Simultaneous wide and small angle operando neutron total scattering to probe electrolyte ordering in supercapcitors

Dr Chris Howard
University College London
Industry Co-Sponsor
ISIS Neutron and Muon Source
Project Description
Achieving net-zero emissions targets demands new methods for the efficient storage of energy from renewable sources. Here supercapacitors show extraordinary promise, but despite rapid progress, substantial development are still necessary to overcome current limitations in energy and power density. Energy in supercapacitors is stored in the electrical double layer (EDL) of adsorbed ions on high surface area electrodes. However, the structure of EDL has never been measured in atomistic detail due to a lack of suitable methods.

Atomistically-resolved measurements of these systems can be uniquely investigated by the multi-lengthscale diffractometer NIMROD at the ISIS neutron source. The scattering, augmented using multiple isotopically-distinct datasets, is analysed with the aid of computer models, to revealed a full 3D structure in the liquid. NIMROD allows simultaneous analysis of Small-angle scattering, giving details of the pore structure and electrolyte composition in the electrodes, and analysis of the wide angle scattering reveals the solvation structure of the ions and the organisation of the ions and of hydrogen-containing solvents at the electrode surfaces that underpin charge storage.

This 4-year PhD project will develop an operando electrochemical cell for use on NIMROD to make for the first time detailed measurements of the EDL in supercapacitors as a function of charge. A further development will be the enhancement of simulation-based analysis tools specific to high surface area and charged materials. This detailed measurement of the structure of the EDL is only possible at NIMROD and the understanding gained will provide profound insights for those optimising supercapacitors and beyond.

Key Techniques
• Operando Wide Q range total Neutron scattering using NIMROD at ISIS: The NIMROD instrument combines the traditionally separate techniques of Small-Angle Scattering (SANS) and neutron diffraction. SANS affords information of the structure of collections of atoms. For supercapacitors it allows us to observe changes of composition within nano-pores in the electrode and changes in structure of the electrolyte itself within the porous material.

• Operando Raman spectroscopy (RS). RS is sensitive to the charge state of graphitic materials, including the electrodes used for supercapacitors. Building on previous operando studies of batteries, we will build capabilities in the hardware and analysis of RS to complement the structural studies.

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Joshua Bailey

Being part of the CDT-ACM was an all-round fantastic experience; I not only received great training in a range of advanced characterisation techniques, but I also made strong links with industry and strong bonds with my cohort which have both led to fruitful collaborations.