Research Proposal for the Computational Study on Redox Stability of Electrolytes in Li-Air Battery in the Presence of Superoxide Anion Radical using Density Functional Theory with an Explicit Solvent Model

It has been widely recognized, both in the scientific and industrial communities, that
one of the major obstacles which prevents the broader uptake of electric vehicles is
the limitation on the range of such vehicles. This is due to the limited gravimetric
and volumetric electrical energy storage densities in existing batteries. For electric
vehicles to gain greater market penetration the future batteries have to be much
lighter and more powerful. Massive efforts have been devoted in the development
of new practical batteries and several possible alternative battery chemistries have
been proposed. The lithium-air (Li-air) battery is one of the most attractive because
it uses oxygen from air instead of storing an oxidizer internally, which means it
could in principle provide a very high electrical storage density. Furthermore, aprotic
Li-air battery provides an addition advantage in having been demonstrated to be
rechargeable. However, it has been well documented that the development of a
practical aprotic Li-air battery is facing some major difficulties1, one of which being
the oxidation of the aprotic organic electrolyte at the high potential used during the
recharging process

Many of the organic electrolytes used, such as organic carbonate-based solvents, have
limited anodic oxidation stability and are prone to oxidation at even lower potential in
the presences of typical catalytically active materials. This is important for the Li-air
battery as the oxidative stability of the electrolyte can be reduced in the presence of
catalysts. Therefore, gaining a fundamental understanding of the oxidative stabilities
of various electrolytes remains key in developing a suitable electrolyte for the aprotic
Li-air battery.

Much effort has already been devoted to this field. Many of the work focus on
investigating the reaction mechanisms through which the reactive oxygen species
attack various electrolytes2,3,4. While Bryantsev et al.2 used density functional
theory (DFT) with an implicit solvent model to compute the reactivity of a series of
electrolytes towards nucleophilic substitutions by superoxide, Laino and Curioni3
investigated the reactivity of lithium peroxide towards propylene carbonate, a
common electrolyte in Li-ion batteries, by means of DFT-based molecular dynamics
with an explicit solvent model. This work will build upon the work of Bryantsev,
and will investigate the stabilities of a range of different classes of electrolytes in
the presence of the superoxide anion radical using computational methods. DFT
calculations will be used to provide an estimate of the energies involved reactions, but
instead of the continuum solvent model chosen by Bryantsev et al.2 and Zhang et al.4,
an explicit solvent model will be employed in this study. The simplest model will be
employed in this exercise where only the electrolytes and the superoxide are included
in DFT computations, while the solids and the external potential are ignored. The
results of our calculations will be compared to those using the continuum model and
experimental data, and the merits of various methods will be discussed. Through this
exercise we hope to gain a better understanding on how the electrolytes interact with
the superoxide, which will be helpful in the search of a stable electrolyte in the future.