Li/LiFePO4 batteries with room temperature ionic liquid as electrolyte

Room temperature ionic liquid (RTIL) was prepared on basis of N-methyl-N-butylpiperidinium bis(trifluoromethanesulfonyl)imide (PP14TFSI), which showed a wide electrochemical window (−0.1–5.2 V vs. Li+/Li) and is theoretically feasible as an electrolyte for batteries with metallic Li as anodes. The addition of vinylene carbonate (VC) improved the compatibility of PP14TFSI-based electrolyte towards lithium anodes and enhanced the formation of solid electrolyte interphase film to protect lithium anodes from corrosion. Accordingly, Li/LiFePO4 cells initially delivered a discharge capacity of about 127 mAh g−1 at a current density of 17 mA g−1 in the ionic liquid with the addition of VC and showed better cyclability than in the neat ionic liquid. Electrochemical impedance spectroscopy disclosed that the addition of VC enhanced Li-ion diffusion and depressed interfacial resistance significantly.