Exceptional long-life performance of lithium-ion batteries using ionic liquid-based electrolytes

Advanced ionic liquid-based electrolytes are herein characterized for application in high performance lithium-ion batteries. The electrolytes based on either N -butyl- N -methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (Pyr 14 TFSI), N -butyl- N -methylpyrrolidinium bis(fluoro-sulfonyl)imide (Pyr 14 FSI), N -methoxy-ethyl- N -methylpyrrolidinium bis(trifluoromethane-sulfonyl)imide (Pyr 12O1 TFSI) or N-N -diethyl- N -methyl- N -(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)imide (DEMETFSI) ionic liquids and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt are fully characterized in terms of ionic conductivity, viscosity, electrochemical properties and lithium-interphase stability. All IL-based electrolytes reveal suitable characteristics for application in batteries. Lithium half-cells, employing a LiFePO 4 polyanionic cathode, show remarkable performance. In particular, relevant efficiency and rate-capability are observed for the Py 14 FSI-LiTFSI electrolyte, which is further characterized for application in a lithium-ion battery composed of the alloying Sn-C nanocomposite anode and LiFePO 4 cathode. The IL-based full-cell delivers a maximum reversible capacity of about 160 mA h g −1 ( versus cathode weight) at a working voltage of about 3 V, corresponding to an estimated practical energy of about 160 W h kg −1 . The cell evidences outstanding electrochemical cycle life, i.e. , extended over 2000 cycles without signs of decay, and satisfactory rate capability. This performance together with the high safety provided by the IL-electrolyte, olivine-structure cathode and Li-alloying anode, makes this cell chemistry well suited for application in new-generation electric and electronic devices. A lithium ion battery using an ionic liquid electrolyte reveals enhanced safety and exceptionally long life, extended to thousands of cycles.