Molecularly engineered organic copolymers as high capacity cathode materials for aqueous proton battery operating at sub-zero temperatures

High-performance aqueous all-organic rechargeable batteries are promising candidates for cost-effective, safe, and environment-friendly next-generation energy storage devices. Herein, two organic copolymers with nanorod-like morphology (AN-TA, and AN-PA), composed of different tertiary amines, are synthesized as the cathode material for an aqueous proton battery. The individual copolymer electrodes possess the dominated diffusion-controlled electrode kinetics resulting from the proton insertion/de-insertion along with the surface-controlled processes in 2 M HCl and 2 M H₂SO₄. Among the two copolymers, AN-PA exhibits the maximum specific capacity of 145 mAh g⁻¹ at 1 A g⁻¹ and then, even at the higher current density of 10 A g⁻¹, it possesses the capacity as 110 mAh g⁻¹ in 2 M HCl. The assembled aqueous proton battery comprising of AN-PA as a cathode delivers the capacity of 80 mAh g⁻¹ at 1 A g⁻¹ in 2 M HCl. The maximum deliverable energy density of 33.9 Wh kg⁻¹ is achieved at the power density of 423 W kg⁻¹. Notably, our proton battery can well operate at the sub-zero temperature of −25 °C with a cell voltage of 1.1 V. More importantly, the device retains 84 % of the initial capacity after 1000 cycles at 2 A g⁻¹ and exhibits the retention of specific capacity of about > 93% when compared to that of room temperature.