An alternating copolymer-based bipolar cathode material for efficient symmetric sodium-dual-ion batteries

Abstract

Organic bipolar electrodes are capable of facilitating both n-type and p-type reactions for energy storage, typically offering high theoretical specific capacities. This article presents the design and synthesis of a new bipolar polymer cathode material, PDQZ, which is synthesized by copolymerization of phenanthroline diketone with dihydrophenazine. Dihydrophenazine works to store anions while phenanthroline diketone could store sodium ions. In a sodium-based half-cell, PDQZ demonstrates an energy density of 597 W h kg⁻¹ and a reversible specific capacity of 318 mA h g⁻¹ at a current density of 0.5C, with a capacity retention rate of 85% after 300 cycles. Notably, even after 4000 cycles at 10C, the capacity retention rate remains at 78%. Furthermore, symmetrical batteries are successfully assembled based on PDQZ, which shows the “ready-to-charge” characteristic, providing a discharge specific capacity of 112 mA h g⁻¹ at 1 A g⁻¹. More excitingly, stable cycling performance over 2000 cycles is achieved in symmetric cells, with an average decay rate as low as 0.02% per cycle. These results highlight the promising application potential of the bipolar PDQZ in energy storage, and may also shed light on future design of bipolar polymer electrode materials.