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Endogenous Dynamic Nuclear Polarization for Sensitivity Enhancement in Solid-State NMR of Electrode Materials
journal contribution
posted on 2020-03-20, 12:08 authored by Adi Harchol, Guy Reuveni, Vitalii Ri, Brijith Thomas, Raanan Carmieli, Rolfe H. Herber, Chunjoong Kim, Michal LeskesRational design of materials for
energy storage systems relies
on our ability to probe these materials at various length scales.
Solid-state NMR spectroscopy is a powerful approach for gaining chemical
and structural insights at the atomic/molecular level, but its low
detection sensitivity often limits applicability. This limitation
can be overcome by transferring the high polarization of electron
spins to the sample of interest in a process called dynamic nuclear
polarization (DNP). Here, we employ for the first time metal ion-based
DNP to probe pristine and cycled composite battery electrodes. A new
and efficient DNP agent, Fe(III), is introduced, yielding lithium
signal enhancement up to 180 when substituted in the anode material
Li4Ti5O12. In addition for being
DNP active, Fe(III) improves the anode performance. Reduction of Fe(III)
to Fe(II) upon cycling can be monitored in the loss of DNP activity.
We show that the dopant can be reactivated (return to Fe(III)) for
DNP by increasing the cycling potential window. Furthermore, we demonstrate
that the deleterious effect of carbon additives on the DNP process
can be eliminated by using carbon free electrodes, doped with Fe(III)
and Mn(II), which provide good electrochemical performance as well
as sensitivity in DNP-NMR. We expect that the approach presented here
will expand the applicability of DNP for studying materials for frontier
challenges in materials chemistry associated with energy and sustainability.
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Keywords
carbon additivesdetection sensitivityElectrode Materials Rational designDNP processtime metal ion-based DNPDNP activitySolid-state NMR spectroscopySensitivity EnhancementSolid-State NMRlithium signal enhancementbattery electrodesEndogenous Dynamic Nuclear Polarizationlimits applicabilitymaterials chemistryanode material Li 4 Ti 5 O 12FeDNP-NMRelectrochemical performancelength scalesfrontier challengesenergy storage systemsDNP agentanode performance
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