posted on 2023-04-13, 20:43authored byHonghao Yang, Junyi Ji, Hongjiao Li, Bin Liang
Salt-concentrated nonaqueous electrolytes,
due to their
special
properties in increasing the stability of batteries by the formation
of anion-derived solid electrolyte interphases (SEIs), have attracted
considerable attention in recent years. Despite extensive efforts
to explore the microscopic solvation structures of electrolyte solutions,
a clear relationship between the microstructures and electrolyte performance,
especially the Li-ion conductivity, is still in demand. In this work,
we performed ab initio molecular dynamics (AIMD) simulations as well
as density function theory (DFT) calculations for three as-designed
electrolytes, namely lithium bis(fluorosulfonyl)imide (LiFSI)
with acetonitrile (AN), 1,2-dimethoxyethane (DME), and 2,2-dimethyl-3,6,9-trioxa-2-siladecane
(siloxane). We observed that for the above electrolytes at high concentrations,
Li-ion conduction proceeds when the solvation structure changes from
one form to another in a few tens of fs, involving the binding/debinding
of both the solvent and FSI anion with the Li-center. The dynamics
of binding between the solvents and Li decrease with the increase
in the strength of the solvation sheath, which is influenced by the
polarity of the solvent. The steric shielding effect was clearly detected
in the siloxane-LiFSI system which became almost nonconductive at
a concentration of 3 mol L–1. It should be noted
that despite the high concentration of each electrolyte (≥5
mol L–1), there is still a certain amount of free
solvents according to the simulation results. Our results deepen the
understanding of the Li-ion conduction process in salt-concentrated
electrolytes and provide guidelines for designing high-performance
electrolytes.