Ionic transport in highly concentrated lithium bis(fluorosulfonyl)amide electrolytes with keto ester solvents: structural implications for ion hopping conduction in liquid electrolytes

Abstract

The hopping/exchange-dominated Li ion transport is attributed to liquid electrolytes with solvent-bridged, chain-like Li ion coordination and aggregated ion pairs.

Rate Performance of LiCoO₂ Half-cells Using Highly Concentrated Lithium Bis(fluorosulfonyl)amide Electrolytes and Their Relevance to Transport Properties

“…[17][18] In contrast, in GBL-based electrolytes, Li + ions diffuse faster than the solvent and the anion in the high-concentration region (c ≈ 6 mol•dm −3 ). This unique Li + ion diffusion behavior is not interpreted by the physical diffusion mechanism based on the Stokes-Einstein rule, and agrees well with our recent observations for sulfolane-, 12,19 keto ester-, 20 and dinitrile-based concentrated electrolytes. 21 In these highly concentrated electrolytes, a solvent molecule coordinated to two different, neighboring Li + ions, forming a chain-like Li-ion coordination structure consisting of solvent bridges (−Li + −solvent−Li + −) and aggregated ion pairs (AGG, LixXy (x-y) , where X denotes counter anions).…”

“…14,15 The experimental details for PFG-NMR are described elsewhere. 20 Raman spectra were recorded using a Raman spectrometer with a 785-nm laser (NRS-4100, JACSO); the instrument was calibrated using a polypropylene standard. The spectroscopic resolution was 4.6 cm −1 .…”

Anion effects on the solvation structure and properties of imide lithium salt-based electrolytes

“…Rapid progress in the energy industry leads to the wide application of lithium-ion batteries (LIBs) as portable or stationary energy storage devices due to their advantages in terms of energy density, energy efficiency and moderate working temperature. [1][2][3][4] The demands on higher energy density stimulate the development of LIBs. For example, the energy density of 18 650 cells, based on a graphite anode and a 4.2 V cathode, has increased from 80 W h kg À1 to 300 W h kg À1 in the past three decades.…”

Deep eutectics and analogues as electrolytes in batteries

“…In the quest for alternative electrolytes, Watanabe's group recently reported a series of liquid 1:1 equimolar mixtures composed of LiFSI and ketoesters with two carbonyl coordinating sites of increasing intramolecular distance (methyl pyruvate MP, methyl acetoacetate MA, and methyl levulinate ML, with zero, one or two methylene groups between the two carbonyl groups, respectively). 148 MP-and ML-based electrolytes exhibited high viscosities exceeding 1000 mPa s at 30°C, leading to a relatively low conductivity of 10 -4 S cm -1 (Table 2). For unclear reasons, the MA-based electrolyte showed a one-order of magnitude lower viscosity, and higher conductivity and diffusion constants.…”

“…The transport mechanism of the mixtures was investigated and it turned out to be different from Li-glymes complexes. 148 In the glyme-Li salt solvate ILs, the Li ion transport tipycally occurs via the physical diffusion mechanism (vehicle mechanism). Contrarily, in the LiFSI:ketoester systems other transport mechanisms, namely Li ion hopping/exchange (analogous to the proton-hopping Grotthuss or structural diffusion mechanism), make a significant contribution to Li ion diffusion.…”