Silicon-carbon negative electrode material for lithium battery and preparation method of silicon-carbon negative electrode material
A silicon-carbon anode material is prepared using a high molecular polymer coating and phase separation technique to stabilize silicon particles, addressing the challenges of complex preparation and poor performance in silicon-based anodes, achieving improved energy density and cycle stability.
Patent Information
- Application Number
- CN202510636098.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-05-16
- Publication Date
- 2025-07-15
AI Technical Summary
The preparation process of existing lithium-ion batteries silicon carbon anode materials is complex, has high cost and poor circulation performance, making it difficult to meet the needs of high energy density and long cycle life.
A polymer is used as a carbon source, and a uniform polymer coating layer is formed on the surface of the silicon powder with phase separation technology. After calcination treatment, it is converted into a conductive carbon layer to form a silicon carbon negative electrode material with a core-shell structure.
It has achieved simplified preparation process, reduced costs, improved the cycle stability and energy density of the material, and has excellent charging and discharging performance and long cycle life, and is environmentally friendly.
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Figure CN120319786A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a silicon-carbon negative electrode material for lithium batteries and a preparation method thereof. Background Art
[0002] At present, the negative electrode materials of lithium-ion batteries mainly use carbon materials, such as natural graphite, heat-treated graphite, etc. The theoretical capacity of graphite negative electrode is only about 372 mAh / g, and the energy density is limited, which makes it difficult to meet the needs of high energy density batteries. Silicon is regarded as an important candidate to replace graphite to increase battery capacity because of its extremely high theoretical specific capacity (about 4200 mAh / g). However, the silicon negative electrode will undergo a huge volume expansion of nearly 300% during the charging and discharging process, resulting in particle pulverization, active material shedding, and continuous reconstruction of the solid electrolyte interface (SEI), resulting in low initial coulombic efficiency and insufficient cycle life.
[0003] In response to the silicon expansion problem, researchers proposed a method of combining silicon with carbon materials. Carbon materials can act as a "buffer support" to inhibit the volume change of silicon particles due to their excellent conductivity and stable framework structure, thereby significantly improving the cycle stability. Silicon-carbon composite materials effectively alleviate the volume expansion of silicon through carbon coating or carbon skeleton structure, and improve the conductivity and cycle performance of the composite negative electrode. Although a variety of silicon-carbon composite negative electrode materials have been reported, the existing technology generally has problems such as complex preparation process, high cost, and the cycle performance still needs to be improved. For example, traditional nano-silicon preparation processes mostly use methods such as vapor deposition and sputtering, which have many steps and high equipment requirements, greatly increasing production costs; existing silicon-carbon composite materials often have defects such as low initial efficiency, poor conductivity, and fast cycle capacity decay, which are difficult to meet the needs of large-scale commercial applications. Summary of the invention
[0004] The purpose of the present invention is to provide a method for preparing a silicon-carbon negative electrode material for lithium batteries, which is used to solve the problems of complex preparation process and high cost of silicon-carbon negative electrode materials in the prior art and poor cycle performance of the obtained silicon-carbon negative electrode materials.
[0005] The present invention also provides a silicon-carbon negative electrode material for lithium batteries to solve the problem of poor electrochemical performance of silicon-carbon negative electrode materials in the prior art.
[0006] In order to solve the above problems, the present invention proposes a method for preparing a silicon-carbon negative electrode material for lithium battery, and the technical solution adopted is: A preparation method of a silicon-carbon anode material for lithium batteries, comprising the following steps: mixing a polymer solution and silicon powder to obtain a mixture, and preparing microspheres with a polymer layer coating silicon through a phase separation method; roasting the microspheres with a polymer layer coating silicon to obtain microspheres with a conductive carbon layer coating silicon, thereby obtaining the silicon-carbon anode material for lithium batteries.
