Silicon-carbon negative electrode material with high specific capacity and application of silicon-carbon negative electrode material in lithium ion battery
By using modification methods such as alkane-modified alkenylated quaternary ammonium salts and carboxylated graphene in silicon-carbon composite electrodes, the structure and composition are optimized, and the existing silicon-carbon composite electrodes are insufficient in performance under high current density, achieving high specific capacity and good cycling performance, which is suitable for fast charging and discharge applications.
Patent Information
- Application Number
- CN202510210774.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-02-25
- Publication Date
- 2025-06-06
AI Technical Summary
The existing silicon-carbon composite electrodes have insufficient performance under high current density and complex preparation processes, resulting in increased production costs and difficult cycling stability and specific capacity to meet the needs of fast charging and discharge.
By preparing a silicon-carbon negative electrode material with high specific capacity, and using modification methods such as alkane-modified alkenylated quaternary ammonium salt and carboxylated graphene, the structure and composition of the silicon-carbon composite electrode are optimized to improve its specific capacity and cyclic stability under high current density.
It achieves high specific capacity and good cycle performance. The first discharge specific capacity reaches 1425.6mAh/g, and remains above 900mAh/g after 2000 cycles, making it suitable for fast charging and discharging applications.
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Figure BDA0005285940660000101
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of negative electrode materials, and in particular to a silicon-carbon negative electrode material with high specific capacity and application thereof in lithium ion batteries. Background Art
[0002] With the rapid development of electric vehicles and renewable energy storage technology, lithium-ion batteries, as a highly efficient energy storage device, have received widespread attention. The performance of lithium-ion batteries mainly depends on the properties of their negative electrode materials. Although traditional graphite negative electrode materials have good cycle stability, their theoretical specific capacity is only 372mAh / g, which cannot meet the needs of high energy density batteries. Therefore, the development of new high-specific capacity negative electrode materials has become a research hotspot.
[0003] Silicon, as a negative electrode material with a high theoretical specific capacity (about 4200mAh / g), is highly favored due to its abundant resources and excellent electrochemical properties. However, silicon undergoes significant volume changes during the charge and discharge process, resulting in structural damage to the electrode material and decreased cycle performance. This volume change is mainly due to the chemical reaction between lithium ions and silicon during the charge and discharge process, which causes the expansion and contraction of silicon particles, and then causes cracks and peeling of the electrode. This not only affects the cycle life of the battery, but may also lead to safety hazards of the battery.
[0004] To overcome these problems, researchers have tried to composite silicon with other materials (such as carbon materials) to improve its conductivity and mechanical stability. The design of silicon-carbon composite electrodes aims to combine the high specific capacity of silicon and the good conductivity of carbon to achieve higher energy density and better cycle performance. However, silicon-carbon composite electrodes still face some challenges. First, the compatibility problem between silicon and carbon may lead to insufficient uniformity of the composite material, affecting the overall performance of the electrode. Second, although carbon materials can improve conductivity, the volume change of silicon will still affect the structural stability of the electrode during high-rate discharge. In addition, the preparation process of the composite material is complicated, which may lead to an increase in production costs. In addition, the performance of silicon-carbon composite electrodes at high current density is also insufficient. Although the composite material improves the specific capacity to a certain extent, the transfer rate of lithium ions may be limited during rapid charging and discharging, resulting in the actual performance of the battery failing to meet expectations. Therefore, how to optimize the structure and composition of silicon-carbon composite electrodes to improve their specific capacity and cycle stability at high current density remains the focus of current research. Summary of the invention
[0005] In view of this, the purpose of the present invention is to propose a silicon-carbon negative electrode material with high specific capacity and its application in lithium-ion batteries, so as to optimize the structure and composition of the silicon-carbon composite electrode to improve its specific capacity and cycle stability at high current density.
