Preparation method and application of graphite-loaded silicon negative electrode material based on rapid joule heat

Abstract

This invention discloses a method for preparing graphite-supported silicon anode materials based on rapid Joule heating and its application, relating to the field of lithium-ion battery anode material technology. The invention includes immersing three-dimensional porous graphite in a TEOS-ethanol mixed solution, allowing it to soak thoroughly under vacuum conditions, and then naturally drying it; subsequently immersing it in a dilute ammonia solution, reacting it at room temperature, and drying it to obtain a SiO2 / graphite precursor; subjecting the precursor to a rapid Joule heating ultra-high temperature, short-time reduction reaction followed by cooling to room temperature to obtain graphite-supported silicon composite powder; preparing a tannic acid-acrylic acid-vinylpyrrolidone ternary composite binder, mixing the graphite-supported silicon composite powder, the ternary composite binder, and a conductive agent in a specific ratio, and ball milling with water to obtain a uniform slurry; and finally coating, drying, and rolling to obtain a graphite-supported silicon anode. The preparation method of this invention is simple, easy to operate, and easily industrialized, and the resulting graphite-supported silicon anode material exhibits high specific capacity and good cycle performance.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery anode material technology, specifically to a method for preparing and applying a graphite-supported silicon anode material based on rapid Joule heating. Background Technology

[0002] Lithium-ion batteries have been widely used in portable electronic devices, electric vehicles, and large-scale energy storage systems due to their advantages such as high energy density, long cycle life, and environmental friendliness. With the rapid upgrading of the new energy industry, the market's demands for battery energy density and cycle stability are becoming increasingly stringent. As a core component of lithium-ion batteries, the performance of the anode material directly determines the overall performance of the battery.

[0003] Silicon possesses an ultra-high theoretical specific capacity (4200 mAh / g), more than 10 times that of traditional graphite anodes (372 mAh / g), and is considered an ideal anode material for next-generation high-energy-density lithium-ion batteries. However, silicon undergoes a volume expansion of over 300% during lithium insertion / extraction, leading to electrode structure pulverization, active material shedding, and repeated rupture and reconstruction of the SEI film, ultimately causing rapid capacity decay and severely limiting its commercial application.

[0004] To address the volume expansion problem of silicon, researchers typically employ a synergistic strategy of "supporting framework + high-performance binder." Graphite, due to its excellent conductivity, high mechanical strength, and superior volume stability, is often used as a support for silicon. Among them, graphite with a three-dimensional porous structure (such as graphite worms) can provide buffer space for silicon volume changes through its pore structure, while simultaneously constructing a continuous conductive network. However, traditional high-temperature calcination reduction methods (such as hydrogen reduction) for preparing graphite-supported silicon composite materials suffer from problems such as slow heating rates (<10℃ / min) and long reaction times (several hours to tens of hours). For example, in the invention patent application CN117117125A, entitled "Preparation Method of Porous Graphite / Silicon Suboxide Composite Lithium-ion Battery Anode Material," the graphite material needs to be annealed in an H2 atmosphere at 1000–1200℃ for 3–4 hours. However, prolonged high temperatures can easily cause the porous structure of graphite to collapse, weakening its supporting role and failing to effectively alleviate the volume expansion of silicon.

[0005] Furthermore, the binder, acting as the "glue" for the electrode structure, is crucial to the stability of the electrode. Traditional PVDF binders are non-polar polymers with weak interfacial bonding to silicon (a polar surface) and cannot adapt to changes in silicon volume. While water-soluble binders (such as CMC and SBR) have slightly better adhesion, they lack toughness and still cannot meet the requirements for long-term cycling. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing graphite-supported silicon anode materials based on rapid Joule heating and its application, so as to solve the problems of silicon volume expansion and structural stability and improve the cycle performance of silicon anode materials.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing graphite-supported silicon anode material based on rapid Joule heating, comprising the following steps:

[0008] S1: Three-dimensional porous graphite was immersed in a TEOS-ethanol mixed solution, soaked thoroughly under vacuum, and then dried naturally; then immersed in a dilute ammonia solution, and dried after the reaction was completed at room temperature to obtain the SiO2 / graphite precursor.

