Anion chemistry enabled positive valence conversion to achieve a record high-voltage organic cathode for zinc batteries

Abstract

Chalcogens undergoing positive valence conversions show great potential to achieve a high discharge voltage in batteries; however, such reactions with high reversibility are difficult to achieve because element O/S/Se are inherently electron acceptors. Herein, by incorporating the chalcogens with the unique triphenylphosphine-based structure (strong electron-withdrawing groups), a high-potential triphenylphosphine selenide organic cathode (TP-Se) is developed. Facilitated by a Zn²⁺/trifluoromethanesulfonate (OTF⁻) hosting mechanism, the (TP-Se)⁻ to (TP-Se)⁰ to (TP-Se)⁺ conversion is realized. The dual-ion Zn‖TP-Se batteries exhibit a flat discharge plateau at 1.96 V and a superior discharge capacity. Benefiting from the stable triphenylphosphine molecular structures and optimized hybrid electrolytes, excellent cycling performance is also attained (up to 85.3% capacity retention after 4,300 cycles). Moreover, the Zn‖TP-Se battery also delivers a remarkable rate performance. The system is attractive due to its high discharge voltage, which is higher than ever reported for organic cathodes of zinc batteries.