Transitioning Towards Asymmetric Gel Polymer Electrolytes for Lithium Batteries: Progress and Prospects

Abstract The utilization of liquid electrolytes (LEs) concerns inevitable dendrite growth and safety issues. In contrast, solid polymer electrolytes suffer from unsettled low ionic conductivity and interfacial impedance issues. The intermediary gel polymer electrolytes (GPEs) improve safety by incorporating a sturdy polymer matrix and ionic conductivity as an advantage of percolating LEs responsible for gelation. The overall stability and compatibility of GPEs with different electrode materials depend on the polymers, plasticizers, and precursors utilized. No single polymer has a wide energy gap to exhibit stability against Li metal anodes and oxidative stability against high‐voltage cathodes. Thereafter, symmetric GPEs (SGPEs) possess limitations while simultaneously satisfying the two electrode requirements, which hinders their practical applications. Asymmetric GPEs (ASGPEs) generally comprise a bilayer or gradient structure, wherein the side contacting the cathode is modified to promote oxidative stability for a stable cathode electrolyte interface (CEI). The corresponding side in contact with the anode is modified to be mechanically and chemically compatible with dendritic lithium. Overall, asymmetric structural engineering enables electrode compatibility while maintaining the physical competency of GPEs. Herein, the focus is to summarize the current transition from SGPEs to asymmetric ones, which promotes multifunctionality while overcoming specific constraints associated with the electrodes.