Intrinsic blocking effect of SiOx on the side reaction with a LiPF6-based electrolyte

Silicon has attracted significant attention as a promising anode material owing to its highest theoretical capacity. However, the commercialization of Si faces numerous challenges because of the huge volumetric effect and side reaction with LiPF6. SiOx, a derivative of Si, has received wide interest for its smaller volume change rate compared with that of Si. However, the side reaction with electrolytes has been ignored and seldom studied. In this work, we studied the side reactivity of Si and SiOx electrodes with a LiPF6-based electrolyte. The negative Gibbs free energy change (−ΔG) of SiOx is approximately 20% that of Si, while the reaction activation energy (Ea) of SiOx is nearly 2 times higher than that of Si, indicating that the much higher energy barrier of SiOx could indeed prevent the side reaction. The carbon coating on SiOx could further improve the resistance to this side reaction. These results indicate another important mechanism why SiOx is a more stable and a better cyclic anode material than Si for Li-ion batteries.