Lithium-air battery research is being conducted as part of an EU-FP7 research project ‘STABLE’. This emerging battery technology has potential for surpassing the capacities of current generation Li-ion technologies. Conceptually, Li-air batteries are more complex than their Li-ion counterparts as they require the use of atmospheric O2 to form the main discharge product Li2O2 (shown schematically). This requirement, coupled with the use of a pure lithium anode, has necessitated extensive research focused upon optimization of the various battery components (i.e. anode, cathode and electrolyte). We are interested in the fundamental electrochemical processes occurring during charging and discharging of the Li-air system. Specifically, the role of catalyst materials in allowing for a rechargeable system is being investigated.
We work with a range of transparent conducting nanomaterials and thin films to investigate the links between composition, structure and arrangement and their optical properties. TCO materials have an inherent trade off between conductivity and broad-band transparency and by playing with the dispersion of the materials and methods to grade the refractive index to match the air interface (or that of an encapsulant or electrolyte), can infer better transparency, antireflection and absorbance characteristics. We also measure charge transport phenomena in TCO nanowires (and other semiconducting nanowires) such as field emission, workfunction determination, junction formation and metal contacts to layers of nanowires in device-like structures. Arrays and assemblies of TCO materials with percolating electrical conduction and combinations of enhanced transparency are also being investigated for improving light extraction efficiencies in several forms of light emitting devices.
Electrochemical engineering of phonon transport in Si nanomaterials and structures can be important for influencing and improving several properties such as quantum confined emission, enhanced light absorption and to vary electrical and thermal conductivity (thermoelectrics). We achieve nanostructuring, surface roughness, porosity (random and periodic) by electrochemical and electroless etching a variety of 1D, 2D and 3D structures. these materials come in the form of ordered or random array of rods and wires, and as vertical or in-plane photonic or phononic crystals. Raman scattering spectroscopy is used to study the phonon transport of the nanomaterials by utilizing both ex-situ and in-situ temperature measurements. The experimental data can be used to examine the behaviour of phonon transport within the structures and correlate the thermal effects to the different phonon interactions present in such materials by modelling of phonon transport/dispersion. Thus, we are able to pinpoint the desirable structures within a material which can be exploited to influence the materials physical properties.
Our work with Li-ion battery nanomaterials looks at the influence and benefits of material structure, composition, size, shape and defined 2- and 3D assembly on Li-ion cell performance. The research focuses on cation insertion and removal processes in a range of semiconducting and metal oxide active battery materials and how problems associated with structural and chemical changes during operation can be mitigated through nanomaterial design and analysis. We also develop new materials and electrode material pairs for high performance Li-ion cells and in situ and operando spectroscopies and photonic probes for battery performance assessment, materials analysis, and diagnostics.