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

Abstract Rechargeable batteries based on nonmetal charge carriers like NH 4 + recently have attracted intensive attention due to high safety, environmental friendliness, low cost, and fast kinetics. However, NH 4 + 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 (NR 4 + )‐based dual‐ion battery (DIB) working at a high voltage of 3.8 V, which was enabled by a conjugated ladder polymer poly(benzobisimidazobenzophenanthroline) (BBL) anode for NR 4 + storage and a graphite cathode for anion uptake. The BBL functions as an efficient NR 4 + host by carbonyl/enol transformation, delivering a high capacity of 120 mAh g −1 , low average potential, high stability, and excellent rate performance. In the redox process, the electronic and ionic conductivities of BBL change periodically, accompanied by 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 −1 and 6865 W kg −1 based on mass of graphite, superior rate performance, and high cycling stability without capacity attenuation. Our work demonstrates the feasibility of NR 4 + as cation carrier and its efficient host, which will inspire novel designs for high‐performance nonmetallic energy storage devices.