion during the preparation process, the obtained nano-silicon powder has poor dispersion uniformity in the silicon-carbon negative electrode material. Good dispersion performance enables nano-silicon powder to be evenly distributed in the electrode material, increasing the contact area between the silicon powder and other electrode materials and the electrolyte. During the charge and discharge process, more silicon atoms can participate in the electrochemical reaction, thereby increasing the capacitance of the battery; nano-silicon powder with good dispersibility has a more uniform and stable contact with the electrolyte, which can reduce unnecessary side reactions between the surface of the silicon powder and the electrolyte. During the charge and discharge process, lithium-ion insertion and extraction are more smooth, and at the same time, the tight combination can also reduce the shedding of active substances and improve the first efficiency; combining the fact that in Comparative Example 7, the nano-silicon powder is not modified with a silane coupling agent, the capacity is significantly reduced. Since the surface-modified nano-silicon powder has more surface active groups, it binds more tightly to porous carbon and lithium carbonate, further improving the first efficiency. At the same time, the surface modification process increases the dispersibility of nano-silicon powder and avoids the formation of silicon powder aggregates. Since the distribution of active sites on the surface of the aggregates is uneven, it is easy to cause the aggravation of local side reactions, consume more lithium ions and electrolytes, and reduce the first-week efficiency; at the same time, the three-dimensional porous structure of porous carbon provides sufficient buffer space for nano-silicon, reducing the damage of the volume change of silicon during the charge and discharge process to the material structure, maintaining the integrity of the material structure, ensuring the smoothness of the electron and ion transmission channels, and increasing the capacitance and first efficiency. During the preparation process of porous carbon, microwave-assisted heating makes the structure of porous carbon more uniform and the pore size distribution more reasonable, further improving the dispersion uniformity of nano-silicon powder in the material and enhancing the material performance;In Comparative Examples 3-4, the omission of lithium carbonate and titanium dioxide significantly reduces the capacity and initial efficiency of the battery. Lithium carbonate decomposes during charge and discharge to produce lithium salts, which react with silicon to form a lithium-silicon alloy, reducing the volume change amplitude of silicon and stabilizing the material structure, thus facilitating the improvement of specific capacitance and first-cycle efficiency. Meanwhile, the addition of titanium dioxide improves the electron conduction performance of the material and optimizes the transmission path of lithium ions in the material, thereby increasing the capacitance and initial efficiency. In summary, by controlling iron nanoparticles, nanosilica powder with a particle size of 8-10 nm is prepared. Through the synergistic effect of silane modification of nanosilica powder and porous carbon loading, the dispersion uniformity of nanosilica powder in the anode material is improved. In combination with lithium carbonate and titanium dioxide additives, the capacitance and initial efficiency of the battery material are further enhanced, and the service life of the battery is prolonged.

[0066] Example 7 is the same as Example 1;

[0067] Examples 8-12 refer to the preparation method and parameter conditions of Example 7, with the differences shown in Table 2.

[0068] Table 3 Parameter Changes in Examples 7-12

[0069]

[0070] Comparative Example 9 refers to Example 7, with the difference that porous carbon-loaded nanosilica powder is not added.

[0071] Comparative Example 10 refers to Example 7, with the difference that it is not coated with aluminum phosphate;

[0072] Comparative Example 11 refers to Example 7, with the difference that ultrasonic-assisted gel formation is not carried out during the aluminum phosphate coating process;

[0073] Comparative Example 12 refers to Example 7, with the difference that the thickness of the aluminum phosphate coating layer is 100 nm;

[0074] Comparative Example 13 refers to Example 7, with the difference that the thickness of the aluminum phosphate coating layer is 50 nm;

[0075] Comparative Example 14 refers to Example 7, with the difference that it is first coated with carbon and then coated with aluminum phosphate by the sol-gel method;

[0076] Comparative Example 15 refers to Example 7, with the difference that nanosilica powder is not modified with aminopropyltriethoxysilane;

[0077] Experimental Example 2 Rate Retention Test

[0078] The lithium-ion coin cells prepared in Examples 7-12 and Comparative Examples 9-15 were tested for rate retention through an electrochemical test system; the rate retention was tested through the 1C rate retention and 2C rate retention;

[0079] 1C rate retention: After fully charging at 0.2C, discharge at 1C and 0.2C respectively, and divide the 0.2C discharge capacity by the 1C discharge capacity;

[0080] 5C rate retention: After fully charging at 0.2C, discharge at 5C and 0.2C respectively, and divide the 0.2C discharge capacity by the 5C discharge capacity; The test results are shown in Table 4.

