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

Abstract

The application 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. The application overcomes the problems of low battery capacity and poor cycle stability of a battery assembled by using the silicon-carbon negative electrode material as a negative electrode material. By controlling the particle size of iron nanoparticles, pretreated silicon powder is prepared through a temperature rising reaction, and then the silicon powder is washed and modified by using a silane coupling agent to obtain nano silicon powder; porous carbon is prepared by using microwave-assisted high-temperature calcination on phenolic resin; the nano silicon powder and lithium carbonate are added into the porous carbon for ball milling, titanium dioxide is added for secondary ball milling, and aluminum phosphate coating is carried out; then, the 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 negative electrode sheet manufacturing and battery assembling; by controlling the particle size of the nano powder and loading the porous carbon, the battery capacity is improved; by microwave-assisted high-temperature calcination and the synergistic effect of the carbon coating layer and the lithium carbonate, the cycle stability of the battery is improved, and the comprehensive performance of the battery is effectively improved.

Description

Technical Field

[0001] This invention relates to the field of battery anode material technology, specifically a method for preparing a high-capacity silicon-carbon anode material. Background Technology

[0002] With the rapid development of electronic devices and the rise of the new energy vehicle industry, higher demands are being placed on battery performance. Among various battery anode materials, silicon-carbon materials have become a highly promising research subject due to their high theoretical specific capacity. Silicon has a theoretical specific capacity as high as 4200 mAh / g, far exceeding that of traditional graphite anode materials (theoretical specific capacity is about 372 mAh / g), giving silicon-carbon materials a significant advantage in improving battery energy density.

[0003] However, current silicon-carbon materials still have many problems. On the one hand, their actual specific capacity is far lower than the theoretical value. During charging and discharging, silicon undergoes huge volume changes during lithium insertion and extraction, which leads to the destruction of the material structure, electrode pulverization, and consequently, poor electrical contact between the active material and the current collector, hindering electron transport and severely affecting the material's specific capacity, thus failing to fully realize its high theoretical capacity advantage.

[0004] On the other hand, when the battery is charged and discharged, the volume change of silicon will continue to accumulate, causing continuous damage to the electrode structure. At the same time, under high-rate charge and discharge conditions, the volume change of silicon intensifies, the electrode polarization phenomenon becomes severe, and the internal resistance of the battery increases rapidly. This will not only significantly reduce the charging and discharging efficiency of the battery, but also cause the cycle life of the battery to be drastically shortened, making it difficult to meet the requirements of fast charging and discharging and long cycle life in practical applications.

[0005] In summary, existing technologies address the overall performance improvement of silicon-carbon anode materials through various methods such as optimizing material structure and surface coating modification, but the problems of low capacitance and poor cycle stability of silicon-carbon anode materials remain unresolved.

[0006] To address this, a method for preparing high-capacity silicon-carbon anode materials is proposed. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing high-capacity silicon-carbon anode materials. By controlling the particle size of iron nanoparticles, pretreated silicon powder is obtained through a heated reaction, followed by cleaning and modification with a silane coupling agent to obtain nano-silicon powder. Phenolic resin is then subjected to microwave-assisted high-temperature calcination to produce porous carbon. The nano-silicon powder and lithium carbonate are added to the porous carbon and ball-milled, followed by the addition of titanium dioxide and further ball-milling, and then coated with aluminum phosphate. The carbon layer is then coated with phenolic resin as a carbon source and sintered at high temperature. The resulting silicon-carbon material is used for anode sheet fabrication and battery assembly. By controlling the particle size of the nanoparticles and synergistically loading the porous carbon, the battery capacity is improved. Microwave-assisted high-temperature calcination and the synergistic effect of the carbon coating layer and lithium carbonate enhance the cycle stability of the battery, effectively improving its overall performance.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] This invention provides a method for preparing a high-capacity silicon-carbon anode material, the preparation of which includes the following steps:

[0010] S1 uses iron nanoparticles as a catalyst, introduces silane gas, and heats the reaction to obtain pretreated silicon powder; the pretreated silicon powder is ultrasonically cleaned, centrifuged, and modified with a silane coupling agent to obtain nano-silicon powder.

[0011] S2 prepares phenolic resin by adding a curing agent to phenol and formaldehyde under the action of dilute hydrochloric acid; porous carbon is obtained by microwave-assisted heating and segmented calcination of the phenolic resin.

[0012] S3 involves ball milling nano-silicon powder, porous carbon, and lithium carbonate in a dispersant to obtain a supported silicon matrix; the supported silicon matrix is ​​then milled with titanium dioxide and coated with aluminum dihydrogen phosphate to obtain a coated phosphorus-carbon silicon matrix; wherein the mass ratio of porous carbon, nano-silicon powder, and lithium carbonate is 18-20:8-10:1; and the aluminum phosphate thickness in the coated phosphorus-carbon silicon matrix is ​​62-80 nm.

[0013] S4 obtains a resin sol by sol-gel method using phenolic resin; disperses the phosphorus-carbon silicon matrix in the resin sol, ages and dries, and sinterstens at high temperature to obtain carbon silicon material; the carbon coating thickness in the carbon silicon material is 108-124 nm.

[0014] S5 prepares silicon carbide materials and additives into a slurry; the slurry is cast onto copper foil, and then cold-pressed, trimmed, and cut into sheets to obtain silicon-carbon anode materials.

