In this work, we obtained improved electrochemical performance of LiNi0.5Mn1.5O4 cathode by using a monomer unit of conducting polymer, N-methylpyrrole (MPL), as an electrolyte additive. The effects of MPL on the performance of high voltage LiNi0.5Mn1.5O4 cathode were investigated via the combination of cycling test, cyclic voltammetry, electrochemical impedance spectroscopy and surface analysis. By incorporating 0.3wt% MPL into electrolyte, the capacity retention of Li/LiNi0.5Mn1.5O4 cell after 200 cycles is improved from 83.2% to 89.5% at room temperature (ca. 25°C) and from 59.1% to 87.4% at elevated temperature (55°C). Moreover, the discharge capacity of the cell with 0.3wt% MPL increase by 8% and 18% at 2C and 3C rates respectively. It is proposed that the electrochemical polymerization of MPL take place on the initial charge process and consequently create a thin, stable and conductive film on the LiNi0.5Mn1.5O4 surface. The collective effects of this cathode/electrolyte interphase (CEI) film stabilize the interface between cathode and electrolyte and alleviate the electrolyte decomposition during extended cycling, leading to improved performance of Li/LiNi0.5Mn1.5O4 cell.