Reduced Intercalation Energy Barrier by Rich Structural Water in Spinel ZnMn2O4 for High-Rate Zinc-Ion Batteries

Aqueous zinc-ion batteries are considered promising next-generation systems for large-scale energy storage due to low cost, environmental friendliness, and high reversibility of the Zn anode. However, the interfacial charge-transfer resistance for the insertion of divalent Zn2+ into cathode materials is normally high, which limits the kinetics of Zn2+ transfer at the cathode/ electrolyte interface. This study reveals the presence of rich structural water in spinel ZnMn2O4 (ZnMn2O4 center dot 0.94H(2)O, denoted as ZMO), synthesized by a scalable and low-temperature process, significantly overcoming the great interfacial charge-transfer resistance. ZMO exhibits excellent electrochemical performance toward Zn storage, that is, high capacity (230 and 101 mA h g(-1) at 0.5 and 8 A g(-1)), high specific energy/specific power (329 W h kg-1/706 W kg(-1) and 134 W h kg-1/11,160 W kg(-1)), and stable cycle retention (75% after 2000 cycles at 4 A g(-1)) can be achieved. On the contrary, the controlled sample ZMO-450 with deficient structural water, prepared by post-heat treatment of ZMO at 450 degrees C, demonstrates limited discharge capacity (45 and 15 mA h g(-1) at 0.5 and 8 A g(-1)). As examined by electrochemical impedance spectroscopy, rich structural water in ZMO effectively reduces the activation energy barrier upon Zn2+ insertion, rendering fast interfacial kinetics for Zn storage. Benefiting from rich structural water in ZMO, the involvement of Zn2+ during the charge/discharge process exhibits good reversibility, as characterized by X-ray diffraction and X-ray photoelectron spectroscopy.

Automated summary

This study demonstrates that spinel ZnMn2O4 with rich structural water significantly improves the interfacial charge-transfer resistance, leading to excellent electrochemical performance for Zn storage. The involvement of Zn2+ during the charge/discharge process exhibits good reversibility, indicating the potential for practical applications in aqueous zinc-ion batteries.