Preventing Interdiffusion during Synthesis of Ni-Rich Core–Shell Cathode Materials

Surface reactions between Ni-rich cathode materials and electrolytes limit the achievable specific capacity and lifetime in the high energy density Li-ion batteries based on these cathode materials. A core–shell approach, which contains a less reactive shell-phase on top of a high-capacity core-phase, can be used to reduce these surface reactions. However, interdiffusion of the elements in the core and shell phases can occur during calcination, which limits the choice of elements to be used in the shell phase and the temperature window of synthesis, and often increases the minimum shell thickness. Tungsten oxide (WO3) coating on the surface of precursors leads to the formation of LixWyOz secondary phases during the heat treatment with LiOH·H2O. These LixWyOz phases infuse into the grain boundaries and prevent interdiffusion between the core and shell phases. Tungsten-containing Ni-rich core–shell cathode materials with Mn- or Al-based shells show enhanced electrochemical performance because of reduced surface reactivity due to the core–shell microstructure and additional mechanical strength owing to the presence of LixWyOz phases in the grain boundaries.