Stabilized Co<sup>3+</sup>/Co<sup>4+</sup> Redox Pair in In Situ Produced CoSe<sub>2−</sub><i><sub>x</sub></i>‐Derived Cobalt Oxides for Alkaline Zn Batteries with 10 000‐Cycle Lifespan and 1.9‐V Voltage Plateau
Yongchao Tang, Xuejin Li, Haiming Lv, Dong Xie, Wenlong Wang, Chunyi Zhi, Hongfei Li
Abstract
Abstract In aqueous alkaline Zn batteries (AZBs), the Co 3+ /Co 4+ redox pair offers a higher voltage plateau than its Co 2+ /Co 3+ counterpart. However, related studies are scarce, due to two challenges: the Co 3+ /Co 4+ redox pair is more difficult to activate than Co 2+ /Co 3+ ; once activated, the Co 3+ /Co 4+ redox pair is unstable, owing to the rapid reduction of surplus Co 3+ to Co 2+ . Herein, CoSe 2− x is employed as a cathode material in AZBs. Electrochemical analysis recognizes the principal contributions of the Co 3+ /Co 4+ redox pair to the capacity and voltage plateau. Mechanistic studies reveal that CoSe 2− x initially undergoes a phase transformation to derived Co x O y Se z , which has not been observed in other Zn//cobalt oxide batteries. The Se doping effect is conducive to sustaining abundant and stable Co 3+ species in Co x O y Se z . As a result, the battery achieves a 10 000‐cycle ultralong lifespan with 0.02% cycle −1 capacity decay, a 1.9‐V voltage plateau, and an immense areal specific capacity compared to its low‐valence oxide counterparts. When used in a quasi‐solid‐state electrolyte, as‐assembled AZB delivers 4200 cycles and excellent tailorability, a promising result for wearable applications. The presented effective strategy for obtaining long‐cyclability cathodes via a phase transformation‐induced heteroatom doping effect may promote high‐valence metal species mediation toward highly stable electrodes.