Quaternary ammonium room-temperature ionic liquid including an oxygen atom in side chain/lithium salt binary electrolytes: ionic conductivity and 1H, 7Li, and 19F NMR studies on diffusion coefficients and local motions

A room-temperature ionic liquid (RTIL) of a quaternary ammonium cation having an ether chain, N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoromethylsulfonyl)amide (DEME-TFSA), is a candidate for use as an electrolyte of lithium secondary batteries. In this study, the electrochemical ionic conductivity, sigma, of the neat DEME-TFSA and DEME-TFSA-Li doped with five different concentrations of lithium salt (LiTFSA) was measured and correlated with NMR measurements of the diffusion coefficients D and the spin-lattice relaxation times T1 of the individual components DEME (1H), TFSA (19F), and lithium ion (7Li). The ion conduction of charged ions can be activated with less thermal energy than ion diffusion which contains a contribution from paired ions in DEME-TFSA. In the doped DEME-TFSA-Li samples, the sigma and D values decreased with increasing salt concentration, and within the same sample generally DLi