[0081] Table 4 Rate retention test of Examples 7 - 12 and Comparative Examples 9 - 15

[0082]

[0083]

[0084] It can be seen from the results in Table 4 that in Comparative Example 9, the rate retention of the battery material prepared without loading nano-silicon powder on porous carbon decreased significantly compared with Examples 7-12. Since porous carbon has a three-dimensional porous structure, it provides sufficient buffer space for silicon. When silicon undergoes volume expansion, it can be accommodated by the porous structure, reducing the mutual extrusion between silicon particles and maintaining the integrity of the material structure. Combining with Comparative Example 15, the nano-silicon powder without being modified by a silane coupling agent also showed a significant decrease in rate retention. After silane modification, the possibility of agglomeration between silicon powders was avoided, and they were evenly distributed in the porous carbon structure, which was beneficial to the transmission of electrons and ions, ensuring the performance stability of the material during multiple cycles. In addition, the microwave-assisted heating technology in the preparation of porous carbon made the porous carbon structure more uniform and the pore size distribution more reasonable, further optimizing the transmission paths of electrons and ions and improving the rate retention. In addition, the surface-modified nano-silicon powder was more tightly combined with porous carbon, lithium carbonate, etc., making the insertion and extraction of lithium ions smoother, avoiding obstacles encountered by lithium ions during transmission, resulting in an increase in battery internal resistance and capacity loss. In Comparative Examples 10-11, the rate retention of the battery material prepared without aluminum phosphate coating and without using ultrasonic-assisted gelation decreased significantly. Since during high-rate charge and discharge, lithium ions inside the battery need to be rapidly transmitted in the electrode material, aluminum phosphate has good ionic conductivity, and the introduction of the coating layer can provide a rapid diffusion channel for lithium ions, reducing the battery internal resistance and accelerating the transmission speed of lithium ions in the electrode material. The results of Comparative Examples 12-13 showed that the thickness of the coating layer would indirectly affect the rate performance. When the thickness was small, it could not fully play its role in providing a rapid ion diffusion channel, the transmission speed of lithium ions was limited, and the rate retention was difficult to effectively improve. In addition, a thinner coating layer was insufficient in suppressing the volume change of silicon and reducing electrode polarization. A thicker and uniform coating layer increased the overall resistance of the material, hindered electron transmission, and poor electron conduction would affect the charge and discharge performance of the battery. At the same time, the flexibility of the material decreased and the rate retention decreased. A uniform coating layer could better suppress the volume change of silicon during high-rate charge and discharge. Electrode polarization would hinder the normal transmission of lithium ions and reduce the battery performance, while the aluminum phosphate coating layer reduced this hindrance and improved the rate retention. In Comparative Example 14, by changing the coating order of the coating layer, the rate retention of the obtained battery material decreased significantly. Since the carbon layer was coated first, the carbon layer would cover some active sites on the surface of the silicon-carbon negative electrode material. When the aluminum phosphate was coated subsequently, it was difficult to form a uniform and complete aluminum phosphate coating layer, resulting in a reduction or blockage of the lithium ion diffusion channel and a decrease in rate performance. In addition, the presence of the carbon layer might affect the buffering and inhibitory effect of the aluminum phosphate coating layer on the volume change of silicon. The elastic modulus of the carbon layer was different from that of aluminum phosphate, and during the volume expansion and contraction of silicon, the synergistic effect between the two materials might be poor, leading to easier damage to the electrode structure and exacerbation of the electrode polarization phenomenon, resulting in a reduction in rate performance;In summary, by adjusting the preparation sequence of the aluminum phosphate coating layer, using ultrasonic-assisted gelation technology for aluminum phosphate coating, controlling the thickness of the coating layer, improving the quality and uniformity of the coating layer, loading nano-silicon powder on porous carbon, treating the surface of nano-silicon powder, the rate retention of the battery material is improved under the synergistic effect.

