Effect of surface Li3PO4 coating on LiNi0.5Mn1.5O4 epitaxial thin film electrodes synthesized by pulsed laser deposition

The effect of Li3PO4 coating was investigated for LiNi0.5Mn1.5O4 epitaxial thin film electrodes synthesized on SrTiO3 substrates by pulsed laser deposition (PLD). Amorphous Li3PO4 with a thickness of 1-4 nm was coated at room temperature onto 30 nm thick epitaxial LiNi0.5Mn1.5O4 thin films with (111), (110) and (100) lattice orientations. Electrodes with the surface coating exhibit high charge-discharge capacities and small capacity degradation during cycling experiments in the high voltage region. X-ray absorption near edge structure (XANES) and hard X-ray photoelectron spectroscopy (HAXPES) analyses indicate a higher manganese valence for the electrode surface of the Li3PO4 stacked LiNi0.5Mn1.5O4 film than that for the surface of a pristine LiNi0.5Mn1.5O4 film. Thus, surface coating affects the manganese valence near the electrode surface and improves the cycling characteristics.