Functional Metal Oxide Coatings from Molecular Precursors for Energy Applications


Type
Thesis
Change log
Authors
Riesgo Gonzalez, Victor  ORCID logo  https://orcid.org/0000-0002-2433-8562
Abstract

The ability to create and optimise new interfaces is essential to develop and optimise materials for use in sustainable energy storage and conversion technologies. In this thesis, the solution-deposition of coatings from molecular precursors is explored as a promising approach towards this end. First, a facile method for the deposition of electrocatalytically active zirconium-based films for photoelectrochemical water oxidation is developed. The films were derived from three novel alkoxy cage compounds containing Zr and a first-row transition metal (Co, Fe or Cu). The deposition of a Co-doped ZrO2 coating onto the BiVO4 photoanode lowers its onset potential by 0.12 V to 0.21 V vs. the reversible hydrogen electrode (RHE) and increases the maximum photocurrent density by ∼50% to 2.41 mA cm-2 compared to the uncoated BiVO4. In the next chapter, a new solution deposition method to coat the Li-ion battery cathode LiNi0.8Mn0.1Co0.1O2 (NMC811) with Al2O3 using aluminium isopropoxide (AIP) is developed. High-field solid-state nuclear magnetic resonance spectroscopy (SSNMR) probes the formation of γ-LiAlO2 at 600 °C and doping of aluminium into NMC811 starting at 500 – 600 °C. NMC811 coated with amorphous Al2O3 (200 – 400 °C) had a capacity retention comparable to pristine NMC811, while higher annealing temperatures led to more crystalline coatings and surface Al-doping which were found to increase the rate of degradation of NMC811 upon cycling. Finally, LiAlO2 coatings are deposited onto NMC811 using heterobimetallic alkoxides: LiAl[(OCH2Ph)4], LiAl[(OiPr)4] and LiAl[(OtBu)4]. The later showing the most promise as a coating precursor due to its high solubility in tetrahydrofuran (THF), low temperature decomposition (283 °C) and reaction with hydroxyl groups present on the surface of NMC811. This coating was tested on polycrystalline NMC811 (PC-NMC811) and Al2O3 coated single-crystal NMC811 (Al2O3/SC-NMC811). Significant improvements in capacity retention (17.2% more C/2 capacity retained after 107 cycles vs. Al2O3/SC-NMC811) were seen in the LiAlO2/Al2O3/SC-NMC811 system. Furthermore, coating PC-NMC811 that was previously degraded by soaking in water improved the capacity retention (50.1% more capacity retention at C/2 after 215 cycles vs. uncoated PC-NMC811 soaked in water and annealed at 400 °C) suggesting that the combination of a LiAlO2 coating and subsequent annealing step can recover NMC811 surfaces that have been previously degraded by soaking in water.

Description
Date
2023-03-28
Advisors
Wright, Dominic
Grey, Clare
Keywords
Batteries, Chemistry, Coatings, Deposition, Electrocatalysis, Electrochemistry, Inorganic, Materials, Molecular, Oxides, Precursors, Single-source, Synthesis
Qualification
Doctor of Philosophy (PhD)
Awarding Institution
University of Cambridge
Sponsorship
EPSRC (2136150)