Dual-Salt-Containing Polymer Interlayer Stabilizes Solid-State Li-Metal Batteries with LiCoO2 Cathodes

Composite polymer electrolytes (CPEs) made of poly(ethylene oxide) (PEO) have potential applicability in future solid-state rechargeable Li-metal batteries (LMBs). However, the interfacial instability between high-voltage cathodes (HVC) and PEO-based CPEs currently limits their use in high-energy-density (HED) LMBs. In this study, an innovative interface engineering method is demonstrated to enhance interfacial stability by impregnating LiTFSI and LiDFOB dissolved in molten poly(ethylene glycol) dimethyl ether (PEGDME) in the cathode-contacting layer. The resulting dual-salt-containing polymer interphase displays high ionic conductivity, improved film-forming properties, and robustness. The interface-modified PEO-based CPEs have good interfacial adhesion with HVC. When charged to 4.3 V in the CPEs, the LiCoO2||Li cell delivers a superior rate capability at 60 °C, achieving stable cycling while retaining 87.2% of the initial capacity after 200 cycles at 60 °C and 86.6% after 460 cycles at 50 °C. This work provides a novel and viable approach to enhance the interface stability between PEO-based CPEs and high-voltage cathodes, advancing the development of safe LMBs with HED.