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

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 (Li_5.7Co_0.7Fe_0.3O₄) 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 Li_5.7Co_0.7Fe_0.3O₄. 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 Li_5.7Co_0.7Fe_0.3O₄ at the end of the charge. Consequently, the delithiated Li_xCo_0.7Fe_0.3O₄ 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.