Suppression of voltage depression in Li-rich layered oxide by introducing GaO4 structural units in the Li₂MnO₃-like nano-domain

Highlights: • To suppress the voltage depression, Ga ions were doped into the host lattice of Li-rich layered oxide using site-specific doping process. • Results of TEM and EXAFS spectroscopy revealed that the Ga ions were predominantly located at tetrahedral site in Li layer of Li₂MnO₃-like component. • The modified Li-rich layered oxide showed greatly reduced voltage depression due to increased structural stability of Li₂MnO₃-like component. • First principal calculations and Ex-situ XRD analyses imply that the formation of GaO₄ structural unit increased activation barrier for cation migration into Li layer. Li-rich layered oxides show high reversible capacities (≥250 mA h/g) in rechargeable lithium-ion batteries. However, their energy densities are considerably reduced upon cycling due to a voltage depression originated from the layered-to-spinel phase transition. In this study, the influence of site-specific Ga-doping on the electrochemical properties of Li-rich layered oxide is investigated. A powder of Li-rich layered oxide is treated in acid, and then annealed with a Ga source at low temperature (300 °C) to insert Ga ions into the powder. Transmission electron microscopy and extended X-ray absorption fine structure analyses indicate that the Ga ions are predominantly doped into the tetrahedral sites of Li₂MnO₃-like nano-domains in Li-rich layered oxide. Cyclability tests with 18650 full cells clearly reveal that the voltage depression is suppressed by the treatment. Ex-situ X-ray diffraction and first principles calculation results imply that the formation of tetrahedral GaO₄ unit in the Li₂MnO₃-like domain improves the structural stability of Li-rich layered oxide upon cycling.