An Energy‐Dense Nonmetal Dual‐Ion Battery Enabled by Weakly Interacted Ionic Liquid and a Ladder Polymer

ABSTRACT Dual‐ion batteries (DIBs) have drawn extensive attention for energy storage applications. Ionic liquid (IL) with non‐flammability and a wide potential window is a promising electrolyte for energy‐dense and safe DIBs, which, however, suffer from limited capacity and sluggish kinetics due to strong ion interaction in IL electrolytes and lack of compatible hosts. Here, we prepare a weakly interacted IL electrolyte by introducing competitive hydrogen bonds into the IL matrix, and propose a high‐capacity yet quick‐charge polymer anode, poly(benzobisimidazobenzophenanthroline) (BBL), as an advanced cation host. Kinetics of both bulk ion diffusion and ion insertion into electrodes are significantly accelerated. Consequently, the assembled graphite//BBL DIB exhibits a high working voltage up to 3.5 V, durable longevity, a maximum energy density of 252 Wh/kg, and a power density of 6396 W/kg (based on anode mass), outperforming other nonmetal DIBs. Our work demonstrates ion kinetics modulation and ion host innovation as efficient strategies for designing advanced nonmetal energy devices.