ST CATHERINE'S COLLEGE GRADUATE SCHOLARSHIPS 2020
Further information can be downloaded *here*
DEPARTMENT OF MATERIALS
Three projects on the materials chemistry and electrochemistry of batteries: lithium-air, all solid state lithium and sodium-ion batteries (Peter Bruce)
1. The materials chemistry and electrochemistry of the lithium-air battery
Energy storage represents one of the major scientific challenges of our time. Pioneering work in Oxford in the 1980s led to the introduction of the lithium-ion battery and the subsequent portable electronics revolution (iPad, mobile phone).
Theoretically the Li-air battery can store more energy than any other device, as such it could revolutionise energy storage. The challenge is to understand the electrochemistry and materials chemistry of the Li-air battery and by advancing the science unlock the door to a practical device. The Li-air battery consists of a lithium metal negative electrode and a porous positive electrode, separated by an organic electrolyte. On discharge, at the positive electrode, O2 is reduced to O22- forming solid Li2O2, which is oxidised on subsequent charging. It is the organic analogue of the oxygen reduction/oxygen evolution reaction in aqueous electrochemistry. The project will involve understanding the electrochemistry of O2 reduction in Li+ containing organic electrolytes to form Li2O2 and its reversal on charging. The use for redox mediators to facilitate the O2 reduction and evolution. The exploration of new electrolyte solutions and their influence of the reversibility of the reaction. The project will use a range of electrochemical, spectroscopic (Raman, FTIR, XPS, in situ mass spec.) and microscopic (AFM, TEM) methods to determine the mechanism of O2 reduction (presence and nature of intermediates e.g. superoxide) and its kinetics. Our aim is not to build devices but to understand the underlying science. We seek highly qualified, ambitious, imaginative, hard-working and self-motivated candidates. Further details may be obtained by contacting simultaneously Dr Erez Cohen at firstname.lastname@example.org, Dr Paul Adamson at email@example.com and Miki Bennett at firstname.lastname@example.org.
2. Challenges facing all-solid-state batteries
Degredation mechanisms in an all-solid-state Lithium-ion battery
Degradation Mechanisms at the Li10GeP2S12/LiCoO2 Cathode Interface in an All-Solid-State Lithium-Ion Battery
There is increasing worldwide motivation to research and develop all-solid-state batteries in order to achieve better safety, higher energy density, as well as wider operating temperature energy storages, as compared to conventional Li-ion batteries using liquid electrolytes. All solid state batteries consist of a solid electrolyte as the main component, an intercalation cathode, e.g. LiCoO2, and an anode with the ultimate goal of implementing a lithium metal anode. The project will involve advancing the fundamental understanding from material to cell level. Synthesis of new Li+ conducting solid electrolytes and characterisation of their structural, electrochemical, electrical, and mechanical properties will be required. The work will include investigation of phenomena at solid electrode/solid electrolyte interfaces, something that is central to progressing solid state batteries but is not well understood, e.g. charge transfer, parasitic reactions, occurring at the interfaces of the electrolytes with both cathodes and anodes. Further parameters affecting the cycleability of the all-solid-state batteries will need to be identified. A range of characterisation techniques will be used, including X-ray and neutron diffraction, electron microscopy, NMR, Raman and IR spectroscopy, X-ray tomography, as well as several electrochemical techniques such as EIS and cycling. We seek highly qualified, ambitious, imaginative, hard-working and self-motivated candidates. Further details may be obtained by contacting simultaneously Dr Erez Cohen at email@example.com, Dr Paul Adamson at firstname.lastname@example.org and Miki Bennett at email@example.com.
3. The materials chemistry and electrochemistry of lithium and sodium-ion batteries
Lithium-ion batteries have revolutionised portable electronics and are now used in electric vehicles. However new generations are required for future applications in transport and storing electricity from renewable sources (wind, wave, solar). Such advances are vital to mitigating climate change. Sodium is more abundant than lithium and so attractive especially for applications on the electricity grid. Lithium and sodium ion batteries both consist of intercalation compounds as the negative and positive electrodes. The charge and discharge involves shuttling Li+ or Na+ ions between the two intercalation hosts (electrodes) across the electrolyte. In the case of Li-ion batteries currently the most common technology is still graphite (anode) and LiCoO2 (cathode). However, the development of increased energy storage in Li ion systems drives research to discover new materials. In the case of Na-ion batteries whilst the principles are analogous to that of the Li-ion battery, as yet there are no preferred candidates as electrodes, which provides excellent motivation for further work.
The project will involve synthesising and characterising a number of Na/Li containing transition metal oxides. This will utilise synthesis methods such as sol-gel, hydrothermal and solid state, characterisation will involve X-ray and Neutron diffraction, solid state NMR, XPS, FTIR, TEM and SEM. Additionally it is important to understand the processes at the interfaces between the intercalation oxides and the organic electrolyte. For such the interfacial studies FTIR, Raman, in situ mass spec and XPS will be the main techniques. We seek highly qualified, ambitious, imaginative, hard-working and self-motivated candidates. Further details may be obtained by contacting simultaneously Dr Erez Cohen at firstname.lastname@example.org, Dr Paul Adamson at email@example.com and Miki Bennett at firstname.lastname@example.org.
