Determination of Diffusion Mechanisms in Battery Materials using Quasi-Elastic Neutron Scattering Techniques. / Willis, Toby.

2017. 211 p.

Research output: ThesisDoctoral Thesis

Unpublished

Documents

Abstract

The diffusion of ions within a battery material is inherently important to
its capacity to charge and discharge electrons through a circuit during its normal operation. Understanding the pathways ions use to diffuse within a crystal
structure, identifying where the barrier to movement is small, can inform the
direction of future battery research. Two crystalline materials, Na0.8CoO2 and
Li0.29La0.57TiO3, have been studied using a combination of experimental and
computational techniques due to their promising characteristics.
NaxCoO2 is closely related to the commercially dominant LixCoO2 cathode
material. They are intercalation materials with rigid CoO2 layers that the Na or
Li ions can diffuse between. The effect of ordering of the Na ions within a layer
on the diffusion rate has been studied with molecular dynamics simulations by
first principles density functional theory calculations using CASTEP. Clustering
of ions is observed to enhance the diffusion rate by opening up short range pathways with a greatly reduced energy barrier to diffusion. The diffusion rate of
Na0.8CoO2 was measured using quasi-elastic neutron scattering with the signal
varying according to the self-correlation function, effectively providing a value for the average time an ion stays in one site between 'hops'.
Li0.29La0.57TiO3 is a solid electrolyte with ionic conduction rates equivalent to
liquid and polymer based systems. The use of a solid electrolyte has significant
advantages, particularly its improved stability and safety. Using single crystal
X-ray diffraction, structures of several crystals have been identified, including a
completely novel Ruddlesden-Popper structure previously unreported in literature. Quasi-elastic neutron scattering over a large temperature range is used to measure the diffusion rate and activation energy. The hopping geometry is found to be consistent with the predictions of molecular dynamics simulations.
Original languageEnglish
QualificationPh.D.
Awarding Institution
Supervisors/Advisors
Award date1 Mar 2017
Publication statusUnpublished - 2017
This open access research output is licenced under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.

ID: 27677465