Liquid and Polymer Gel Electrolytes for Lithium Batteries Composed of Room-Temperature Molten Salt Doped by Lithium Salt

The lithium ion binary room-temperature molten salt (i.e., ionic liquid), was prepared by mixing 1-ethyl-3-methylimidazolium tetrafluoroborate with The ionic conductivity of was 7.4 mS cm−1 at 20°C and lower than that of A solidified named was prepared by in situ polymerization of poly(ethyleneglycol) diacrylate with The ionic conductivity of the homogeneous transparent membrane obtained was smaller than that of The thermal decomposition temperatures of these "ionic media" measured by thermogravimetry-differential thermal analysis showed that and have high thermal stability around 300°C. The cathodic limit of was ca. 1.1 V vs. measured by linear sweep voltammetry. To test the possibility of use of these ionic media for lithium-ion batteries, demonstration cells of or were assembled. The capacity retention after 50 cycles was 93.8% of the initial capacity in the cell. Discharge potential profile of the cell showed decline probably due to the concentration polarization in the gelled electrolyte. Liquid and gelled electrolytes composed of "lithium ion coexisting room-temperature molten salt" are shown to function as nonflammable electrolytes in the lithium-ion batteries. © 2003 The Electrochemical Society. All rights reserved.