Effect of surface Li_3PO_4 coating on LiNi_(0.5)Mn_(1.5)O_4 epitaxial thin film electrodes synthesized by pulsed laser deposition

摘要

The effect of Li_3PO_4 coating was investigated for LiNi_(0.5)Mn_(1.5)O_4 epitaxial thin film electrodes synthesized on SrTiO_3 substrates by pulsed laser deposition (PLD). Amorphous Li_3PO_4 with a thickness of 1-4 nm was coated at room temperature onto 30 nm thick epitaxial LiNi_(0.5)Mn_(1.5)O_4 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 Li_3PO_4 stacked LiNi_(0.5)Mn_(1.5)O_4 film than that for the surface of a pristine LiNi_(0.5)Mn_(1.5)O_4 film. Thus, surface coating affects the manganese valence near the electrode surface and improves the cycling characteristics.