Lithium ion battery silicon-carbon negative electrode material and preparation method thereof
By using flake graphite, nanosilicon particles and modified polyacrylonitrile to coat silicon composite materials in lithium-ion batteries to form a silicon carbon negative electrode material with a three-dimensional conductive network and a hydrogen bond network, the performance degradation caused by volume expansion of silicon-based materials in lithium-ion batteries is solved, and efficient electrochemical performance and long-life battery applications are achieved.
Patent Information
- Application Number
- CN202510372544.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-27
- Publication Date
- 2025-06-13
AI Technical Summary
The theoretical specific capacity of traditional graphite negative electrode materials in lithium-ion batteries is relatively low, and the silicon-based materials have a serious volume expansion effect during the embedded/delivery process, resulting in problems such as electrode structure powderization, continuous reconstruction of SEI film, and separation of active substances and current collectors, which in turn leads to rapid attenuation of capacity and a sharp decline in cycle life.
Silicon carbon anode material with three-dimensional conductive network and hydrogen bond network is prepared by using flake graphite, nanosilicon particles and modified polyacrylonitrile (cPAN) coated silicon composite materials through ball milling and high-temperature calcination.
The first Coulomb efficiency and cycling performance of the negative electrode material of lithium-ion battery is significantly improved, the silicon volume expansion rate is reduced, and the stability of the electrode structure and electron ion transmission rate are enhanced.
Smart Images
Figure CN120149375A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of lithium batteries, and particularly to a silicon-carbon anode material for lithium-ion batteries and a preparation method thereof. Background Art
[0002] With the transformation of the global energy structure and the promotion of the carbon neutrality goal, lithium-ion batteries, as the core energy storage devices for new energy vehicles, smart grids, and portable electronic devices, have an increasingly urgent need to improve their energy density and cycle life. Due to the relatively low theoretical specific capacity (372 mAh / g) of traditional graphite anode materials, they can no longer meet the development requirements of high-energy-density batteries. Developing new high-capacity anode materials has become a key direction to break through the performance bottleneck of lithium-ion batteries.
[0003] Silicon-based materials are considered to be one of the most promising anode candidate materials for next-generation high-energy-density lithium-ion batteries due to their extremely high theoretical specific capacity (the theoretical capacity of Li 15 Si 4 phase reaches 3579 mAh / g at room temperature, about 10 times that of graphite), moderate lithium insertion potential (0.4 V vs. Li + / Li), and abundant natural reserves. However, silicon has a severe volume expansion effect (about 300%) during the lithium insertion / extraction process, leading to problems such as electrode structure pulverization, continuous reconstruction of the solid electrolyte interface (SEI) film, and detachment of active materials from the current collector, which in turn causes rapid capacity decay and a sharp decline in cycle life, severely restricting its commercial application.
[0004] In recent years, the academic and industrial communities have carried out a series of innovative research on the above problems: (1) alleviating volume expansion through nanostructure design (such as nanoparticles, porous structures, core-shell structures); (2) constructing silicon-based composites (such as Si / C, Si / MO X 、Si / metal alloys) to improve conductivity and structural stability; (3) developing new binders and electrolyte additives to optimize interface properties. Among these studies, silicon-based composites have received significant recognition as a suitable method. Generally, coating modification of the silicon surface in silicon-based composites is mainly to reduce the continuous etching of the active material surface by the electrolyte and to play a certain buffering role in the volume expansion effect of silicon. In the research on surface modification of silicon, conductive polymers have received extensive attention due to their elasticity, toughness, conductivity, and multifunctional interfaces, such as polyaniline (PANI), polypyrrole (PPy), and polyacrylonitrile (PAN). At the same time, introducing carbon-based materials into silicon anodes has been proven to effectively improve the electrochemical performance of silicon anodes, such as graphite, carbon nanotubes (CNT), or porous carbon.
[0005] The paper "Preparation and Performance of Polyacrylonitrile Pyrolytic Carbon Coated Silicon Anode Materials for Lithium-Ion Batteries, Chen Chao" discloses that: First, nano-silicon and graphite are compounded, and after ball milling for 60 h, polyacrylonitrile is used to coat it, then ball milling is continued for 10 h, and then high-temperature calcination is carried out. The obtained composite material has good electrochemical performance. This report requires long-time ball milling treatment and heat treatment, and the electrochemical performance of the obtained material, especially the cycle stability, also needs to be improved.
[0006] In summary, although certain progress has been made in existing research, it still faces technical challenges such as complex material preparation processes, low initial efficiency (<85%), and insufficient long-cycle stability (>500 cycles with a capacity retention rate <80%). Summary of the Invention
[0007] One of the objectives of the present invention is to provide a silicon-carbon anode material for lithium-ion batteries to solve the above problems.
