In situ catalytic growth 3D multi-layers graphene sheets coated nano-silicon anode for high performance lithium-ion batteries

Silicon (Si) has been considered as the next generation ideal anode material for lithium-ion batteries because of its highest theoretical capacity (4200 mAh.g(-1)) and affluent reserves in nature. However, the severe volume expansion and unstable solid electrolyte interface (SEI) film of Si electrode during lithiation/delithiation, as well as the poor electron conductivity have seriously restricted its commercial application. In this work, in situ catalytic growth graphene on the surface of nano-Si (Si@Graphene) composite is successfully developed through a novel electroless deposition approach with Ni as the catalyst. The as-prepared Si@Graphene composite exhibits excellent cycling stability and rate capability, which retains a reversible discharge capacity up to 1909 mAh g(-1) after 100 cycles at 0.2 A g(-1), and is able to deliver a discharge capacity of 975 mAh g(-1) even at a high current density of 52 A g(-1). The results indicate that a folded multi-layers graphene could be uniformly grown on the nano-Si particles by permeating the Ni catalytic layer using the triethylene glycol (triglycol) as carbon source. The folded multi-layers graphene could maintain the framework structure of the composite during the electrochemical cycling for its excellent mechanical performance and outstanding flexibility, which could relieve volume expansion/shrinkage of Si during repeated Li+ intercalation/extraction. Moreover, the strong connection between the graphene and nano-Si in three dimensional also could provide abundant transport pathway for the electron transportation to the surface of Si particles. The most important thing is that the multi-layer graphene could protect the nano-Si particles from being directly exposed to the electrolyte, which is beneficial for maintaining the stability of SEI films.