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Stark Tuning Rates of Organic Carbonates Used in Electrochemical Energy Storage Devices
journal contribution
posted on 2019-04-09, 00:00 authored by Jarred
Z. Olson, Samuel H. Schneider, Patrik K. Johansson, Ting S. Luk, Cody W. SchlenkerLithium ion batteries
frequently employ carbonate-based electrolyte
solvents to support reversible lithium ion storage in response to
electric fields applied to the electrode/electrolyte junction. Although
these fields are critical for controlling beneficial and deleterious
electrochemical reactions alike, quantifying their magnitude is a
persistent challenge that inhibits our fundamental understanding of
high-voltage electrochemical energy storage devices. In this study,
we utilize complementary experimental techniques of vibrational Stark
spectroscopy and vibrational solvatochromism in conjunction with molecular
dynamics simulations to determine the vibrational sensitivity (Stark
tuning rate, Δμ⇀) of the carbonyl group (CO) in
response to an electric field for diethyl carbonate (DEC), ethylene
carbonate (EC), and fluoroethylene carbonate (FEC). We first determine
that the response of the CO group in each solvent to an externally
applied electric field exhibits a second derivative line shape characteristic
of the linear Stark effect. We find the magnitude of this response
to be unique for each carbonate solvent based on a field-frequency
calibration; Δμ⇀DEC = 0.37 cm–1/(MV/cm), Δμ⇀EC = 0.31 cm–1/(MV/cm), and Δμ⇀FEC = 0.57 cm–1/(MV/cm). We then leverage
two electrostatic expressions to converge
upon an angle-dependent equilibrium (open circuit) interfacial field
for archetypal Li-ion battery electrode/electrolyte junctions. Based
upon this convergence model, which depends explicitly on the dielectric
function of the electrode interface and the projection of the field
onto the dipole axis of the CO group, we estimate local fields
spanning approximately 30–50 MV/cm at LiCoO2 and
84–132 MV/cm at graphite interfaces. This quantitative benchmark
of Δμ⇀ for some of the most commonly used electrolyte
solvents lays the groundwork for proofing future electrostatic materials
design strategies, for example, by controlling electrochemical reaction
dynamics using extrinsic interface modifiers.
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Stark Tuning Ratesvibrational Stark spectroscopyElectrochemical Energy Storage Devices Lithium ion batteriesdiethyl carbonateconvergence modelcarbonyl grouplithium ion storageangle-dependent equilibriumelectrochemical reaction dynamicsOrganic CarbonatesDECLiCoO 2graphite interfacesmaterials design strategiesextrinsic interface modifiersECMVdielectric functionvibrational solvatochromismfield exhibitsvibrational sensitivitycmproofing futureFECfield-frequency calibrationelectrochemical reactionsline shapeStark effectcarbonate-based electrolyte solventsfluoroethylene carbonateelectrode interfaceresponseelectrolyte solventsdynamics simulationselectrochemical energy storage devices
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