[0008] To achieve the above objective, the technical solution adopted by the present invention is as follows: A silicon-carbon anode material for lithium-ion batteries, and the material is composed of raw materials in the following mass percentages:
[0009] Flake graphite: 3 - 20%, silicon nanoparticles: 70 - 90%, polyacrylonitrile: 5 - 15%, totaling 100%.
[0010] As a preferred technical solution, the flake graphite uses natural flake graphite, with a particle size distribution of 30 - 50 μm and a purity >99.5 wt%. Due to its layered structure, ball milling during the preparation of the composite material will open its interlayers, facilitating the deposition of Si@cPAN particles on the flake graphite to form a three-dimensional network structure; the purity of the nano-silicon particles >99.9 wt%, and the particle size distribution is 80 - 100 nm. Compared with micron silicon, it can reduce the volume expansion efficiency, and a stable SEI film can be achieved through methods such as surface coating modification. Combining with flake graphite to form a three-dimensional conductive network can effectively shorten the lithium-ion diffusion distance and improve the rate performance. The average molecular weight of the used polyacrylonitrile is between 100,000 and 150,000. After modification, it can effectively restrain the volume expansion of silicon particles on the surface and reduce the occurrence of side reactions with the electrolyte.
[0011] Another objective of the present invention is to provide a preparation method for the above-mentioned silicon-carbon anode material for lithium-ion batteries. The technical solution adopted is as follows, including the following steps:
[0012] (1) Weigh silicon nanoparticles and polyacrylonitrile and add them to a solution, stir at 60°C - 100°C for 10 - 16 h, and then perform vacuum drying; calcine the dried powder under an inert gas condition at 300 - 500°C for 1 - 3 h to obtain a modified polyacrylonitrile-coated silicon composite material;
[0013] (2) Mix the modified polyacrylonitrile-coated silicon composite material obtained in step (1) with flake graphite in an ethanol solution, perform ultrasonic treatment and then ball milling for 2 h to 10 h, and then centrifuge and dry to obtain the silicon-carbon negative electrode material.
[0014] As a preferred technical solution, in step (1), the solution is N,N-dimethylformamide.
[0015] As a preferred technical solution, in step (1), the inert gas is argon.
[0016] As a preferred technical solution, in step (1), the ratio of the sum of the masses of silicon nanoparticles and polyacrylonitrile to the volume of the added solvent is 1 g:(5 - 15) ml.
[0017] As a preferred technical solution, in step (2), the ratio of the sum of the masses of the modified polyacrylonitrile-coated silicon composite material and flake graphite to the volume of the ethanol solution is 1 g:(20 - 50) ml.
[0018] Coating PAN on the surface of silicon nanoparticles by the liquid-phase coating method, and generating a flexible conductive cyclized polyacrylonitrile (cPAN) layer after low-temperature heat treatment in an inert atmosphere. The cPAN coating effectively buffers the volume change of Si. In addition, the cPAN coating can also establish a hydrogen bond network between the silicon particles and the carboxyl binder CMC, so that good electrical contact is maintained between the active substances. Due to its layered structure, flake graphite can form a three-dimensional through-conductive network between Si@cPAN particles, providing mechanical support for the entire electrode, increasing the electron transport path, and forming a stable SEI film on the entire electrode surface through synergistic action with cPAN, thereby improving the cycling performance and rate performance of the electrode.
[0019] Compared with the prior art, the advantages of the present invention are as follows: The modified polyacrylonitrile-coated silicon negative electrode material prepared with flake graphite as the substrate in the present invention has a significantly improved initial Coulombic efficiency and a significantly improved cycling performance. Moreover, the preparation process is simple, the cost is reduced, and it is easy to industrialize.
[0020] Specifically, compared with the prior art, the preparation method of the present application is more simple, does not require long-time ball milling treatment and heat treatment, and the obtained material has good cycling stability. At 0.5 A g -1 After 150 cycles, there is still a reversible capacity of 1392.2 mAh g -1 At the same time, the present application enhances the stability of the electrode structure under the dual synergistic effect of the three-dimensional conductive structure composed of flake graphite and the hydrogen bond network existing between the cPAN coating, the binder CMC and the silicon particles, effectively restricts the volume expansion of silicon, and the expansion rate is reduced to 68.3%. The electron and ion transport rate of the material is increased, and the initial Coulombic efficiency of the composite material is increased to 90.2%. Description of the Drawings
[0021] Figure 1 This is the SEM image of the graphite flake-supported modified polyacrylonitrile-coated silicon composite material prepared in Example 2 of the present invention;
[0022] Figure 2 This is the SEM image of the modified polyacrylonitrile-coated silicon composite material prepared in Comparative Example 1 of the present invention;
[0023] Figure 3 This is the impedance comparison diagram of the composite materials prepared in Example 2 and Comparative Examples 1 and 2 of the present invention;
[0024] Figure 4 This is the cycling performance diagram of the graphite flake-supported modified polyacrylonitrile-coated silicon composite material prepared in Example 2 of the present invention at a current density of 0.5 A / g. Detailed Description of the Invention
[0025] The present invention will be further described below in conjunction with the embodiments.
