Energy storage characteristics and mechanism of organic-conjugated polyanthraquinoneimide for metal-free dual-ion batteries

Organic materials have gained significant attention in the battery energy storage field due to their good reaction kinetics and designable properties. However, conventional organic materials typically exhibit poor cycling stability in dual-ion batteries because of their high solubility and low electron conductivity. Herein, an organic conjugated polyanthraquinoneimide (PAQI) with stacked layered porous nanosheet structures by a one-step solvothermal process. After polymerization, not only the solubility of PAQI in electrolytes was reduced, but also the utilization of the active site (C=O) was significantly increased to enhance the electronic conductivity. Moreover, PAQI also exhibited a high ion diffusion coefficient (0.946 × 10−10 ∼ 1.293 × 10−10 cm2 s−1) and showed excellent electrochemical performance as the anode for a metal-free dual-ion battery, with a discharge specific capacity of up to 128 mAh g−1 and a capacity retention rate of 80% after 200 cycles under a high rate of 2 C (1 C = 228 mA g−1). Meanwhile, cyclic voltammetry tests and reaction kinetic calculations revealed that PAQI was a pseudocapacitive storage mechanism combining diffusion control and surface capacitance processes (the capacitance contribution is 82.59 % at a scan rate of 0.9 mV s−1). These abundant stacked layered porous nanosheet structures provided a new route for research and development of the next-generation green metal-free dual-ion batteries.