Tailoring Oxygen Redox Activity and Accelerating Li⁺ Diffusion via Ti Substitution Within Li-O-Vacancy Configurations

Layered oxide cathode with a Li-O-vacancy configuration offers high capacity by leveraging additional oxygen redox reactions. However, it faces severe challenges of sluggish kinetics of oxygen redox reactions and lattice oxygen loss, resulting in slow Li⁺ diffusion and rapid electrochemical degradation. Herein, Ti is introduced as electrochemical inactive element into Li-O-vacancy configuration to form Mn/vacancy/Ti arrangement within transition metal layers of layered oxide, achieving a marked increase in average output voltage at high current density compared with Ti-free counterpart. Not only voltage hysteresis between charge and discharge processes can be significantly reduced, but rate capability can be heightened in Li_4/7[□_1/7Ti_1/7Mn_5/7]O₂ by means of retrained over-potential and improved Li⁺ diffusivity. Furthermore, theoretical calculations suggest that these improvements stem from Ti substitution, which elongates the Li─O bond and lowers the Li⁺ migration energy barrier. Besides, in situ differential electrochemical mass spectrometry and soft X-ray absorption spectroscopy reveal the modified Li-O-vacancy configuration enables reversible anionic and cationic redox behaviors during cycling. These findings provide a promising strategy for tailoring oxygen redox activity and accelerating Li⁺ diffusion kinetics in layered cathode materials with oxygen redox chemistry.