[0026] In the following embodiments and comparative examples, the flake graphite used is natural flake graphite with a particle size distribution of 30-50 μm and a purity > 99.5 wt.%, and the nano-silicon particles used have a purity > 99.9 wt.% and a particle size distribution of 80-100 nm.
[0027] Example 1:
[0028] A silicon-carbon anode material for a lithium-ion battery, and its preparation method is as follows:
[0029] (1) Add 0.9 g of nano-silicon particles and 0.1 g of polyacrylonitrile to 7 ml of N,N-dimethylformamide solution, stir at 80 °C for 12 h until the solvent evaporates, and then transfer it to a vacuum oven for drying at 120 °C; calcine the dried powder in a tube furnace filled with argon at 400 °C for 2 h to induce the cyclization of polyacrylonitrile to obtain a modified polyacrylonitrile-coated silicon composite material;
[0030] (2) Mix 0.95 g of the modified polyacrylonitrile-coated silicon composite material prepared in step (1) with 0.05 g of flake graphite in 30 ml of ethanol, ultrasonically mix it for 2 h to make it completely mixed, ball-mill the mixed dispersion at a speed of 500 r / min for 3 h, and then centrifuge and dry it to obtain a graphite flake-supported modified polyacrylonitrile-coated silicon composite material, that is, a silicon-carbon anode material.
[0031] Example 2:
[0032] A silicon-carbon anode material for a lithium-ion battery, and its preparation method is as follows:
[0033] (1) Add 0.9 g of nano-silicon particles and 0.1 g of polyacrylonitrile to 7 ml of N,N-dimethylformamide solution, stir at 80 °C for 12 h until the solvent evaporates, then transfer it to a vacuum oven and dry at 120 °C; Calcinate the dried powder in a tube furnace filled with argon at 400 °C for 2 h to induce the cyclization of polyacrylonitrile, and obtain a modified polyacrylonitrile-coated silicon composite material;
[0034] (2) Mix 0.9 g of the modified polyacrylonitrile-coated silicon composite material prepared in step (1) with 0.1 g of flake graphite in 30 ml of ethanol, ultrasonically mix for 2 h to make it completely mixed, ball-mill the mixed dispersion at a speed of 500 r / min for 3 h, and then centrifuge and dry to obtain a graphite flake-supported modified polyacrylonitrile-coated silicon composite material.
[0035] Example 3:
[0036] A silicon-carbon anode material for lithium-ion batteries, and its preparation method is as follows:
[0037] (1) Add 0.9 g of nano-silicon particles and 0.1 g of polyacrylonitrile to 7 ml of N,N-dimethylformamide solution, stir at 80 °C for 12 h until the solvent evaporates, then transfer it to a vacuum oven and dry at 120 °C; Calcinate the dried powder in a tube furnace filled with argon at 400 °C for 2 h to induce the cyclization of polyacrylonitrile, and obtain a modified polyacrylonitrile-coated silicon composite material;
[0038] (2) Mix 0.85 g of the modified polyacrylonitrile-coated silicon composite material prepared in step (1) with 0.15 g of flake graphite in 30 ml of ethanol, ultrasonically mix for 2 h to make it completely mixed, ball-mill the mixed dispersion at a speed of 500 r / min for 3 h, and then centrifuge and dry to obtain a graphite flake-supported modified polyacrylonitrile-coated silicon composite material.
[0039] Comparative Example 1
[0040] Compared with Example 2, the difference in this comparative example is only that; in step (2), no flake graphite is added, and the rest is the same as in Example 1.
[0041] Comparative Example 2
[0042] Compared with Example 2, the difference in this comparative example is only that; in step (1), no polyacrylonitrile is added, and the rest is the same as in Example 1.