[0006] Based on the above purpose, the present invention provides a silicon-carbon negative electrode material with high specific capacity, which is obtained by calcining a silicon-carbon precursor. The preparation method of the silicon-carbon precursor is as follows:
[0007] (1) Under a nitrogen atmosphere, triethanolamine and isocyanoethyl methacrylate are added to dichloromethane, stirred at room temperature for 10-14 hours, and rotary evaporated to obtain an olefinated tertiary amine;
[0008] (2) under nitrogen atmosphere, adding olefinic tertiary amine and hydroquinone to dichloromethane, stirring for 20-40 minutes, then adding hexadecane bromide and ethyl bromide, heating to 40-50° C., stirring and reflux reaction for 20-28 hours, and rotary evaporation to obtain alkane-modified olefinic quaternary ammonium salt;
[0009] (3) Under a nitrogen atmosphere, add alkane-modified olefinic quaternary ammonium salt, triethoxysilane and hydroquinone to xylene, stir for 20-40 minutes, then add palladium carbon catalyst, raise the temperature to 115-125° C., stir and react for 1.5-2.5 hours, filter, and rotary evaporate to obtain modified triethoxysilane;
[0010] (4) adding graphene oxide to deionized water, ultrasonicating for 20-40 min, then adding sodium carbonate and sodium chloroacetate, stirring at 0° C. for 20-40 min, then heating to 40-50° C., stirring for 20-28 h, centrifuging, washing, and vacuum drying to obtain carboxylated graphene;
[0011] (5) Add silicon nanoparticles to a mixed solution of ethanol and deionized water, perform ultrasonic treatment for 20-40 min, then add modified triethoxysilane and carboxylated graphene, adjust the pH to 8-8.5 with aqueous ammonia, raise the temperature to 55-65° C., stir for 5-7 h, centrifuge, wash, and dry to obtain a silicon-carbon precursor.
[0012] Preferably, in step (1), the weight ratio of triethanolamine, isocyanoethyl methacrylate and dichloromethane is 5:18:100-200.
[0013] Preferably, in the step (2), the ratio of olefinated tertiary amine, hydroquinone, dichloromethane, hexadecane bromide and ethyl bromide is 15-25:0.15-0.25:100-200:5.9-9.9:1.7-2.8.
[0014] Preferably, in step (3), the weight ratio of alkane-modified olefinic ammonium salt, triethoxysilane, hydroquinone and xylene is 15-25:18-30:0.15-0.25:100-200.
[0015] Preferably, the amount of palladium-carbon catalyst added in step (3) is 1% by weight of triethoxysilane.
[0016] Preferably, in the step (4), the ratio of graphene oxide, deionized water, sodium carbonate and sodium chloroacetate is 0.5-2:50-200:5-20:10-30.
[0017] Preferably, in step (5), the weight ratio of silicon nanoparticles, ethanol, deionized water, modified triethoxysilane and carboxylated graphene is 8-12:80-120:15-45:15-25:0.5-2.
[0018] Preferably, the high specific capacity silicon-carbon negative electrode material is obtained by heating a silicon-carbon precursor to 850-950° C. in an argon atmosphere, calcining for 5-7 hours, and cooling to room temperature.
[0019] Furthermore, the silicon-carbon negative electrode material with high specific capacity provided by the present invention can be used in lithium-ion batteries.
[0020] Beneficial effects of the present invention:
[0021] The silicon-carbon negative electrode material prepared by the present invention exhibits remarkable superior performance, with an initial discharge capacity of up to 1425.6 mAh / g. After 2000 cycles, the discharge capacity remains above 900 mAh / g, indicating that the material has good cycle performance. In addition, at high rate current density, the material can still maintain a high specific capacity, showing its excellent electrical conductivity and ionic conductivity, and is suitable for fast charge and discharge applications.
[0022] The present invention adopts the modification method of alkane-modified alkenyl quaternary ammonium salt to significantly improve the cycle performance of the material and the specific capacity under high current density. This modification improves the dispersibility of graphene on the surface of silicon nanoparticles through electrostatic action, forms a uniform composite material, reduces inter-particle aggregation, thereby increasing the effective reaction area of the electrode, and promoting the rapid transmission of lithium ions. At the same time, the alkane component in the alkane-modified alkenyl quaternary ammonium salt regulates the density of the carbon layer on the surface of the silicon nanoparticles, optimizes the conductivity and mechanical stability of the electrode, reduces the structural damage caused by volume change in the charge and discharge process, and in addition, the introduction of carboxylated graphene also effectively improves the cycle performance of the material and the specific capacity under high current density, further enhancing the overall performance of the material. DETAILED DESCRIPTION
[0023] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments.
[0024] In a specific embodiment of the present invention, the particle size of the silicon nanoparticles is 200 nm, and the sheet size of the graphene oxide is 2.5 μm.