[0085] Example 13 is the same as Example 1;

[0086] Examples 14-18 refer to the preparation method and parameter conditions of Example 13, and the differences are shown in Table 5.

[0087] Table 5 Parameter changes in Examples 13-18

[0088]

[0089] Comparative Example 16 refers to Example 13, and the difference is that porous carbon-loaded nano-silicon powder is not added.

[0090] Comparative Example 17 refers to Example 13, and the difference is that microwave-assisted heating technology is not used.

[0091] Comparative Example 18 refers to Example 13, and the difference is that it is directly calcined at high temperature without preheating calcination and high-temperature calcination processes.

[0092] Comparative Example 19 refers to Example 13, and the difference is that the cooling rate is 15°C / min.

[0093] Comparative Example 20 refers to Example 13, and the difference is that carbon layer coating is not carried out.

[0094] Comparative Example 21 refers to Example 13, and the difference is that lithium carbonate is not added.

[0095] Comparative Example 22 refers to Example 13, and the difference is that nano-silicon powder is not modified with aminopropyltriethoxysilane.

[0096] Experimental Example 3 Cycle performance measurement

[0097] The lithium-ion button batteries prepared in Examples 13-18 and Comparative Examples 16-22 are first discharged to 5 mV at 0.5C, 0.05C, 0.02C, and 0.01C in an environment of 25°C, and then charged to 1.5V at 0.1C, and the discharge specific capacity of the first cycle is recorded. Then, 500 cycles of discharge and charge are carried out. The charge rate during the cycle is 0.5C, and the discharge rate is 1C. The charge specific capacity of the 500th cycle is recorded; the cycle capacity retention rate = the discharge specific capacity of the first cycle / the discharge specific capacity of the 500th cycle × 100%, calculate the cycle capacity retention rate, test three groups, and calculate the average capacity retention rate of the three groups of batteries after 500 cycles. The test results are shown in Table 6.

[0098] Table 6 Cyclic performance measurement of Examples 13 - 18 and Comparative Examples 16 - 22

[0099] Example Capacity retention rate / % Example 13 83.8 Example 14 83.2 Example 15 82.6 Example 16 82.2 Example 17 83.5 Example 18 82.4 Comparative Example 16 65.5 Comparative Example 17 72.8 Comparative Example 18 70.6 Comparative Example 19 68.2 Comparative Example 20 72.6 Comparative Example 21 71.2 Comparative Example 22 70.8