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

[0016] Preferably, the preparation of the nano-silicon powder in S1 includes the following steps:

[0017] Iron nanoparticles were placed in a reaction chamber, and the gas was purged three times until atmospheric pressure was reached. Silane gas was introduced at a flow rate of 100-200 sccm, while argon gas was introduced at a flow rate of 600 sccm as a carrier gas to obtain a mixed system. The temperature of the mixed system was rapidly increased to 600-700℃, and the reaction was carried out for 15-25 minutes. Then, the silane gas was stopped, and the reaction system was rapidly cooled to room temperature using argon gas. The nano-silicon powder settled to the bottom of the reaction chamber and was collected by an electrostatic collector to obtain pretreated silicon powder. The pretreated silicon powder was added to deionized water, and treated silicon powder was obtained by ultrasonic cleaning and centrifugation. Ethanol was added to aminopropyltriethoxysilane to obtain a silane coupling agent solution. The treated silicon powder was slowly added to the silane coupling agent solution, ultrasonicated, and vacuum dried to obtain nano-silicon powder with a particle size of 8-10 nm.

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

[0019] Phenol, a 35% (w / w) aqueous solution of formaldehyde, and a 10% (w / w) dilute hydrochloric acid were mixed and heated to 80-100°C for 3 hours. After cooling, a first mixture was obtained. Melamine was added to the first mixture and heated to 70-90°C to obtain a second mixture. The second mixture was then sieved, washed, and dried to obtain phenolic resin.

[0020] Phenolic resin powder was placed in a quartz crucible and then placed in the reaction chamber of a high-temperature furnace for ventilation. Microwave-assisted heating was then performed with a power of 400-600W, maintaining a preheating temperature of 200-400℃ for 30 minutes. The temperature was then increased to 800-1000℃ and held for 3 hours to obtain the reaction system. Heating of the reaction system was then stopped, and the cooling rate was controlled by nitrogen at 5-8℃ / min until the system was cooled to room temperature to obtain porous carbon.

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

[0022] Polyvinylpyrrolidone was dissolved in ethanol and stirred until homogeneous to obtain a mixed solution. Nano-silicon powder and lithium carbonate were added to a ball mill, porous carbon was added, and the mixed solution was slowly added. The mixture was then ball-milled to obtain a supported silicon matrix.

[0023] Titanium dioxide was added to the supported silicon matrix, and the matrix was ball-milled again for 5 hours to obtain a dispersed silicon matrix. Aluminum dihydrogen phosphate was dissolved in anhydrous ethanol to prepare a 1 mol / L solution. Deionized water was added, and concentrated hydrochloric acid was added dropwise to adjust the pH of the solution to 3. The solution was ultrasonically stirred for 8 hours under a constant temperature water bath at 60-80℃ to obtain a sol. The dispersed silicon matrix was added to the sol and stirred to obtain a mixed solution. The mixed solution was aged at room temperature and vacuum dried to obtain a dried product. The dried product was calcined at 500-600℃ for 3 hours to obtain a phosphorus-carbon silicon matrix.

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

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

[0026] Phenolic resin was dissolved in anhydrous ethanol to prepare a 20% (w / w) solution. Ammonia was added to adjust the pH to 9 to obtain a resin solution. The resin solution was reacted in a water bath at 60-90℃ for 6 hours to obtain a resin sol. The phosphorus-carbon silicon matrix was dispersed in the resin sol and stirred for 3 hours. The mixture was then transferred to a sealed container and aged at room temperature for 12-18 hours. After vacuum drying, the calcined material was obtained. The calcined material was placed in a high-temperature furnace and sintered at 600-800℃ with a heating rate of 15-20℃ / min for 3 hours to obtain a carbon silicon material.

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

[0028] Silicon carbon materials and additives are mixed and dispersed in deionized water to form a slurry; the slurry is cast onto copper foil by a scraper method and baked at 85°C for 3 hours, then cold-pressed, trimmed, and cut into sheets, and then dried under vacuum at 90°C for 18 hours to obtain silicon-carbon anode materials;

[0029] The additives are graphite, carbon black, and polyvinylidene fluoride; the mass ratio of graphite, silicon carbide, 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. This invention obtains nano-silicon powder with a particle size of 8-10 nm by controlling iron nanoparticles. By utilizing the synergistic effect of silane-modified nano-silicon powder and porous carbon support, the dispersion uniformity of nano-silicon powder in the negative electrode material is improved. The improved dispersion uniformity increases the contact area between silicon powder and other electrode materials and electrolytes, allowing more silicon atoms to participate in the electrochemical reaction, thereby significantly improving the battery capacity.

[0032] 2. This invention improves the rate retention of battery materials by adjusting the preparation sequence of the aluminum phosphate coating layer, using ultrasonic-assisted gelation technology to coat aluminum phosphate and control the coating layer thickness, and combining porous carbon-loaded nano-silicon powder and surface treatment of nano-silicon powder.

[0033] 3. This invention utilizes porous carbon-supported nano-silicon powder, combined with microwave-assisted heating and segmented calcination processes. Simultaneously, by leveraging the synergistic effect of the carbon coating layer and lithium carbonate, it reduces structural damage to the battery during cycling, significantly enhancing the cycle performance of the battery material. The three-dimensional porous structure of the porous carbon accommodates the volume expansion of silicon, increasing buffering performance and dispersing effect on silicon. The uniform structure facilitates the transport of electrons and ions, ensuring the stability of the material's performance during multiple cycles.

