Effects of charging protocols on the cycling performance for high-energy lithium-ion batteries using a graphite-SiOx composite anode and Li-rich layered oxide cathode

High-energy lithium-ion batteries (LIBs) using Si-based anode and Li-rich layered oxide (LLO) cathode suffer severe capacity degradation during cycling, which is directly affected by the charging protocols. In this paper, the effect of constant current (CC) and constant current-constant voltage (CC-CV) charging on the cycling performance of graphite-SiOx/LLO pouch-type batteries is studied. Unexpectedly, after 300 cycles, the batteries under the CC-CV protocol show capacity retention of 71.22%, batteries under the CC protocol, however, show capacity retention of only 64.02%. For the batteries using the CC protocol, the electrochemical test results reveal an unstable change in the electrode/electrolyte interface resistance and bigger lithium ion diffusion resistance. The postmortem analyses further indicate a solid electrolyte interface (SEI) film with lower chemical stability and a greater loss of active lithium and Si in the anode. Compared with the CC protocol, the batteries under the CC-CV protocol possess a more stable SEI film and a smaller loss of active lithium and Si. This work has certain reference significance for optimizing the charging protocol.