[0009] S2: The precursor is filled between the electrodes of the rapid Joule heating device, ensuring an argon environment. The peak temperature is set to 2500℃, the heating time to 1-10s, and the heating rate to ≥1000℃ / s. After the reaction, the mixture is cooled to room temperature and graphite-supported silicon composite powder is collected.

[0010] S3: Weigh tannic acid, acrylic acid and vinylpyrrolidone in a mass ratio of 1:(3~4):(1~2), add them to deionized water, stir to dissolve, then add 1% of potassium persulfate of the total mass of the three materials, heat to fully undergo free radical copolymerization, cool and add an appropriate amount of antioxidant, stir evenly to obtain a ternary composite adhesive.

[0011] S4: Mix graphite-supported silicon composite powder, ternary composite binder and conductive agent in proportion, add water and ball mill to obtain a uniform slurry; coat the slurry onto a copper foil current collector, and obtain a graphite-supported silicon anode by drying and rolling.

[0012] Preferably, in step S1 above, the three-dimensional porous graphite is a graphite worm with a specific surface area of ​​50–1000 m². 2 / g; The volume ratio of TEOS to ethanol in the TEOS-ethanol mixed solution is 1:(5~8).

[0013] Preferably, in step S3 above, the amount of antioxidant is 0.5% of the total mass of the three materials, which is used to inhibit the oxidative degradation of tannic acid and improve the storage stability of the binder.

[0014] Preferably, in step S3 above, the free radical copolymerization reaction is carried out at 80°C for 4.5 to 5 hours.

[0015] Preferably, in step S4 above, the mass ratio of graphite-supported silicon composite powder, ternary composite binder, and conductive agent is 8:1:1, and the conductive agent is one or more of conductive carbon black, acetylene black, and Ketjen black.

[0016] Preferably, in step S1 above, the three-dimensional porous graphite is soaked in the mixed solution for 12 hours; the mass concentration of the dilute ammonia solution is 10%, the reaction time at room temperature is 4 hours, the drying temperature is 80°C, and the drying time is 6 hours.

[0017] Preferably, in step S4 above, the drying temperature is 100℃, the vacuum degree is ≤10Pa, the time is 12h, and the roller pressure is 1MPa.

[0018] Another technical solution provided by the present invention: a graphite-supported silicon anode material based on rapid Joule heating prepared by the above preparation method.

[0019] Preferably, the graphite is a graphite worm with a three-dimensional porous structure, and elemental silicon is uniformly distributed inside the pores and on the surface of the graphite.

[0020] Another technical solution provided by the present invention is the application of the above-mentioned graphite-supported silicon anode material in lithium-ion batteries.

[0021] Compared with the prior art, the beneficial effects of the present invention are:

[0022] 1. The preparation method of graphite-supported silicon anode material based on rapid Joule heating uses a rapid Joule heating method to generate ultra-high temperature instantaneously through millisecond-level Joule heating pulses. It can quickly complete the SiO2 reduction reaction before excessive consumption or structural damage of graphite, perfectly preserving the original three-dimensional porous structure of graphite. This structure can provide sufficient buffer space for the volume expansion of silicon and construct a continuous conductive network, effectively solving the dual problems of silicon volume expansion and poor conductivity.

[0023] 2. Tannic acid (TA) molecules contain a large number of hydroxyl and carboxyl groups, which can form strong interactions with hydroxyl groups on the silicon surface; the polymer formed after the polymerization of acrylic acid (AA) has good toughness. The combination of the two can construct a dynamic hydrogen bond network, but there is still room for improvement in terms of interfacial coating integrity and electrochemical stability. Vinylpyrrolidone (NVP) molecules contain active vinyl double bonds and amide groups. Vinyl groups can undergo free radical copolymerization with acrylic acid, and amide groups can form strong hydrogen bonds with hydroxyl groups on the silicon surface and phenolic hydroxyl groups of tannic acid. At the same time, NVP has good hydrophilicity and interfacial activity, which can improve the dispersibility of slurry. This method for preparing graphite-supported silicon anode materials based on rapid Joule heating introduces NVP into the tannic acid-acrylic acid system, forming a dual cross-linked network of "covalent bonds + hydrogen bonds," which combines strong adhesion, high toughness, and interfacial stability. The phenolic hydroxyl groups of tannic acid, the carboxyl groups of acrylic acid, and the amide groups of vinylpyrrolidone work synergistically to form strong interactions with the hydroxyl groups on the silicon surface, the functional groups of graphite, and the copper foil, thereby enhancing the interfacial bonding force. The flexible segments and dynamic hydrogen bond network can adapt to changes in the volume of silicon, preventing electrode pulverization and detachment. The interfacial activity of vinylpyrrolidone can improve the slurry dispersibility and ensure uniform electrode thickness.

