Synthesis and electrochemical properties of nano-Si/C composite anodes for lithium-ion batteries

Phenolic resin was coated on the surface of nano-Si by a microencapsulation technique, and then carbonized under Ar protection to prepare a nano-Si/C composite. The composites were first prepared using 4 different mass ratios (1:2, 1:4, 1:6, 1:8) of phenolic resin to nano-Si. The obtained average thicknesses of amorphous carbon coating were 7, 4.5, 3.7, 2.8 nm, respectively. By comparing the cycling and rate capability, the best electrochemical performance was obtained when this ratio was 1:4, with a 4.5 nm amorphous carbon coating. The electrochemical properties of this material were then comprehensively evaluated, showing excellent electrochemical performance as an anode material for Li-ion batteries. At a current density of 100 mAg⁻¹, the material had a first specific discharge capacity of 2 382 mAhg⁻¹, a first charge specific capacity of 1667 mAhg⁻¹, and an initial coulombic efficiency of 70%. A discharge specific capacity of 835.6 mAhg⁻¹ was retained after 200 cycles with a high coulombic efficiency of 99.2%. In addition, the nano-Si/C composite demonstrated superior rate performance. Under current densities of 100, 200, 500, 1 000 and 2 000 mAg⁻¹, the average specific discharge capacities were 1 716.4, 1 231.6, 911.7, 676.1 and 339.8 mAh g⁻¹, respectively. When the current density returned to 100 mA g⁻¹, the specific capacity returned to 1 326.4 mAh g⁻¹.