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

Rechargeable batteries based on nonmetal 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 3.8 V, 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^-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 NR₄ ⁺ as cation carrier and its efficient host, which will inspire novel designs for high-performance nonmetallic energy storage devices.