Revealing the Solid-Electrolyte Interphase for Water-in-Salt Electrolytes

Rechargeable batteries have a vital role to play in meeting our future energy needs, with Li-ion chemistries already widely deployed in portable electronics and electric vehicles. However, increasing deployment of intermittent renewable energy sources requires grid-scale battery storage solutions, where energy density is less critical, but cost, safety and lifetime are even greater priorities. This project aims to investigate aqueous Na and K-ion batteries, that offer lower cost and improved safety for grid-scale applications, compared to Li-ion batteries. 

The focus will be on using concentrated aqueous electrolytes known as water-in-salt (WIS), that avoid flammable organic solvents altogether. A very high salt concentration expands the electrochemical stability window of WIS electrolytes by altering the activity of water, whilst decomposition of the salt can further extend the stable potential window by producing a solid electrolyte interphase (SEI) that supresses further side reactions. However, the nature of this SEI and its stability at the low potentials where alkali-ions intercalate into common anode materials (e.g. graphite) remains extremely limited, in part due to the SEI’s tendency to dissolve on electrode rinsing. This project will therefore apply interface-sensitive operando techniques developed in the group for probing the chemistry of electrode-electrolyte interfaces with X-rays (XPS, NEXAFS) and Neutrons (NR). The understanding developed will then be used to develop approaches for forming a desired SEI composition to enable long-term battery cycling. This will include the use of additional salts in the electrolyte as well as coating electrodes with precursor layers that decompose to form the SEI. 

The successful candidate will develop experience in battery fabrication, electrochemical characterisation and the application of X-ray photoelectron spectroscopy to study battery materials. They will also periodically access large-scale user facilities at the nearby Diamond Light Source and ISIS Neutron Source to perform operando measurements during electrochemical cycling, and learn how to analyse NEXAFS and NR data.

Any questions concerning the project can be addressed to Dr Robert Weatherup (

General enquiries on how to apply can be made by e mail to  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

Electrode-Electrolyte Interface


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