With the continuous development of lithium-ion batteries, the graphite anode material on the market has approached its theoretical specific capacity (372mAh/g), and the low theoretical specific capacity can no longer meet people’s needs. There is an urgent need to develop a material with a higher specific capacity to solve the problem. this problem. Among the many new lithium-ion battery anode materials, silicon (Si) has high theoretical specific capacity (4200mAh/g), low lithium insertion potential (0.4~0.6V) and abundant reserves (26.4% in the earth’s crust). It has received widespread attention.
Silicon-carbon anodes and silicon-oxygen anodes combine the advantages of high conductivity and stability of carbon materials with the high specific capacity of silicon materials. The process is relatively mature and the overall electrochemical performance is better. They have become a new direction leading the development of the lithium battery anode material industry. . Among them, the silicon-oxygen route has made rapid progress and has entered the industrial application stage. It is mainly used in the field of power batteries, but the cost is relatively high. Silicon-carbon anodes have greater application prospects because of their higher specific capacity and high first-time efficiency. Although silicon-based alloy anode materials have a significant improvement in specific capacity compared to graphite anode materials, they have not yet been used on a large scale due to their high process difficulty, high production costs, and low first charge and discharge efficiency.
Silicon-carbon anode refers to a mixture of nano-silicon and carbon materials. By reducing the particle size of the silicon-based material to the nanometer level, it can have more voids to buffer the stress and deformation generated by silicon during the process of deintercalating lithium ions. In the preparation process of silicon-carbon anode, nano-silicon particles need to be prepared first, and the outermost layer is coated with carbon to form a shell-core structure. The current commercial capacity of silicon-carbon anode is below 450mAh/g. It has high initial efficiency, but its volume expansion is large, so its cycle performance is relatively poor.
Silicon-oxygen negative electrode refers to a mixture of silicon oxide and graphite materials. Compared with silicon materials, the volume expansion of silicon oxide materials during the lithium insertion process is greatly reduced (the volume expansion of silicon oxide during the lithium insertion process About 118%, silicon is more than 300%), so its cycle performance is greatly improved. In addition, the silicon-oxygen anode has low efficiency for the first time, high production cost, and non-standardized preparation process. At present, the relatively mature technical route is a carbon-coated silicon oxide structure. Usually silicon oxide for lithium batteries is prepared first, and then carbon coating and other subsequent processes are performed.
In general, the advantage of silicon-oxygen anode is that it has good cycle life, but the first efficiency is low. The first efficiency can be improved through technologies such as prelithiation. The advantage of silicon-carbon anode is that it has high first efficiency but low cycle life. The risk of expansion and breakage can be reduced and the cycle life can be improved through nanometerization of silicon.