Investigation of an Intermediate Temperature Molten Lithium Salt Based on Fluorosulfonyl(trifluoromethylsulfonyl)amide as a Solvent-Free Lithium Battery Electrolyte

Abstract

The asymmetric amide anion, such as (fluorosulfonyl)(trifluoromethylsulfonyl)amide (fTfN–), formed intermediate temperature molten lithium salts at 100 °C, which was the lowest among the lithium single molten salts composed of conventional halogenide, nitrate, perchlorate, and perfluoro anions. The molten Li[fTfN] was highly viscous (17 Pa·s at 110 °C, however, it was classified as a good ionic liquid by Walden plot analysis, which indicates the good-dissociation between Li+ and fTfN–. Due to the high transport number of the lithium cation (0.94), the Li[fTfN] behaves as a single lithium-ion conducting material. The Li[fTfN] possesses an electrochemical window (5.0 V) due to the oxidative resistance of the perfluoro anion. The charge and discharge for a conventional composite positive electrode containing LiCoO2 or LiFePO4 was successful. In particular, LiFePO4 showed a high capacity and Coulombic efficiency at 0.1–5 C.

Understanding Electrochemical Stability and Lithium Ion‐Dominant Transport in Concentrated Poly(ethylene carbonate) Electrolyte

“…A situation similar to the PEC electrolyte may have occurred in these highly concentrated liquid electrolytes. Also, Kubota and Matsumoto reported a very high t + for molten lithium (fluorosulfonyl)(trifluoromethylsulfonyl)imide. We believe that the aggregated ions in the highly concentrated PEC electrolytes exist like a molten salt, in which C=O groups cause the aggregated ions to be molten and movable, without tightly coordinating to Li + .…”

Recent Advances in Ionic Liquids for Lithium Secondary Batteries

“…It was quite interesting that both the melting point and viscosity have the same tendency toward the size of the anion. The Li[fTfN] can be used as a onium-free lithium single molten salt from 100 °C to the decomposition temperature (300 °C) [ 57 ]. Such an onium-free lithium single salt will be useful to focus on the latent potential and also the limitation of perfl uoroanions for battery applications.…”

Electrochemical Deposition of Alkali Metal in Low-Melting Alkali Metal Perfluorosulfonylamides

“…5 The synthesized products were identified by elemental analysis. Residual moisture was confirmed to be below 50 ppm by a Karl Fischer moisture meter (MITSUBISHI, CA-07).…”

“…We reported that lithium (fluorosulfonyl)(trifluoromethylsulfonyl)amide, denoted as Li[fTfN], can be used as a molten salt electrolyte for the lithium secondary battery without dissolving it in organic solvents, room temperature ionic liquids (RTIL), and even the other alkali metal salts. 5 Furthermore, its cation mixture can be used around room temperature and its lithium secondary battery showed higher rate performance and cycle stability. 6 In order to apply the novel low-melting molten salts, it is significant to investigate their physicochemical and electrochemical properties.…”