Aluminium oxide (Al2O3)-modified LiNi0.5Mn1.5O4 (LNMO) thin-film electrodes were prepared by pulsed laser deposition and effects of surface modification on interfacial reactions of LNMO were studied. The modification by Al2O3 was carried out successively after the deposition of LNMO thin-film. Field-emission Scanning Electron Microscope results show that Al2O3 disperses uniformly in nano-scale on the film electrodes. Charge/discharge behavior of the batteries under a high cutoff voltage of 4.9V vs. Li is highly improved by using Al2O3 modification, especially at elevated temperature. The electrochemical properties of LNMO thin-film electrodes are also affected by the thickness of coating. It is found that 20nm thick Al2O3 coating layer improves thermal stability most obviously among them. At 55°C, 84.1% of its initial capacity at 1C-rate can be retained after 100 cycles, and as the rate increases from 0.2 to 10C the reversible capacity can still maintain 80.7mAhg−1, which are greatly improved compared to pristine, 6 and 40nm thick Al2O3 modified samples.