Evaluation of LiNiO2 with minimal cation mixing as a cathode for Li-ion batteries

Abstract

The electric vehicle (EV) market has grown tremendously in recent years, and is driving the development of lithium-ion batteries (LIBs) for energy storage. To meet the demand for high-energy–density and low-cost LIBs, Co-free and Ni-rich cathodes (e.g., LiNiO2; LNO) and Si anodes are being investigated. However, drawbacks of LNO, such as cation mixing, processing challenges, and safety risks significantly limit its commercialization. Increasing the oxygen partial pressure (pO2) during calcination of LNO has been shown to maintain its structural order and electrochemical performance. However, the mechanism by this observation is not well understood. In this research, three pO2 conditions were applied during the calcination of LNO cathodes. The calcination pO2 affects the sub-surface of LNO rather than the bulk region. Synchrotron spectroscopy and in-situ pressure analysis confirmed that Ni2+ and excess Li are present on the sub-surface of the LNO processed at the lowest pO2. Increasing the pO2 decreases the off-stoichiometry of LNO by providing additional oxygen to compensate for oxygen loss, especially at the sub-surface. A detailed mechanism by which the calcination pO2 affects LNO is proposed. An LIB with the LNO cathode calcined at the highest pO2 had a high initial capacity of 239.8 mA h g−1 (93.4 %), excellent fast charging cycle retention of half-cell and full cell at 55 °C, little gas evolution during cycling, and almost no weight change during storage in air. This calcining strategy prevents the cation mixing limitation of LNO, taking it one step closer to future EV application.