[0034] 4. This invention introduces porous carbon structure to support nano-silicon powder. During the loading process, lithium carbonate is added to control the dispersion uniformity of the nano-silicon powder. The lithium carbonate is used to generate carbon dioxide at high temperature to create pores, and a lithium-silicon alloy is formed to suppress the volume expansion of silicon. Then, phenolic resin is used as a carbon source to coat the carbon layer on the surface of the structure, which effectively reduces the expansion rate of the negative electrode material. The porous carbon buffers the expansion of silicon, and lithium carbonate and carbon coating layer synergistically suppress silicon expansion from the inside and outside, thereby reducing the expansion of the negative electrode of the battery material and extending the battery life. Attached Figure Description

[0035] Figure 1 This is a flowchart of the preparation method of the high-capacity silicon-carbon anode material obtained in Example 1 of the present invention. Detailed Implementation

[0036] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] Please see Figure 1 This invention provides a method for preparing a high-capacity silicon-carbon anode material. Figure 1 The following is a flowchart of the preparation method of the high-capacity silicon-carbon anode material obtained in Example 1 of the present invention. The technical solution is as follows:

[0038] Example 1

[0039] Iron nanoparticles with a diameter of 8 nm were placed inside the reaction chamber, and the pressure inside the reaction chamber was reduced to 1 × 10⁻⁶ using a vacuum pump. -3The pressure was lowered below 100 Pa, and then high-purity argon gas was introduced into the reaction chamber to restore the pressure to atmospheric pressure. This operation was repeated 3 times. Silane gas was introduced at a flow rate of 200 sccm (standard cubic centimeters per minute), while argon gas was introduced at a flow rate of 600 sccm as a carrier gas to obtain a mixed system. The temperature of the mixed system was rapidly increased to 700℃, and the reaction was allowed to proceed for 20 minutes. The iron particles gradually aggregated and grew on the surface to form the reaction product. After the reaction was completed, the silane gas was stopped, but argon gas was continued to be introduced at a flow rate of 800 sccm. The reaction system was rapidly cooled to room temperature using argon gas. The nano-silicon powder settled to the bottom of the reaction chamber and was collected by an electrostatic collector to obtain pretreated silicon powder. The pretreated silicon powder was then added to... In deionized water, ultrasonic cleaning was performed at a frequency of 50 kHz for 60 min. The mixture was then centrifuged at 10,000 r / min for 15 min to remove the supernatant. This cleaning and centrifugation process was repeated three times to obtain treated silicon powder. Ethanol was added to aminopropyltriethoxysilane, and the mixture was stirred at 300 r / min for 1 h at room temperature using a magnetic stirrer to obtain a silane coupling agent solution. 100 parts of the treated silicon powder were slowly added to the silane coupling agent solution, and the mixture was ultrasonically treated at 60 kHz with a power of 200 W at 60 °C for 2 h. The mixture was then placed in a vacuum drying oven and dried at 80 °C for 10 h to obtain nano-silicon powder with a particle size of 8-10 nm.

[0040] Phenol, a 35% aqueous solution of formaldehyde, and a 10% dilute hydrochloric acid were mixed in a mass ratio of 1:0.8:0.3. The mixture was heated to 100°C and stirred for 3 hours at 800 rpm. After cooling, a first mixture was obtained. Eight parts of melamine were added to 100 parts of the first mixture, and the mixture was heated to 80°C and stirred at 500 rpm for 2 hours to obtain a second mixture. The second mixture was then sieved, washed, and dried to obtain phenolic resin.

[0041] Phenolic resin powder was placed in a quartz crucible, which was then placed in the reaction chamber of a high-temperature furnace. The furnace door was closed, and the vacuum pump was started to reduce the pressure inside the reaction chamber to 1×10⁻⁶. -3 Below Pa, nitrogen gas was slowly introduced, and the vacuuming and inert gas filling operations were repeated. The microwave power was set to 500W, and the temperature in the reaction chamber was raised from room temperature to 300℃ at a heating rate of 10℃ / min. After preheating for 30 minutes, the microwave generator was turned off, and the conventional heating mode of the high-temperature furnace was switched. The temperature was raised to 800℃ at a heating rate of 15℃ / min and held for 3 hours to obtain the reaction system. The heating of the reaction system was stopped, and the cooling rate was controlled by nitrogen at 5℃ / min to cool to room temperature to obtain porous carbon.

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

[0043] Add 10 parts of titanium dioxide to 100 parts of the supported silicon matrix, and place it in a ball mill again. Ball mill at 400 r / min for 5 h to obtain a uniformly mixed dispersed silicon matrix. Dissolve aluminum dihydrogen phosphate in 5 ml of anhydrous ethanol to prepare a 1 mol / L solution. Add deionized water to maintain the molar ratio of water to aluminum dihydrogen phosphate at 8:1. Add concentrated hydrochloric acid to adjust the pH of the solution to 3. Stir at 200 r / min for 8 h under ultrasonic assistance in a constant temperature water bath at 80 °C. The ultrasonic frequency is 30 kHz and the ultrasonic power is 150 W to obtain a sol. Add the dispersed silicon matrix to the sol and continue stirring for 2 h to obtain a mixed solution. Transfer the mixed solution to a sealed container and age at room temperature for 24 h. Place it in a vacuum drying oven and dry at 100 °C for 10 h to obtain a dried product. Place the dried product in a high temperature furnace and calcine at 600 °C for 3 h to obtain a phosphorus-carbon silicon matrix.

[0044] The prepared phenolic resin was dissolved in anhydrous ethanol to prepare a 20% (w / w) solution. Ammonia was added to adjust the pH to 9 to obtain a resin solution. The resin solution was reacted in a constant temperature water bath at 80℃ with a stirring speed of 200 r / min for 6 h to obtain a resin sol. The phosphorus-carbon silicon matrix was dispersed in the resin sol and stirred for 3 h. It was then transferred to a sealed container and aged at room temperature for 15 h. It was then dried in a vacuum drying oven at 80℃ for 8 h to obtain the material to be calcined. The material to be calcined was placed in a high-temperature furnace and sintered at 800℃ with a heating rate of 20℃ / min and a holding time of 3 h to prepare the carbon silicon material.

