Improved electrochemical properties of LiNiCoMnO cathode material via Li-reactive coating with metal phosphates.

Ni-rich layered oxides are promising cathode materials due to their high capacities. However, their synthesis process retains a large amount of Li residue on the surface, which is a main source of gas generation during operation of the battery. In this study, combined with simulation and experiment, we propose the optimal metal phosphate coating materials for removing residual Li from the surface of the Ni-rich layered oxide cathode material LiNiCoMnO. First-principles-based screening process for 16 metal phosphates is performed to identify an ideal coating material that is highly reactive to LiO. By constructing the phase diagram, we obtain the equilibrium phases from the reaction of coating materials and LiO, based on a database using a DFT hybrid functional. Experimental verification for this approach is accomplished with Mn(PO), Co(PO), Fe(PO), and TiPO. The Li-removing capabilities of these materials are comparable to the calculated results. In addition, electrochemical performances up to 50 charge/discharge cycles show that Mn-, Co-, Fe-phosphate materials are superior to an uncoated sample in terms of preventing capacity fading behavior, while TiPO shows poor initial capacity and rapid reduction of capacity during cycling. Finally, Li-containing equilibrium phases examined from XRD analysis are in agreement with the simulation results.