Stabilizing Layered Structure in Aqueous Electrolyte via O2‐Type Oxygen Stacking

Abstract Despite the high energy density of O3‐type layered cathode materials, the short cycle life in aqueous electrolyte hinders their practical applications in aqueous lithium‐ion batteries (ALIBs). In this work, it is demonstrated that the structural stability of layered LiCoO₂ in aqueous electrolyte can be remarkably improved by altering the oxygen stacking from O3 to O2. As compared to the O3‐type LiCoO₂, the O2‐type LiCoO₂ exhibits significantly improved cycle performance in neutral aqueous electrolyte. It is found that the structural degradation caused by electrophilic attack of proton can be effectively mitigated in O2‐type layered structure. With O2 stacking, CoO₆ octahedra in LiCoO₂ possess stronger CoO bonds while Co migration from Co layer to Li layer is strongly hampered, resulting in enhanced structural stability against proton attack and prolonged cycle life in aqueous electrolyte. The findings in this work reveal that regulating oxygen stacking sequence is an effective strategy to improve the structural stability of layered materials for ALIBs.