3 research outputs found
Additive Effect on Reductive Decomposition and Binding of Carbonate-Based Solvent toward Solid Electrolyte Interphase Formation in Lithium-Ion Battery
The
solid–electrolyte interphase (SEI) formed through the
reductive decomposition of solvent molecules plays a crucial role
in the stability and capability of a lithium-ion battery (LIB). Here
we investigated the effects of adding vinylene carbonate (VC) to ethylene
carbonate (EC) solvent, a typical electrolyte in LIBs, on the reductive
decomposition. We focused on both thermodynamics and kinetics of the
possible processes and used density functional theory-based molecular
dynamics with explicit solvent and Blue-moon ensemble technique for
the free energy change. We considered Li<sup>+</sup> in only EC solvent
(EC system) and in EC solvent with a VC additive (EC/VC system) to
elucidate the additive effects. In addition to clarifying the equilibrium
properties, we evaluated the free energy changes along several EC
or VC decomposition pathways under one-electron (1e) reduction condition.
Two-electron (2e) reduction and attacks of anion radicals to intact
molecules were also examined. The present results completely reproduce
the gaseous products observed in the experiments. We also found a
new mechanism involving the VC additive: the VC additive preferentially
reacts with the EC anion radical to suppress the 2e reduction of EC
and enhance the initial SEI formation, contrary to the conventional
scenario in which VC additive is sacrificially reduced and its radical
oligomerization becomes the source of SEI. Because our mechanism needs
only 1e reduction, the irreversible capacity at the SEI formation
will decrease, which is also consistent with the experimental observations.
These results reveal the primary role of VC additive in the EC solvent
Unusual Stability of Acetonitrile-Based Superconcentrated Electrolytes for Fast-Charging Lithium-Ion Batteries
The development of a stable, functional
electrolyte is urgently
required for fast-charging and high-voltage lithium-ion batteries
as well as next-generation advanced batteries (e.g., Li–O<sub>2</sub> systems). Acetonitrile (AN) solutions are one of the most
promising electrolytes with remarkably high chemical and oxidative
stability as well as high ionic conductivity, but its low stability
against reduction is a critical problem that hinders its extensive
applications. Herein, we report enhanced reductive stability of a
superconcentrated AN solution (>4 mol dm<sup>–3</sup>).
Applying
it to a battery electrolyte, we demonstrate, for the first time, reversible
lithium intercalation into a graphite electrode in a reduction-vulnerable
AN solvent. Moreover, the reaction kinetics is much faster than in
a currently used commercial electrolyte. First-principle calculations
combined with spectroscopic analyses reveal that the peculiar reductive
stability arises from modified frontier orbital characters unique
to such superconcentrated solutions, in which all solvents and anions
coordinate to Li<sup>+</sup> cations to form a fluid polymeric network
of anions and Li<sup>+</sup> cations