Analysis of effects of the state of charge on the formation and growth of the deposit layer on graphite electrode of pouch type lithium ion polymer batteries

The breakdown of the protective solid electrolyte interface (SEI) layer formed on lithium ion battery anodes can initiate further electrolyte decomposition and the formation of non-uniform and electronically insulating reaction products on the surface of the graphite particles. The results from this study indicate that raising both the lower and upper ends of the state of charge (SOC) increased the rate of the electrolyte decomposition side reaction to form a thick deposit surface film. This deposit layer contained lithium that can no longer participate in the reversible electrochemical reaction. In addition, the high cycling potential coupled with high charge rate created a large lithium concentration gradient that led to some particles detachment from the current collector and isolation in the electrochemical process.