[0007] The beneficial effects of the present invention are as follows: The preparation method of the silicon-carbon anode material for lithium batteries of the present invention uses a polymer as a carbon source, combines the phase separation technology to form a uniform polymer coating layer on the surface of the silicon powder, obtains microspheres with a polymer layer coating silicon, and roasts the microspheres with a polymer layer coating silicon to obtain microspheres with a conductive carbon layer coating silicon, thereby obtaining the silicon-carbon anode material for lithium batteries. This silicon-carbon anode material for lithium batteries has excellent charge-discharge performance, rate performance, and cycle stability, and thus has a good cycle life. A novel preparation method of a silicon-carbon anode material proposed by the present invention aims to significantly improve the silicon-carbon anode material in terms of energy density, cycle life, and safety by optimizing the material structure and improving the preparation process, providing a new solution for the development of lithium-ion battery technology. Specifically: (1) Simple preparation process: The process flow only includes the precipitation and roasting of polymers in the phase separation technology, without expensive equipment or complex steps, short production cycle, and process controllability; (2) Low cost: The polymer used as a carbon source is easily available and low in price, the preparation conditions are mild, and the comprehensive production cost is significantly reduced; (3) Uniform structure: In the microspheres with a conductive carbon layer coating silicon, the silicon particles are uniformly coated with a conductive carbon layer, forming a core-shell structure. This uniform structure effectively buffers the volume expansion of silicon, inhibits particle pulverization and the repeated formation of the SEI layer, and improves the cycle life; (4) Long cycle life: Due to the supporting effect of the conductive carbon layer on silicon, the capacity attenuation of the silicon-carbon anode material for lithium batteries of the present invention is significantly slowed down during multiple charge-discharge cycles, and the cycle life is excellent; (5) High energy density: Due to the high theoretical capacity of silicon, the silicon-carbon anode material for lithium batteries of the present invention has an energy density much higher than that of a pure graphite anode; at the same time, the uniform conductive carbon layer coating improves the initial Coulomb efficiency, making the available capacity of the material more sufficient; (6) Environmentally friendly: Using a polymer as a carbon source avoids the use of toxic solvents and complex chemical agents, and the process is green and environmentally friendly.
[0008] In order to enable the polymer to fully wrap the silicon powder to obtain microspheres with a polymer layer coating silicon, preferably, the mass ratio of the silicon powder to the polymer in the polymer solution is 5:(1.5 - 4), and the particle size of the silicon powder is 50 - 5000 nm.
[0009] In order to use environmentally friendly polymers as carbon sources, further reduce production costs, and promote environmental protection, preferably, the polymer in the polymer solution is selected from one of polylactic acid, polycaprolactone, poly(lactide-co-caprolactone), polycarbonate, polyethylene terephthalate, polyglycolide, poly(lactide-co-glycolide), and the molecular weight of the polymer is 30,000 - 80,000.
[0010] In order to fully dissolve the polymer in the polymer solution, preferably, the preparation method of the polymer solution includes: mixing the polymer and an organic solvent to obtain a polymer solution; wherein, the organic solvent is selected from one of dichloromethane, chloroform, hexafluoroisopropanol, dimethyl sulfoxide, N,N-dimethylformamide.
[0011] In order to further improve the dissolution degree of the polymer, preferably, the ratio of the mass of the polymer to the volume of the organic solvent is (1.5 - 4 g) : (80 - 150 mL).
[0012] In order to form a uniform polymer coating layer on the surface of silicon powder by combining the phase separation technology, preferably, the preparation of the microspheres with a polymer layer coating silicon from the mixed solution by the phase separation method specifically includes: adding a non-solvent to the mixed solution to initiate phase separation to obtain a suspension of microspheres with a polymer layer coating silicon, and then filtering and drying to obtain the microspheres with a polymer layer coating silicon.
[0013] In order to fully carry out phase separation, preferably, the non-solvent is selected from one of water, methanol, ethanol, isopropanol, and the volume ratio of the non-solvent to the organic solvent is (10 - 20) : (8 - 15).
[0014] In order to fully remove the non-solvent and the organic solvent, preferably, the drying temperature is room temperature - 60 °C and the time is 12 - 13 h.
[0015] In order to fully convert the polymer coating layer into a conductive carbon layer, preferably, the heating rate of the calcination treatment is 5 - 10 °C / min, the temperature is 500 - 1200 °C, and the time is 1 - 10 h.
[0016] The present invention also provides a silicon-carbon anode material for lithium batteries, and the technical solution adopted is: A silicon-carbon anode material for lithium batteries is prepared by the preparation method of the silicon-carbon anode material for lithium batteries as described above.
