Lithium bis(fluorosulfonyl)imide (LiFSI) has been investigated as a conducting salt of liquid electrolytes for lithium-ion batteries. It shows high solubility in most polar solvents, and a concentration of 5 M (mol dm(-3)) is reached in dimethyl carbonate (DMC) despite its low dielectric constant. LiFSI shows a thermal stability up to 180 degrees C on the thermogravimetric test. Compared with the LiPF(6)/carbonate electrolytes, the LiFSI-based ones show higher ionic conductivities over a wide temperature range (-50 to 50 degrees C) and higher lithium-ion transference numbers (t(Li+)) of 0.5-0.6. The conductivities of the LiFSI/DMC electrolyte over the 0.1-5 M concentration range obey a modified Casteel-Amis equation. The temperature dependence of 1 M LiFSI/DMC/EMC (3:7, v/v) is governed by the Vogel-Tammann-Fulcher relationship. The Fourier transform infrared spectra of the LiFSI/DMC electrolytes at different concentrations are systematically investigated. DMC shows significant spectral variations upon adding LiFSI, indicating strong interaction of Li(+) cations with the solvent molecules. We also found that the compatibility with graphite anode and LiFePO(4) cathode in the LiFSI-based electrolyte is as good as that in the LiPF(6)-based one, though aluminum (Al) corrosion occurs above 4 V vs Li(+)/Li. LiFSI is a very good contender to replace the latter, with increased performances and safety. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3514705] All rights reserved.

https://iopscience.iop.org/article/10.1149/1.3514705/pdf

Transport and Electrochemical Properties and Spectral Features of Non-Aqueous Electrolytes Containing LiFSI in Linear Carbonate Solvents

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Electrolyte Formulations Based on Dinitrile Solvents for High Voltage Li-Ion Batteries

Solid polymer electrolytes are important materials in realizing safe and flexible energy storage devices The present study looks at correlation between solvation structure and the ion-conductive behavior of poly(ethylene carbonate) (PEC)/lithium bis(fluorosulfonyl)imide (LiFSI) electrolytes which have high Li transference number (t+) and show unusual salt-concentration dependence of conductivity From FT-IR and Raman spectroscopy, we determined that Li ions interact with carbonyl (C═O) groups and also with FSI ions, which can be referred to as contact ion pair or aggregate 7Li magic-angle-spinning NMR spectroscopy and density functional theory calculations for model species suggest that a loose coordination structure, in which Li ions interact with C═O groups and FSI ions with appropriate strength, allows the electrolytes to have both reasonable conductivity and high t+ with a flexible and transparent character A high salt dissociation rate is generally considered essential in SPEs, but the presence of

Correlation between Solvation Structure and Ion-Conductive Behavior of Concentrated Poly(ethylene carbonate)-Based Electrolytes

Poly(ethylene carbonate)-based polymer electrolytes with lithium salts (LiX; X=TFSI, ClO4, BF4 and PF6) were prepared and measured their lithium transference numbers (t +) for the comparison between different anion radius and salt concentrations. The LiTFSI electrolytes showed highest t + and Li-ion conductivities of all samples at 80 oC, and these values increased with increasing salt concentration. From the results of FT-IR measurements for all concentrated samples, it was revealed that the changes of a band fraction divided at around 1720 cm-1 for interacted carbonyl groups with Li+ (C=O --- Li+) strongly relate to the mobility of Li+.

Effect of Anions on Lithium Ion Conduction in Poly(ethylene carbonate)-based Polymer Electrolytes

Ion-conductive polymer electrolytes are remarkable materials that have recently been proposed for use as flexible solid electrolytes in next-generation energy storage devices. In particular, the author has proposed the synthesis of novel polymer electrolytes with very high ionic conductivities and the essential properties of polymeric materials. This review describes the synthesis of alternating copolymers of CO2 with epoxides and their application as novel ion-conductive polymers in the place of typical polyether-based systems. The Li salt electrolytes of poly(ethylene carbonate) (PEC) and of other polycarbonates with different side groups exhibit unique ion-conductive properties, such as increasing conductivity with higher salt concentrations, very high Li transference numbers and good electrochemical stability. The Li-ion conductivity of a PEC-lithium bis(fluorosulfonyl)imide LiFSI electrolyte was estimated to be greater than 10−4 S cm−1, and excellent battery performance of this material was also demonstrated at room temperature. In this focus review, alternating copolymers of carbon dioxide with epoxides have been synthesized and studied as novel ion-conductive polymers. The Li salt electrolytes of poly(ethylene carbonate) (PEC) and of other polycarbonates having different side groups exhibited remarkable ion-conductive properties including the following: increased conductivity with increasingly higher salt concentrations, very high values for the Li+ transference number, and good electrochemical stability. The Li-ion conductivity of a highly concentrated PEC-LiFSI electrolyte was estimated to be greater than 10−4 S cm−1, and excellent battery performance was demonstrated at room temperature.

Yanping Wu

Papers

Ion-molecule interactions in solutions of lithium perchlorate in propylene carbonate + diethyl carbonate mixtures: an IR and molecular orbital study.