Fabrication of LiNi0.5Mn1.5O4 thin film cathode by PVP sol–gel process and its application of all-solid-state lithium ion batteries using Li1 + xAlxTi2 − x(PO4)3 solid electrolyte

LiNi0.5Mn1.5O4 thin film on Au and LATP substrates was fabricated by the PVP sol–gel method. The LiNi0.5Mn1.5O4 thin film prepared on Au showed intrinsic electrochemical redox reaction at 4.7V vs. Li/Li+. The thin film exhibited an excellent electrochemical performance. The discharge capacity at a rate of 1 C was 145 mA h g− 1, which was 98% of theoretical capacity (148 mA h g− 1). The thin film kept high capacity 125 mA h g− 1, even at 10 C. In order to construct all-solid-state battery, LiNi0.5Mn1.5O4 thin film electrodes were prepared on LATP electrolytes at 600, 700, and 800 °C. The thin film prepared on LATP showed a reversible current response, indicating that the thin film on LATP worked as the cathode. However, the observed current response was quite small due to impurities originated from the reaction between the thin film and LATP during heat treatment. The amount of impurity phase was increased with increasing heat treatment temperature. In order to improve the electrochemical properties of the interface between LiNi0.5Mn1.5O4 and LATP electrolytes, the optimization of preparation process such as fabrication of a buffer layer, which has non-reactive nature with both LiNi0.5Mn1.5O4 and LATP, is required.