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. [ABSTRACT FROM AUTHOR]