Investigating Li Microstructure Formation on Li Anodes for Lithium Batteries by in Situ ⁶Li/⁷Li NMR and SEM

Abstract

The growth of lithium microstructures during battery cycling has, to date, prohibited the use of Li metal anodes and raises serious safety concerns even in conventional lithium-ion rechargeable batteries, particularly if they are charged at high rates. The electrochemical conditions under which these Li microstructures grow have, therefore, been investigated by in situ nuclear magnetic resonance (NMR), scanning electron microscopy (SEM) and susceptibility calculations. Lithium metal symmetric bag cells containing LiPF 6 in EC: DMC electrolytes were used. Distinct 7 Li NMR resonances were observed due to the Li metal bulk electrodes and microstructures, the changes in peak positions and intensities being monitored in situ during Li deposition. The changes in the NMR spectra, observed as a function of separator thickness and porosity (using Celgard and Whatmann glass microfiber membranes) and different applied pressures, were correlated with changes in the type of microstructure, by using SEM. Isotopically enriched 6 Li metal electrodes were used against natural abundance predominantly 7 Li metal counter electrodes to investigate radiofrequency (rf) field penetration into the Li anode and to confirm the assignment of the higher frequency peak to Li dendrites. The conclusions were supported by calculations performed to explore the effect of the different microstructures on peak position/broadening, the study showing that Li NMR spectroscopy can be used as a sensitive probe of the both the amount and type of microstructure formation.

Real-time 3D imaging of microstructure growth in battery cells using indirect MRI

“…3 displays orthogonal cross-sections of the B 0 field map obtained from the susceptibility calculations and a histogram showing the variation in the B 0 field across the full voxel. A significant perturbation of 10-15 ppm is observed in the B 0 field close to the dendrite, matching well with 7 Li MRI (7, 10) and NMR (6,8,21) results, where the signals from the dendrites are observed to shift by up to 15 ppm relative to the bulk metal resonance. The effects are long-ranged, impacting the local field for all of the positions inside the voxel, albeit by small amounts.…”

“…NMR measurements are sensitive to dendrite growth and are also able to resolve different lithium microstructure morphologies through chemical shift measurements (6)(7)(8)(9). MRI approaches provide additional spatial information, allowing specific structural changes to be localized, thereby enhancing the utility of the methods and simplifying interpretation (7,10,11).…”

Visualizing electromagnetic fields in metals by MRI

“…[12][13][14]17,[22][23][24] Interestingly, the 3d CSI sheds new light on previous bulk metal NMR studies. For instance, in an earlier study, 12 a similar shift difference between NMR peaks was observed at and ⊥ orientations (relative to B 0 ) of the major faces of a thinner metal strip, by carrying out two separate experiments.…”

Correlating Structure and Properties of Super‐Concentrated Electrolyte Solutions: 17O NMR and Electrochemical Characterization

“…In order to deeply investigate the processes occurring in the novel electrochemical energy storage systems based on lithium metal anode, the combination of electrochemical techniques with bulk and advanced spectroscopic ones is mandatory. In this context, nuclear magnetic resonance (NMR) spectroscopy plays a key role to understand the processes taking place in a battery . NMR exploits the magnetic properties of atomic nuclei to find out information on the chemical environment in molecules and solids, as well as on its changes over time.…”

“…In this context, nuclear magnetic resonance (NMR) spectroscopy plays a key role to understand the processes taking place in a battery. [13][14][15][16] NMR exploits the magnetic properties of atomic nuclei to find out information on the chemical environment in molecules and solids, as well as on its changes over time. This last task is fulfilled by measuring the relaxation times of chemical species, namely T 1 and T 2 .…”