Atomic-layer-deposition (ALD) coatings have been increasingly used to improve battery performance. However, the electrochemical and mechanistic roles remain largely unclear, especially for ALD coatings on electrodes that undergo significant volume changes (up to 100%) during charging/discharging. Here we investigate an anode consisting of tin nanoparticles (SnNPs) with an ALD-Al2O3 coating. For the first time, in situ transmission electron microscopy unveiled the dynamic mechanical protection of the ALD-Al2O3 coating by coherently deforming with the SnNPs under the huge volume changes during charging/discharging. Battery tests in coin-cells further showed the ALD-Al2O3 coating remarkably boosts the cycling performance of the Sn anodes, comparing with those made of bare SnNPs. Chemomechanical simulations clearly revealed that a bare SnNP debonds and falls off the underlying substrate upon charging, and by contrast the ALD-Al2O3 coating, like ion-conductive nanoglue, robustly anchors the SnNP anode to the substrate during charging/discharging, a key to improving battery cycle performance.

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In this research, acid hydrolyzed starch, B-type microcrystalline starch, and amorphous starch were prepared from natural corn starch. X-ray diffraction (XRD) and Raman spectroscopy were used to analyze the structure of these four types of starches. The Raman spectrum scattering peaks have decreased vibration wave numbers because of the changes of crystal type, and the intensity of each Raman peak is related to the size of the crystalline region. By identifying the scattering peak area in Raman spectrum as the crystalline region and the total area under the scattering curve minus the fluorescent area as the sum of the amorphous and crystalline regions, we have established a useful method for calculating the crystallinity of starch samples by Raman spectra. The comparison of results by Raman spectra with those by X-ray diffraction indicated that when the sample had high crystallinity, the difference between XRD and Raman spectrum results is small. When the sample crystallinity was low, the error of this method was only slightly larger. Therefore, Raman spectroscopy could be used as an efficient method for evaluation of the relative crystallinity of starches.

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