Non-conjugated linkage enabling a quinone-based cathode material with long cycle life and high energy density for aqueous zinc batteries

Small-molecule quinones are promising cathode materials for aqueous zinc batteries with high theoretical capacity and desirable voltage. However, they usually exhibit high solubility in aqueous electrolytes, resulting in the loss of active material and a short cycle life. An efficient solution is to introduce linkages for benzoquinones (BQs) to enlarge molecular size; nevertheless, at the same time this adds dead weight, and the usually extended conjugation leads to the decreased redox potential of carbonyl groups. Herein, we present a phenyl cross-linked tri-p-benzoquinone (Ph-tri-BQ) cathode material for aqueous zinc batteries. Its solubility is greatly reduced to below 0.002% of the solubility for BQ. Besides, the weak electron-donation property and weight of the phenyl linkage are further shared by three BQs. Therefore, Ph-tri-BQ achieves a high capacity of 402 mA h g(-1) with a 1.03 V discharge voltage plateau at 0.2 A g(-1). Upon a 500 times increase in current density to 100 A g(-1), the cathode still retains 221 mA h g(-1) capacity at 0.91 V discharge voltage together with an ultra-long lifespan of 150 000 cycles. The energy storage mechanism is identified as the redox reactions on carbonyl sites with Zn2+/H+ co-storage.