Boosting the cyclability of tetracyanoquinodimethane (TCNQ) as cathode material in aqueous battery with high valent cation

7,7,8,8-tetracyanoquinodimethane (TCNQ) is a low-cost redox active organic compound which has high theoretic specific capacity. But when it is used as cathode material in batteries , it always suffers from fast performance decaying because of material dissolution. In this work, Al 3+ salt is added in a Na 2 SO 4 /ZnSO 4 aqueous electrolyte to stabilize the crystalline structure of TCNQ and depress its solubility. Surprisingly, we found the insertion/extraction of high valent cations (Al 3+ and Zn 2+ ) in TCNQ is highly reversible, which leads to synergistic improvement of both specific capacity and cycle life. The obtained cathode exhibits a reversible capacity of 245.8 mAh g -1 at 0.5 A g -1 and a cycle-life of 1000 rounds at 3 A g -1 . Our work demonstrates that molecular organic electrode materials are very different from conventional inorganic cathode materials in terms of high valent cation intercalation reversibility. Adding high valent cation salts is a simple and effective way to enhance the electrochemical performance of molecular organic electrode materials, and consequently build low cost, high performance aqueous rechargeable batteries.