[0045] Graphite, silicon carbide, carbon black, and polyvinylidene fluoride (PVDF) binder were mixed in a mass ratio of 65:30:1.5:3.5 and dispersed in deionized water to form a uniform slurry. The slurry was cast onto copper foil using a scraper method and baked at 85°C for 3.5 hours. After that, it was cold-pressed, trimmed, and cut into pieces. Then, it was dried under vacuum at 90°C for 18 hours to obtain a high-capacity silicon-carbon anode material. The high-capacity silicon-carbon anode material, separator, and electrolyte (the electrolyte composition is 1 mol / L LiPF6 + EC / DMC (1:4) + 2% FEC) were assembled into a lithium-ion coin cell.

[0046] Examples 2-6 follow the same preparation method and parameter conditions as Example 1, with differences shown in Table 1.

[0047] Table 1. Parameter variations in Examples 1-6

[0048]

[0049]

[0050] Comparative Example 1 is the same as Example 1, except that porous carbon-supported nano-silicon powder is not added.

[0051] Comparative Example 2 is the same as Example 1, except that polyvinylpyrrolidone dispersion is not used in the process of porous carbon-supported nano-silicon powder.

[0052] Comparative Example 3 is the same as Example 1, except that lithium carbonate is not added;

[0053] Comparative Example 4 is the same as Example 1, except that titanium dioxide is not added;

[0054] Comparative Example 5 is the same as Example 1, except that the added iron nanoparticles are 10-15 nm.

[0055] Comparative Example 6 is the same as Example 1, but differs from the use of commercially available nanoparticles with a particle size of 20-50 nm;

[0056] Comparative Example 7 is the same as Example 1, but differs from the post-processing operation that does not involve ultrasonic cleaning and centrifugation.

[0057] Comparative Example 8 is the same as Example 1, except that it does not use aminopropyltriethoxysilane-modified nano-silicon powder;

[0058] Experiment Example 1: Capacitance Test

[0059] The lithium-ion coin cells prepared in Examples 1-6 and Comparative Examples 1-8 were tested for performance using an electrochemical testing system; their capacity was determined by first-efficiency testing and first-charge specific capacity testing.

[0060] First-time efficiency test: Discharge capacity from 0.2C to 2.5V divided by the first charge capacity from 0.1C to 1.5V × 100%;

[0061] First charge specific capacity: In an environment of 25℃, charge to 1.5V at 0.1C and record the charging 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] As shown in Table 2, the catalyst iron nanoparticles used in Comparative Example 5 had a particle size of 10-15 nm, and the prepared silicon nanoparticles had a particle size range of 15-30 nm. Compared with the 8-10 nm silicon nanoparticles prepared in Examples 1-6, the silicon powder particle size was significantly improved. Combined with the results of Comparative Example 6, it can be seen that by using large-particle silicon powder, the capacity of the prepared silicon-carbon anode material was significantly reduced compared with Examples 1-8. This is because small-particle silicon nanoparticles have a larger specific surface area, which can provide more lithium-ion intercalation sites, thereby improving the capacity. Comparative Example 7 avoided introducing problems during the preparation of silicon nanoparticles through post-processing. Introducing dust and impurities ensures the purity of the nano-silicon powder. High-purity nano-silicon powder reduces the obstruction of lithium-ion transport by impurities, improving initial efficiency. If the nano-silicon powder particle size is too large, the lithium-ion insertion path lengthens, leading to a decrease in specific capacity. Increased impurities also consume lithium ions, reducing initial efficiency. In Comparative Examples 1-2, without introducing porous carbon to load the nano-silicon powder or without using a dispersant during preparation, the resulting nano-silicon powder exhibits poor dispersion uniformity in the silicon-carbon anode material. Good dispersion performance ensures uniform distribution of the nano-silicon powder in the electrode material, increasing the contact area between the silicon powder and other electrode materials and the electrolyte. During charge and discharge, more... Silicon atoms can participate in electrochemical reactions, thereby increasing the battery's capacity. Well-dispersed nano-silicon powder has more uniform and stable contact with the electrolyte, reducing unnecessary side reactions between the silicon powder surface and the electrolyte. During charging and discharging, lithium ion insertion and extraction are smoother, and the tighter bonding reduces the shedding of active material, improving the initial efficiency. In contrast, in Comparative Example 7, the capacity of nano-silicon powder without silane coupling agent modification was significantly reduced. However, the increased surface active groups of the surface-modified nano-silicon powder resulted in a tighter bond with porous carbon and lithium carbonate, further improving the initial efficiency. Simultaneously, the surface modification process increased the activity of the nano-silicon powder... Dispersion is achieved to avoid the formation of silicon powder agglomerates. Due to the uneven distribution of active sites on the surface of agglomerates, local side reactions are easily aggravated, consuming more lithium ions and electrolyte, and reducing the first-cycle efficiency. At the same time, the three-dimensional porous structure of porous carbon provides sufficient buffer space for nano-silicon, reducing the damage to the material structure caused by the volume change of silicon during charging and discharging, maintaining the integrity of the material structure, ensuring unobstructed electron and ion transport channels, and improving capacitance and first-cycle efficiency. In the preparation process of porous carbon, microwave-assisted heating makes the porous carbon structure 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 absence of lithium carbonate and titanium dioxide significantly reduced the battery capacity and initial efficiency. Lithium carbonate decomposes during charge / discharge to produce lithium salts, which react with silicon to form a lithium-silicon alloy. This reduces the volume change of silicon, stabilizes the material structure, and improves specific capacity and initial efficiency. Simultaneously, the addition of titanium dioxide improves the electronic conductivity of the material, optimizing the lithium-ion transport path and thus increasing capacity and initial efficiency. In summary, by controlling iron nanoparticles to prepare nano-silicon powder with a particle size of 8-10 nm, and through the synergistic effect of silane-modified nano-silicon powder and porous carbon loading, the dispersion uniformity of nano-silicon powder in the anode material is improved. Combined with lithium carbonate and titanium dioxide additives, this further enhances the battery material's capacity and initial efficiency, and extends battery life.