[0024] 3. While Joule heating can alleviate volume expansion, it is limited by interfacial stability; ternary binders can improve structural stability, but it is difficult to overcome the cycle capacity bottleneck. This invention combines the two, which greatly improves the electrochemical performance of the material. The resulting graphite-supported silicon anode material has high initial discharge specific capacity, first coulombic efficiency, and capacity retention after 100 cycles. It also has high discharge specific capacity at a high current density of 2A / g and excellent rate performance. At the same time, the ternary binder can participate in the formation of the SEI film, generate a dense protective layer, suppress side reactions, and reduce the impedance growth rate.

[0025] 4. The preparation method and application of graphite-supported silicon anode material based on rapid Joule heating significantly shortens the production cycle due to the rapid Joule heating reaction time of only 1 to 10 seconds; the binder is prepared as a water-soluble system, which is environmentally friendly and pollution-free, and the storage stability is improved to more than 6 months after the addition of antioxidants; the electrode is prepared using a traditional coating process, which does not require additional equipment modification and is suitable for large-scale production. Attached Figure Description

[0026] Figure 1 This is a SEM image of the graphite-supported silicon composite powder obtained after rapid Joule heating and cooling in Example 1 of the present invention.

[0027] Figure 2 This is a SEM image of the graphite-loaded silicon anode obtained after rolling in Example 1 of the present invention.

[0028] Figure 3 The specific capacity performance test graphs are shown for embodiments and comparative examples of the present invention.

[0029] Figure 4 The graphs show the cycle retention performance test results of the embodiments and comparative examples of the present invention. Detailed Implementation

[0030] This invention achieves rapid reduction of SiO2 and complete preservation of the porous graphite structure through rapid Joule heating. Combined with the "covalent + hydrogen bond" dual crosslinking network effect of the tannic acid-acrylic acid-vinylpyrrolidone ternary composite binder, it synergistically enhances the structural stability, interfacial adhesion, and electrochemical performance of the electrode, ultimately obtaining a graphite-supported silicon anode material with high specific capacity, long cycle life, and easy industrialization. The preparation method includes the following:

[0031] Three-dimensional porous graphite is immersed in a TEOS-ethanol mixed solution (for reference, the volume ratio of TEOS to ethanol can be 1:5 to 1:8. Under this ratio, TEOS can be uniformly dispersed and fully penetrate into the graphite pores, avoiding SiO2 agglomeration and ensuring uniform distribution of elemental silicon after subsequent reduction). The immersion is carried out under vacuum conditions (e.g., vacuum evacuation for 30 minutes and immersion for 12 hours), and then naturally dried. Then, it is immersed in a dilute ammonia solution (mass concentration can be 10%) to catalyze the hydrolysis of TEOS to generate SiO2, forming a uniform SiO2 coating on the graphite surface and in the pores. After the reaction is completed at room temperature, it is dried to obtain the SiO2 / graphite precursor. For reference, the room temperature reaction time can be 4 hours, the drying temperature can be 80℃, and the drying time can be 6 hours.

[0032] In a preferred embodiment, the aforementioned three-dimensional porous graphite employs graphite worms, and the specific surface area is further preferably 50–1000 m². 2 / g;

[0033] The precursor was filled between the electrodes of the rapid Joule heating device, ensuring an argon environment (specifically, after sealing the cavity, a vacuum was drawn and filled with high-purity argon gas with a purity ≥99.999%, and this vacuum argon gas replacement was repeated 3 times). The peak temperature was set to 2500℃, the heating time to 1-10s, and the heating rate to ≥1000℃ / s (to ensure that SiO2 is completely reduced to elemental silicon and that the graphite structure is not destroyed). After the reaction, the mixture was cooled to room temperature, and the graphite-supported silicon composite powder was collected.

