Stablizing the Interface Between Polymer Electrolyte and Lithium by Concentration Polarization-Induced Phase Transformation

Solid-state batteries are attractive for next-generation energy storage as they have better safety and are potentially compatible with high-capacity lithium metal anodes. Solid polymer electrolytes have advantages of easy processing and low cost, but they face challenges in interfacial stability with electrode materials and low conductivities. We recently observed a reversible phase separation in polymer electrolytes arising from concentration polarization in the electrolyte, which results in a mechanically strong coating on lithium metal surface due to mechano-chemical coupling. The effects of such phase separation are characterized by optical microscopy, stimulated Raman microscopy, AFM and phase field simulation to understand the mechanisms. The strategy is applied to LiFePO4/Li cells which shows much better performance than cells without such phase transformaion.