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

[0067] Examples 8-12 follow the same preparation method and parameter conditions as in Example 7, with differences shown in Table 2.

[0068] Table 3. Parameter changes in Examples 7-12

[0069]

[0070] Comparative Example 9 is the same as Example 7, but without the addition of porous carbon-supported nano-silicon powder.

[0071] Comparative Example 10 is the same as Example 7, but differs from the one without aluminum phosphate coating;

[0072] Comparative Example 11 is the same as Example 7, but differs from Example 7 in that the aluminum phosphate coating process does not involve ultrasonic-assisted gelation;

[0073] Comparative Example 12 is the same as Example 7, except that the aluminum phosphate coating thickness is 100 nm;

[0074] Comparative Example 13 is the same as Example 7, except that the aluminum phosphate coating thickness is 50 nm;

[0075] Comparative Example 14 is the same as Example 7, but differs from the previous method of first carbon coating followed by aluminum phosphate coating via sol-gel method;

[0076] Comparative Example 15 is the same as Example 7, except that it does not use aminopropyltriethoxysilane modified nano-silicon powder;

[0077] Experimental Example 2: Ratio Retention Rate Test

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

[0079] 1C rate retention rate: After being fully charged at 0.2C, discharged at 1C and 0.2C respectively, the 1C discharge capacity is divided by the 0.2C discharge capacity;

[0080] 5C rate retention rate: After being fully charged at 0.2C, the battery was discharged at 5C and 0.2C respectively. The 5C discharge capacity was divided by the 0.2C discharge capacity. The test results are shown in Table 4.

[0081] Table 4. Magnification Retention Rate Tests of Examples 7-12 and Comparative Examples 9-15

[0082]

[0083]

[0084] As shown in Table 4, in Comparative Example 9, the rate retention rate of the battery material prepared without porous carbon-supported nano-silicon powder was significantly lower than that of Examples 7-12. Because porous carbon has a three-dimensional porous structure, it provides ample buffer space for silicon. When silicon undergoes volume expansion, it can be accommodated by the porous structure, reducing the mutual compression between silicon particles and maintaining the integrity of the material structure. Similarly, in Comparative Example 15, the rate retention rate of nano-silicon powder without silane coupling agent modification also showed a significant decrease. Silane modification avoids the possibility of silicon powder agglomeration and ensures uniform distribution within the porous carbon structure, which is beneficial for electron and ion transport and guarantees the stability of the material's performance during multiple cycles. Furthermore, the microwave-assisted heating technique used in the preparation of porous carbon... This technique makes the porous carbon structure more uniform and the pore size distribution more reasonable, further optimizing the electron and ion transport paths and improving rate retention. In addition, the surface-modified nano-silicon powder binds more tightly with porous carbon and lithium carbonate, making lithium ion insertion and extraction smoother and preventing lithium ions from encountering obstacles during transport, which would increase battery internal resistance and capacity loss. In Comparative Examples 10-11, the battery materials prepared without aluminum phosphate coating and without ultrasonic-assisted gelation showed significantly lower rate retention. Because lithium ions need to be rapidly transported within the electrode material during high-rate charging and discharging, aluminum phosphate has good ion conductivity, and the introduction of the coating layer can provide a rapid diffusion channel for lithium ions, reducing battery internal resistance and improving capacity retention. The results of Comparative Examples 12-13 show that the thickness of the coating layer indirectly affects rate performance. A thinner coating layer cannot fully utilize its role in providing a fast ion diffusion channel, limiting lithium-ion transport speed and making it difficult to effectively improve rate retention. Furthermore, a thinner coating layer is insufficient in suppressing silicon volume change and reducing electrode polarization. A thicker, uniform coating layer increases the overall resistance of the material, hindering electron transport. Poor electron conduction affects the battery's charge and discharge performance, while reducing material flexibility and rate retention. A uniform coating layer can better suppress silicon volume change during high-rate charge and discharge. Electrode polarization hinders normal lithium-ion transport, reducing battery performance. Meanwhile, phosphorus... The aluminum phosphate coating reduces this obstacle and improves the rate retention rate. In Comparative Example 14, by changing the coating order, the rate retention rate of the battery material was significantly reduced. Because the carbon layer was coated first, it covered some of the active sites on the surface of the silicon-carbon anode material. When aluminum phosphate was coated subsequently, it was difficult to form a uniform and complete aluminum phosphate coating, which led to a reduction or obstruction of lithium-ion diffusion channels and a decrease in rate performance. In addition, the presence of the carbon layer may affect the buffering and suppression effect of the aluminum phosphate coating on silicon volume changes. The elastic modulus of the carbon layer is different from that of aluminum phosphate. During the expansion and contraction of silicon volume, the synergistic effect between the two materials may be poor, making the electrode structure more susceptible to damage, exacerbating electrode polarization, and reducing rate performance.In summary, by adjusting the preparation sequence of the aluminum phosphate coating layer, utilizing ultrasonic-assisted gelation technology for aluminum phosphate coating, and controlling the coating layer thickness, the quality and uniformity of the coating layer were improved. Furthermore, by using porous carbon-loaded nano-silicon powder and treating the surface of the nano-silicon powder, the rate retention rate of the battery material was improved through a synergistic effect.

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

[0086] Examples 14-18 follow the same preparation method and parameter conditions as in Example 13, with differences shown in Table 5.

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

[0088]

[0089] Comparative Example 16 is the same as Example 13, but without the addition of porous carbon-supported nano-silicon powder.

[0090] Comparative Example 17 is the same as Example 13, but differs from Example 17 in that it does not use microwave-assisted heating technology.

