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.