All‐Organic Rechargeable Battery with Reversibility Supported by “Water‐in‐Salt” Electrolyte

Rechargeable batteries with organic electrodes are preferred to those with transition-metal-containing electrodes for their environmental friendliness, and resource availability, but all such batteries reported to date are based on organic electrolytes, which raise concerns of safety and performance. Here an aqueous-electrolyte all-organic rechargeable battery is reported, with a maximum operating voltage of 2.1 V, in which polytriphenylamine (PTPAn) and 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTCDA)-derived polyimide (PNTCDA) serve as cathode and anode material, respectively. A key feature of the design is use of a "water-in-salt" electrolyte to bind "free" water; this impedes the side reaction of water oxidation, thereby enabling excellent reversibility in aqueous solution. The battery can deliver a maximum energy density of 52.8 Wh kg^-1 , which is close to most of the all-organic batteries with organic electrolytes. The battery exhibits a supercapacitor-like high power of 32 000 W kg^-1 and a long cycle life (700 cycles with capacity retention of 85 %), due to the kinetics not being limited by ion diffusion at either electrode.