[0091] Comparative Example 18 is the same as Example 13, but differs from the previous example which did not undergo preheating and high-temperature calcination processes and instead underwent direct high-temperature calcination.

[0092] Comparative Example 19 is the same as Example 13, except that the cooling rate is 15°C / min.

[0093] Comparative Example 20 is the same as Example 13, but differs from the one without carbon coating.

[0094] Comparative Example 21 is the same as Example 13, except that lithium carbonate is not added.

[0095] Comparative Example 22 is the same as Example 13, but differs from Example 13 in that it does not use aminopropyltriethoxysilane modified nano-silicon powder.

[0096] Experimental Example 3 Cyclic Performance Determination

[0097] The lithium-ion coin cells prepared in Examples 13-18 and Comparative Examples 16-22 were subjected to discharge at 25°C to 5mV at 0.5C, 0.05C, 0.02C, and 0.01C, followed by charging at 0.1C to 1.5V. The discharge specific capacity of the first cycle was recorded. Then, 500 discharge and charge cycles were performed, with a charging rate of 0.5C and a discharging rate of 1C. The charge specific capacity of the 500th cycle was recorded. The cycle capacity retention rate was calculated as (first cycle discharge specific capacity / 500th cycle discharge specific capacity) × 100%. Three groups of batteries were tested, and the average capacity retention rate of the three groups after 500 cycles was calculated. The test results are shown in Table 6.

[0098] Table 6 Cyclic performance determination 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] As shown in Table 6, the battery material prepared in Comparative Example 16 without porous carbon-supported nano-silicon powder exhibited a significantly lower cycle capacity retention rate compared to Examples 13-18. Because porous carbon possesses a three-dimensional porous structure, this structure provides ample buffer space for silicon. During charge and discharge, silicon undergoes significant volume changes, and the porous structure of porous carbon can accommodate this volume expansion, reducing the mutual compression between silicon particles and maintaining the integrity of the material structure. Combined with Comparative Examples 17-18, microwave-assisted heating technology was used to assist in segmented calcination. In the initial stage of calcination, preheating at a lower temperature ensured uniform heating of the phenolic resin, promoting its initial decomposition and structural rearrangement; then, high-temperature calcination was performed. Calcination, by shortening the calcination time, yields a more uniform porous carbon structure with a more reasonable pore size distribution, further optimizing its buffering performance and silicon dispersion effect. The uniform structure facilitates electron and ion transport, ensuring the material's performance stability during multiple cycles and improving battery cycle performance. A comparison of Comparative Example 19 with Examples 13-18 shows that with increasing cooling rate, the capacity retention rate of the battery material after 500 cycles significantly decreases. This is because rapid cooling causes rapid changes in internal thermal stress in the porous carbon, and the varying cooling rates at different parts of the material can lead to significant stress concentration, resulting in microstructural defects in the porous carbon. Slow cooling can alleviate the internal thermal stress in the porous carbon. Slow release allows atoms sufficient time to rearrange, maintaining a uniform structure and reasonable pore size distribution. Simultaneously, the stable porous carbon structure provides a buffer space for nano-silicon, reducing interparticle compression during volume changes and facilitating electron and ion transport. In multiple charge-discharge cycles, it continuously provides good support and buffering for silicon, maintaining electrode integrity and improving battery cycle stability. Examples 20-21, without the addition of lithium carbonate and carbon coating, show decreased cycle stability in the resulting battery material. Lithium carbonate decomposes during charge-discharge to produce lithium salts, which can react with silicon powder to form a lithium-silicon alloy, reducing the volume change of silicon. Meanwhile, the carbon coating acts as a physical... The barrier restricts the expansion direction of silicon, enhances the structural stability of the material, reduces electrode pulverization, and promotes interfacial fusion between the carbon layer and the coated carbon-silicon matrix through high-temperature calcination, forming a tighter chemical bond between the carbon layer and the matrix, enhancing the overall strength of the material, further suppressing expansion, and reducing structural damage to the battery during cycling under synergistic effect, thus improving the battery's cycle performance. In Comparative Example 22, since the nano-silicon powder was not modified, the bonding force with highly microporous porous carbon, lithium carbonate, etc. was weakened. During multiple cycles, the loose bonding of the material led to lithium-ion transport obstruction and active material shedding, reducing the battery's specific capacity and further reducing the battery's cycle performance.In summary, this invention improves the cycle performance of battery materials by using porous carbon-supported nano-silicon powder, synergistically employing microwave-assisted heating and a stepwise calcination process. Furthermore, the synergistic effect of the carbon coating and lithium carbonate enhances the structural stability of the material, reduces structural damage during battery cycling, and further improves cycle performance.

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

[0102] Examples 20-24 follow the same preparation methods and parameters as Example 19, with differences shown in Table 7.

[0103] Comparative Example 23 is the same as Example 19, but without the addition of porous carbon-supported nano-silicon powder.

[0104] Comparative Example 24 is the same as Example 19, except that lithium carbonate is not added.

[0105] Comparative Example 25 is the same as Example 19, except that no carbon layer coating is applied.

[0106] Comparative Example 26 is the same as Example 19, except that the thickness of the carbon layer coating is 300 nm.

[0107] Comparative Example 27 is the same as Example 19, except that the thickness of the carbon layer coating is 30 nm.

[0108] Comparative Example 28 is the same as Example 19, except that lithium carbonate and titanium dioxide are added simultaneously before the phosphorus coating process.

[0109] Comparative Example 29 is the same as Example 19, but differs from the method of first carbon coating and then sol-gel coating of aluminum phosphate.

