Understanding the steric effect of graphene in graphene wrapped silicon suboxides anodes for Li-ion batteries

Due to high electrical conductivity and excellent mechanical properties, graphene has attracted extensive attention for Li-ion batteries, but generally as a functional additive with the content ≤1 wt%. Unfortunately, single graphene sheets and orderly stacked graphene films are likely to impede Li-ion transportation as a physical barrier. Herein, we compare pure graphene anodes with different stacking manners and SiO anodes wrapped with variant mass of graphene to unveil the steric hindrance. The rapidly fading capacity indicates a serious steric effect on lithium-ion diffusion once graphene mass loading goes beyond the critical value of ∼0.3 mg cm−2. When graphene stacked to parallel Li-ion diffusion direction, it delivers near-theoretical specific capacity, even for thick electrode up to 5.5 mg cm−2. Furthermore, no remarkably adverse impact from graphene is shown in graphene wrapped SiO anodes even with 19 wt% graphene and at 4C in the half cells. Importantly, polarization associated voltage leap and average voltage demonstrate a significant steric effect when the graphene mass loading exceeds 0.33 mg cm−2 in the commercial level pouch cells. In conclusion, the steric effect on electrochemical performances can be eliminated once the critical value of graphene mass loading in the electrode is below ∼0.3 mg cm−2.