[0017] The beneficial effects of the present invention are: The silicon-carbon anode material for lithium batteries of the present invention has high energy density, excellent rate performance, cycle stability and safety. Description of the Drawings
[0018] Figure 1 SEM image of the silicon-carbon anode material for lithium batteries prepared by the preparation method of the silicon-carbon anode material for lithium batteries in Embodiment 1 of the present invention.
[0019] Figure 2 SEM image of the silicon-carbon anode material for lithium batteries prepared by the preparation method of the silicon-carbon anode material for lithium batteries in Embodiment 3 of the present invention. Detailed Description of the Invention
[0020] In the prior art, the preparation process of silicon-carbon anode materials is complex, the cost is high, and the cycling performance of the obtained silicon-carbon anode materials is poor. The present invention proposes a preparation method of a silicon-carbon anode material for lithium batteries, which includes the following steps: mixing a polymer solution and silicon powder to obtain a mixed solution, and preparing microspheres with a polymer layer coated on silicon by a phase separation method; roasting the microspheres with a polymer layer coated on silicon to obtain microspheres with a conductive carbon layer coated on silicon, thereby obtaining a silicon-carbon anode material for lithium batteries.
[0021] The technical concept of the present invention is as follows: in the preparation method of the silicon-carbon anode material for lithium batteries of the present invention, a polymer is used as a carbon source, and combined with the phase separation technology, the polymer precipitates and forms a uniform polymer coating layer on the surface of the silicon powder to obtain microspheres with a polymer layer coated on silicon; roasting the microspheres with a polymer layer coated on silicon enables the polymer layer to be converted into a conductive carbon layer by roasting, obtaining microspheres with a conductive carbon layer coated on silicon, which can effectively buffer the volume expansion of silicon, inhibit particle pulverization and the repeated formation of the SEI layer, and improve the cycling life; at the same time, the conductive carbon layer improves the initial Coulomb efficiency, making the available capacity of the material more sufficient, and finally obtaining a silicon-carbon composite anode material with a carbon-coated silicon microsphere structure. The silicon-carbon anode material and its preparation method of the present invention significantly improve the silicon-carbon anode material in terms of energy density, cycling life and safety by optimizing the material structure and improving the preparation process, providing a new solution for the development of lithium-ion battery technology.
[0022] Specifically, the preparation method of the silicon-carbon anode material for lithium batteries includes the following steps: First, preparation of the polymer solution: Mix the polymer and the organic solvent, and fully dissolve it under mechanical stirring to obtain a uniform polymer solution; wherein, the ratio of the mass of the polymer to the volume of the organic solvent is (1.5 - 4 g):(80 - 150 mL); the polymer in the polymer solution is selected from one of polylactic acid, polycaprolactone, poly(lactide - co - caprolactone), polycarbonate, polyethylene terephthalate, polyglycolide, poly(lactide - co - glycolide), the molecular weight of the polymer is 30000 - 80000; the organic solvent is selected from one of dichloromethane, chloroform, hexafluoroisopropanol, dimethyl sulfoxide, N,N - dimethylformamide; Second, preparation of the polymer - coated silicon microspheres: Gradually add silicon powder to the polymer solution and carry out magnetic stirring to make the silicon powder evenly dispersed; slowly add the non - solvent to the stirring system to initiate phase separation; at this time, the polymer precipitates from the organic solvent and coats on the surface of the silicon powder, generating an aqueous - phase suspension of polymer - coated silicon microspheres; filter and collect the suspension of polymer - coated silicon microspheres, naturally dry at room temperature and dry under vacuum at room temperature - 60 °C for 12 - 13 h to obtain dry polymer - coated silicon microspheres; wherein, the mass ratio of the silicon powder to the polymer in the polymer solution is 5:(1.5 - 4), the particle size of the silicon powder is 50 - 5000 nm; the non - solvent is selected from one of water, methanol, ethanol, isopropanol, and the volume ratio of the non - solvent to the organic solvent is (10 - 20):(8 - 15); Finally, calcination treatment: Place the dry polymer - coated silicon microspheres in a tube furnace, heat them up to 500 - 1200 °C at a heating rate of 5 - 10 °C / min under nitrogen protection, and hold for 1 - 10 h to obtain silicon - carbon composite anode materials for lithium batteries with a conductive carbon layer - coated silicon microspheres, and cool to room temperature. The following will describe the implementation process of the present invention in detail with specific examples. However, those skilled in the art will understand that the following examples are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. Additionally, it should be noted that for the sake of description, only the parts related to the invention are shown in the examples. It should be noted that, without conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The following will describe the present application in detail with reference to the embodiments. It should be noted that the endpoints and any values within the ranges disclosed in this text are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed in this text.
