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

Abstract

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 (Pyr₁₄TFSI), N-butyl-N-methylpyrrolidinium bis(fluoro-sulfonyl)imide (Pyr₁₄FSI), N-methoxy-ethyl-N-methylpyrrolidinium bis(trifluoromethane-sulfonyl)imide (Pyr_12O1TFSI) 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 LiFePO₄ polyanionic cathode, show remarkable performance. In particular, relevant efficiency and rate-capability are observed for the Py₁₄FSI–LiTFSI electrolyte, which is further characterized for application in a lithium-ion battery composed of the alloying Sn–C nanocomposite anode and LiFePO₄ 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.