[0100] It can be seen from the results in Table 6 that in Comparative Example 16, without loading nano-silicon powder on porous carbon, the cyclic capacity retention rate of the prepared battery material is significantly lower than that in Examples 13-18. Since porous carbon has a three-dimensional porous structure, this structure provides sufficient buffer space for silicon. During charge and discharge processes, silicon undergoes a large volume change. The porous structure of porous carbon can accommodate the volume expansion of silicon, reduce the mutual extrusion between silicon particles, and maintain the integrity of the material structure. Combining Comparative Examples 17-18, through microwave-assisted heating technology for auxiliary staged calcination, at the initial stage of calcination, preheating is first carried out at a lower temperature to uniformly heat the phenolic resin inside, promote its preliminary decomposition and structural rearrangement; then high-temperature calcination is carried out to shorten the calcination time. The obtained porous carbon structure is more uniform and the pore size distribution is more reasonable, further optimizing its buffering performance and the dispersion effect on silicon. The uniform structure is conducive to the transmission of electrons and ions, ensuring the performance stability of the material during multiple cycles and improving the cycling performance of the battery; The comparison results between Comparative Example 19 and Examples 13-18 show that with the increase in the cooling rate, the capacity retention rate of the battery material after 500 cycles decreases significantly. Since during rapid cooling, the thermal stress inside the porous carbon changes rapidly, and there are differences in the cooling rates of different parts inside the material, which may cause large stress concentrations, resulting in defects in the microstructure of the porous carbon; Slow cooling can slowly release the thermal stress inside the porous carbon, allowing atoms to have enough time to rearrange, thereby maintaining its uniform structure and reasonable pore size distribution. At the same time, the stable porous carbon structure can provide a buffer space for nano-silicon, reduce the mutual extrusion between particles during the volume change of silicon during charge and discharge, which is conducive to the transmission of electrons and ions. During multiple charge and discharge cycles, it can continuously provide good support and buffering for silicon, maintain the integrity of the electrode, and improve the cycling stability of the battery; In Examples 20-21, without the addition of lithium carbonate and carbon layer coating, the cycling stability of the obtained battery material decreases. Lithium carbonate will decompose to produce lithium salts during charge and discharge processes, which can react with silicon powder to form a lithium-silicon alloy, reducing the amplitude of the volume change of silicon. At the same time, the carbon coating layer acts as a physical barrier, restricting the expansion direction of silicon and enhancing the structural stability of the material, reducing electrode pulverization. Through high-temperature calcination, the interfacial fusion between the carbon layer and the coated carbon-silicon matrix is promoted, forming a tighter chemical bond connection between the carbon layer and the matrix, enhancing the overall strength of the material, further suppressing expansion, and reducing the structural damage of the battery during cycling under the synergistic effect, improving the cycling performance of the battery; In Comparative Example 22, due to the lack of modification treatment of nano-silicon powder, the binding force with high-microporous porous carbon, lithium carbonate, etc. is weakened. During multiple cycles, due to the loose combination of the materials, the transmission of lithium ions is hindered and the active substances fall off, reducing the specific capacity of the battery and further reducing the cycling performance of the battery;In summary, in the present invention, by using porous carbon-supported nano-silicon powder, and synergistically using microwave-assisted heating and a stepwise calcination process, the cycling performance of the battery material is improved. At the same time, through the synergistic effect of the carbon coating layer and lithium carbonate, the structural stability of the material is enhanced, the structural damage during battery cycling is reduced, and the cycling performance is further improved.

[0101] Example 19 is the same as Example 1;

[0102] Examples 20 - 24 refer to the preparation method and parameter conditions of Example 19, with the differences shown in Table 7.

[0103] Comparative Example 23 refers to Example 19, with the difference that porous carbon-supported nano-silicon powder is not added.

[0104] Comparative Example 24 refers to Example 19, with the difference that lithium carbonate is not added.

[0105] Comparative Example 25 refers to Example 19, with the difference that carbon layer coating is not performed.

[0106] Comparative Example 26 refers to Example 19, with the difference that the thickness of the carbon layer coating is 300 nm.

[0107] Comparative Example 27 refers to Example 19, with the difference that the thickness of the carbon layer coating is 30 nm.

[0108] Comparative Example 28 refers to Example 19, with the difference that lithium carbonate and titanium dioxide are added simultaneously before the phosphorus coating process.

[0109] Comparative Example 29 refers to Example 19, with the difference that aluminum phosphate coating is performed by sol-gel method after carbon coating.

[0110] Experimental Example 4 Thickness Expansion Rate Test

[0111] Measure the thickness of the negative electrode sheet before assembling the battery for Examples 19 - 24 and Comparative Examples 23 - 29, denoted as D1. When the battery is assembled in an environment of 25°C, the negative electrode sheet is in a fully inserted state; disassemble the battery and test the thickness of the negative electrode sheet in the fully inserted state, denoted as D2. The thickness of the foil used is 9 μm. Calculate the thickness expansion rate according to the following formula: Thickness expansion rate = (D2 - D1) / (D1 - 9) × 100%, and the test results are shown in Table 8.

