Local Structures of Niobium-Containing Cation-Disordered Rocksalt Materials: Cobalt-Free Cathodes for Lithium-Ion Batteries
type: CreativeWork
description: Electrochemical capacity improvements on current state-of-the-art cathode materials for Li-ion batteries such as LiCoO2 are becoming limited, and new families of materials with inherently greater capacities are required to more effectively meet the world’s energy storage demands. Li-excess and cation-disordered materials have shown promise as materials with significantly higher capacities, supposedly achieved in part through reversible anionic redox, in addition to traditional transition metal redox. They also allow for a broad compositional range, enabling the substitution of expensive, toxic elements such as Co for more abundant, cheaper, and safer transition metal species. However, the physical mechanisms controlling their structure, redox behaviour and ionic mobility are not yet well understood. Hence, this vast and largely untapped phase space is currently the subject of extensive investigation. This thesis presents the motivations, aims and findings of a project exploring the structural properties and electrochemical performance of the Ni and Mn members of the promising family of cathode materials Li1+xNbyMzO2 (x + y + z = 1, M = Mn, Ni). A range of complementary techniques are employed, including X-ray diffraction, neutron total scattering, solid state nuclear magnetic resonance, X-ray absorption spectroscopy and magnetic susceptibility measurements. These techniques are used in combination with electrochemical cycling to probe the local and long-range structures of these compounds, and their evolution with charge and discharge. The occurrence of short-range cation order in Li1.25Nb0.25Mn0.5O2 is reported and rationalised based on the principle of electroneutrality, combined with the accommodation of Mn Jahn-Teller and Nb second order Jahn-Teller distortions within the material. This cation ordering is found to be highly sensitive to the synthesis conditions and to have significant implications for the electrochemical performance of the material. It is demons…
abstract: Electrochemical capacity improvements on current state-of-the-art cathode materials for Li-ion batteries such as LiCoO2 are becoming limited, and new families of materials with inherently greater capacities are required to more effectively meet the world’s energy storage demands. Li-excess and cation-disordered materials have shown promise as materials with significantly higher capacities, supposedly achieved in part through reversible anionic redox, in addition to traditional transition metal redox. They also allow for a broad compositional range, enabling the substitution of expensive, toxic elements such as Co for more abundant, cheaper, and safer transition metal species. However, the physical mechanisms controlling their structure, redox behaviour and ionic mobility are not yet well understood. Hence, this vast and largely untapped phase space is currently the subject of extensive investigation. This thesis presents the motivations, aims and findings of a project exploring the structural properties and electrochemical performance of the Ni and Mn members of the promising family of cathode materials Li1+xNbyMzO2 (x + y + z = 1, M = Mn, Ni). A range of complementary techniques are employed, including X-ray diffraction, neutron total scattering, solid state nuclear magnetic resonance, X-ray absorption spectroscopy and magnetic susceptibility measurements. These techniques are used in combination with electrochemical cycling to probe the local and long-range structures of these compounds, and their evolution with charge and discharge. The occurrence of short-range cation order in Li1.25Nb0.25Mn0.5O2 is reported and rationalised based on the principle of electroneutrality, combined with the accommodation of Mn Jahn-Teller and Nb second order Jahn-Teller distortions within the material. This cation ordering is found to be highly sensitive to the synthesis conditions and to have significant implications for the electrochemical performance of the material. It is demons…
author: Jones, Michael Alan
language: eng
keywords: Batteries, Li-ion Batteries, Disorder, Order, Diffraction, Nuclear Magnetic Resonance, Pair Distribution Function
license: https://www.rioxx.net/licenses/all-rights-reserved/
date published: 2021-11-17
date modified: 2026-07-22T22:24:30Z
provider: Cambridge University
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: University of Cambridge

PropertyValue
property ID: DOI
value: 10.17863/CAM.83213