Comparative study of lithium secondary batteries using nonvolatile safety electrolytes

The physical properties and electrochemical performances were systematically compared among a quaternary ammonium cation-based room-temperature ionic liquid electrolyte (ILE), a solid polymer electrolyte (SPE), and a conventional organic liquid electrolyte (OLE). The ionic conductivity, an interface impedance at the Li/electrolyte, and the activation energy at the interface were in the order of OLE > ILE > SPE. Cells using ILE and SPE exhibited sufficiently high discharge capacities of approximately 160 mAh g(-1) at the 100th cycle using LiFePO4 cathode. The required operation temperatures at a rate of 1C discharge, for which the discharge capacity at 1C was >90% of that obtained at C/8, were 363 K using SPE and 333 K using ILE. (C) 2007 The Electrochemical Society.