[0110] Experiment Example 4: Thickness Expansion Rate Test

[0111] The thickness of the negative electrode sheet in Examples 19-24 and Comparative Examples 23-29 before battery assembly was measured and denoted as D1. The assembled batteries were placed in an environment of 25°C to ensure the negative electrode sheet was fully embedded. The batteries were then disassembled, and the thickness of the fully embedded negative electrode sheet was measured and denoted as D2. The thickness of the foil used was 9 μm. The thickness expansion rate was calculated according to the following formula: Thickness expansion rate = (D2-D1) / (D1-9)×100%. The test results are shown in Table 8.

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

[0113]

[0114]

[0115] As shown in Table 7, the expansion rate of the battery material obtained in Comparative Example 23 without the addition of porous carbon-supported nano-silicon powder is significantly improved compared to Examples 19-2. The three-dimensional porous structure of porous carbon provides a buffer space for silicon. When silicon expands in volume, the porous structure can accommodate part of the expansion volume, reducing the mutual compression between silicon particles and alleviating the damage to the electrode structure caused by silicon expansion, thereby reducing the battery expansion rate. In Comparative Example 24, the expansion rate is significantly improved due to the absence of lithium carbonate. During the calcination process, the high-temperature heating of lithium carbonate can release carbon dioxide to create pores, reserving space for the volume change of the material. At the same time, the high-temperature reduction of lithium carbonate to lithium salt can play a role in supplementing the lithium source and pre-intercalating lithium. During charging and discharging, the silicon reacts further to form a lithium-silicon alloy. The crystal structure and electron cloud distribution of this alloy change, resulting in more stable structural changes during lithium-ion insertion and extraction. This effectively suppresses silicon volume expansion and reduces the battery's expansion rate. Comparative results 25-27 show that the carbon coating acts as a physical barrier, restricting the expansion direction of silicon. When silicon undergoes volume expansion, the carbon coating provides a certain degree of constraint, preventing irregular expansion and reducing electrode structure deformation caused by silicon expansion. Furthermore, the carbon coating enhances the material's structural stability and improves its mechanical properties, making the electrode more robust during charging and discharging, reducing electrode pulverization, and further reducing... The expansion rate of the battery is caused by changes in its internal structure; however, a thin carbon layer cannot effectively constrain the expansion of silicon, and silicon particles easily break through the carbon layer's limitations, expanding irregularly in all directions, leading to increased electrode structure deformation and a relatively higher expansion rate. An excessively thick carbon layer increases the overall rigidity of the material; when silicon expands in volume, the carbon layer itself may crack or detach because it cannot adapt to the silicon expansion, thus losing its ability to constrain silicon expansion. On the other hand, an excessively thick carbon layer may affect the electron and ion transport efficiency, leading to increased internal resistance of the battery, generating more heat, further exacerbating the volume change of silicon, and resulting in an increased negative electrode expansion rate. In Comparative Example 28, the order of lithium carbonate addition was changed; lithium carbonate forms lithium... Silicon alloys alter the expansion characteristics of silicon from within, while titanium dioxide provides external support by 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 work together to resist expansion stress, enabling the anode material to better maintain structural integrity and further reduce the expansion rate. However, the addition of lithium carbonate still significantly improves upon the results in Examples 19-24. The addition of lithium carbonate during the loading process of nano-silicon powder can improve the uniformity of dispersion of nano-silicon powder and lithium carbonate, while also contributing to the bonding ability of nano-silicon powder with porous carbon, thus preventing the expansion rate from increasing due to the shedding of nano-silicon and the reduction in the formation of lithium-silicon alloy during charging and discharging.Compared to Examples 19-24, Comparative Example 29 showed a significantly increased expansion rate. After the carbon layer was applied first, its presence interfered with the aluminum phosphate coating's suppression of silicon volume changes. Because the elastic modulus of the carbon layer differs from that of aluminum phosphate, the two materials exert different constraints on silicon during volume expansion, failing to form an effective synergistic effect. Compared to the order of aluminum coating followed by carbon coating, the volume change of silicon is more difficult to suppress in this case, leading to an increased expansion rate of the battery's negative electrode during charging and discharging. Simultaneously, this situation compromises structural stability. During subsequent charging and discharging, due to structural instability, the electrode is more prone to pulverization, reducing its activity. The deterioration of electrical contact between the material and the current collector leads to an increase in the battery's internal resistance, further exacerbating internal heat generation and volume changes. This results in an increased expansion rate of the negative electrode, affecting the battery's lifespan and overall performance. In summary, by introducing a porous carbon structure to support nano-silicon powder, and adding lithium carbonate during the loading process to control the dispersion uniformity of the nano-silicon powder, while the carbon dioxide generated at high temperatures creates pores, the resulting lithium-silicon alloy further suppresses silicon volume expansion. Combined with phenolic resin as a carbon source material, a carbon layer is coated on the structural surface, effectively constraining silicon expansion and further reducing the expansion rate of the negative electrode material, thereby improving the battery's lifespan and overall performance.