[0025] Embodiment 1:
[0026] (1) Under a nitrogen atmosphere, 5 g of triethanolamine and 18 g of isocyanoethyl methacrylate were added to 100 g of dichloromethane, stirred at room temperature for 10 h, and rotary evaporated to obtain an olefinated tertiary amine;
[0027] (2) Under nitrogen atmosphere, 15 g of olefinic tertiary amine and 0.15 g of hydroquinone were added to 100 g of dichloromethane, stirred for 20 min, and then 5.9 g of hexadecane bromide and 1.7 g of ethyl bromide were added. The temperature was raised to 40° C., stirred and refluxed for 20 h, and rotary evaporated to obtain an alkane-modified olefinic quaternary ammonium salt;
[0028] (3) Under a nitrogen atmosphere, 15 g of alkane-modified quaternary ammonium salt, 18 g of triethoxysilane and 0.15 g of hydroquinone were added to 100 g of xylene, stirred for 20 min, and then 0.18 g of palladium-carbon catalyst was added. The temperature was raised to 115° C., stirred for reaction for 1.5 h, filtered, and rotary evaporated to obtain modified triethoxysilane;
[0029] (4) adding 0.5 g of graphene oxide to 50 g of deionized water, ultrasonicating for 20 min, then adding 5 g of sodium carbonate and 10 g of sodium chloroacetate, stirring at 0 ° C for 20 min, then heating to 40 ° C, stirring for 20 h, centrifuging, washing, and vacuum drying to obtain carboxylated graphene;
[0030] (5) 8 g of silicon nanoparticles were added to a mixed solution of 80 g of ethanol and 15 g of deionized water, and ultrasonicated for 20 min. Then, 15 g of modified triethoxysilane and 0.5 g of carboxylated graphene were added, the pH was adjusted to 8.1 with ammonia water, the temperature was raised to 55 ° C, stirred for 5 h, centrifuged, washed, and dried to obtain a silicon-carbon precursor;
[0031] (6) The silicon-carbon precursor is heated to 850° C. in an argon atmosphere, calcined for 5 h, and cooled to room temperature to obtain a silicon-carbon negative electrode material with a high specific capacity.
[0032] Embodiment 2:
[0033] (1) Under a nitrogen atmosphere, 5 g of triethanolamine and 18 g of isocyanoethyl methacrylate were added to 150 g of dichloromethane, stirred at room temperature for 12 h, and rotary evaporated to obtain an olefinated tertiary amine;
[0034] (2) Under a nitrogen atmosphere, 20 g of olefinic tertiary amine and 0.2 g of hydroquinone were added to 150 g of dichloromethane, stirred for 30 min, and then 7.9 g of hexadecane bromide and 2.2 g of ethyl bromide were added. The temperature was raised to 45° C., stirred and refluxed for 24 h, and rotary evaporated to obtain an alkane-modified olefinic quaternary ammonium salt;
[0035] (3) Under nitrogen atmosphere, 20 g of alkane-modified quaternary ammonium salt, 24 g of triethoxysilane and 0.2 g of hydroquinone were added to 150 g of xylene, stirred for 30 min, and then 0.24 g of palladium-carbon catalyst was added. The temperature was raised to 120° C., stirred for reaction for 2 h, filtered, and rotary evaporated to obtain modified triethoxysilane;
[0036] (4) adding 1 g of graphene oxide to 100 g of deionized water, ultrasonicating for 30 min, then adding 10 g of sodium carbonate and 18 g of sodium chloroacetate, stirring at 0 ° C for 30 min, then heating to 45 ° C, stirring for 24 h, centrifuging, washing, and vacuum drying to obtain carboxylated graphene;
[0037] (5) adding 10 g of silicon nanoparticles to a mixed solution of 100 g of ethanol and 30 g of deionized water, ultrasonicating for 30 min, then adding 20 g of modified triethoxysilane and 1 g of carboxylated graphene, adjusting the pH to 8.3 with ammonia water, heating to 60 ° C, stirring for 6 h, centrifuging, washing, and drying to obtain a silicon-carbon precursor;
[0038] (6) The silicon-carbon precursor is heated to 900° C. in an argon atmosphere, calcined for 6 h, and cooled to room temperature to obtain a silicon-carbon negative electrode material with a high specific capacity.
