Regulating Li Extraction in Transition Metal Layer for High-Performance Li-Excess Layered Oxide Cathode with...

In lithium-excess layered oxide cathodes, the extra lithium within transition metal (TM) layers (i.e., Li_[TM]) can trigger anionic redox to provide additional capacity. However, substantial extraction of Li_[TM] may induce irreversible/detrimental local structural rearrangements. The conventional edge-shared connecting configuration between LiO₆ and TMO₆ octahedra facilitates interlayer migration of Li_[TM]. In contrast, the face-shared configuration has the potential to limit the mobility of Li_[TM], but this metastable configuration cannot be harvested via traditional calcination. Herein, during Na-to-Li ion exchange in P2 phase Na_0.66[Li_0.22TM_0.78]O₂ precursor, we observe that the random gliding of TMO₂ layers yielding Li_0.66[Li_0.22TM_0.78]O₂ with O2/O6 intergrowth structure. Despite the random gliding, the functional face-shared configuration is successfully obtained and proven to effectively restrict interlayer migration of Li_[TM] during charging. Consequently, we observe the suppressed formation of aggregated vacancies and O-O dimers within the TM layers. Ultimately, our synthesized O2/O6 Li-excess demonstrates enhanced structural reversibility and improved capacity/voltage retention. This oxygen-stacking engineering provides a compelling strategy for developing cathodes with enhanced local structural reversibility.