Solvation Structure Analysis of Lithium Ion in Concentrated Lithium Salt Solutions Using Raman Spectroscopy
K. Fujii, H. Fujino
BUNSEKI KAGAKU(分析化学), 2018, 67, 727-732.
DOI : 10.2116/bunsekikagaku.67.727

Abstract: Electrolyte solutions are one of the key liquid materials in the development of high-performance lithium-ion batteries (LIBs). Recently, a new concept, “superconcentrated electrolyte”, i.e., solvent-in-salt in liquid state, was proposed and widely investigated in terms of not only electrochemistry, but also physical chemistry and/or solution chemistry. In this work, we report on a structural study of lithium-ion complexes in highly salt-concentrated electrolytes, lithium bis(trifluoromethanesulfonyl)amide (LiTFSA) salt in N,N-dimethylpropionamide (DMPA), using Raman spectroscopy with the aid of density functional theory (DFT) calculations. In the range of the Li salt concentration, cLi = 0 – 3.2 mol dm−3, the individual solvation numbers of DMPA and TFSA species around Li ions [n(DMPA) and n(TFSA), respectively] were quantitatively determined and the relation between the Li ion complex structure and cLi was discussed at the molecular level.