Lithium difluorophosphate-modified PEO-based solid-state electrolyte for high-voltage lithium batteries

It is of great significance for broadening the electrochemical window of poly(ethylene oxide) (PEO)-based solid electrolyte to match with high voltage lithium cobalt oxide for the commercial application of solid-state lithium-ion batteries. In this paper, LiPO2F2 was introduced as an additive to increase the stability of PEO-based polymer solid electrolytes. After LiPO2F2 addition, the oxidative decomposition voltage of PEO increased from 3.8 to 4.8 V. The LiCoO2/PEO-LiTFSI-LiPO2F2/Li cell showed a specific discharge capacity of 103.2 mAh g(-1) at 0.2 C after 100 cycles with a capacity retention of 83.8%, which is much better than that of LiCoO2/PEO-LITFSI/Li cell (maintained at 8.7 mAh g(-1) after only 70 cycles). The improved electrochemical performance can be attributed to the LiPO2F2 decomposition earlier than PEO during the cycles, and the products acted as a protective layer to stabilize PEO at high voltage. The novel LiPO2F2-modified PEO electrolyte strategy provides a new approach for solid-state batteries, especially for their high voltage applications.