- Probing redox in Li-ion battery cathode materials using TEM - Prof P D Nellist / Prof P G Bruce / Dr R J Nicholls
Transmission electron microscopy (TEM) is now capable of imaging individual atoms in materials, and electron spectroscopy data can provide atomic-scale information about the elements present and the nature of the bonding. Oxford Materials is one of the leading departments in high-precision quantitative measurements of materials using these methods. These methods have great potential for measuring structure and local chemistry to explain the performance of Li battery materials and to guide their development.
There are several outstanding questions regarding the nature of redox and challenges associated with structural stability and oxygen loss in high-capacity cathode materials including anion-redox and Ni-rich cathodes. Electron energy-loss spectroscopy in the transmission electron microscope can reveal information about oxidation states at very high spatial resolutions, and can be used alongside atomic-resolution imaging to relate chemical and structural changes and gain understanding of the fundamental processes in these materials. The project will involve experimental work, including microscope operation, and some computational modelling to enable interpretation of the spectroscopy data.
- Operando Tomographic Characterisation of Electrochemical Energy Storage Devices - Professor James Marrow/Professor Mauro Pasta/Professor Peter Bruce
Electrochemical energy storage devices such as lithium ion batteries have recently facilitated a revolution in mobile electronics and communications technologies. In order to use batteries for electromobility and grid storage of renewable energy, more energy dense, safer and larger scale devices need to be developed.
During use of such electrochemical energy storage devices, the cyclic transport of ions can develop gradients of composition and stress, which may interact with each other and can create damage. This often leads to a decreased cycling efficiency, shortening the device’s lifetime. Relying solely on external analysis of the performance characteristics and post mortem destructive characterisation of the microstructure has its limitations. Recent work to study degradation 'in operando' (e.g. https://dx.doi.org/10.1038/s41563-019-0438-9) has shown the insights that In situ X-ray computed tomography can provide. Current work is now applying in situ synchrotron X-ray diffraction and neutron imaging methods to investigate these mechanisms.
This project will further explore the potential to achieve a quantitative understanding of the internal strain, stress and microstructure changes through in situ and in operando observations, linked to the ongoing work in the materials department on a range of energy storage materials. This project is most suited to graduates with a physics, materials science, chemistry or engineering background.
- Understanding battery chemistry with in-situ electron microscopy - Dr Alex W Robertson and Prof Peter G Bruce
Lithium-ion batteries have revolutionised the way we think of energy storage, allowing for powerful devices that fit the palm of our hands, and massive battery arrays to supplement intermittent renewables. However there are fundamental limitations; the recent high profile fires that occurred in the Samsung Galaxy Note phones, and the 2013 grounding of the Boeing Dreamliner fleet, both illustrate this. The materials failures that occurred in these batteries risk becoming increasingly prevalent as we push Li-ion batteries to their maximum potential. New battery systems will be needed, such as Na-ion or Li-air, and a more fundamental understanding of the materials degradation mechanisms will be required to prevent failure.
Transmission electron microscopy (TEM) permits the characterisation of a material’s structure down to the atomic level, along with its chemical constitution by spectroscopy. TEM has been around for many years, but recent advances have seen the profile of this venerable technique rise dramatically, with a 2017 Nobel Prize awarded for its application to biological systems. Using TEM to aid the understanding of battery chemistry has been historically difficult, as most battery chemistry occurs in solution. However, recent developments now allow for liquid phases to be studied within the TEM, permitting an unprecedented insight into the processes that occur in a battery during operation. The student, working with the world-leading battery and electron microscopy communities within the Materials Department, will harness TEM to understand the fundamental chemical and materials processes that occur in batteries.
This EPSRC-funded 3.5 year DPhil in Materials DTP studentship will provide full fees and maintenance for a student with home fee status (this status includes an EU student who has spent the previous three years (or more) in the UK undertaking undergraduate study). Candidates with EU fee status are eligible for a fees-only award, but normally would have to provide funding for their living costs from another source such as personal funds or a scholarship. The stipend will be at least £16,009 per year. Information on fee status can be found at http://www.ox.ac.uk/admissions/graduate/fees-and-funding/fees-and-other-charges.
Candidates are considered in the January 2020 admissions cycle which has an application deadline of 24 January 2020.
Any questions concerning the project can be addressed to Dr Alex Robertson (email@example.com). General enquiries on how to apply can be made by e mail to firstname.lastname@example.org. You must complete the standard Oxford University Application for Graduate Studies. Further information and an electronic copy of the application form can be found at http://www.ox.ac.uk/admissions/postgraduate_courses/apply/index.html.