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 Li 6 CoO 4 (Li 5.7 Co 0.7 Fe 0.3 O 4 ) 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 Li 5.7 Co 0.7 Fe 0.3 O 4 . 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 Li 5.7 Co 0.7 Fe 0.3 O 4 at the end of the charge. Consequently, the delithiated Li x Co 0.7 Fe 0.3 O 4 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.