Abstract:

Silicon, which is the anode material of lithium-ion batteries, has become a popular research topic owing to its ultrahigh theoretical specific capacity of 4200 mA·h/g. However, the volume of silicon-based materials changes significantly during lithium removal. The expansion and contraction rates become 300%, causing the electrode materials to collapse during charging and discharging and considerably reducing the life cycle of a battery. To resolve this problem, a hydrothermal method is developed to obtain double-layer graphene and carbon-coated silicon for achieving a three-dimensional (3D) conductive network structure. The experimental results show that the silicon/carbon/graphene three-layer structure exhibits an excellent electrochemical performance (e.g., ultralong cycle life and high charge-discharge ratio) as the negative electrode material of the lithium-ion batteries. An electrode having this structure that has been charged and discharged 50 times with a current density of 0.2 A/g has a specific capacity of more than 2469 mA·h/g. When 300 charging and discharging cycles are achieved, a current density of 2 A/g realizes a specific capacity of more than 1500 mA·h/g. The specific capacity remains constant at 471 mA·h/g; however, an excellent recovery ability and rate performance can be observed under a super-large current density of 32 A/g, indicating that the 3D conductive network structure composite material increases the strength, toughness, and conductivity of the original material. Therefore, the method and design of composite materials can considerably inhibit the volume effect of silicon as a negative material, which significantly impacts the research and development of lithium-ion battery electrode materials.

Key words: lithium-ion battery, silicon, anode material, graphene, double-layer coated