Mixures of ionic liquid and organic carbonates as electrolyte with improved safety and electrochemical performance in Li-ion batteries

The worldwide demand for clean, low-fuel-consumming transport is promoting thedevelopment of safe, high energy and power electrochemical storage and conversion systems.Lithium-ion batteries (LIBs) are today considered the best technology for these applications,a fact also demonstrated by the great interest of hybrid (HEV) and electric vehicle (EV)manufactures for these batteries. However, conventional lithium-ion batteries combine highenergy materials with flammable organic solvents and, hence, can suffer premature failure ifsubjected to abusive conditions because of heat-evolving, spontaneous reactions which leadto fire and explosion. Safety now represents the main drawback holding up the lithium-iontechnology from wide application in HEVs. A very promising class of safe and greenelectrolytes is that based on ionic liquids (ILs), namely, low temperature molten salts whichhave important physical chemical properties like high boiling/decomposition points (evenover 400 ◦C), low melting points, thermal and electrochemical stability and appreciableconductivity above RT. This unique combination of favorable properties makes ILs veryappealing as safe electrolyte media in lithium-ion batteries, and IM14 PF6 formed by N-nbutyl-N-methyl-imidazolium cation [IM14+] and hexafluorophosphate anion [PF6-] with thelithium hexafluorophosphate as dissolved lithium salt is a good choice as an IL-basedelectrolyte because of the wide electrochemical stability window of this IL [1]. Its chemicalstructure is shown in Fig 1.