Towards Ni-rich layered oxides cathodes with low Li/Ni intermixing by mild molten-salt ion exchange for lithium-ion batteries

Abstract

In the conventional synthesis of layered transition metal oxides, the high-temperature process not only causes lithium loss due to evaporation, but also facilitate the inevitable cation mixing of Li+ and Ni2+, resulting in severe shifts in their stoichiometric ratios and thus structure instability. Herein, we report a universal ion-exchange method to prepare Ni-rich layered oxide materials LiNi0.85Co0.06Mn0.09O2 (NCM85) with low Li/Ni intermixing at a low reaction temperature of 300 °C, where sodium-based layered oxides (NaNi0.85Co0.06Mn0.09O2) were used as precursors for ion exchange with Li+ ion in lithium molten salts. By studying the effects of ion-exchange time and additional heat treatment on the structure and performance of the layered oxide materials, we established the processing-structure-performance relationships for Ni-rich NCM85 materials. Moreover, we further demonstrated the universality of this ion-exchange method and processing-structure-performance relationships for other layered oxide materials including LiNi0. 5Co0.2Mn0.3O2 and LiNi0.5Mn0.5O2. We anticipate that such universal method of ion exchange and universal processing-structure-performance relationships can guide the rational design and synthesis of other layered oxide materials for lithium-ion batteries.