Role of Ordered Ni Atoms in Li Layers for Li‐Rich Layered Cathode Materials

Abstract

Li‐rich layered oxide materials are promising candidates for high‐energy Li‐ion batteries. They show high capacities of over 200 mAh g−1 with the additional occupation of Li in their transition metal layers; however, the poor cycle performance induced by an irreversible phase transition limits their use in practical applications. In recent work, an atomic‐scale modified surface, in which Ni is ordered at 2c sites in the Li layers, significantly improves the performance in terms of reversible capacity and cycling stability. The role of the incorporated Ni on this performance, however, is not yet clearly understood. Here, the effects of the ordered Ni on Li battery performance are presented, based on first‐principles calculations and experimental observations. The Ni substitution suppresses the oxygen loss by moderating the oxidation of oxygen ions during the delithiation process and forms bonds with adjacent oxygen after the first deintercalation of Li ions. These NiO bonds contribute to the formation of a solid surface, resulting in the improved cycling stability. Moreover, the multivalent Ni suppresses Mn migration to the Li‐sites that causes the undesired phase transition. These findings from theoretical calculations and experimental observations provide insights to enhance the electrochemical performance of Li‐rich layered oxides.

Doping Li-rich cathode material Li2MnO3 : Interplay between lattice site preference, electronic structure, and delithiation mechanism

“…Our results are thus in contrast to those reported by other research groups, often obtained in DFT+U calculations, according to which partially delithiated (and even some fully lithiated) Li 2 MnO 3 -based materials show metallic behavior. [20][21][22] Like in the case of undoped Li 2 MnO 3 discussed earlier (Sec. II), experiments should be performed to confirm the nature of bulk electronic conduction.…”

Suppressing Surface Lattice Oxygen Release of Li‐Rich Cathode Materials via Heterostructured Spinel Li4Mn5O12 Coating

“…The coated material maintains layered structure combing rhombohedral symmetry with an R m space group and monoclinic symmetry of the Li/Mn ordering superlattice within 20–25°, same as the pristine Li‐rich material. Related lattice parameters based on high‐symmetric R m space group are listed in Tables S2 and S3 (Supporting Information), respectively . The lattice parameter c expands upon the treatment, which is in coincidence with lithium content reduction revealed by ICP results and the binding energy of nickel.…”

Synchronous Tailoring Surface Structure and Chemical Composition of Li‐Rich–Layered Oxide for High‐Energy Lithium‐Ion Batteries

“…Beyond that, the dynamic behavior of chemical composition and their interaction play crucial role in battery performance . For the layered LiMO 2 (M = Mn, Ni, Co, etc) component, Ni provides a high‐specific capacity but poor cyclic stability because of the unstable Ni 4+ ion in the high cut‐off voltage when it directly contacts with electrolyte .…”