Influence of flake size and porosity of activated graphene on the performance of silicon/activated graphene composites as lithium-ion battery anodes

Activated graphene is one of the most promising conductive materials since in-plane pores on the graphene can facilitate fast ion diffusion. Acid treatment is a common method to produce activated graphene (AG), which changes the porosity and flake size of AG simultaneously. However, the study considering both flake size and porosity is very limited. To unveil the effect of both factors, a series of AG with different flake sizes and porosity is synthesized by varying acid treatment time. After compositing them with silicon nanoparticles, silicon/reduced activated graphene (Si/rAG) composites are electrochemically tested as lithium-ion battery anode materials. After a detailed investigation, this study proves that Si/rAG-4 h electrode delivers the best rate and cycling performance among samples due to optimal structure properties of AG-4 h. With increasing the chemical etching time, in-plane pore size gets bigger which increases lithium-ion diffusivity, while AG flakes become smaller that decreases electrical conductivity. The trade-off between electrical conductivity and lithium-ion diffusivity which significantly impacts the electrochemical performance is well studied. Therefore, this investigation provides a good guideline that shows how activated graphene-based composites should be designed for high-performance electrochemical devices.