Lithium battery silicon carbon composite anode material -Lithium - Ion Battery Equipment
Lithium batteries have the advantages of high energy density, long cycle life and less environmental pollution, and have become the focus of research around the world, and have been widely used in computers, mobile phones and other portable electronic devices. However, with the rapid development of electric vehicles and advanced electronic devices, higher requirements have been placed on the energy density of lithium batteries. How to improve the energy density of lithium batteries, the key lies in the improvement of electrode materials and performance. At present, the anode materials of commercial lithium batteries are mainly graphite materials, due to their low theoretical specific capacity (only 372mAh/g) and poor rate performance. Therefore, scientists are devoted to the study of new high-capacity anode materials. Silicon has attracted much attention due to its high theoretical specific capacity (4200mAh/g), its low lithium-deintercalation voltage platform (<0.5V), and its reaction with the electrolyte. With low activity, abundant reserves in the earth's crust, and low price, it has broad development prospects as a negative electrode material for lithium batteries. However, the volume of silicon undergoes a huge change (>300%) during the process of lithium deintercalation, resulting in the rapid pulverization and shedding of the active material during the charge-discharge cycle, resulting in the loss of electrical contact between the electrode active material and the current collector. At the same time, due to the huge volume expansion of the silicon material, the solid electrolyte interfacial film cannot exist stably in the electrolyte, resulting in reduced cycle life and capacity loss. In addition, the low conductivity of silicon severely limits the full utilization of its capacity and the rate capability of silicon electrode materials. At present, the methods to solve these problems include: nanometerization, compounding and other methods. Nanoscale and silicon-carbon composite technology is the focus of scientists' research, and significant progress has been made to improve the cycle performance and rate capability of silicon anode materials.(Lithium - Ion Battery Equipment)
This paper summarizes the research progress of silicon-carbon composite technology, including four aspects: silicon/graphite composites, silicon/amorphous carbon composites, silicon/carbon nanotube composites and silicon/graphene composites.
Carbon materials are one of the preferred active matrices for silicon-based composites, mainly because carbon materials have good electrical conductivity and small volume changes. In addition, carbon materials are light in weight and rich in sources. After the silicon material is coated with carbon, the electrical conductivity of the material can be enhanced, the agglomeration between silicon nanoparticles and the volume expansion of the material can be prevented, and a relatively stable and smooth solid electrolyte interface film can be formed on the carbon surface, thereby increasing the cycle life. , to improve the magnification performance.
Silicon/graphite composites
Graphite acts as a structural buffer layer, and at the same time, graphite can accommodate huge volume changes during charging and discharging. Wu et al. [9] prepared silicon-graphite composites with special structures by high-energy mechanical ball milling. The silicon-graphite composites exhibited excellent cycle performance. At a current density of 237mA/g, the electrochemical window was 0.03-1.5V, and the first reversible capacity was 1592mAh/g, and has good rate capability.
Su et al. prepared graphene-coated silicon-graphite composites by spray drying and heat treatment. The composites have excellent electrochemical properties. At a current density of 50mA/g, the first charge capacity is 820.7mAh/g, and the first Coulomb efficiency is 77.98%; under the condition of high current density of 500 mA/g, the first reversible capacity is still as high as 766.2 mAh/g, and it exhibits excellent cycling and rate performance.
Zhang et al. prepared Si-Co-C composites by high-energy ball milling. Electrochemical tests showed that the first charge and discharge capacities were 1068.8mAh/g and 1283.3mAh/g, respectively, and the first Coulomb efficiency was 83.3%. After 25 cycles, the reversible capacity was 620 mAh/g, and after 50 cycles, the reversible capacity remained stable above 600 mAh/g.
Jeong et al. synthesized carbon-coated silicon-graphite composites by hydrothermal carbonization, showing excellent electrochemical performance, with a specific capacity as high as 878.6mAh/g, and a capacity retention rate of 92.1% after 150 cycles. The carbon layer is conducive to the transfer of electrons, and at the same time, it can be used as a buffer layer for the volume effect of silicon during the charging and discharging process.
This paper summarizes the research progress of silicon-carbon composite technology, including four aspects: silicon/graphite composites, silicon/amorphous carbon composites, silicon/carbon nanotube composites and silicon/graphene composites.
Carbon materials are one of the preferred active matrices for silicon-based composites, mainly because carbon materials have good electrical conductivity and small volume changes. In addition, carbon materials are light in weight and rich in sources. After the silicon material is coated with carbon, the electrical conductivity of the material can be enhanced, the agglomeration between silicon nanoparticles and the volume expansion of the material can be prevented, and a relatively stable and smooth solid electrolyte interface film can be formed on the carbon surface, thereby increasing the cycle life. , to improve the magnification performance.
Silicon/graphite composites
Graphite acts as a structural buffer layer, and at the same time, graphite can accommodate huge volume changes during charging and discharging. Wu et al. [9] prepared silicon-graphite composites with special structures by high-energy mechanical ball milling. The silicon-graphite composites exhibited excellent cycle performance. At a current density of 237mA/g, the electrochemical window was 0.03-1.5V, and the first reversible capacity was 1592mAh/g, and has good rate capability.
Su et al. prepared graphene-coated silicon-graphite composites by spray drying and heat treatment. The composites have excellent electrochemical properties. At a current density of 50mA/g, the first charge capacity is 820.7mAh/g, and the first Coulomb efficiency is 77.98%; under the condition of high current density of 500 mA/g, the first reversible capacity is still as high as 766.2 mAh/g, and it exhibits excellent cycling and rate performance.
Zhang et al. prepared Si-Co-C composites by high-energy ball milling. Electrochemical tests showed that the first charge and discharge capacities were 1068.8mAh/g and 1283.3mAh/g, respectively, and the first Coulomb efficiency was 83.3%. After 25 cycles, the reversible capacity was 620 mAh/g, and after 50 cycles, the reversible capacity remained stable above 600 mAh/g.
Jeong et al. synthesized carbon-coated silicon-graphite composites by hydrothermal carbonization, showing excellent electrochemical performance, with a specific capacity as high as 878.6mAh/g, and a capacity retention rate of 92.1% after 150 cycles. The carbon layer is conducive to the transfer of electrons, and at the same time, it can be used as a buffer layer for the volume effect of silicon during the charging and discharging process.
