Stabilized Co3+/Co4+ Redox Pair in In Situ Produced CoSe2−x-Derived Cobalt Oxides for Alkaline Zn Batteries with 10 000-Cycle Lifespan and 1.9-V Voltage Plateau

Abstract

In aqueous alkaline Zn batteries (AZBs), the Co³⁺/Co⁴⁺ redox pair offers a higher voltage plateau than its Co²⁺/Co³⁺ counterpart. However, related studies are scarce, due to two challenges: the Co³⁺/Co⁴⁺ redox pair is more difficult to activate than Co²⁺/Co³⁺; once activated, the Co³⁺/Co⁴⁺ redox pair is unstable, owing to the rapid reduction of surplus Co³⁺ to Co²⁺. Herein, CoSe<inf>2−</inf><inf>x</inf> is employed as a cathode material in AZBs. Electrochemical analysis recognizes the principal contributions of the Co³⁺/Co⁴⁺ redox pair to the capacity and voltage plateau. Mechanistic studies reveal that CoSe<inf>2−</inf><inf>x</inf> initially undergoes a phase transformation to derived Co<inf>x</inf>O<inf>y</inf>Se<inf>z</inf>, which has not been observed in other Zn//cobalt oxide batteries. The Se doping effect is conducive to sustaining abundant and stable Co³⁺ species in Co<inf>x</inf>O<inf>y</inf>Se<inf>z</inf>. 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.