A donor-acceptor conjugated bipolar polymer with multielectron redox sites for long-cycle-life and high-rate aqueous zinc dual-ion batteries

Aqueous zinc-ion batteries (AZIBs) have hugely latent advantages in large-scale energy storage due to its innate safety, reasonable price, and sustainability. However, most AZIB cathode materials suffer from short cycling life and poor rate performance. Herein, a bipolar donor-acceptor (D-A) conjugated microporous polymer (PTZ-BDTB), consisting of electron-withdrawing benzo[1,2-b:4,5-b’]dithiophene-4,8-dione (BDTB) units and electron-donating phenothiazine (PTZ) units, is developed as the cathode material of aqueous zinc dual-ion batteries (AZDIBs). The D-A type structure design could reduce the band gap, thus promoting electron transfer in the polymer framework. Therefore, the PTZ-BDTB cathode in a 30 mol/kg (m) ZnCl₂ water-in-salt electrolyte exhibits a high reversible capacity of 202 mA h g⁻¹ at 0.05 A g⁻¹ with excellent rate performance (109 mA h g⁻¹ at 15 A g⁻¹), which is far superior to its counterpart polymers PPTZ and PB-BDTB. Impressively, PTZ-BDTB shows ultra-stable cycle performance with capacity retention ratios of 76.2% after 460 cycles at 0.05 A g⁻¹ and 96% after 27000 cycles at 5 A g⁻¹. PTZ-BDTB also exhibits a low self-discharge ability with capacity retention about 76.4% after resting the battery for 28 days. These results demonstrate that D-A type structural design is a promising strategy for constructing high performance cathode materials for AZDIBs.