Fabrication of double core-shell Si-based anode materials with nanostructure for lithium-ion battery

Yolk-shell structure is considered to be a well-designed structure of silicon-based anode. However, there is only one point (point-to-point contact) in the contact region between the silicon core and the shell in this structure, which severely limits the ion transport ability of the electrode. In order to solve this problem, it is important that the core and shell of the core-shell structure are closely linked (face-to-face contact), which ensures good ion diffusion ability. Herein, a double core-shell nanostructure (Si@C@SiO₂) was designed for the first time to improve the cycling performance of the electrode by utilising the unique advantages of the SiO₂ layer and the closely contacted carbon layer. The improved cycling performance was evidenced by comparing the cycling properties of similar yolk-shell structures (Si@void@SiO₂) with equal size of the intermediate shell. Based on the comparison and analysis of the experimental data, Si@C@SiO₂ had more stable cycling performance and exceeded that of Si@void@SiO₂ after the 276^th cycle. More interestingly, the electron/ion transport ability of electrode was further improved by combination of Si@C@SiO₂ with reduced graphene oxide (RGO). Clearly, at a current density of 500 mA g^-1, the reversible capacity was 753.8 mA h g^-1 after 500 cycles, which was 91% of the specific capacity of the first cycle at this current density.