Mechanism of high Li-ion conductivity in poly(vinylene carbonate)-poly(ethylene oxide) cross-linked network based electrolyte revealed by solid-state NMR

Solid polymer electrolytes (SPEs) have become increasingly important in advanced lithium-ion batteries (LIBs) due to their improved safety and mechanical properties compared to organic liquid electrolytes. Cross-linked polymers have the potential to further improve the mechanical property without trading off Li-ion conductivity. In this study, focusing on a recently developed cross-linked SPE, i.e., the one based on poly (vinylene carbonate)-poly (ethylene oxide) based cross-linked network (PVCN), we used solid-state NMR techniques to investigate the fundamental interaction between the chain segments and Li ions, as well as the lithium-ion motion. By utilizing homonuclear/heteronuclear correlation, CP (Cross-Polarization) kinetics, and spin-lattice relaxation experiments, etc., we revealed the structural characteristics and their relations to lithium-ion mobilities. It is found that the network formation prevents poly (ethylene oxide) chains from crystallization, which could create sufficient space for segmental tumbling and Li-ion conduction. As such, the mechanical property is greatly improved with even higher Li-ion mobilities compared to the poly (vinylene carbonate) or poly (ethylene oxide) based SPE analogues.