Abstract
All-solid-state batteries potentially offer safe, high-energy-density electrochemical energy storage, yet are plagued with issues surrounding Li microstructural growth and subsequent cell death. We use 7Li NMR chemical shift imaging and electron microscopy to track Li microstructural growth in the garnet-type solid electrolyte, Li6.5La3Zr1.5Ta0.5O12. Here, we follow the early stages of Li microstructural growth during galvanostatic cycling, from the formation of Li on the electrode surface to dendritic Li connecting both electrodes in symmetrical cells, and correlate these changes with alterations observed in the voltage profiles during cycling and impedance measurements. During these experiments, we observe transformations at both the stripping and plating interfaces, indicating heterogeneities in both Li removal and deposition. At low current densities, 7Li magnetic resonance imaging detects the formation of Li microstructures in cells before short-circuits are observed and allows changes in the electrochemical profiles to be rationalized.
Highlights
All-solid-state batteries are one of the most promising technologies to improve safety and energy density of Libased batteries.[1]
Symmetrical Li−LLZTO−Li cells were assembled by placing Li metal disks on either side of LLZTO pellets (Figure 1a)
We note that no 7Li magnetic resonance imaging (MRI) signal is seen connecting the two electrodes, indicating that the structure that caused the short-circuit is below the detection limit of the NMR measurement
Summary
All-solid-state batteries are one of the most promising technologies to improve safety and energy density of Libased batteries.[1]. We show that 7Li NMR chemical shift imaging (CSI) provides chemical and spatial information on Li microstructural growth in Li−LLZTO−Li symmetric cells (where LLZTO is Ta-doped LLZO). Ex situ 7Li CSI measurements performed after applying different current densities indicate that 7Li magnetic resonance imaging (MRI) is a useful tool to detect Li microstructural growth prior to the observation of obvious symptoms in the voltage profiles during galvanostatic cycling. Ta-doped powder, the calcined and ball-milled Ta-doped powder, and the sintered Ta-doped powder were collected and compared to the LLZO cubic phase reported in the literature.[20] The measurements were performed at room temperature and 2θ ranged from 10 to 70°. A total echo time of 700 μs was used with a field of view of 20 mm (nominal resolution of 300 μm)
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