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

Claims

1. A method for preparing a high-capacity silicon-carbon anode material, characterized in that: The preparation of the silicon-carbon anode material includes the following steps: Using S1 iron nanoparticles as a catalyst, silane gas is introduced to react and pretreated silicon powder is obtained; the pretreated silicon powder is ultrasonically cleaned, centrifuged, and modified with a silane coupling agent to obtain nano-silicon powder; wherein the particle size of the nano-silicon powder is 8-10 nm. Phenolic resin is prepared by adding a curing agent to phenol and formaldehyde under the action of dilute hydrochloric acid; porous carbon is obtained by microwave-assisted heating and segmented calcination of the phenolic resin. S3. The nano-silicon powder, porous carbon, and lithium carbonate are ball-milled in a dispersant to obtain a supported silicon matrix; the supported silicon matrix is ​​then milled with titanium dioxide to obtain a dispersed silicon matrix; aluminum dihydrogen phosphate is dissolved in anhydrous ethanol to prepare a 1 mol / L solution, deionized water is added, and concentrated hydrochloric acid is added dropwise to adjust the pH of the solution to 3. The solution is then ultrasonically stirred for 8 hours under a constant temperature water bath at 60-80℃ to obtain a sol; the dispersed silicon matrix is ​​added to the sol to coat 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; the thickness of the aluminum phosphate in the coated phosphorus-carbon silicon matrix is ​​62-80 nm; S4. The phenolic resin is used to obtain a resin sol by sol-gel method; the coated phosphorus-carbon silicon matrix is ​​dispersed in the resin sol, aged, and sintered at high temperature to obtain a carbon silicon material; the carbon coating thickness in the carbon silicon material is 108-124 nm. S5 The silicon carbide material and additives are formulated into a slurry, and the silicon-carbon anode material is obtained by cold pressing, edge trimming and sheet cutting.

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

3. The method for preparing a high-capacity silicon-carbon anode material according to claim 1, characterized in that: The preparation of the nano-silicon powder described in S1 includes the following steps: The iron nanoparticles were placed in a reaction chamber, and the gas was purged three times until atmospheric pressure was reached. Silane gas was introduced at 100-200 sccm, while argon gas was introduced as a carrier gas at a flow rate of 600 sccm to obtain a mixed system. The temperature of the mixed system was rapidly increased to 600-700℃, and the reaction was carried out for 15-25 minutes. Then, the silane gas was stopped, and the reaction system was rapidly cooled to room temperature using the argon gas. The nano-silicon powder settled to the bottom of the reaction chamber and was collected by an electrostatic collector to obtain the pretreated silicon powder. The pretreated silicon powder was added to deionized water, and the treated silicon powder was obtained by ultrasonic cleaning and centrifugation. Ethanol was added to aminopropyltriethoxysilane to obtain a silane coupling agent solution. The treated silicon powder was slowly added to the silane coupling agent solution, ultrasonicated, and vacuum dried to obtain 8-10 nm nano-silicon powder.

4. The method for preparing a high-capacity silicon-carbon anode material according to claim 1, characterized in that: The preparation of the porous carbon described in S2 includes the following steps: The phenol, a 35% (w / w) aqueous solution of formaldehyde, and a 10% (w / w) dilute hydrochloric acid are mixed and heated to 80-100°C for 3 hours. After cooling, a first mixture is obtained. Melamine is added to the first mixture and heated to 70-90°C to obtain a second mixture. The second mixture is then sieved, washed, and dried to obtain phenolic resin. The phenolic resin powder was placed in a quartz crucible and then placed in the reaction chamber of a high-temperature furnace for ventilation. Microwave-assisted heating was then performed with a microwave power of 400-600W, maintaining a preheating temperature of 200-400℃ for 30 minutes. The temperature was then increased to 800-1000℃ and held for 3 hours to obtain the reaction system. Heating of the reaction system was then stopped, and the cooling rate was controlled by nitrogen at 5-8℃ / min until the porous carbon was obtained.

5. The method for preparing a high-capacity silicon-carbon anode material according to claim 1, characterized in that: The preparation of the phosphorus-carbon silicon substrate described in S3 includes the following steps: Polyvinylpyrrolidone was dissolved in ethanol and stirred until homogeneous to obtain a mixed solution. The nano-silicon powder and the lithium carbonate were added to a ball mill, the porous carbon was added, and the mixed solution was slowly added. The mixture was then ball-milled to obtain a supported silicon matrix. Titanium dioxide was added to the supported silicon matrix, and the mixture was placed in a ball mill and milled for 5 hours to obtain a dispersed silicon matrix. Aluminum dihydrogen phosphate was dissolved in anhydrous ethanol to prepare a 1 mol / L solution. Deionized water was added, and concentrated hydrochloric acid was added dropwise to adjust the pH to 3. The solution was then ultrasonically stirred for 8 hours under a constant temperature water bath at 60-80°C to obtain a sol. The dispersed silicon matrix was added to the sol, and the mixture was stirred to obtain a mixed solution. The mixed solution was aged at room temperature and vacuum dried to obtain a dried product. The dried product was calcined 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 ultrasonic assistance frequency is 20-40kHz, and the ultrasonic assistance power is 100-200W.

6. The method for preparing a high-capacity silicon-carbon anode material according to claim 1, characterized in that: The preparation of the silicon carbide material described in S4 includes the following steps: The phenolic resin was dissolved in anhydrous ethanol to prepare a 20% (w / w) solution. Ammonia was added to adjust the pH to 9 to obtain a resin solution. The resin solution was reacted in a water bath at 60-90°C for 6 hours to obtain a resin sol. The coated phosphorus-carbon silicon matrix was dispersed in the resin sol and stirred for 3 hours. The mixture was then transferred to a sealed container and aged at room temperature for 12-18 hours. After vacuum drying, the calcined material was obtained. The calcined material was placed in a high-temperature furnace and sintered at 600-800°C at a heating rate of 15-20°C / min for 3 hours to obtain the silicon-carbon material.

7. The method for preparing a high-capacity silicon-carbon anode material according to claim 1, characterized in that: The preparation of the silicon-carbon anode material described in S5 includes the following steps: The silicon carbide material and the additives are mixed and dispersed in deionized water to form a slurry; the slurry is cast onto copper foil by a scraper method and baked at 85°C for 3 hours, then cold-pressed, trimmed, and cut into sheets, and then dried under vacuum at 90°C for 18 hours to obtain the silicon-carbon anode material. The additives are graphite, carbon black, and polyvinylidene fluoride; the mass ratio of graphite, silicon carbide, carbon black, and polyvinylidene fluoride is 65:30:1.5:3.5.

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