In Situ Magnetic Resonance Characterizations of Rechargeable Batteries

Magnetic resonance techniques, including nuclear magnetic resonance spectroscopy (NMR), magnetic resonance imaging (MRI), and electron magnetic resonance (EPR), are non-invasive techniques used to examine both surface chemistry and bulk properties. These techniques employ nuclear or electron spins as probes for interrogating structures and dynamics. We have employed these techniques in situ to understand the working and failing mechanisms of rechargeable batteries. Utilizing in situ ⁷Li NMR, we determined the lithiation and delithiation sequence and rates at different structural sites in high-voltage transition metal oxide cathodes. Via in situ ¹⁷O NMR, we evaluated the reactivity of various oxygen species in these high-voltage transition metal oxide cathodes and the reversibility of these O redox reactions. In conjunction with in situ EPR, we discovered the synergy of the hybridized O_2p and TM_3d orbitals to deliver additional capacities in Li transition metal oxide materials and the subsequent stabilization of the structures to ensure reversibility. Combined in situ NMR and EPR also prove beneficial to elucidating redox mechanisms in organic cathode materials. Our recent work has demonstrated the efficacy of in situ 7Li MRI in identifying new dendrite formation mechanisms in solid-state batteries and new phenomena in the dendrite formation process. In situ tracer-exchange NMR is useful for mapping out ion transport pathways in complex ion conductors and distinguishing dendrite formation mechanisms at different charge states. In summary, in situ magnetic resonance techniques are useful for uncovering structural and dynamic aspects of energy materials with spatial and temporal resolution.