Electrochemical properties of LiMn0.4Fe0.6PO4 with polyimide-based gel polymer electrolyte for high safety and improvement of rate capability

The electrochemical performance of LiMn0.4Fe0.6PO4, prepared by modified mechanical activation, as the cathode active material for lithium batteries was tested with an ionic liquid-based electrolyte using an electrospun polyimide matrix. The ionic liquid electrolyte of 0.5 M lithium bis(trifluoromethanesulfonylimide) (LiTFSI) in 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonylimide) (BMImTFSI) was incorporated in an electrospun polyimide (PI) film to prepare the ionic liquid-based polymer electrolyte (ILPE). This PI-based ILPE exhibited good mechanical strength and high thermal stability. Impedance spectroscopy was applied to investigate the electrolyte/electrode resistance over time. The impedance resistance of a Li/ILPE/Li cell was found to increase over time to 7 days, decreasing thereafter. Impedance experiments further indicated good cycling stability for the cell when tested at room temperature. The cell based on Li/ILPE/LiMn0.4Fe0.6PO4 exhibited an initial discharge capacity of 163.6 mAh g−1 at 0.1 C-rate at room temperature. Finally, a high capacity and good cycling performance could be obtained even using the high current density of 2C.