[0043] Performance test example:
[0044] Assemble button cells using the composite materials prepared in Examples 1, 2, 3 and Comparative Examples 1 and 2 as the anode materials for lithium-ion batteries. The specific method is as follows:
[0045] The graphite sheet-supported modified polyacrylonitrile-coated silicon composites and modified polyacrylonitrile-coated silicon composites prepared in Examples 1, 2, 3 and Comparative Examples 1, 2 were used as the anode materials of the battery. They were homogenized with conductive carbon black and binder sodium carboxymethyl cellulose in a ratio of 8:1:1. The slurry was coated on copper foil with a scraper and then dried in a vacuum drying oven for 12 h. The copper foil loaded with the electrode material was cut into button cell electrode sheets (12 mm) using a punching machine; a lithium metal sheet was used as the counter electrode, and a button cell was assembled in a glove box. After the assembled battery was left stationary for 12 h, various electrochemical performances were tested.
[0046] It can be seen from Figure 1 that the shear stress generated during high-energy ball milling is beneficial to the dispersion of graphite nanosheets, enabling silicon nanoparticles to be uniformly embedded between the graphite nanosheets, forming a three-dimensional network structure.
[0047] It can be seen from Figure 2 that the modified polyacrylonitrile-coated silicon nanocomposites agglomerate together, which is not conducive to effectively exerting the polymer confinement effect of modified polyacrylonitrile.
[0048] It can be seen from Figure 3 that the electrochemical impedance value of the graphite sheet-supported modified polyacrylonitrile-coated silicon composite is significantly smaller than that of the modified polyacrylonitrile-coated silicon composite. The synergistic effect of the graphite sheet and modified polyacrylonitrile effectively enhances the charge transfer in the electrode.
[0049] It can be seen from Figure 4 that after cycling 150 times at a current density of 0.5 A / g, the composite anode material still has a reversible specific capacity of 1392.2 mAh / g.
[0050] In addition, the inventor also tested the specific capacity of the material in Example 2 at a current density of 0.2 A / g, which is 2396.2 mAh g-1, and still has a specific capacity of 984.6 mAh g-1 after cycling 150 times at a current density of 1 A / g, indicating that the prepared anode material has excellent cycling performance and has obvious performance improvement compared with the material with the optimal performance disclosed in the paper "Preparation and Performance of Polyacrylonitrile Pyrolytic Carbon-Coated Silicon Anode Materials for Lithium-Ion Batteries, Chen Chao".
[0051] Table 1 Initial Charge Specific Capacity and Initial Coulombic Efficiency
[0053] The results show that the anode material prepared by the present invention has a good initial Coulombic efficiency.
[0054] Table 2 Discharge Specific Capacity after Cycling 150 times at 0.5 A g -1 -1
[0056] The results show that the negative electrode material prepared by the present invention has good cycle performance.
[0057] Conclusion: The silicon-carbon negative electrode material prepared by the present invention has excellent initial Coulomb efficiency and cycle performance.
[0058] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.
Claims
1. A lithium-ion battery silicon-carbon negative electrode material, characterized in that: The material is composed of the following raw materials in percentage by mass: Flake graphite: 3-20%, silicon nanoparticles: 70-90%, polyacrylonitrile: 5-15%, totaling 100%.
2. The lithium-ion battery silicon-carbon negative electrode material according to claim 1, characterized in that: The flake graphite has a particle size distribution of 30 to 50 μm and a purity of >99.5wt%; the silicon nanoparticles have a particle size distribution of 80 to 100 nm and a purity of >99.9wt%; and the average molecular weight of the polyacrylonitrile is between 100,000 and 150,000.
3. The method for preparing the silicon-carbon negative electrode material for lithium-ion batteries according to claim 1 or 2, characterized in that: The steps include: (1) Weighing silicon nanoparticles and polyacrylonitrile and adding them to a solution, stirring at 60°C to 100°C for 10 to 16 hours, and then vacuum drying; calcining the dried powder under an inert gas condition at 300 to 500°C for 1 to 3 hours to obtain a modified polyacrylonitrile-coated silicon composite material; (2) The modified polyacrylonitrile-coated silicon composite material obtained in step (1) is mixed with flake graphite in an ethanol solution, subjected to ball milling for 2 h to 10 h after ultrasonic treatment, and then centrifuged and dried to obtain a silicon-carbon negative electrode material.
4. The preparation method according to claim 3, characterized in that: In step (1), the solution is N,N-dimethylformamide.
5. The preparation method according to claim 3, characterized in that: In step (1), the inert gas is argon.
6. The preparation method according to claim 3, characterized in that: In step (1), the ratio of the sum of the masses of silicon nanoparticles and polyacrylonitrile to the volume of the added solvent is 1 g: (5 to 15) ml.
7. The preparation method according to claim 3, characterized in that: In step (2), the ratio of the sum of the mass of the modified polyacrylonitrile-coated silicon composite material and the flake graphite to the volume of the ethanol solution is 1 g: (20-50) ml.