Interdiffusion of Cations from Metal Oxide Surface Coatings into LiCoO₂ During Sintering

Surface coatings on positive electrode materials can improve their electrochemical performance in lithium ion batteries, especially at high operating voltages. Cations in the surface coating can diffuse into the positive electrode material during sintering steps after coating. A simple “two-pellet” method was used to measure the concentration profiles of M = Al 3+, Mg 2+ ions from the pure MO x coating layer to the pure LiCoO 2 matrix after heat treatment at various temperatures using energy dispersive spectroscopy. The interdiffusion coefficients between M atoms and Co increase with heating temperature. Accordingly, the diffusion distances of M and Co between the MO x and the LiCoO 2 are affected by the sintering temperature and time. The activation barrier for diffusion was determined using the Arrhenius equation to be about 88 kJ/mol for the Al 3+ /Co 3+ couple and about 100 kJ/mol for the Mg 2+ /Co 3+ couple. The measured and fitting diffusion constants were used to simulate the diffusion Al 3+ in a 100 nm Al 2 O 3 coating layer on spherical LiCoO 2 particles during heat treatment. These results will be very helpful to guide the design of surface-modified positive electrode materials.