Solvent-free synthesis of a naphthoquinone-based bipolar organic cathode towards practical durable lithium organic batteries

Quinone-based compounds are considered as one of the most promising organic electrode materials due to their high theoretical capacity and excellent redox reversibility. However, some common high-capacity small-molecule compounds, such as benzoquinone, naphthoquinone, etc., are usually soluble in organic electrolytes, causing serious shuttle effects that lead to poor cycling stability and low actual capacity. Therefore, designing and preparing organic electrodes with high capacity and good solvent resistance are essentially important for their practical applications. In this paper, we adopted a solvent-free method to synthesize a naphthoquinone-based small molecule, 2,2-(1,4-phenylbis(azo))dinaphthalenone (DNQPA), based on a nucleophilic substitution reaction between 2-chloro-1,4-naphthoquinone and p-phenylenediamine, for enhancing the conjugation and introducing intramolecular hydrogen bonds. After compounding with graphene, the solubility of DNQPA in electrolytes is greatly reduced, and when used as the cathode of LIBs, excellent cycling stability was achieved. The composite cathode exhibited a high initial capacity of 290 mA h g(-1) at 1 A g(-1) and still maintained a capacity of 258.1 mA h g(-1) after 1000 cycles. At 5 A g(-1), the capacity can be maintained at 215.8 mA h g(-1) even after 9000 cycles (85.6% of the initial capacity) with an average decay rate as low as 0.0014%, better than most previously reported carbonyl small molecule cathode materials. This study provides an attractive solvent-free method for the scalable and low-cost synthesis of high-performance organic cathodes of LIBs and paves the way for the practical applications of organic electrode materials in energy storage.

Automated summary

In this study, a naphthoquinone-based small molecule DNQPA was synthesized using a solvent-free method to enhance its properties. Compounded with graphene, the solubility of DNQPA in electrolytes was significantly reduced, resulting in excellent cycling stability when used as a cathode in LIBs. The DNQPA-graphene composite cathode exhibited high initial capacity and maintained a high capacity after a large number of cycles. This study provides an attractive solvent-free method for the scalable synthesis of high-performance organic cathodes and paves the way for practical applications of organic electrode materials in energy storage.