[0034] Weigh tannic acid, acrylic acid, and vinylpyrrolidone (NVP) at a mass ratio of 1:(3~4):(1~2) (this ratio balances bonding strength, toughness, and electrochemical stability; in particular, when the NVP ratio is <1, the interfacial coating and dispersion effect is insufficient, and when the ratio is >2, the crosslinking density of the copolymer system is too high, the toughness of the adhesive decreases, and the electrode is prone to brittleness). Add them to deionized water, stir to dissolve, and then add 1% of potassium persulfate (initiator) of the total mass of the three materials. Heat to fully undergo free radical copolymerization reaction. For reference, the reaction can be carried out at 80℃ for 4.5~5h. After cooling, add an appropriate amount of antioxidant (which can be controlled at 0.5% of the total mass of the three materials; vitamin C can be used) to inhibit the oxidative degradation of tannic acid and improve the storage stability of the adhesive. Stir evenly to obtain a ternary composite adhesive.

[0035] Graphite-supported silicon composite powder, ternary composite binder, and conductive agent are mixed in proportion and ball-milled with water to obtain a uniform slurry. The slurry is coated onto a copper foil current collector, and after drying and rolling, a graphite-supported silicon anode is obtained. For reference, the drying temperature can be 100℃, the vacuum degree should be controlled to not exceed 10Pa, the drying time can be 12h, and the rolling pressure can be 1MPa.

[0036] In a preferred embodiment, the mass ratio of graphite-supported silicon composite powder, ternary composite binder, and conductive agent is 8:1:1, and the conductive agent can be further selected from one or more of conductive carbon black, acetylene black, and Ketjen black.

[0037] The present invention will be further illustrated below through several embodiments and comparative examples. However, the following embodiments are not all embodiments of the present invention and should not be regarded as an absolute limitation on the scope of protection of the present invention.

[0038] Example 1

[0039] (1) Preparation of SiO2 / graphite precursor: Take 1g of graphite worms (specific surface area 400 m²) 2 The graphite worms were immersed in a 50 mL mixture of TEOS and ethanol at a volume ratio of 1:5, placed in a vacuum desiccator for 30 min, soaked for 12 h, and then naturally dried. The impregnated graphite worms were then immersed in a 10% dilute ammonia solution, reacted at room temperature for 4 h, and dried at 80 °C for 6 h to obtain the SiO2 / graphite precursor.

[0040] (2) Preparation of graphite-supported silicon composite powder: The precursor was filled between the electrodes of the rapid Joule heating device, the cavity was sealed, vacuumed and filled with high-purity argon (≥99.999%), and the vacuum argon was replaced 3 times. The peak temperature was set to 2500℃, the heating time to 5s, and the heating rate to 1200℃ / s. After the reaction was started, it was naturally cooled to room temperature, and the graphite-supported silicon composite powder was collected.

[0041] (3) Preparation of ternary composite adhesive: Take 2g tannic acid (TA), 7g acrylic acid (AA) and 3g vinylpyrrolidone (NVP), add them to 30mL of deionized water and stir until completely dissolved; add 0.12g potassium persulfate (1% of the total mass of monomers), stir evenly and place in an 80℃ constant temperature water bath for 5h; after cooling to room temperature, add 0.06g vitamin C (antioxidant), stir evenly, and obtain a light brown viscous ternary composite adhesive (solid content about 35%).

[0042] (4) Preparation of graphite-supported silicon anode: Graphite-supported silicon composite powder, Ketjen black and ternary composite binder were weighed in a mass ratio of 80:10:10, and an appropriate amount of deionized water was added. The mixture was ball-milled for 4 hours to obtain a uniform slurry. The slurry was coated onto a copper foil current collector and dried at 100°C and a vacuum degree ≤10Pa for 12 hours. After being rolled by a 1MPa double roller mill, the graphite-supported silicon anode was obtained.

[0043] Example 2

[0044] In the ternary composite adhesive, tannic acid: acrylic acid: vinylpyrrolidone = 1:4:1 (2g TA, 8g AA, 2g NVP), and the remaining steps are the same as in Example 1.

