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

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 (p(O2)) 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 p(O2) conditions were applied during the calcination of LNO cathodes. The calcination p(O2) 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 p(O2). Increasing the p(O2) 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 p(O2) affects LNO is proposed. An LIB with the LNO cathode calcined at the highest p(O2) 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 degrees 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.

Automated summary

The rapid growth of the electric vehicle market has driven the development of lithium-ion batteries. Researchers are investigating Co-free and Ni-rich cathodes, such as LiNiO2, and Si anodes to meet the demand for high-energy-density and low-cost batteries. However, challenges with LiNiO2, such as cation mixing and safety risks, hinder its commercialization. Increasing the oxygen partial pressure during the calcination process of LiNiO2 has been found to improve its structural and electrochemical performance. This study proposes a mechanism by which the calcination oxygen partial pressure affects LiNiO2 and demonstrates that this strategy can enhance the performance of lithium-ion batteries.