Unconventional high-temperature cycling stability of O2-type Li0.75[Li0.25Mn0.75]O2 cathode

Lithium-rich manganese-based oxides are promising cathode materials for high-energy lithium-ion batteries but suffer from capacity deterioration due to oxygen release, irreversible structural changes, and detrimental secondary reactions—all of which are known to be exacerbated at elevated temperatures, leading to inferior high-temperature cycling performance. Here, we report the discovery of an unconventional temperature-dependent behavior in an O2-type ${\text{Li}}_{0.75}\left[{\text{Li}}_{0.25}{\text{Mn}}_{0.75}\right]O_2$ cathode, which exhibits significantly improved cycling stability at an elevated temperature (55°C) compared with room temperature (RT), delivering high capacities of up to 300 mAh g⁻¹. Combined structural and electrochemical analyses reveal that an in situ-formed ramsdellite-like surface layer, with tunnels oriented parallel to the crystallite surface, effectively protects the O-redox activity within the layered core but impedes the Li⁺ diffusion into and out of the particle at RT. However, Li⁺ diffusion through this protective surface layer is kinetically unlocked at elevated temperatures, resulting in improved capacity and cycling stability.