Understanding the Layered Silicon/Graphite Composite Electrode Design from the Perspective of Porosity Evolution

Abstract

The recently reported silicon/graphite (Si/Gr) composite electrode with a layered structure is a promising approach to achieve high capacity and stable cycling of Si-based electrodes in lithium-ion batteries. However, there is still a need to clarify why particular layered structures are effective and why others are ineffective or even detrimental. In this work, an unreported mechanism dominated by the porosity evolution of electrodes is proposed for the degradation behavior of layered Si/Gr electrodes. First, the effect of layering sequence on the overall electrode performance is investigated experimentally, and the results suggest that the cycling performance of the silicon-on-graphite (SG) electrode is much superior to that of the graphite-on-silicon electrode. To explain this phenomenon, a coupled mechanical–electrochemical porous electrode model is developed, in which the porosity is affected by the silicon expansion and the local constraints. The modeling results suggest that the weaker constraint of the silicon layer in the SG electrode leads to a more insignificant decrease in porosity, and consequently, the more stable cycling performance. The findings of this work provide new insights into the structural design of Si-based electrodes.