Temperature-dependence of calcination processes of Ni-rich layered oxides

Abstract

High-Ni layered lithium transition metal oxides, LiNi1−x−yMnxCoyO2 (1-x-y≥0.7), show great promise for application in next-generation lithium ion batteries because of their high energy density, low cost, and superior electrochemical properties. However, preparation of stoichiometric LiNi1−x−yMnxCoyO2 oxides with highly ordered layered structure is challenging, largely due to the Li/O loss during high-temperature calcinations. Thus, understanding the reaction mechanism is crucial for calcination design. Herein, X−ray diffraction in combination with nuclear magnetic resonance, are conducted to track the structural evolution in preparing LiNi1−x−yMnxCoyO2 below 500 °C. Our results reveal that a lithiated intermediate, Ni0.7Mn0.15Co0.15(OHy)2Lix, between the precursory transition metal hydroxide and the destination layered LiNi1−x−yMnxCoyO2 phase is generated, bypassing the formation of transition metal oxide phases. The unique reaction enables the calcination optimization at low temperature. Accordingly, high-ordered LiNi0.7Mn0.15Co0.15O2 is achieved via a developed two-step calcination at 500 °C, and it exhibits an excellent electrochemical performance, especially the high initial columbic efficiency.