[0112] Table 7 Thickness Expansion Rate Test for Examples 19 - 24 and Comparative Examples 23 - 29

[0113]

[0114]

[0115] It can be seen from the results in Table 7 that the expansion rate of the battery material obtained without adding porous carbon-supported nano-silicon powder in Comparative Example 23 is significantly higher than that in Example 19-2. The three-dimensional porous structure of the porous carbon provides a buffer space for silicon. When silicon undergoes volume expansion, the porous structure can accommodate part of the expanded volume, reduce the mutual extrusion between silicon particles, relieve the damage to the electrode structure caused by silicon expansion, and thus reduce the expansion rate of the battery. In Comparative Example 24, due to the absence of lithium carbonate, the expansion rate is significantly increased. During the calcination process, lithium carbonate can release carbon dioxide to form pores when heated at high temperature, reserving space for the volume change of the material. At the same time, lithium carbonate is reduced to lithium salt at high temperature, which can play the role of supplementing lithium source and pre-lithiation. During charge and discharge, it further reacts with silicon to form a lithium-silicon alloy. The crystal structure and electron cloud distribution of the lithium-silicon alloy change, and during the process of lithium ion insertion and extraction, the structure change is more stable, thus effectively suppressing the volume expansion of silicon and reducing the expansion rate of the battery. From the results of Comparative Examples 25-27, the carbon coating layer acts as a physical barrier, restricting the expansion direction of silicon. When silicon undergoes volume expansion, the carbon coating layer can exert a certain restraining effect to prevent silicon from expanding randomly, reduce the deformation of the electrode structure caused by silicon expansion. In addition, the carbon coating layer enhances the structural stability of the material, improves the mechanical properties of the material, makes the electrode more firm during charge and discharge, reduces the phenomenon of electrode pulverization, and further reduces the expansion rate of the battery caused by internal structural changes. However, a thinner carbon layer cannot effectively restrain the expansion of silicon, and silicon particles are easy to break through the limitation of the carbon layer and expand randomly around, resulting in an increase in the deformation of the electrode structure and a relatively higher expansion rate. An overly thick carbon layer increases the overall rigidity of the material. When silicon expands in volume, the carbon layer itself may crack or fall off because it cannot adapt to the expansion of silicon, losing the restrictive effect on silicon expansion. On the other hand, an overly thick carbon layer may affect the transmission efficiency of electrons and ions, resulting in an increase in the internal resistance of the battery, generating more heat, further exacerbating the volume change of silicon, and leading to an increase in the expansion rate of the negative electrode. In Comparative Example 28, the addition sequence of lithium carbonate was changed. Lithium carbonate changes the expansion characteristics of silicon from the inside by forming a lithium-silicon alloy, while titanium dioxide provides external support from aspects such as enhancing structural rigidity and optimizing ion transport. When silicon undergoes volume expansion, the low-expansion characteristics of the lithium-silicon alloy and the supporting effect of titanium dioxide cooperate with each other to jointly resist the expansion stress, enabling the negative electrode material to better maintain structural integrity and further reducing the expansion rate. However, the simultaneous addition of lithium carbonate still has a significant increase compared to Examples 19-24. Adding lithium carbonate during the loading process of nano-silicon powder can improve the dispersion uniformity of nano-silicon powder and lithium carbonate, and at the same time help the binding ability of nano-silicon powder and porous carbon, avoiding the increase in expansion rate due to the shedding of nano-silicon and the reduction in the formation of lithium-silicon alloy during charge and discharge;Comparative Example 29 has a significantly higher expansion rate compared to Examples 19 - 24. After carbon layer coating, the presence of the carbon layer interferes with the inhibitory effect of the aluminum phosphate coating layer on the volume change of silicon. Since the elastic modulus of the carbon layer is different from that of aluminum phosphate, when silicon undergoes volume expansion, the ways and degrees of constraint on silicon by the two materials are different, and an effective synergistic effect cannot be formed. Compared with the sequence of coating aluminum first and then carbon layer, the volume change of silicon is more difficult to be inhibited in this case, resulting in an increase in the expansion rate of the battery negative electrode during charge and discharge; at the same time, the structural stability is damaged in this case. During subsequent charge and discharge processes, due to the unstable structure, the electrode is more likely to show pulverization phenomenon, the electrical contact between the active material and the current collector becomes poor, resulting in an increase in the internal resistance of the battery, further exacerbating the heat generation and volume change inside the battery, causing the expansion rate of the battery negative electrode to rise, affecting the service life and comprehensive performance of the battery; In summary, by introducing a porous carbon structure to load nano - silicon powder, while adding lithium carbonate during the loading process to control the dispersion uniformity of nano - silicon powder, the high - temperature generated carbon dioxide performs a pore - forming effect, and the composite - formed lithium - silicon alloy further inhibits the volume expansion of silicon. Collaborating with phenolic resin as a carbon source material to coat a carbon layer structure on the surface of the structure, effectively constraining the expansion of silicon, further reducing the expansion rate of the negative electrode material, and improving the service life and comprehensive performance of the battery.

