Non-aqueous lithium-oxygen batteries are promising energy storage devices as
they can offer ultrahigh specific capacities and energy densities. However, issues, such
as high charge overpotential, sluggish reaction kinetics, and dendrite growth, have
hindered the commercialization of the technology. The primary objective of this thesis
aims to use first-principles modeling techniques to unravel the underlying reaction
mechanisms of non-aqueous lithium-oxygen batteries, and to provide solutions to
address the critical issues.
In the aspect of the cathode side of non-aqueous lithium-oxygen batteries, we
calculate the bulk thermodynamic properties and surface energies of the insulated main
discharge product Li
2O
2 and the conductive possible byproduct Li
3O
4. Results show
that the s...[
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Non-aqueous lithium-oxygen batteries are promising energy storage devices as
they can offer ultrahigh specific capacities and energy densities. However, issues, such
as high charge overpotential, sluggish reaction kinetics, and dendrite growth, have
hindered the commercialization of the technology. The primary objective of this thesis
aims to use first-principles modeling techniques to unravel the underlying reaction
mechanisms of non-aqueous lithium-oxygen batteries, and to provide solutions to
address the critical issues.
In the aspect of the cathode side of non-aqueous lithium-oxygen batteries, we
calculate the bulk thermodynamic properties and surface energies of the insulated main
discharge product Li
2O
2 and the conductive possible byproduct Li
3O
4. Results show
that the standard formation Gibbs free energy of bulk Li
3O
4 is marginally higher than
that of Li
2O
2, but the surface energy of Li
3O
4 is much lower. Low surface energy
results in both lowered nucleation energy and formation Gibbs free energy in the
nanometer regime, allowing the Li
3O
4 nano particles to nucleate ahead of Li
2O
2 during
the discharge process and to exist stably when particle sizes are smaller than about 40
nm. The decomposition of Li
3O
4 during the charge process can lead to a lower voltage
plateau.
To further reduce the charge overpotential and enhance the reaction kinetics on
the cathode side, we study the catalytic mechanism of a representative catalyst rutile RuO
2. For the oxygen reduction reaction (ORR), it is found that rutile RuO
2 can
provide large adsorption energies toward LiO
2 and Li
2O
2, thus resulting in high initial
discharge voltages. For the oxygen evolution reaction (OER), we propose that the OER
may also occur at the two-phase interface of Li
2O
2/RuO
2 in addition to the three-phase
interface, where rutile RuO
2 provides pathways for the lithium ions while oxygen
evolves from the exposed surfaces of Li
2O
2. Calculation results show that our proposed
catalytic scenario is both thermodynamically and kinetically viable. In addition to
rutile RuO
2, we also study the catalytic activity of RuO
2’s polymorph, RuO
2
monolayer. Computational results show that the RuO
2 monolayer exhibits a higher
catalytic activity than the rutile RuO
2 does, making it a promising catalytic material
for non-aqueous lithium-oxygen batteries.
To address the dendrite growth problem on the anode side, two strategies are
explored. One is to develop new lithium ion intercalation anode materials with high
capacity. Based on DFT calculations, we propose that when using graphene as a
substrate as well as a protective layer of silicene, the van der Waals heterostructure of
silicene and graphene (Si/G) can serve as a prospective anode material for lithium and
sodium batteries. The other strategy is to add artificial interlayer between the lithium
metal anode and liquid electrolyte. With the aid of first-principles calculations, we
found that the two-dimensional (2D) crystal, h-BN, is a good candidate for the artificial
interlayer which can mitigate dendrite growth, prevent the decomposition of liquid
electrolyte and ensure sufficient lithium ion conductivity.
Keywords: First-principles modeling; Non-aqueous lithium-oxygen batteries; Li
3O
4;
Rutile RuO
2; RuO
2 monolayer; Silicene; Lithium metal anode; h-BN; 2D crystals;
Proton exchange membrane
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