Interface modification in high voltage spinel lithium-ion battery by using N-methylpyrrole as an electrolyte additive

In this work, we obtained improved electrochemical performance of LiNi 0.5 Mn 1.5 O 4 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 LiNi 0.5 Mn 1.5 O 4 cathode were investigated via the combination of cycling test, cyclic voltammetry , electrochemical impedance spectroscopy and surface analysis . By incorporating 0.3   wt% MPL into electrolyte, the capacity retention of Li/LiNi 0.5 Mn 1.5 O 4 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 0.3   wt% 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 LiNi 0.5 Mn 1.5 O 4 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/LiNi 0.5 Mn 1.5 O 4 cell.