[0023] In the following examples and comparative examples, the particle size of the silicon powder is 50 - 5000 nm, and the remaining raw materials used are all ordinary commercially available products that can be directly purchased or can be prepared according to the conventional techniques in the art.
[0024] I. Examples of the preparation method of the silicon-carbon anode material for lithium batteries of the present invention Example 1 The preparation method of the silicon-carbon anode material for lithium batteries provided in this example includes the following steps: First, the preparation of the polymer solution: Mix 2.0 g of polylactic acid (PLA, molecular weight 80000) and 100 mL of dichloromethane (DCM), and fully dissolve it under mechanical stirring to obtain a uniform PLA solution; Second, the preparation of microspheres with a polymer layer coating silicon: Gradually add 5.0 g of silicon powder to the PLA solution and perform magnetic stirring to disperse the silicon powder evenly; Slowly add 200 mL of distilled water dropwise to the stirring system to initiate phase separation; At this time, PLA precipitates from DCM and coats the surface of the silicon powder, generating an aqueous-phase suspension of microspheres with a PLA layer coating silicon; Filter and collect the suspension of microspheres with a PLA layer coating silicon, and dry it naturally at room temperature and then dry it under vacuum at 60 °C for 12 h to obtain dry microspheres with a PLA layer coating silicon; Finally, calcination treatment: Place the dry microspheres with a PLA layer coating silicon in a tubular furnace, heat it to 700 °C at a heating rate of 10 °C / min under nitrogen protection, and hold for 2 h to obtain microspheres with a conductive carbon layer coating silicon, and cool to room temperature to obtain the silicon-carbon anode material for lithium batteries.
[0025] Example 2 The preparation method of the silicon-carbon anode material for lithium batteries provided in this example includes the following steps: First, the preparation of the polymer solution: Mix 2.0 g of polycaprolactone (PCL, molecular weight 80000) and 80 mL of hexafluoroisopropanol, and fully dissolve it under mechanical stirring to obtain a uniform PCL solution; Secondly, preparation of microspheres with a polymer layer coating silicon: Gradually add 5.0 g of silicon powder to the PCL solution and carry out magnetic stirring to disperse the silicon powder evenly; Slowly add 150 mL of deionized water dropwise to the stirring system to initiate phase separation; At this time, PCL precipitates from hexafluoroisopropanol and coats the surface of the silicon powder, generating a suspension of microspheres with a PCL layer coating silicon containing an aqueous phase; Filter and collect the suspension of microspheres with a PCL layer coating silicon, naturally dry at room temperature and dry under vacuum at room temperature for 12 h to obtain dry microspheres with a PCL layer coating silicon; Finally, calcination treatment: Place the dry microspheres with a PCL layer coating silicon in a tube furnace, heat up to 500 °C at a heating rate of 5 °C / min under nitrogen protection, and hold for 10 h to obtain microspheres with a conductive carbon layer coating silicon, and cool to room temperature to obtain a silicon-carbon negative electrode material for lithium batteries.
[0026] Example 3 The preparation method of the silicon-carbon negative electrode material for lithium batteries provided in this example includes the following steps: First, preparation of a polymer solution: Mix 1.5 g of polylactic acid (PLA, molecular weight 80000) and 80 mL of dichloromethane (DCM), and fully dissolve under mechanical stirring to obtain a uniform PLA solution; Secondly, preparation of microspheres with a polymer layer coating silicon: Gradually add 5.0 g of silicon powder to the PLA solution and carry out magnetic stirring to disperse the silicon powder evenly; Slowly add 100 mL of ethanol dropwise to the stirring system to initiate phase separation; At this time, PLA precipitates from DCM and coats the surface of the silicon powder, generating a suspension of microspheres with a PLA layer coating silicon containing an aqueous phase; Filter and collect the suspension of microspheres with a PLA layer coating silicon, naturally dry at room temperature and dry under vacuum at 60 °C for 12 h to obtain dry microspheres with a PLA layer coating silicon; Finally, calcination treatment: Place the dry microspheres with a PLA layer coating silicon in a tube furnace, heat up to 800 °C at a heating rate of 5 °C / min under nitrogen protection, and hold for 2 h to obtain microspheres with a conductive carbon layer coating silicon, and cool to room temperature to obtain a silicon-carbon negative electrode material for lithium batteries.
