Understanding The Electrical Double Layer of Localized High Concentration Electrolytes
Li-ion batteries are an essential component of our portable electronics, and have become increasingly important for transportation and the storage of intermittent renewable energy in residential properties. The current electrolyte formulations used in these Li-ion batteries have a number of safety concerns, however, such as the flammability of the carbonate solvents. There is thus a need to develop new, safer battery electrolyte formulations that either do not use these carbonate solvents, such as water-in-salt electrolytes, or that include other solvents to suppress flammability. In the latter case, localized high concentration electrolytes (LHCEs) are a promising class of such electrolytes, which can be considered as a conventional battery electrolyte with a high salt concentration, which is then diluted to the standard 1M concentration with a non-flammable co-solvent. There is significant potential for LHCEs to replace conventional battery electrolytes given their similar chemistries, good transport properties and excellent interfacial stability, which is associated with the highly fluorinated co-solvents leading to formation of a stable solid electrolyte interphases (SEI) from.
Improving the interfacial stability and cycling performance of the LHCEs, requires a detailed understanding of how the electrolyte components arrange at an electrified interface, as what accumulates at the interface plays a critical role in what ends up reacting and forming the SEI. Although models exist to explain the structure of the electrical double layer (EDL) that forms at interfaces in dilute electrolytes, very little is known about the structure of the EDL formed in LHCEs. Therefore, the aim of this project is to reveal the structure of the EDL formed in LHCEs using experimental and simulation approaches, and then understand how this relates to the promising stability of LHCEs.
Experimentally, interface-sensitive operando techniques will be used to probe the electrode-electrolyte interfaces with X-rays (XPS, NEXAFS) and Neutrons (NR). This will allow the EDL of the electrolyte to be probed, and the early onset of the SEI formation to be characterised. To compliment these experiments, theory and simulation techniques will be used to provide atomistic insight. As classical force fields are known to have significant deficiencies when simulating EDLs, and reaching the required time and length scales is challenging with ab initio molecular dynamics, we will instead develop a machine learning (ML) interatomic potential to simulate the EDL of LHCEs. The structure of LHCEs at a Li-metal anode will be investigated, and the dynamics of charging characterised. These results will be compared against the experimental results. Moreover, as ML force fields are reactive, the reactions occuring at the Li-metal anodes will also be investigated.
Any questions concerning the project can be addressed to Dr Zac Goodwin (zac.goodwin@materials.ox.ac.uk) or Prof Robert Weatherup (robert.weatherup@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.
