Abstract: The lightweight development of portable electronic devices and the industrialization of new-energy vehicles are driving explosive growth in the demand for high-energy-density lithium-ion batteries (LIBs). Against this backdrop, Ni-rich layered oxide and Lithium-rich layered oxides (LLOs) cathode materials have attracted intensive interest because of their high capacity, high energy density, and low cost. This review first clarifies the fundamental origins of capacity in Ni-rich layered oxide cathode and LLO cathodes. The former derive their capacity primarily from transition-metal cation redox (MCR), whereas the latter exploit the coupled contributions of MCR and oxygen anionic redox (OAR). Activating lattice oxygen in layered oxides at high states of delithiation to trigger OAR and provide additional capacity has become a key route to overcome the energy-density ceiling of conventional cathodes. We then examine the core challenges facing Ni-rich layered oxide cathode and LLO cathodes from the perspective of atomic-scale microstructural evolution. In particular, to address crystal-structure degradation and poorly controlled OAR in high-specific-energy cathodes, emerging approaches based on composite-structure construction inside/outside grains and regulation of LiMn₆ hexatomic-ring with π-bond ring are discussed. These strategies enable substantial improvements in overall electrochemical performance and provide mechanistic guidance for the design and development of next-generation high-specific-energy cathode materials.

Key words: Lithium-ion battery, High-energy density, Lithium-rich Mn-based layered cathode material, LiMn₆ hexatomic-ring, π-bond ring, Modification strategy