[0027] Example 4 The preparation method of the silicon-carbon negative electrode material for lithium batteries provided in this example includes the following steps: First, preparation of a polymer solution: Mix 4 g of polylactic acid (PLA, molecular weight 80000) and 150 mL of dichloromethane (DCM), and fully dissolve under mechanical stirring to obtain a uniform PLA solution; Secondly, preparation of microspheres with a polymer layer coating silicon: Gradually add 5.0 g of silicon powder to the PLA solution and carry out magnetic stirring to disperse the silicon powder evenly; slowly add 150 mL of distilled water dropwise to the stirring system to initiate phase separation; at this time, PLA precipitates from DCM and coats the surface of the silicon powder, generating a suspension of microspheres with a water-containing PLA layer coating silicon; filter and collect the suspension of microspheres with a PLA layer coating silicon, naturally dry at room temperature and dry under vacuum at 60 °C for 12 h to obtain dry microspheres with a PLA layer coating silicon; Finally, calcination treatment: Place the dry microspheres with a PLA layer coating silicon in a tubular furnace, heat up to 1200 °C at a heating rate of 10 °C / min under nitrogen protection, and hold for 1 h to obtain microspheres with a conductive carbon layer coating silicon, cool to room temperature to obtain a silicon-carbon negative electrode material for lithium batteries.
[0028] Example 5 The preparation method of the silicon-carbon negative electrode material for lithium batteries provided in this example includes the following steps: First, preparation of a polymer solution: Mix 2 g of polyethylene terephthalate (PET, molecular weight 80000) and 80 mL of dichloromethane (DCM), and fully dissolve under mechanical stirring to obtain a uniform PET solution; Secondly, preparation of microspheres with a polymer layer coating silicon: Gradually add 5.0 g of silicon powder to the PET solution and carry out magnetic stirring to disperse the silicon powder evenly; slowly add 150 mL of deionized water dropwise to the stirring system to initiate phase separation; at this time, PET precipitates from DCM and coats the surface of the silicon powder, generating a suspension of microspheres with a water-containing PET layer coating silicon; filter and collect the suspension of microspheres with a PET layer coating silicon, naturally dry at room temperature and dry under vacuum at 60 °C for 12 h to obtain dry microspheres with a PET layer coating silicon; Finally, calcination treatment: Place the dry microspheres with a PET layer coating silicon in a tubular furnace, heat up to 700 °C at a heating rate of 10 °C / min under nitrogen protection, and hold for 2 h to obtain microspheres with a conductive carbon layer coating silicon, cool to room temperature to obtain a silicon-carbon negative electrode material for lithium batteries.
[0029] Example 6 The preparation method of the silicon-carbon negative electrode material for lithium batteries provided in this example includes the following steps: First, preparation of a polymer solution: Mix 2 g of polylactic acid (PLA, molecular weight 80000) and 80 mL of chloroform, and fully dissolve under mechanical stirring to obtain a uniform PLA solution; Secondly, preparation of microspheres with a polymer layer coating silicon: Gradually add 5.0 g of silicon powder to the PLA solution and carry out magnetic stirring to evenly disperse the silicon powder; slowly add 150 mL of isopropanol to the stirring system to initiate phase separation; at this time, PLA precipitates from chloroform and coats the surface of the silicon powder, generating a suspension of microspheres with a PLA layer coating silicon containing an aqueous phase; filter and collect the suspension of microspheres with a PLA layer coating silicon, naturally dry at room temperature and dry under vacuum at 60 °C for 12 h to obtain dry microspheres with a PLA layer coating silicon; Finally, calcination treatment: Place the dry microspheres with a PLA layer coating silicon in a tube furnace, heat up to 700 °C at a heating rate of 10 °C / min under nitrogen protection, and hold for 2 h to obtain microspheres with a conductive carbon layer coating silicon, cool to room temperature to obtain a silicon-carbon negative electrode material for lithium batteries.
