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Title: Atomic and electronic structure of complex metal oxides during electrochemical reaction with lithium
Author: Griffith, Kent Joseph
ISNI:       0000 0004 7226 3694
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2018
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Lithium-ion batteries have transformed energy storage and technological applications. They stand poised to convert transportation from combustion to electric engines. The discharge/charge rate is a key parameter that determines battery power output and recharge time; typically, operation is on the timescale of hours but reducing this would improve existing applications and open up new possibilities. Conventionally, the rate at which a battery can operate has been improved by synthetic strategies to decrease the solid-state diffusion length of lithium ions by decreasing particle sizes down to the nanoscale. In this work, a different approach is taken toward next-generation high-power and fast charging lithium-ion battery electrode materials. The phenomenon of high-rate charge storage without nanostructuring is discovered in niobium oxide and the mechanism is explained in the context of the structure–property relationships of Nb2O5. Three polymorphs, T-Nb2O5, B-Nb2O5, and H-Nb2O5, take bronze-like, rutile-like, and crystallographic shear structures, respectively. The bronze and crystallographic shear compounds, with unique electrochemical properties, can be described as ordered, anion-deficient nonstoichiometric defect structures derived from ReO3. The lessons learned in niobia serve as a platform to identify other compounds with related structural motifs that apparently facilitate high-rate lithium insertion and extraction. This leads to the synthesis, characterisation, and electrochemical evaluation of the even more complicated composition–structure–property relationships in ternary TiO2–Nb2O5 and Nb2O5–WO3 phases. Advanced structural characterisation including multinuclear solid-state nuclear magnetic resonance spectroscopy, density functional theory, X-ray absorption spectroscopy, operando high-rate X-ray diffraction, and neutron diffraction is conducted throughout to understand the evolution of local and long-range atomic structure and changes in electronic states.
Supervisor: Grey, Clare P. Sponsor: Winston Churchill Foundation of the United States of America ; Cambridge International Trust
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
Keywords: battery ; energy storage ; lithium-ion battery ; NMR ; XRD ; neutron diffraction ; X-ray diffraction ; X-ray absorption ; XANES ; EXAFS ; X-ray absorption near edge structure ; extended X-ray absorption fine structure ; XAS ; nuclear magnetic resonance ; solid-state NMR ; niobium ; tungsten ; titanium ; electrochemistry ; DFT ; density functional theory ; NMR calculations ; NMR crystallography ; Clare Grey ; high-rate ; high-power ; fast charging ; electric vehicles ; redox chemistry ; inorganic chemistry ; materials chemistry ; chemistry ; operando ; in situ ; niobium oxide ; tungsten oxide ; titanium oxide ; bronze ; crystallographic shear ; block structure ; Wadsley-Roth phase ; crystallography ; crystal chemistry