Preparation And Investigation Of Si@NiSi₂/Ni/C Compostie As An Anode Material For Li-ion Batteries

Currently among various energy storage devices such as Ni-Cd, Ni-MH, Li-ion and so on, lithium-ion batteries（LIBs） which have higher energy density and portability have drawn extensive attention all over the world and have been widely used in portable electronics and electric vehicles. The specific capacity of a battery is mainly determined by the cathode and anode materials and the further development of lithium-ion batteries is limited by the relatively low capacity of the electrodes. Great efforts have been devoted to anode materials to research new electrode materials with higher stable capacity.In this work, a novel nano-sized core-shell Si@Ni Si₂/Ni/C composite was synthesized using silicon powder, NiCl₂ solution, ammonium hydroxide and phenolic resin as the raw materials. The core was silicon and the shell was a mixture of Ni Si₂ and Ni. Comparing the different performance of Si/C, Ni Si₂/Si and Si@Ni Si₂/Ni/C composite, the core-shell structure of Si@Ni Si₂/Ni/C composite has the best electrochemical performance as anode material for lithium-ion batteries.The silicon powder, NiCl₂ solution and ammonium hydroxide were used to obtain Si/Ni（OH）2 precursor by precipitation. The silicon particles surrounded by Ni Si₂ and Ni phases to form Si@Ni Si₂/Ni composite after thermal reduction at 300 oC. In addition, a carbon layer, using a phenolic resin as the carbon source, was coated on the Si@Ni Si₂/Ni surface by a pyrolysis process at 850 oC. After 105 cycles, the Si@Ni Si₂/Ni/C composite electrode showed a specific capacity of 1194 m Ah/g which was significantly higher than the Si/C and Ni Si₂/Si anode materials. The capacity retention of Si@Ni Si₂/Ni/C composite anode was 98 % and when the current density increased, the Si@Ni Si₂/Ni/C composite electrode had a slight capacity decrease. While the current density decreased to 100 m A/g, the capacity returned back to a higher standard. Thus the synthesized Si@Ni Si₂/Ni/C composite can successfully improved the electronic conductivity and inhibited the volume expansion of silicon and then stabled the structure.This work had advantages of simple synthesis method, low cost, and abundant raw materials. Therefore, the core-shell carbon coated structure of the Si@Ni Si₂/Ni/C nanocomposite as an anode material has great potential for use in lithium ion batteries.