Designing borate-based lithium ionic liquids with high lithium ionic conductivity

Electrolyte solutions for next-generation secondary batteries are required to have high ionic conductivity and Li + ion transport number. However, these are in a trade-off relationship. Here, we prepared lithium salts containing anion with solvation ability, LiB(OCH 2 CH 2 ) n OCH 3 ) 4 (LiB(G n ) 4 , n = 3 or 4) to control intermolecular interactions between Li + ion and solvent/anion. The thermal, transport, and electrochemical properties of LiB(G n ) 4 were investigated. The prepared LiB(G n ) 4 yields liquids at room temperature due to intermediate-length glyme chains and exhibits a similar thermal behavior as ionic liquids. The LiB(G n ) 4 shows higher partial ionic conductivity of Li + ion than that of the previous studies because the LiB(G n ) 4 has both a high ionic conductivity and high transference number at room temperature. The infrared spectra of LiB(G n ) 4 agree with the theoretical spectrum of solvate ion with glyme side chain coordinated to Li + ion, LiB(G n ) 4 exhibits high oxidative stability. The design of electrolyte solutions based on intermolecular interactions can be useful to develop materials for next-generation secondary batteries. • A new lithium ionic liquid consisting of the anion with solvate ability was investigated synthesized. • The prepared ionic liquid exhibits high partial ionic conductivity of Li + ion. • Li + ion conduction via ligand exchange occurs in the prepared ionic liquid. • The design of electrolyte based on intermolecular interactions can be useful to develop materials for batteries.