Microscopic study of Ni-rich cathode formation from ALD multilayered thin films

Abstract

Temperature conditions are significant for the crystal structure formation of prospective cathode materials, determining their further performance and cycle life. The paper presents the results of a detailed analysis of the multilayer thin films before and after heat treatment. The investigated multilayer structures consist of a two-layer system of an amorphous nickel-doped Li-O layer and a NiO·CoO layer obtained by atomic-layer deposition on Si substrate. It was shown that annealing at 800 °C for 5 min is sufficient to form a crystalline film with energy favorable spherical-like Li-Ni-Co-O structures on the surface with a size of 50–150 nm. Chemical mapping after heat treatment using EDX showed the formation of Ni-rich (spherical-like structures) and Co-O intermediate layers. The electron energy loss spectroscopy results confirm the presence of Li in the top Ni-rich layer and are embedded in its crystalline structure. X-ray and electron diffraction showed a polycrystalline cathode structure of lithium-containing nickel and cobalt oxides.