[0116] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a high-capacity silicon-carbon negative electrode material, characterized in that: The preparation of the silicon-carbon negative electrode material comprises the following steps: S1 iron nanoparticles are used as a catalyst, silane gas is introduced, and the reaction is performed to obtain pre-treated silicon powder; the pre-treated silicon powder is ultrasonically cleaned, and the silane coupling agent is used to modify the pre-treated silicon powder to obtain nano silicon powder; wherein the particle size of the nano silicon powder is 8-10nm; S2 phenol and formaldehyde are reacted with dilute hydrochloric acid and a curing agent is added to obtain a phenolic resin; the phenolic resin is subjected to microwave-assisted heating and staged calcination to obtain porous carbon; S3: ball-milling the nano silicon powder, the porous carbon and lithium carbonate in a dispersant to obtain a loaded silicon matrix; grinding the loaded silicon matrix with titanium dioxide, and coating it with aluminum dihydrogen phosphate to obtain a coated phosphorus carbon silicon matrix; wherein the mass ratio of the porous carbon, the nano silicon powder and the lithium carbonate is 18-20:8-10:1; and the thickness of aluminum phosphate in the coated phosphorus carbon silicon matrix is ​​62-80nm; S4: obtain resin sol by sol-gel method; disperse the coated phosphorus carbon silicon matrix in the resin sol, age, and sinter at high temperature to obtain carbon silicon material; the carbon coating thickness in the carbon silicon material is 108-124nm; S5 prepares the carbon silicon material and the auxiliary agent into slurry, and obtains the silicon carbon negative electrode material by cold pressing, trimming and cutting.

2. The method for preparing a high-capacity silicon-carbon negative electrode material according to claim 1, characterized in that: The silane coupling agent is aminopropyltriethoxysilane; the curing agent is melamine; and the dispersant is polyvinyl pyrrolidone.

3. The method for preparing a high-capacity silicon-carbon negative electrode material according to claim 1, characterized in that: The preparation of the nano silicon powder described in S1 comprises the following steps: The iron nanoparticles are placed in a reaction chamber, and the air is ventilated three times to normal pressure, and the silane gas is introduced at a flow rate of 100-200 sccm, and argon gas is introduced as a carrier gas at a flow rate of 600 sccm to obtain a mixed system; the temperature of the mixed system is rapidly increased to 600-700°C, and the reaction is carried out for 15-25 minutes, and then the introduction of the silane gas is stopped, and the reaction system is rapidly cooled to room temperature by the argon gas, and the nano silicon powder is precipitated to the bottom of the reaction chamber, and the pretreated silicon powder is collected by an electrostatic collector to obtain the pretreated silicon powder; the pretreated silicon powder is added to deionized water, and the treated silicon powder is obtained by ultrasonic cleaning and centrifugal separation; ethanol is added to aminopropyltriethoxysilane to obtain a silane coupling agent solution; the treated silicon powder is slowly added to the silane coupling agent solution, ultrasonicated, and vacuum dried to obtain the 8-10nm nano silicon powder.

