Anion Coordination Characteristics of Ion-pair Complexes in Highly Concentrated Aqueous Lithium Bis(trifluoromethane- sulfonyl)amide Electrolytes

Abstract

We report on the structures of Li-ion complexes in salt-concentrated aqueous electrolytes based on lithium bis(trifluoromethanesulfonyl)amide (LiTFSA), particularly focusing on the anion coordination behavior of the ion-pair complexes in the high concentration region cLi > 3.0 mol dm-3. Quantitative data analysis of the Raman spectra revealed the following. (1) Li ions do not coordinate with TFSA anions at lower cLi (<3.0 mol dm-3) to exist as ion pair-free ions. (2) In the concentrated region (cLi = 3.0-4.0 mol dm-3), the TFSA anions coordinate as monodentate ligands (mono-TFSA) with Li ions to form ion-pair complexes and coexist with free TFSA in the bulk. (3) Further increasing the cLi (4.0-5.2 mol dm-3) results in both monodentate and bidentate coordination (bi-TFSA) modes of TFSA anions to Li ions, yielding complicated ion-pair complexes in the first coordination sphere. The Walden plots, based on ionic conductivity and viscosity data, implied that the ion-conducting mechanism in the highly salt-concentrated region was considerably different from that in the dilute region (i.e., vehicle mechanism).

Influence of electrolyte structural evolution on battery applications: Cationic aggregation from dilute to high concentration

“…[ 62 ] (B) Raman spectra of aqueous electrolytes with different LiTFSI salt concentrations. [ 24 ] (C) Raman scattering factors (left) and the corresponding species distribution functions (right) as the function of the molar fraction of LiTFSA [ 72 ]…”

“…Moreover, the detailed solution structure evolution from dilute to concentrated electrolytes were presented in Figure 1C, in which the variation from free TFSI − to CIP TFSI − , and then to the bidentate TFSI − and/or the oligomer TFSI − . [ 72 ]…”

“…[62] (B) Raman spectra of aqueous electrolytes with different LiTFSI salt concentrations. [24] (C) Raman scattering factors (left) and the corresponding species distribution functions (right) as the function of the molar fraction of LiTFSA [72] corresponding to the decreased trend of solution viscosity and conductivity. Recently, Hwang et al [28] gave a detailed demonstration about the ion speciation and related content of 0.1-3 M LiPF 6 and LiBF 4 in PC solvent.…”

Correction: Local structure of a highly concentrated NaClO4 aqueous solution-type electrolyte for sodium ion batteries

“…Similar behavior was also reported in concentrated LiTFSA aq. solution 2 and LiFSA in dinitrile electrolytes. 3 The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.…”

Determining the Coordination Number of Li+ and Glyme or Poly(ethylene glycol) in Solution Using Attenuated Total Reflectance-Far Ultraviolet Spectroscopy

“…The ionic conductivity of the electrolytes is affected by the viscosity of the liquid, which is directly related to the liquid structure. [2][3][4] In the solution state, Li + cations and polyethers form complexes characterized by coordination bonds. The structure of these complexes, affected by features such as coordination number, is a critical factor governing the properties of the electrolytes and the lithium reagents.…”