Abstract
We have developed and explored an external automatic tuning/matching (eATM) robot that can be attached to commercial and/or home-built magic angle spinning (MAS) or static nuclear magnetic resonance (NMR) probeheads. Complete synchronization and automation with Bruker and Tecmag spectrometers is ensured via transistor-transistor-logic (TTL) signals. The eATM robot enables an automated “on-the-fly” re-calibration of the radio frequency (rf) carrier frequency, which is beneficial whenever tuning/matching of the resonance circuit is required, e.g. variable temperature (VT) NMR, spin-echo mapping (variable offset cumulative spectroscopy, VOCS) and/or in situ NMR experiments of batteries. This allows a significant increase in efficiency for NMR experiments outside regular working hours (e.g. overnight) and, furthermore, enables measurements of quadrupolar nuclei which would not be possible in reasonable timeframes due to excessively large spectral widths. Additionally, different tuning/matching capacitor (and/or coil) settings for desired frequencies (e.g.7Li and 31P at 117 and 122MHz, respectively, at 7.05 T) can be saved and made directly accessible before automatic tuning/matching, thus enabling automated measurements of multiple nuclei for one sample with no manual adjustment required by the user. We have applied this new eATM approach in static and MAS spin-echo mapping NMR experiments in different magnetic fields on four energy storage materials, namely: (1) paramagnetic 7Li and 31P MAS NMR (without manual recalibration) of the Li-ion battery cathode material LiFePO4; (2) paramagnetic 17O VT-NMR of the solid oxide fuel cell cathode material La2NiO4+δ; (3) broadband 93Nb static NMR of the Li-ion battery material BNb2O5; and (4) broadband static 127I NMR of a potential Li–air battery product LiIO3. In each case, insight into local atomic structure and dynamics arises primarily from the highly broadened (1–25MHz) NMR lineshapes that the eATM robot is uniquely suited to collect. These new developments in automation of NMR experiments are likely to advance the application of in and ex situ NMR investigations to an ever-increasing range of energy storage materials and systems.
Highlights
The development of solid-state materials for energy storage and conversion relies on understanding fundamental relationships between structure and bulk properties such as electronic and ionic conductivity [1,2,3,4,5]
We report on the development and application of an external automatic tuning/matching robot to repeatedly and accurately recalibrate the resonance circuit without manual intervention, e.g. during time-consuming experiments requiring collection of many individual sub-spectra
In addition to the external automatic tuning/matching (eATM) robot itself (Fig. 1c), the equipment includes specially designed rods with adjustable clamping connectors (‘‘fingertips”) that can be attached to the outside of the tuning/matching rods of any commercial or homebuilt static or magicangle spinning (MAS) probehead (Fig. 1d)
Summary
The development of solid-state materials for energy storage and conversion (e.g. in batteries, supercapacitors, and fuel cells) relies on understanding fundamental relationships between structure and bulk properties such as electronic and ionic conductivity [1,2,3,4,5]. Among the major challenges in acquiring and interpreting solid-state NMR spectra of functional energy materials are the presence of extremely large anisotropic interactions that cannot be effectively averaged by standard techniques such as magicangle spinning (MAS) or specialized pulse programs [17,18]. These interactions provide important electronic and structural details about the system of interest, they give rise to broad powder patterns that exceed the NMR probe bandwidth
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