[0030] In this application, the polymer in the polymer solution is selected from one of poly(lactide-co-caprolactone), polycarbonate, polyglycolide, poly(lactide-co-glycolide), and the technical effects obtained are the same as those of the above embodiments.
[0031] In this application, the organic solvent is selected from one of dimethyl sulfoxide and N,N-dimethylformamide, and the technical effects obtained are the same as those of the above embodiments.
[0032] II. Comparative Examples Comparative Example 1 The preparation method of the silicon-carbon negative electrode material provided in this comparative example includes the following steps: Directly mix 5.0 g of silicon powder with 2.0 g of conductive carbon black to obtain a mixed powder, and place the mixed powder in a tube furnace. Under nitrogen protection, keep it at 700 °C for 2 h and then cool to room temperature to obtain a silicon-carbon negative electrode material.
[0033] Comparative Example 2 The preparation method of the silicon-carbon negative electrode material provided in this comparative example includes the following steps: First, directly mix 5.0 g of silicon powder with 2.0 g of polylactic acid powder to obtain a mixed powder, and place the mixed powder in a tube furnace. Under nitrogen protection, keep it at 700 °C for 2 h and then cool to room temperature to obtain a silicon-carbon negative electrode material.
[0034] III. Experimental Examples Experimental Example 1 Carry out SEM characterization on the silicon-carbon negative electrode materials for lithium batteries prepared in the above Example 1 and Example 3. The detection results are as Figure 1 and Figure 2 shown. It can be seen that the particle structures of the silicon-carbon negative electrode materials for lithium batteries prepared in Example 1 and Example 3 are dense and evenly distributed.
[0035] Experimental Example 2 The silicon-carbon anode materials for lithium batteries prepared in the above Examples 1-6 and the silicon-carbon anode materials prepared in Comparative Examples 1 and 2 were subjected to electrochemical performance tests.
[0036] Specifically, the preparation method of the button cell used for testing the electrochemical performance is as follows: Using Li metal as the counter electrode, 0.1C rate charge and discharge test: The silicon-carbon anode materials for lithium batteries prepared in Examples 1-6 and the silicon-carbon anode materials prepared in Comparative Example 1 and Comparative Example 2 were used as the battery anode materials, respectively, and were mixed evenly with CMC, SBR and conductive agent (super P) in a ratio of 80:5:5:10 and coated on copper foil. After vacuum drying, it was used as the negative electrode. Using Li metal as the counter electrode, the electrolyte used was a mixed solution of ethylene carbonate (EC) and dimethyl carbonate (DMC) with 1M LiPF6 in a mass ratio of 1:1, and the separator was a PE / PP / PE composite membrane, and a CR2032 button cell was assembled. The test conditions were: rate charge and discharge at a current density of 0.1C, and the charging voltage was limited to 0.01~2V. The results are shown in Table 1.
[0037] The results are shown in Table 1.
[0038] Table 1 Comparison of battery performance of Examples 1-6 and Comparative Examples 1 and 2
[0039] As can be seen from Table 1, in the batteries obtained with the silicon-carbon anode materials for lithium batteries prepared in Examples 1-6, the first discharge specific capacity of the battery was above 1400 mAh / g, and the highest reached 1650 mAh / g; the initial Coulomb efficiency was above 70%, and the highest reached 82%; after 50 cycles, a capacity of about 1300 mAh / g or more could still be maintained, and the capacity retention rate was above 82%. After 100 cycles, a capacity of about 910 mAh / g or more could still be maintained, and the capacity retention rate was above 65%, showing excellent cycle stability and rate performance.
