Lithium ion conducting ionic liquids as electrolytes for lithium rechargeable batteries

I&EC 260

Hiroyuki Tokuda, htokuda@ynu.ac.jp, Hyunjoo Lee, Hitoshi Shobukawa, Masato Watanabe, and Masayoshi Watanabe. Department of Chemistry and Biotechnology, Yokohama National University and CREST-JST, 79-5 Tokiwadai, Hodogaya-ku, Yokohama, 240-8501, Japan
If task-oriented property, lithium-ion conductivity in this case, can be molecularly designed into ionic liquids, the scope and utility of the ionic liquids will expand to lithium rechargeable batteries. However, conventional lithium salts have relatively high melting points, mainly due to the strong electrostatic interaction. We designed and prepared lithium salts of borates having electron-withdrawing groups, to reduce the anionic basicity, as well as lithium-coordinating ether ligands, to dissociate the lithium cations from the anionic center. The obtained lithium salts were clear and colorless liquids at room temperature. The lithium ionic liquids had self-dissociation ability and conducted lithium ion even in the absence of organic solvents. Lithium secondary batteries using a lithium ionic liquid as the electrolyte and LiFePO4 as the cathode showed coulombic efficiency close to 100 %, and furthermore, discharge capacity after 80th cycle was kept at 90 %, compared with that of the first cycle.