[0039] Embodiment 3:
[0040] (1) Under a nitrogen atmosphere, 5 g of triethanolamine and 18 g of isocyanoethyl methacrylate were added to 200 g of dichloromethane, stirred at room temperature for 14 h, and rotary evaporated to obtain an olefinated tertiary amine;
[0041] (2) Under nitrogen atmosphere, 25 g of olefinic tertiary amine and 0.25 g of hydroquinone were added to 200 g of dichloromethane, stirred for 40 min, and then 9.9 g of hexadecane bromide and 2.8 g of ethyl bromide were added. The temperature was raised to 50° C., stirred and refluxed for 28 h, and rotary evaporated to obtain an alkane-modified olefinic quaternary ammonium salt;
[0042] (3) Under nitrogen atmosphere, 25 g of alkane-modified quaternary ammonium salt, 30 g of triethoxysilane and 0.25 g of hydroquinone were added to 200 g of xylene, stirred for 40 min, and then 0.3 g of palladium carbon catalyst was added. The temperature was raised to 125° C., stirred for reaction for 2.5 h, filtered, and rotary evaporated to obtain modified triethoxysilane;
[0043] (4) adding 2 g of graphene oxide to 200 g of deionized water, ultrasonicating for 40 min, then adding 20 g of sodium carbonate and 30 g of sodium chloroacetate, stirring at 0 ° C for 40 min, then heating to 50 ° C, stirring for 28 h, centrifuging, washing, and vacuum drying to obtain carboxylated graphene;
[0044] (5) adding 12 g of silicon nanoparticles to a mixed solution of 120 g of ethanol and 45 g of deionized water, ultrasonicating for 40 min, then adding 25 g of modified triethoxysilane and 2 g of carboxylated graphene, adjusting the pH to 8.5 with ammonia water, heating to 65 ° C, stirring for 7 h, centrifuging, washing, and drying to obtain a silicon-carbon precursor;
[0045] (6) The silicon-carbon precursor is heated to 950° C. in an argon atmosphere, calcined for 7 h, and cooled to room temperature to obtain a silicon-carbon negative electrode material with a high specific capacity.
[0046] Comparative Example 1:
[0047] The difference between Comparative Example 1 and Example 2 is that the alkane-modified olefinic quaternary ammonium salt in step (3) is replaced by an olefinic tertiary amine;
[0048] The specific steps are as follows:
[0049] (1) Under a nitrogen atmosphere, 5 g of triethanolamine and 18 g of isocyanoethyl methacrylate were added to 150 g of dichloromethane, stirred at room temperature for 12 h, and rotary evaporated to obtain an olefinated tertiary amine;
[0050] (2) Under a nitrogen atmosphere, 20 g of olefinic tertiary amine, 24 g of triethoxysilane and 0.2 g of hydroquinone were added to 150 g of xylene, stirred for 30 min, and then 0.24 g of palladium carbon catalyst was added. The temperature was raised to 120° C., stirred for reaction for 2 h, filtered, and rotary evaporated to obtain modified triethoxysilane;
[0051] (3) 1 g of graphene oxide was added to 100 g of deionized water, ultrasonicated for 30 min, then 10 g of sodium carbonate and 18 g of sodium chloroacetate were added, stirred at 0 ° C for 30 min, then heated to 45 ° C, stirred for 24 h, centrifuged, washed, and vacuum dried to obtain carboxylated graphene;
[0052] (4) adding 10 g of silicon nanoparticles to a mixed solution of 100 g of ethanol and 30 g of deionized water, ultrasonicating for 30 min, then adding 20 g of modified triethoxysilane and 1 g of carboxylated graphene, adjusting the pH to 8.3 with ammonia water, heating to 60 ° C, stirring for 6 h, centrifuging, washing, and drying to obtain a silicon-carbon precursor;
[0053] (5) The silicon-carbon precursor is heated to 900° C. in an argon atmosphere, calcined for 6 h, and cooled to room temperature to obtain a silicon-carbon negative electrode material.