[0040] In the batteries made of the silicon-carbon anode materials prepared in Comparative Examples 1 and 2, the initial discharge specific capacity of the batteries is above 500 mAh / g, with the highest being 800 mAh / g; the initial Coulombic efficiency is at most 60%; after 50 cycles, the remaining capacity is only 12 mAh / g, and after 20 cycles, the remaining capacity is <100 mAh / g. It can be concluded that the cycling performance of the silicon-carbon anode material prepared in Comparative Example 1 is extremely poor, indicating that directly adding conductive carbon black cannot effectively coat the silicon particles and cannot buffer the volume expansion of silicon, and its performance is far inferior to that of the silicon-carbon anode material prepared in the present invention. The cycling performance of the silicon-carbon anode material prepared in Comparative Example 2 is poor. In this preparation method, organic solvents are not used to dissolve polylactic acid and the phase separation technology, and polylactic acid cannot uniformly cover the silicon particles, and can only form a non-uniformly distributed carbon layer. Such a simple mixing method is difficult to obtain a silicon-carbon material with a uniform structure, and its performance is significantly inferior to that of the silicon-carbon anode material prepared in the present invention.
[0041] This shows that the lithium-ion battery silicon-carbon anode material prepared by the preparation method of the lithium-ion battery silicon-carbon anode material of the present invention has excellent charge and discharge performance, rate performance and cycling stability, and thus has a good cycling life, realizing a significant improvement in the energy density, cycling life and safety of the silicon-carbon anode material, and providing a new solution for the development of lithium-ion battery technology.
[0042] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.
Claims
1. A preparation method of a silicon-carbon anode material for lithium batteries, characterized in that, It includes the following steps: mixing a polymer solution and silicon powder to obtain a mixed solution, and preparing microspheres with a silicon core coated with a polymer layer from the mixed solution through a phase separation method; subjecting the microspheres with a silicon core coated with a polymer layer to a calcination treatment to obtain microspheres with a silicon core coated with a conductive carbon layer, thereby obtaining a silicon-carbon negative electrode material for lithium batteries.
2. The preparation method of the silicon-carbon anode material for lithium batteries according to claim 1, characterized in that, The mass ratio of the silicon powder to the polymer in the polymer solution is 5:(1.5 - 4), and the particle size of the silicon powder is 50 - 5000 nm.
3. The preparation method of the silicon-carbon anode material for lithium batteries according to claim 1, characterized in that, The polymer in the polymer solution is selected from one of polylactic acid, polycaprolactone, poly(lactide-co-caprolactone), polycarbonate, polyethylene terephthalate, polyglycolide, poly(lactide-co-glycolide), and the molecular weight of the polymer is 30,000 - 80,000.
4. The preparation method of the silicon-carbon anode material for lithium batteries according to claim 1, characterized in that, The preparation method of the polymer solution includes: mixing a polymer and an organic solvent to obtain a polymer solution; wherein, the organic solvent is selected from one of dichloromethane, chloroform, hexafluoroisopropanol, dimethyl sulfoxide, N,N-dimethylformamide.
5. The preparation method of the silicon-carbon anode material for lithium batteries according to claim 4, characterized in that, The ratio of the mass of the polymer to the volume of the organic solvent is (1.5 - 4 g):(80 - 150 mL).
6. The preparation method of the silicon-carbon anode material for lithium batteries according to claim 4, characterized in that, The specific process of preparing microspheres with a silicon core coated with a polymer layer from the mixed solution through a phase separation method includes: adding a non-solvent to the mixed solution to initiate phase separation, obtaining a suspension of microspheres with a silicon core coated with a polymer layer, and filtering and drying to obtain microspheres with a silicon core coated with a polymer layer.
7. The preparation method of the silicon-carbon anode material for lithium batteries according to claim 6, wherein, The non-solvent is selected from one of water, methanol, ethanol, isopropanol, and the volume ratio of the non-solvent to the organic solvent is (10 - 20):(8 - 15).
8. The preparation method of the silicon-carbon anode material for lithium batteries according to claim 6, characterized in that, The drying temperature is room temperature - 60 °C, and the time is 12 - 13 h.
9. The preparation method of the silicon-carbon anode material for lithium batteries according to claim 1, characterized in that, The heating rate of the calcination treatment is 5 - 10 °C / min, the temperature is 500 - 1200 °C, and the time is 1 - 10 h.
10. A silicon-carbon anode material for lithium batteries, characterized in that, It is prepared by the preparation method of the silicon-carbon negative electrode material for lithium batteries according to any one of claims 1 - 9.