Cathode Materials for Lithium Ion Batteries

The rapid development of technology has necessitated the innovation of new energy storage devices in the form of batteries. Cathode materials for both lithium and sodium ion batteries remain a stumbling block on the road to building better batteries for large-scale applications. Unlike other methods that observe long-range structural information, NMR can uniquely probe the local environment of the mobile ion, offering the ability to ‘watch’ the Li ions as they move through the complex 3D networks making up many useful cathodes. Our research in this area focuses on the study of Li and Na ion dynamics in various layered oxide and polyanionic structures using several advanced NMR techniques such as MATPASS, 2D Exchange Spectroscopy, and one-dimensional selective inversion recovery experiments. Simulations and DFT calculations done in conjunction with ssNMR experiments facilitate a detailed and quantitative understanding of structure and ion dynamics in these materials. Using these tools, we are able to quantify exchange rates for Li (and Na) ions occupying unique crystallographic positions within a structure, ultimately allowing us to attribute inherent local ion dynamics to structural features and electrochemical performance. 

Ongoing research in the Goward group involves the use of both ⁶Li and ⁷Li NMR to identify energy barriers for Li ion hopping in phosphate and fluorophosphate networks such as LiVPO₄F and Li₃Fe₂(PO₄)₃ using a combination of 2D EXSY and selective inversion experiments to quantitatively measure exchange rates.  We have additionally extended these NMR methods to alternative sodium cathode materials, such as Na₂FePO₄F, where we are able to successfully track the desodiation process during electrochemical cycling by ex situ  ²³Na NMR spectroscopy.