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“Water-in-salt” electrolyte for supercapacitors : a molecular dynamics study

Abstract : “Water-in-salt” solvents are a new class of electrolytes with very promising electrochemical properties for energy storage applications. The purpose of this work is to understand the microscopic mechanisms of these superconcentrated electrolytes at play. We use atomistic molecular dynamics to simulate systems of water in LiTFSI at various salt concentrations. On the basis of comparisons of simulated and measured dynamic properties, i.e. the viscosity, diffusion coefficient and conductivity, we systematic test and develop the force fields used for the ions. As a consequence, an optimized force field is proposed, which enables the accurate modeling of such systems. The structural properties are systematically investigated on various aspects for the salt at a superconcentrated state, which shed new light on the connections between ions and water molecules. Apart from these simulations of the bulk electrolytes, we also study the water-in-salt electrolyte at interfaces, in which the capacitive performance of this electrolyte in supercapacitors are explored. The differential capacitance displays a number of nontrivial features accompanying a series of peaks in the potential region from 0 to 3 V. The study of structural evolutions of the interfacial electrolytes shows that many structural changes occur in the layer of adsorbed liquid when the potential of the electrode is changed, which are at the origin of those observed peaks in the differential capacitance.
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  • HAL Id : tel-02613788, version 1

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Zhujie Li. “Water-in-salt” electrolyte for supercapacitors : a molecular dynamics study. Theoretical and/or physical chemistry. Sorbonne Université, 2018. English. ⟨NNT : 2018SORUS482⟩. ⟨tel-02613788⟩

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