Synergistic Na doping and spinel formation for ultrathin cathode–electrolyte interphase films enabling stable lithium-rich manganese cathodes

Lithium-rich manganese-based layered oxides (LR) are promising cathodes for high-energy-density lithium-ion batteries, but their practical application is hindered by severe voltage decay, capacity fading, and interfacial instability caused by oxygen release and sluggish Li + diffusion. Here, we report a rapid surface engineering strategy that integrates Na + doping and spinel phase formation to construct ultra-thin and uniform cathode–electrolyte interphase (CEI) films. Density functional theory calculations reveal that Na + incorporation stabilizes lattice oxygen by forming strong Na O bonds and reduces the Li + diffusion barrier by 0.22 eV. Experimentally, Na + doping expands the Li layer spacing and generates oxygen vacancies, which further facilitate Li + transport. Consequently, the modified cathode exhibits enhanced interfacial stability and suppressed oxygen evolution, leading to a high discharge capacity of 191 mAh·g-1 with 83.6% retention after 300 cycles at 1C, and 107.8 mAh·g −1 even at 10C. This scalable and cost-effective strategy offers new insights into interfacial design for the commercialization of lithium-rich cathodes.