Impact of Electrolyte Chemistry and Solvation on Interphasial Ion Dynamics for Low-Temperature Li Metal Batteries
ECS Meeting Abstracts(2022)
Abstract
The influence of electrolyte chemistry on the ion-desolvation process of charge-transfer in Li-based batteries is a crucial, yet murky aspect of their design and operation. This desolvation process has been shown to be a dominant factor for the low-temperature operation of batteries, where high energy density is necessary, but difficult to achieve. We have applied Li metal batteries in an attempt to provide such metrics, which show extremely disparate performance depending on the electrolyte applied in each cell. Specifically, we have found that the induction of ion-pairing and the inclusion of weakly-bound solvents results in a substantial improvement in both the reversibility and shorting behavior when plating Li at low-temperature, despite significant loss in the bulk ionic conductivity of the solution. To provide a deeper understanding of these experimental observations, we also apply free-energy sampling techniques at 298 and 213 K to simulations involving diethyl ether (DEE) and 1,3-dioxoloane/1,2-dimethoxyethane (DOL/DME) electrolytes, which display bulk solvation structures dominated by ion-pairing and solvent coordination, respectively. We find that the degree of ion-pairing in the electrolyte bulk and at the interphase plays a vital role in assisting the delivery of Li+ to the inner Helmholtz layer, and that the sterics of DME are prone to Li+ over-coordination in solution. This mechanistic reliance of ion-pairing at the interphase conflicts with the preferred solvent-dominated structure of the DOL/DME system, which is further emphasized at 213 K, where simulations predict that the balance between solvent and anion coordination is shifted significantly in favor of solvent. This work endeavors to provide unambiguous evidence of the importance of the solvation structure for interphasial charge-transfer kinetics as well as a mechanistic understanding of the phenomena at the interphase. Figure 1
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Key words
interphasial solvation dynamics,electrolyte chemistry,low-temperature
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