Abstract
Small quinone molecules are promising cathode materials for aqueous zinc batteries. However, they experience fast capacity decay due to dissolution in electrolytes. Herein, we introduce a simple methyl group to a naphthoquinone (NQ) cathode and demonstrate a facile self-saturation strategy. The methyl group exhibits hydrophobic properties together with light weight and a weak electron-donation effect, which allows a good balance among cycling stability, capacity and voltage for cathode materials. The resulting menadione (Me-NQ) presents around one-third solubility of NQ. The former thus rapidly reaches saturation in the electrolyte during cycling, which suppresses subsequent dissolution. Thanks to this process, the Me-NQ cathode preserves 146 mA h g(-1) capacity after 3500 cycles at 5 A g(-1), far exceeding 88 mA h g(-1) for NQ. Me-NQ also delivers a stabilized capacity of 316 mA h g(-1) at 0.1 A g(-1) with only 0.05 V lower average redox voltage than NQ. The co-storage of Zn(2+) and H(+) with the redox reactions on the carbonyl sites of Me-NQ is revealed.