[0054] Comparative Example 2:
[0055] The difference between Comparative Example 2 and Example 2 is that the carboxylated graphene in step (5) is replaced by graphene oxide;
[0056] The specific steps are as follows:
[0057] (1) Under a nitrogen atmosphere, 5 g of triethanolamine and 18 g of isocyanoethyl methacrylate were added to 150 g of dichloromethane, stirred at room temperature for 12 h, and rotary evaporated to obtain an olefinated tertiary amine;
[0058] (2) Under a nitrogen atmosphere, 20 g of olefinic tertiary amine and 0.2 g of hydroquinone were added to 150 g of dichloromethane, stirred for 30 min, and then 7.9 g of hexadecane bromide and 2.2 g of ethyl bromide were added. The temperature was raised to 45° C., stirred and refluxed for 24 h, and rotary evaporated to obtain an alkane-modified olefinic quaternary ammonium salt;
[0059] (3) Under nitrogen atmosphere, 20 g of alkane-modified quaternary ammonium salt, 24 g of triethoxysilane and 0.2 g of hydroquinone were added to 150 g of xylene, stirred for 30 min, and then 0.24 g of palladium-carbon catalyst was added. The temperature was raised to 120° C., stirred for reaction for 2 h, filtered, and rotary evaporated to obtain modified triethoxysilane;
[0060] (4) adding 10 g of silicon nanoparticles to a mixed solution of 100 g of ethanol and 30 g of deionized water, ultrasonicating for 30 min, then adding 20 g of modified triethoxysilane and 1 g of graphene oxide, adjusting the pH to 8.3 with ammonia water, heating to 60 ° C, stirring for 6 h, centrifuging, washing, and drying to obtain a silicon-carbon precursor;
[0061] (5) The silicon-carbon precursor is heated to 900° C. in an argon atmosphere, calcined for 6 h, and cooled to room temperature to obtain a silicon-carbon negative electrode material.
[0062] Comparative Example 3:
[0063] The difference between Comparative Example 3 and Example 2 is that: in step (2), hexadecane bromide is not added;
[0064] The specific steps are as follows:
[0065] (1) Under a nitrogen atmosphere, 5 g of triethanolamine and 18 g of isocyanoethyl methacrylate were added to 150 g of dichloromethane, stirred at room temperature for 12 h, and rotary evaporated to obtain an olefinated tertiary amine;
[0066] (2) Under nitrogen atmosphere, 20 g of olefinic tertiary amine and 0.2 g of hydroquinone were added to 150 g of dichloromethane, stirred for 30 min, and then 5 g of ethyl bromide was added. The temperature was raised to 45° C., stirred and refluxed for 24 h, and rotary evaporated to obtain an alkane-modified olefinic quaternary ammonium salt;
[0067] (3) Under nitrogen atmosphere, 20 g of alkane-modified quaternary ammonium salt, 24 g of triethoxysilane and 0.2 g of hydroquinone were added to 150 g of xylene, stirred for 30 min, and then 0.24 g of palladium-carbon catalyst was added. The temperature was raised to 120° C., stirred for reaction for 2 h, filtered, and rotary evaporated to obtain modified triethoxysilane;
[0068] (4) adding 1 g of graphene oxide to 100 g of deionized water, ultrasonicating for 30 min, then adding 10 g of sodium carbonate and 18 g of sodium chloroacetate, stirring at 0 ° C for 30 min, then heating to 45 ° C, stirring for 24 h, centrifuging, washing, and vacuum drying to obtain carboxylated graphene;
[0069] (5) adding 10 g of silicon nanoparticles to a mixed solution of 100 g of ethanol and 30 g of deionized water, ultrasonicating for 30 min, then adding 20 g of modified triethoxysilane and 1 g of carboxylated graphene, adjusting the pH to 8.3 with ammonia water, heating to 60 ° C, stirring for 6 h, centrifuging, washing, and drying to obtain a silicon-carbon precursor;
[0070] (6) The silicon-carbon precursor is heated to 900° C. in an argon atmosphere, calcined for 6 h, and cooled to room temperature to obtain a silicon-carbon negative electrode material.
