Concentration Dependent Solution Structure and Transport Mechanism in High Voltage LiTFSI-Adiponitrile Electrolytes

• The physiochemical properties of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in adiponitrile (ADN) electrolytes were explored as a function of concentration. The phase diagram and ionic conductivity plots show a distinct relationship between the eutectic composition of the electrolyte and the concentration of maximum ionic conductivity in the 25 degrees C isotherm. We propose a structure-based explanation for the variation of electrolyte ionic conductivity with LiTFSI concentration, where the eutectic concentration is a transitionary region at which the structure changes from solvated contact ion pairs to extended units of [Li-z(ADN)(x)TFSIy](z-y) aggregates. It is found through diffusion coefficient measurements using pulsed-field gradient (PFG) NMR that both D-Li/D-TFSI and D-Li/D-ADN increase with concentration until 2.9 M, where after Li+ becomes the fastest diffusing species, suggesting that ion hopping becomes the dominant transport mechanism for Li+. Variable diffusion-time (Delta) PFG NMR is used to track this evolution of the ion transport mechanism. A differentiation in Li+ transport between the micro and bulk levels that increases with concentration was observed. It is proposed that ion hopping within [Li-z(ADN)(x)TFSIy](z-y) aggregates dominates the micro-scale, while the bulk-scale is governed by vehicular transport. Lastly, we demonstrate that LiTFSI in ADN is a suitable electrolyte system for use in Li-O-2 cells.

Ämnesord

NATURVETENSKAP  -- Kemi -- Oorganisk kemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences -- Inorganic Chemistry (hsv//eng)

NATURVETENSKAP  -- Kemi -- Fysikalisk kemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences -- Physical Chemistry (hsv//eng)

NATURVETENSKAP  -- Kemi -- Materialkemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences -- Materials Chemistry (hsv//eng)

NATURVETENSKAP  -- Fysik -- Annan fysik (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences -- Other Physics Topics (hsv//eng)

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