A Dual-Salt PEO-based polymer electrolyte with Cross-Linked polymer network for High-Voltage lithium metal batteries

Poly(ethylene oxide) (PEO)-based solid electrolyte is one of the most promising candidates to be applied in solid-state lithium (Li) metal batteries (SSLMBs), but its poor ionic conductivity at room temperature and incompatibility with LiCoO2/LiNixMnyCozO2 cathode materials impedes the potential application in ambient-temperature and high energy density batteries. Herein, an ultrathin dual-salt PEO based polymer electrolyte (DPPE) with cross-linked network is engineered to tackle these issues. The formed cross-linked networks greatly increase the amorphous region of PEO and the DPPE exhibits high ionic conductivity of 0.57 mS cm−1 at 30 °C. Furthermore, a LixBOyFz-rich and LiF-rich durable cathode electrolyte interphase (CEI) layer is generated on NCM622 surface on account of preferential decomposition of LiODFB, which isolate PEO based electrolytes from NCM622 cathode materials and effectively suppress the decomposition of PEO segments. Besides, the solvent-free in-situ polymerization method greatly reduces the thickness of DPPE membrane with only 20 μm and contributes to the formation of an optimum DPPE/cathode interface. Improved NCM622|DPPE|Li cell provides prominent cycle performance with a capacity retention of 94.7 % after 100 cycles at 4.2 V under 30 °C. This simple and effective strategy provides a new idea for the practical application of PEO-based solid electrolytes for ambient-temperature high-voltage SSLMB.