Polyquinoneimides as Organic Cathodes for Advanced Potassium-Ion Batteries

Abstract

Due to abundant raw materials, low cost and high theoretical energy density, organic potassium ion batteries (OPIBs) have attracted more and more attention from researchers as next promising battery system. However, some challenges still need to be solved. For example, most small-molecule organic electrode materials faced serious dissolution problem in liquid electrolytes, resulting in poor cycle stability. In particular, there are relatively few reports on the current cathodes with really excellent comprehensive performance (such as: high specific capacity, high working voltage, long life-span and excellent rate performance) for OPIBs. In this article, two polyanthraquinoneimide polymers were successfully synthesized and used as organic cathode materials for potassium ion batteries. Attributed to the large molecular structure of the polymer, PPAQ and PNAQ both were successful to be insoluble in the electrolyte (1 mol/L KPF₆ in DME). After comparison, it was found that PNAQ exhibited better comprehensive electrochemical performance than PPAQ. At a current density of 100 mA/g, PNAQ achieved a stable discharge capacity of 138 mAh/g for 200 cycles and the retention rate was as high as 92%. At the same time, after 750 cycles at a high current density of 800 mA/g, the specific capacity of PNAQ still remained at 71 mAh/g with an average attenuation of only 0.03 mAh/g per cycle. Through an appropriate design process for the molecular structure, we proved that organic polymers could become excellent cathodes for potassium ion batteries.