[0071] Comparative Example 4:
[0072] The difference between Comparative Example 4 and Example 2 is that no ethyl bromide is added in step (2);
[0073] The specific steps are as follows:
[0074] (1) Under a nitrogen atmosphere, 5 g of triethanolamine and 18 g of isocyanoethyl methacrylate were added to 150 g of dichloromethane, stirred at room temperature for 12 h, and rotary evaporated to obtain an olefinated tertiary amine;
[0075] (2) Under nitrogen atmosphere, 20 g of olefinic tertiary amine and 0.2 g of hydroquinone were added to 150 g of dichloromethane, stirred for 30 min, and then 14.1 g of hexadecane bromide was added. The temperature was raised to 45° C., stirred and refluxed for 24 h, and rotary evaporated to obtain an alkane-modified olefinic quaternary ammonium salt;
[0076] (3) Under nitrogen atmosphere, 20 g of alkane-modified quaternary ammonium salt, 24 g of triethoxysilane and 0.2 g of hydroquinone were added to 150 g of xylene, stirred for 30 min, and then 0.24 g of palladium-carbon catalyst was added. The temperature was raised to 120° C., stirred for reaction for 2 h, filtered, and rotary evaporated to obtain modified triethoxysilane;
[0077] (4) adding 1 g of graphene oxide to 100 g of deionized water, ultrasonicating for 30 min, then adding 10 g of sodium carbonate and 18 g of sodium chloroacetate, stirring at 0 ° C for 30 min, then heating to 45 ° C, stirring for 24 h, centrifuging, washing, and vacuum drying to obtain carboxylated graphene;
[0078] (5) adding 10 g of silicon nanoparticles to a mixed solution of 100 g of ethanol and 30 g of deionized water, ultrasonicating for 30 min, then adding 20 g of modified triethoxysilane and 1 g of carboxylated graphene, adjusting the pH to 8.3 with ammonia water, heating to 60 ° C, stirring for 6 h, centrifuging, washing, and drying to obtain a silicon-carbon precursor;
[0079] (6) The silicon-carbon precursor is heated to 900° C. in an argon atmosphere, calcined for 6 h, and cooled to room temperature to obtain a silicon-carbon negative electrode material.
[0080] Performance Testing:
[0081] All electrochemical performance tests were performed at water and oxygen contents below 0.5×10 -6 The CR-2032 button half-cell was assembled in a glove box. The lithium sheet was used as the counter electrode, and the electrolyte was LiPF dissolved in ethylene carbonate and diethyl carbonate (EC / DEC, volume ratio 1:1). 6 (1 mol / L) solution, and the separator is Celgard 2400. The working electrode is prepared by mixing the negative electrode material prepared in the embodiment and the comparative example, Ketjen black, and poly(vinylidene fluoride) (PVDF) in a mass ratio of 8:1:1, adding N-methyl-2-pyrrolidone solvent, stirring for 3 hours, evenly applying it on a copper foil, and vacuum drying it at 80°C for 12 hours.
[0082] The tests of cycle performance, rate performance and specific capacity were all completed in the Blue Electric test system with a voltage range of 0.01-3.0V. The results are shown in Table 1.
[0083] Table 1 Performance test results
[0084]
[0085] Data Analysis:
[0086] It can be seen from the data of Examples 1-3 in Table 1 that the silicon-carbon negative electrode material prepared by the present invention has a high specific capacity. After 2000 cycles, the discharge specific capacity retention rate is as high as 95.6%, indicating that it has good cycle performance. Moreover, under high current density, the silicon-carbon negative electrode material prepared by the present invention can still maintain a relatively high specific capacity, indicating that the material has good electrical conductivity and ion conductivity and is suitable for fast charge and discharge applications.
[0087] It can be seen from the data of Example 2 and Comparative Example 1 in Table 1 that quaternization of olefinic tertiary amines with hexadecane bromide and ethyl bromide can significantly improve the cycle performance and specific capacity at high current density of silicon-carbon negative electrode materials. This is mainly because the alkane-modified olefinic quaternary ammonium salt can improve the dispersion of graphene on the surface of silicon nanoparticles through electrostatic action on the one hand, and this good dispersibility helps to form a uniform composite material, reduce the aggregation between particles, thereby increasing the effective reaction area of the electrode and promoting the rapid transmission of lithium ions. On the other hand, the alkane in the alkane-modified olefinic quaternary ammonium salt can adjust the density of the carbon layer on the surface of the silicon nanoparticles. The appropriate carbon layer density can optimize the conductivity and mechanical stability of the electrode, reduce the structural damage caused by volume change during the charge and discharge process, and thus improve the cycle performance.
[0088] It can be seen from the data of Example 2 and Comparative Example 2 in Table 1 that the carboxylation of the graphene surface can effectively improve the cycle performance and specific capacity of the silicon-carbon negative electrode material at high current density, which is mainly because the carboxylated graphene can be evenly dispersed on the surface of silicon nanoparticles through electrostatic action.
