Modulating Anion Redox Reactions and Structural Evolution Through Fe‐Substitution in Li₆CoO₄ Hyper‐Lithiated Sacrificial Cathodes

Abstract

Utilizing hyper‐lithiated materials can offer a variety of options for designing high‐energy lithium‐ion batteries. As sacrificial cathodes, they compensate for the initial loss of Li+ at the anode. During the first delithiation process, a Fe‐substituted Li6CoO4 (Li5.7Co0.7Fe0.3O4) supplies a large amount of Li+. Especially, the peroxide species formation and oxygen evolution are suppressed even though the charge compensation of oxygen is facilitated in Li5.7Co0.7Fe0.3O4. From a structural viewpoint, the anti‐fluorite structure changes to defective disordered phases during the Li+ extraction, and the proportion of the electrochemical‐inactive phase is more dominant in the case of Li5.7Co0.7Fe0.3O4 at the end of the charge. Consequently, the delithiated LixCo0.7Fe0.3O4 is deactivated in subsequent cycles, reducing unexpected electrochemical reactions after the Li+ provision as sacrificial cathodes. These findings provide a comprehensive understanding of the reaction mechanism of hyper‐lithiated materials and represent a significant step forward in developing high‐performance sacrificial cathodes.