[0045] Example 3

[0046] In the ternary composite adhesive, tannic acid: acrylic acid: vinylpyrrolidone = 1:3:2 (2g TA, 6g AA, 4g NVP), and the remaining steps are the same as in Example 1.

[0047] Example 4

[0048] In the ternary composite adhesive, tannic acid: acrylic acid: vinylpyrrolidone = 1:2:2 (2g TA, 4g AA, 4g NVP), and the remaining steps are the same as in Example 1.

[0049] Comparative Example 1

[0050] 2g of 100nm nano-silicon and 6g of 8μm diameter flake natural graphite were ball-milled for 4 hours to obtain a nano-silicon / graphite composite material. Then, the nano-silicon / graphite composite material, Ketjen black, and styrene-butadiene rubber emulsion binder were weighed at a mass ratio of 80:10:10, and an appropriate amount of deionized water was added. The mixture was ball-milled for 4 hours to obtain a uniform slurry. The slurry was coated onto a copper foil current collector and dried at 100℃ under a vacuum of ≤10Pa for 12 hours. After rolling with a 1MPa two-roll mill, a graphite-supported silicon anode was obtained.

[0051] Comparative Example 2

[0052] Based on Example 1, in step (2) of the preparation of graphite-supported silicon composite powder, the precursor is placed in a tube furnace, and high-purity argon gas (≥99.999%) is continuously introduced to replace the internal air. The heating rate is 5℃ / min, the temperature is set to 2500℃ and heated for 1 hour. After natural cooling, the graphite-supported silicon composite powder is collected. The remaining steps are the same as in Example 1.

[0053] Comparative Example 3

[0054] Based on Example 1, step (3) is omitted. In the preparation of the graphite-supported silicon anode in step (4), styrene-butadiene rubber emulsion binder is used instead of ternary composite binder. The remaining steps are the same as in Example 1.

[0055] Performance testing

[0056] The negative electrode sheets prepared in the above examples and comparative examples were assembled into CR2032 coin cells (with lithium metal as the counter electrode and 1 mol / L LiPF6-EC / DMC / EMC (volume ratio 1:1:1) as the electrolyte). Constant current charge-discharge tests (voltage range 0.01–3.0 V) were performed using the Blue Battery Test System. The electrode microstructure was observed using a scanning electron microscope (SEM).

[0057] Table 1. Test results of the examples and comparative examples

[0058] Initial discharge specific capacity (mAh / g) First Coulomb efficiency (%) Discharge specific capacity (mAh / g) after 100 cycles Capacity retention rate (%) after 100 cycles Example 1 2442 93.9 1998 81.8 Example 2 2427 91.5 1935 79.7 Example 3 2409 86.8 1778 73.8 Example 4 2469 92.3 1989 80.6 Comparative Example 1 1710 77.6 732 42.8 Comparative Example 2 2121 82.7 837 39.5 Comparative Example 3 2422 86.9 1104 45.6

[0059] As shown in Table 1 above, the graphite-supported silicon anode prepared by the method of this invention exhibits excellent electrochemical performance. Compared with Example 1 and Comparative Example 2, the rapid Joule heating and short-time reaction characteristics allow for SiO2 reduction before the graphite structure collapses, fully preserving the three-dimensional porous structure of graphite. This structure provides sufficient buffer space for silicon volume expansion and constructs a continuous conductive network, effectively solving the dual problems of silicon volume expansion and poor conductivity. Compared with Example 1 and Comparative Example 3, the "covalent bond + hydrogen bond" dual crosslinking network formed by tannic acid, acrylic acid, and vinylpyrrolidone in the ternary composite binder possesses strong adhesion, high toughness, and interfacial stability. The phenolic hydroxyl groups of tannic acid, the carboxyl groups of acrylic acid, and the amide groups of vinylpyrrolidone work synergistically with the hydroxyl groups on the silicon surface, the functional groups of graphite, and the copper foil. The strong interactions enhance interfacial bonding. The flexible segments and dynamic hydrogen bond network can adapt to the volume changes of silicon, preventing electrode pulverization and detachment. The interfacial activity of vinylpyrrolidone can improve slurry dispersibility and ensure uniform electrode thickness. Surprisingly, Examples 1 to 4 also showed significantly higher cycle discharge specific capacity and capacity retention than the comparative examples. This may be because although the rapid Joule heating treatment can alleviate volume expansion, it is limited by interfacial stability. While the ternary binder can improve structural stability, it is difficult to overcome the cycle capacity bottleneck. When the two are used together, the rapid self-heating effect of Joule heating promotes the cross-linking reaction of each component in the ternary binder, forming a denser elastic network. This not only inhibits volume expansion but also enhances interfacial ion transport, achieving dual optimization of structure and kinetics, and unexpectedly greatly improving cycle performance.