[0089] It can be seen from the data of Example 2 and Comparative Examples 3 and 4 in Table 1 that quaternizing olefinic tertiary amines using only hexadecane bromide will reduce the cycle performance of the silicon-carbon negative electrode material, and quaternizing olefinic tertiary amines using only ethyl bromide will reduce the specific capacity of the silicon-carbon negative electrode material, especially the specific capacity at high current density. This is mainly because hexadecane bromide and ethyl bromide act as carbon sources on the one hand, and adjust the density of the carbon layer on the other hand, thereby achieving a balance between specific capacity and cycle performance.
[0090] Those skilled in the art should understand that the discussion of any of the above embodiments is merely illustrative and is not intended to imply that the scope of the present invention is limited to these examples. Under the concept of the present invention, the technical features in the above embodiments or different embodiments may be combined, the steps may be implemented in any order, and there are many other variations of the different aspects of the present invention as described above, which are not provided in detail for the sake of simplicity.
Claims
1. A silicon-carbon negative electrode material with high specific capacity, characterized in that: It is obtained by calcining a silicon-carbon precursor, and the preparation method of the silicon-carbon precursor is as follows: (1) Under a nitrogen atmosphere, triethanolamine and isocyanoethyl methacrylate are added to dichloromethane, stirred at room temperature for 10-14 hours, and rotary evaporated to obtain an olefinated tertiary amine; (2) under nitrogen atmosphere, adding olefinic tertiary amine and hydroquinone to dichloromethane, stirring for 20-40 minutes, then adding hexadecane bromide and ethyl bromide, heating to 40-50° C., stirring and reflux reaction for 20-28 hours, and rotary evaporation to obtain alkane-modified olefinic quaternary ammonium salt; (3) Under a nitrogen atmosphere, add alkane-modified olefinic quaternary ammonium salt, triethoxysilane and hydroquinone to xylene, stir for 20-40 minutes, then add palladium carbon catalyst, raise the temperature to 115-125° C., stir and react for 1.5-2.5 hours, filter, and rotary evaporate to obtain modified triethoxysilane; (4) adding graphene oxide to deionized water, ultrasonicating for 20-40 min, then adding sodium carbonate and sodium chloroacetate, stirring at 0° C. for 20-40 min, then heating to 40-50° C., stirring for 20-28 h, centrifuging, washing, and vacuum drying to obtain carboxylated graphene; (5) adding silicon nanoparticles to a mixed solution of ethanol and deionized water, ultrasonicating for 20-40 min, adding modified triethoxysilane and carboxylated graphene, adjusting the pH to 8-8.5 with ammonia water, heating to 55-65° C., stirring for 5-7 h, centrifuging, washing, and drying to obtain a silicon-carbon precursor; In the step (2), the ratio of olefinated tertiary amine, hydroquinone, dichloromethane, hexadecane bromide and ethyl bromide is 15-25: 0.15-0.25: 100-200: 5.9-9.9: 1.7-2.8; In the step (5), the weight ratio of silicon nanoparticles, ethanol, deionized water, modified triethoxysilane and carboxylated graphene is 8-12:80-120:15-45:15-25:0.5-2.
2. The silicon-carbon negative electrode material with high specific capacity according to claim 1, characterized in that: In the step (1), the weight ratio of triethanolamine, isocyanoethyl methacrylate and dichloromethane is 5:18:100-200.
3. The silicon-carbon negative electrode material with high specific capacity according to claim 1, characterized in that: In the step (3), the weight ratio of alkane-modified olefinic quaternary ammonium salt, triethoxysilane, hydroquinone and xylene is 15-25:18-30:0.15-0.25:100-200.
4. The silicon-carbon negative electrode material with high specific capacity according to claim 1, characterized in that: The amount of palladium-carbon catalyst added in step (3) is 1% of the weight of triethoxysilane.
5. The silicon-carbon negative electrode material with high specific capacity according to claim 1, characterized in that: In the step (4), the ratio of graphene oxide, deionized water, sodium carbonate and sodium chloroacetate is 0.5-2:50-200:5-20:10-30.
6. The silicon-carbon negative electrode material with high specific capacity according to claim 1, characterized in that: The high specific capacity silicon-carbon negative electrode material is obtained by heating a silicon-carbon precursor to 850-950° C. in an argon atmosphere, calcining for 5-7 hours, and cooling to room temperature.
7. An application of the high specific capacity silicon-carbon negative electrode material according to any one of claims 1 to 6, characterized in that: For lithium-ion batteries.