Balancing layered ordering and lattice oxygen stability for electrochemically stable high-nickel layered cathode for lithium-ion batteries

Abstract

Despite the high-capacity nature of high-nickel cathode materials, achieving their practical implementation is challenging due to the susceptibility of atomic arrangement to calcining conditions. Extensive studies have enlightened the correlation between layered ordering and calcining conditions; nevertheless, the alterations in the electronic structure of lattice oxygen remain obscure. In this study, by comparing cathode materials with varying degrees of layered ordering, achieved through adjustments in calcination temperature and lithium equivalent, it is shown that although layered ordering increases, it compromises the electronic structure, creating a labile lattice oxygen environment. Fine structural analysis reveals that a higher local Li/O ratio in highly ordered cathode subsequently alters the band structure by narrowing the band gap between Ni 3d and O 2p, which enhances transition metal-oxygen covalency, and reduces the oxygen vacancy formation energy, adversely affecting cyclability. In highly ordered cathode, the tendency of lattice oxygen to reside within a Li-enriched environment arises from the changes in the favorability of non-paired antisite defects contingent upon the calcination temperature and lithium equivalent. This research underscores the need to balance layered ordering and lattice oxygen stability, offering important insights for the future design of high-nickel cathodes.