Solid-State Magnetic Resonance Studies of Reaction Mechanisms and Ion Dynamics in Materials for Energy Storage and Conversion

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The performance of many electrochemical devices, such as batteries and fuel cells, depends on the movement of ions. For example, the movement of lithium ions determines the rate at which a battery can be recharged, and the acceleration performance of an electric vehicle. The recurring theme in our research is to understand these dynamics quantitatively, and site-specifically. In the next phase of our research program we propose to quantify Li+ ion dynamics, and to correlated site-specific dynamics with the crystal structures of important new cathode materials, using 6Li solid-state nuclear magnetic resonance (SS-NMR). Materials of interest include the open-framework tavorites and pyrophosphates. In situ 7Li NMR spectroscopy of cycling lithium ion cells will be implemented to study the electrochemical processes as they happen. In the area of lithium-air cells, the initial excitement over the theoretical capacity of the cells (competitive with gasoline) has been dampened by recent results in the literature, indicating that the electrochemical process is poorly understood. We propose to utilize 7Li and 17O SS-NMR to probe the reaction products as a function of electrolyte composition. This will allow us to determine what governs the favoured electrochemical reaction. Moreover, we propose new in situ studies using hyperpolarized (HP) 129Xe NMR for the first time to probe structural changes of the porous cathodes of lithium-air cells as the electrochemistry proceeds. These tools will substantially advance our ability to answer open questions regarding the performance of materials in these devices. Using in situ NMR spectroscopy of the electrochemical cycling of LIBs and LACs will allow us to identify the intermediate species, and degradation products, as a function of charge and discharge. Finally, in proton-exchange membrane fuel cells, we will probe the proton transport using advanced 1H NMR methods. We aim to characterize novel composites based on protic-ionic liquids, incorporated within polymer hosts, which will provide excellent proton conductivity at high temperature and low relative humidity.