4. The method for preparing a high-capacity silicon-carbon negative electrode material according to claim 1, characterized in that: The preparation of the porous carbon described in S2 comprises the following steps: The phenol, the formaldehyde aqueous solution with a mass percentage concentration of 35% and the dilute hydrochloric acid with a mass concentration of 10% are mixed, heated to 80-100° C., reacted for 3 hours, and cooled to obtain a mixed solution 1; melamine is added to the mixed solution 1, and heated to 70-90° C. to obtain a mixed solution 2; the mixed solution 2 is sieved, washed, and dried to obtain a phenolic resin; The phenolic resin powder is placed in a quartz crucible, placed in a high-temperature furnace reaction chamber, and ventilated; through the microwave-assisted heating, the microwave power is set to 400-600W, the preheating temperature is maintained at 200-400°C, and preheating is performed for 30 minutes; then the temperature is increased to 800-1000°C, and the temperature is kept for 3 hours to obtain a reaction system; the heating of the reaction system is stopped, the cooling rate is controlled to 5-8°C / min by nitrogen, and the porous carbon is cooled to room temperature to obtain the porous carbon.

5. The method for preparing a high-capacity silicon-carbon negative electrode material according to claim 1, characterized in that: The preparation of the coated phosphorus carbon silicon substrate in S3 comprises the following steps: Dissolving polyvinyl pyrrolidone in ethanol and stirring to obtain a mixed solution; adding the nano silicon powder and the lithium carbonate into a ball mill, adding the porous carbon, slowly adding the mixed solution, and ball milling to obtain a loaded silicon matrix; Add titanium dioxide to the loaded silicon matrix, put it into a ball mill again, and ball mill for 5 hours to obtain a dispersed silicon matrix; dissolve the aluminum dihydrogen phosphate in anhydrous ethanol to prepare a 1 mol / L solution, add deionized water, and then drop concentrated hydrochloric acid to adjust the pH value of the solution to 3, and stir it for 8 hours with ultrasonic assistance in a constant temperature water bath at 60-80°C to obtain a sol; add the dispersed silicon matrix to the sol, stir to obtain a mixed glue solution; age the mixed glue solution at room temperature, and vacuum dry to obtain a dried product; calcine the dried product at 500-600°C for 3 hours to obtain the coated phosphorus-carbon silicon matrix; The molar ratio of the deionized water to the aluminum dihydrogen phosphate is 5-10:1; the frequency of the ultrasonic assistance is 20-40kHz, and the power of the ultrasonic assistance is 100-200W.

6. The method for preparing a high-capacity silicon-carbon negative electrode material according to claim 1, characterized in that: The preparation of the carbon silicon material described in S4 comprises the following steps: The phenolic resin is dissolved in anhydrous ethanol to prepare a solution with a mass fraction of 20%, ammonia water is added, and the pH value is adjusted to 9 to obtain a resin solution; the resin solution is reacted in a water bath at 60-90°C for 6 hours to obtain a resin sol; the coated phosphorus carbon silicon matrix is ​​dispersed in the resin sol, stirred for 3 hours, transferred to a closed container, aged at room temperature for 12-18 hours, and vacuum dried to obtain a calcined material; the calcined material is placed in a high-temperature furnace, and high-temperature sintered at 600-800°C with a heating rate of 15-20°C / min, and sintered for 3 hours to obtain the carbon silicon material.

7. The method for preparing a high-capacity silicon-carbon negative electrode material according to claim 1, characterized in that: The preparation of the silicon-carbon negative electrode material in S5 comprises the following steps: The carbon silicon material and the auxiliary agent are mixed and dispersed in deionized water to form a slurry; the slurry is cast on a copper foil by a doctor blade method, and baked at 85° C. for 3 hours, cold pressed, trimmed, and cut into pieces, and then dried at 90° C. under vacuum conditions for 18 hours to obtain the silicon-carbon negative electrode material; The auxiliary agents are graphite, carbon black and polyvinylidene fluoride; the mass ratio of the graphite, the carbon silicon material, the carbon black and the polyvinylidene fluoride is 65:30:1.5:3.5.

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