Probing ionic diffusion in battery materials using NMR

This project falls within the EPSRC Physical Sciences and Energy research areas.
The need for better batteries has never been greater. Due to their high energy densities, lithium ion batteries have revolutionised consumer electronics and are playing a central role in the electrification of transport. In order to support the transition to renewable energy sources and as the automotive sector becomes fully electric, new high-performing materials will be needed. In order to meet this demand, new materials are required for use in Li-ion cells but also for the development of new technologies such as all solid-state batteries. For example, solid electrolytes make the use of a lithium metal anode possible, significantly increasing the energy density. Understanding ionic diffusion in these materials is key to tuning compositions, developing new materials and enabling new battery technologies.
The development of a comprehensive physical picture of ion transport is challenging because in any one material ion transport crosses a large range of time and length scales. Ion transport is divided into microscopic and macroscopic levels, where the macroscopic processes consist of a series of microscopic events. Microscopic processes can be probed using variable-temperature nuclear magnetic resonance spectroscopy (NMR) and NMR relaxometry, however, these techniques are unable to review the long-range lithium diffusion. Pulsed-field gradient (PFG) NMR allows the measurement of macroscopic ionic diffusion through solid materials. PFG is nuclei specific and can therefore provide information about each of the ion's contributions. This technique is highly informative and complementary to Electrochemical Impedance Spectroscopy (EIS). When PFG and EIS can be used successfully in tandem, the mobile ion concentration can be estimated.
This project will involve technique development to enable data collection and analysis to be carried out on a range of battery materials. PFG NMR will be used to measure diffusion coefficients, activation energies and estimate conductivities of a range of important battery materials, such as solid electrolytes. Alongside NMR, a number experimental techniques will be used to provide complementary data. Electrochemical cycling and techniques, such as EIS, will be used to investigate performance. Techniques, including diffraction, microscopy and tomography will provide additional structural data to support models.
The project is co-funded by Johnson Matthey as part of an iCASE studentship.