Balancing the structural order–redox chemistry via lithium content for stable layered oxide cathodes

The electrochemical performance of layered transition-metal oxides is highly sensitive to lithium content, yet the underlying structural and redox mechanisms remain elusive. Here we systematically investigated this relationship using a series of Li$_{1+x}$[Ni$_{0.5}$Mn$_{0.5}$]$_{1−x}$O$_2$ cathodes with tunable lithium content (x = 0, 0.05, 0.10, 0.15, 0.20). Increasing lithium content concertedly reduces lattice parameters, suppresses cation mixing, promotes the formation of honeycomb superstructure, and drives the evolution of superstructure units from LiMn$_6$ to LiNiMn$_5$. In parallel, the surface atomic structure evolves from fully disordered to partially disordered and ultimately to an ordered layered arrangement. Despite these structural improvements, higher lithium content is associated with a marked increase in irreversible oxygen redox activity, as revealed by combined spectroscopic and electrochemical analyses. Together, these findings establish lithium content as a key parameter governing the balance between structural order and redox reversibility. By optimizing this trade-off, we demonstrate a high-performance Li$_{1.1}$Ni$_{0.45}$Mn$_{0.45}$O$_2$ cathode that delivers a specific capacity of 228.0 mAh g$^{−1}$ with 90.4% capacity retention after 100 cycles. ... mehrOur findings provide valuable insights into the chemical composition design of high-energy-density, layered cathodes.