Ionic-liquid-containing polymer interlayer modified PEO-based electrolyte for stable high-voltage solid-state lithium metal battery

Polyethylene oxide (PEO) based solid electrolyte has gained widespread interests owing to its excellent processability, acceptable ionic conductivity and low interfacial resistance toward electrodes. However, the extremely poor compatibility between PEO-based electrolyte and high-voltage cathode restricts its application in high-energy-density batteries, and recent researches indicate that it is also unstable to the Li anode. In this work, a stable ionic-liquid-containing poly(vinylidenefluoride-hexafluoropropylene) (PVDF-HFP)-based electrolyte (IPL) with high ionic conductivity is engineered as an interlayer in PEO-based solid-state batteries, and the experimental results demonstrate that the IPL interlayer can effectively suppress the interfacial side reactions and helps to form a stable interface between PEO-based solid electrolyte and LiCoO2 (LCO) cathode under high voltage. Moreover, the interlayer can enable stable Li stripping and plating for over 1000 h at 0.1 mA cm−2, exhibiting an excellent stability against the Li anode. Therefore, the LCO/Li cells assembled with the IPL interlayer modified PEO-based electrolyte show high discharge capacity of 144.3 mAh g−1 and 169.7 mAh g−1 at 0.2 C under different voltage of 4.3 V and 4.5 V, and the capacity retention is 85.9% and 82.7% after 100 cycles, respectively. This study provides a novel idea for constructing high-performance PEO-based high-voltage solid-state Li batteries.