[0060] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

[0061] Any aspects of this invention not described in detail are well-known to those skilled in the art.

Claims

1. A method for preparing graphite-supported silicon anode material based on rapid Joule heating, characterized in that, Includes the following steps: S1: Three-dimensional porous graphite was immersed in a TEOS-ethanol mixed solution, soaked thoroughly under vacuum, and then dried naturally; then immersed in a dilute ammonia solution, and dried after the reaction was completed at room temperature to obtain the SiO2 / graphite precursor. S2: The precursor is filled between the electrodes of the rapid Joule heating device, ensuring an argon environment. The peak temperature is set to 2500℃, the heating time to 1-10s, and the heating rate to ≥1000℃ / s. After the reaction, the mixture is cooled to room temperature and graphite-supported silicon composite powder is collected. S3: Weigh tannic acid, acrylic acid and vinylpyrrolidone in a mass ratio of 1:(3~4):(1~2), add them to deionized water, stir to dissolve, then add 1% of potassium persulfate of the total mass of the three materials, heat to fully undergo free radical copolymerization, cool and add an appropriate amount of antioxidant, stir evenly to obtain a ternary composite adhesive. S4: Mix graphite-supported silicon composite powder, ternary composite binder and conductive agent in proportion, add water and ball mill to obtain a uniform slurry; coat the slurry onto a copper foil current collector, and obtain a graphite-supported silicon anode by drying and rolling.

2. The method for preparing a graphite-supported silicon anode material based on rapid Joule heating according to claim 1, characterized in that: In step S1, the three-dimensional porous graphite is a graphite worm with a specific surface area of ​​50–1000 m². 2 / g; The volume ratio of TEOS to ethanol in the TEOS-ethanol mixed solution is 1:(5~8).

3. The method for preparing a graphite-supported silicon anode material based on rapid Joule heating according to claim 1, characterized in that: In step S3, the amount of antioxidant used is 0.5% of the total mass of the three materials, which is used to inhibit the oxidative degradation of tannic acid and improve the storage stability of the binder.

4. The method for preparing a graphite-supported silicon anode material based on rapid Joule heating according to claim 1, characterized in that: In step S3, the free radical copolymerization reaction is carried out at 80°C for 4.5–5 hours.

5. The method for preparing a graphite-supported silicon anode material based on rapid Joule heating according to claim 1, characterized in that: In step S4, the mass ratio of graphite-supported silicon composite powder, ternary composite binder, and conductive agent is 8:1:1, and the conductive agent is one or more of conductive carbon black, acetylene black, and Ketjen black.

6. The method for preparing a graphite-supported silicon anode material based on rapid Joule heating according to claim 1, characterized in that: In step S1, the three-dimensional porous graphite is soaked in the mixed solution for 12 hours; the mass concentration of the dilute ammonia solution is 10%, the reaction time at room temperature is 4 hours, the drying temperature is 80°C, and the drying time is 6 hours.

7. The method for preparing a graphite-supported silicon anode material based on rapid Joule heating according to claim 1, characterized in that: In step S4, the drying temperature is 100℃, the vacuum degree is ≤10Pa, the time is 12h, and the roller pressure is 1MPa.

8. A graphite-supported silicon anode material based on rapid Joule heating, prepared by the preparation method according to any one of claims 1 to 7.

9. The graphite-supported silicon anode material according to claim 8, characterized in that: The graphite is a graphite worm with a three-dimensional porous structure, and elemental silicon is uniformly distributed inside and on the surface of the graphite pores.

10. The application of the graphite-supported silicon anode material as described in claim 8 or 9 in lithium-ion batteries.

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