Role of Residual Li and Oxygen Vacancies in Ni-rich Cathode Materials.

Residual Li and oxygen vacancies in Ni-rich cathode materials have a great influence on electrochemical performance, yet their role is still poorly understood. Herein, by simply adjusting the oxygen flow during the high-temperature sintering process, some Li2O can be carried into the exhaust gas and the contents of residual Li and oxygen vacancies in LiNi0.825Co0.115Mn0.06O2 cathodes can be accurately controlled. Residual Li reduces the surficial Li+ diffusion coefficient, thereby limiting the rate property of the cathode. Oxygen vacancies affect the oxygen release energy in the crystal, and the lowest oxygen release energy is found at an oxygen vacancy concentration of 8.35%, resulting in an unstable structure and thereby poor cycle performance. The Ni-rich cathode with low residual Li and oxygen vacancy contents exhibits superior capacity retention (89.55 and 77.66%) at 2C after 300 cycles between 2.7-4.3 and 2.7-4.5 V. These findings clarify the role of residual Li and oxygen vacancies in Ni-rich cathode materials and provide a simple way to obtain high-performance Ni-rich cathodes for high-energy-density Li-ion batteries.