The limited specific capacity of cathode materials is one of the main issues for further enhancement of the energy density of the rechargeable lithium ion batteries. Lithium-rich layered oxides are considered one of the most promising cathode materials because their specific capacities often exceed 200 mAh g^-1 due to the additional lithium occupation in the transition metal layers [1]. However, this lithium arrangement, in turn, triggers cation mixing with the transition metals, driving a phase transition of the overall crystal framework to spinel and/or rocksalt structures during cycling and thereby causing a decrease in the operation voltage and specific capacity [2]. Surface modification has been one of the primary remedies because the given phase transition is typically initiated from the surface of the particle and well-designed surface structures can suppress this transition process from the initial step. In this study, we report an artificially designed high performance surface structure (Li₂MnO₃) bearing a consistent lithium-rich layered framework with the host, in which nickel is regularly arranged between the transition metal layers. X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), scanning transmission electron microscopy (STEM), and electrochemical impedance spectroscopy (EIS) characterizations reveal that the prepared surface structure effectively suppresses unwanted phase transitions, leading to substantially improved cycling and rate performance. The structure and electrochemical properties of the surface-modified lithium-rich layered oxide electrode will be discussed, along with a detailed reaction mechanism.

[1]  C. S. Johnson et al., Electrochem. Commun. 6, 1085 (2004).

[2]  K. G. Gallagher et al., Electrochem. Commun. 33, 96 (2013).