A polyimide anode with high capacity and superior cyclability for aqueous Na-ion batteries

A redox-active and water-insoluble polyimide can reversibly bind 2 Na⁺ ions per molecular unit, demonstrating a high capacity of 130 mA h g⁻¹, a strong rate capability at 10 C rate and excellent capacity retention of 91.2% over 1000 cycles, offering a low cost and environmentally benign anode for aqueous Na-ion batteries.