Fast-ion conductors are critical to the development of solid-state batteries. The effects of mechanochemical synthesis that lead to increased ionic conductivity in an archetypical sodium-ion conductor Na 3 PS 4 are not fully understood. We present here a comprehensive analysis based on diffraction (Bragg, pair distribution function), spectroscopy (impedance, Raman, NMR, INS) and ab-initio simulations aimed at elucidating the synthesis-property relationships in Na 3 PS 4. We consolidate previously reported interpretations about the local structure of ball-milled samples, underlining the sodium disorder and showing that a local tetragonal framework more accurately describes the structure than the originally proposed cubic one. Through variable-pressure impedance spectroscopy measurements, we report for the first time the activation volume for Na + migration in Na 3 PS 4 , which is ~30% higher for the ball-milled samples. Moreover, we show that the effect of ball-milling on increasing the ionic conductivity of Na 3 PS 4 to ~10-4 S/cm can be reproduced by applying external pressure on a sample from conventional high temperature ceramic synthesis. We conclude that the key effects of mechanochemical synthesis on the properties of solid electrolytes can be analyzed and understood in terms of pressure, strain and activation volume. File list (2) download file view on ChemRxiv Na3PS4_mechanical_v10.1.pdf (2.18 MiB) download file view on ChemRxiv SI_Na3PS4_mechanical_v10.1.pdf (2.38 MiB)
We investigated the lithium peroxide (Li 2 O 2 ) and pore size distribution in lithium−O 2 battery electrodes at different states of charge using transmission X-ray microscopy coupled with Zernike phase contrast to carry out nanocomputed tomography. We report that such a technique enables us, at the nanoscale, to distinguish light elements such as carbon and Li 2 O 2 in Li− O 2 battery cathode electrodes. We verified by wave-propagation simulation that this approach efficiently improves the contrast of images in comparison with pure absorption. The Li 2 O 2 distribution and thickness, interphases, and pore network are visualized and quantified, giving a valuable insight into our cathode architecture. From this 3D analysis, we highlight modifications of the air-cathode morphology and the Li 2 O 2 spatial organization as well as their potential implication in terms of carbon surface passivation and pore-clogging. After the full recharge process, this technique can also reveal the spatial distribution of the residual Li 2 O 2 and other byproducts.
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