From Detrimental to Functional: Regulating Residual Alkalis as an Interface Resource on Layer‐Structured Transition‐Metal Oxide Cathodes

Layered oxide cathode materials have garnered significant attention owing to their high specific capacity, facile synthesis and compositional tunability. Nevertheless, their synthesis process unavoidably leads to the presence of residual alkaline species, such as lithium hydroxide (LiOH), lithium carbonate (Li 2 CO 3 ), sodium hydroxide (NaOH) and sodium carbonate (Na 2 CO 3 ). These interfacial byproducts can subsequently induce moisture absorption, slurry degradation and interfacial side reactions, thereby impeding performance enhancement and large‐scale commercialization. This review systematically elucidates the formation mechanisms of residual alkalis in layered oxides with particularly emphasis on the influence of synthesis parameters and storage conditions. It further clarifies the specific roles of residual alkalis in constraining electrode performance and in conjunction with recent research advances, proposes potential mitigation strategies. Finally, the functional design strategies governed by residual alkali and the dual‐edged effects on various components of the battery system are discussed with the aim of further enhancing the electrochemical performance of layered oxide materials. Overall, this study systematically elucidates the formation mechanisms and regulation approaches of interfacial residual alkali, thereby providing important guidance for the development of high‐performance lithium‐/sodium‐ion batteries.