A 3.8V Quaternary Ammonium‐Based Dual‐Ion Battery Enabled by a Conjugated Ladder Polymer

Rechargeable batteries based on non‐metal charge carriers like NH4+ recently have attracted intensive attention due to high safety, environmental friendliness, low cost and fast kinetics. However, NH4+ electrolytes suffer from a narrow electrochemical potential window, making it challenging to construct high‐voltage and energy‐dense devices. Here we report a quaternary ammonium (NR4+)‐based dual‐ion battery (DIB) working at a high voltage of 3.8V, which was enabled by a conjugated ladder polymer poly(benzobisimidazobenzophenanthroline) (BBL) anode for NR4+ storage and a graphite cathode for anion uptake. The BBL functions as an efficient NR4+ host by carbonyl/enol transformation, delivering a high capacity of 120 mAh/g, low average potential, high stability and excellent rate performance. In the redox process, the electronic and ionic conductivities of BBL change periodically, accompanied with the formation of radical anion (●−) and diradical dianion (2●−). In combination with an anion‐intercalation graphite cathode, the assembled graphite//BBL DIB exhibits a maximum energy/power density up to 232 Wh/kg and 6865 W/kg based on mass of graphite, superior rate performance and high cycling stability without capacity attenuation. Our work demonstrates the feasibility of NR4+ as cation carrier and its efficient host, which will inspire novel design for high‐performance non‐metallic energy storage devices.