Surface reinforcement doping to suppress oxygen release of Li-rich layered oxides

Abstract Li-rich layered oxides can deliver ultrahigh capacities which stem from a blend of cationic redox and mostly lattice oxygen redox. However, the oxygen redox reaction often leads to structure transition and oxygen release from the material surface. Herein, the surface doping of B is conducted via a molten salt method, which creates a thin reinforcement layer containing stable B–O bonds. X-ray photoelectron spectroscopy reveals that the doping of B only acts on the material surface and cannot inhibit oxygen redox in the bulk. Differential electrochemical mass spectroscopy measurement demonstrates that the surface protective layer effectively reduces the oxygen release of LLOs. A combination of X-ray diffraction and transmission electron microscope analyses confirm the enhanced structural stability. As a consequence, the target material displays a high reversible capacity of 275 mAh g−1 at 0.1C and a suppressed voltage decay rate of 2.5 mV per cycle during the first 80 cycles (at 0.2C, 2.0–4.8V). The findings highlight the essential role of stable surface oxygen framework in cycling stability, and demonstrate the effectiveness of surface reinforcement doping in reducing oxygen release.