Improving the Stability Limits of Water-in-Salt Electrolytes

Rechargeable batteries are playing an increasingly critical role in vehicle electrification and grid-scale energy storage, with lithium-ion chemistries already widely deployed. The growing integration of intermittent renewable energy sources, however, places new demands on grid-scale storage, where cost, safety, and operational lifetime are more important than energy density. This project will investigate aqueous lithium-ion electrolytes, which offer reduced cost and enhanced safety compared with the conventional organic electrolytes used in commercial lithium-ion batteries.

The research will focus on environmentally friendly, fluorine-free water-in-salt electrolytes (WiSEs), which avoid flammable organic solvents and costly fluorine-containing salts. At high concentrations, these electrolytes expand the electrochemical stability window by altering water and ion activity, while decomposition of salts and cosolvents can further stabilise operation through the formation of a solid electrolyte interphase (SEI). Although significant progress has been made in understanding WiSEs, commercially viable formulations and clear design principles for optimised mixtures remain to be established.

This project will investigate the influence of salt concentration and cosolvent identity on the electrochemical stability of water. Through this you will gain experience in battery fabrication, electrochemical characterisation, and advanced X-ray spectroscopy (XPS and NEXAFS). There will be opportunities to access large-scale user facilities, such as Diamond Light Source, to perform operando measurements during cycling and develop expertise in the analysis of complex spectroscopy data. The influence of electrolyte composition on coordination environments may also be explored through classical molecular dynamics simulations and thermodynamic lattice fluid theories, with modelling results compared directly to experimental measurements.

Any questions concerning the project can be addressed to Prof Robert Weatherup (robert.weatherup@materials.ox.ac.uk) or Dr Conor Phelan (conor.phelan@materials.ox.ac.uk).

General enquiries on how to apply can be made by e mail to graduate.studies@materials.ox.ac.uk.  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 https://www.ox.ac.uk/admissions/graduate/applying-to-oxford.