Materials degradation—the main limiting factor for widespread application of alloy anodes in battery systems—was assumed to be worse in sodium alloys than in lithium analogues due to the larger sodium-ion radius. Efforts to relieve this problem are reliant on the understanding of electrochemical and structural degradation. Here we track three-dimensional structural and chemical evolution of tin anodes in sodium-ion batteries with in situ synchrotron hard X-ray nanotomography. We find an unusual (de)sodiation equilibrium during multi-electrochemical cycles. The superior structural reversibility during 10 electrochemical cycles and the significantly different morphological change features from comparable lithium-ion systems suggest untapped potential in sodium-ion batteries. These findings differ from the conventional thought that sodium ions always lead to more severe fractures in the electrode than lithium ions, which could have impact in advancing development of sodium-ion batteries.

Anisotropy, or alternatively, isotropy of phase transformations extensively exist in a number of solid-state materials, with performance depending on the three-dimensional transformation features. Fundamental insights into internal chemical phase evolution allow manipulating materials with desired functionalities, and can be developed via real-time multi-dimensional imaging methods. Here, we report a five-dimensional imaging method to track phase transformation as a function of charging time in individual lithium iron phosphate battery cathode particles during delithiation. The electrochemically driven phase transformation is initially anisotropic with a preferred boundary migration direction, but becomes isotropic as delithiation proceeds further. We also observe the expected two-phase coexistence throughout the entire charging process. We expect this five-dimensional imaging method to be broadly applicable to problems in energy, materials, environmental and life sciences.

cycle stability. [6][7][8] A bottleneck for high performance in Na batteries is the cathode side in which the specify capacity is lower than 200 mA h g −1 because typical intercalation compound cathodes generally only accommodate one sodium ion per transition metal core. [9,10] In order to enhance energy densities of Na-based batteries, one way is to increase the upper cell reaction voltage limit during charge, [11,12] which is particularly challenging for Na-based battery cathodes due to the lower chemical potentials (2.71 V for Na + /Na vs 3.04 V for Li + /Li, with respect to standard hydrogen electrode). What is more, instability of electrolytes and undesirable side reactions at high voltages also pose additional challenges.The other way to achieve high capacity is to design materials in which more Na ions per metal can be incorporated reversibly. Similar to the lithium-ion system, conversion materials have been expected to be a promising candidate in the sodiumion system because they have the potential to accommodate over one sodium ion in the structure. However, undesirable drawbacks of conversion materials in lithiumion batteries such as poor cycle stability, low reversibility, and large voltage hysteresis also occur in Na-ion batteries. [13,14] Despite decades of research efforts and numerous reports in lithium ion system, the mechanisms underpinning the conversion reactions in sodium batteries, in particular irreversibility and large voltage hysteresis are less understood. [15][16][17] In this work, phase transformation and distribution in sodium-metal sulfide batteries has for the first time been imaged by in operando synchrotron full-field transmission X-ray microscopy (TXM) during multiple charge/discharge cycles. FeS was selected as the model material owing to its representative property and high theoretical capacity (≈610 mA h g −1 ). [18] 2D chemical phase evolution and composition information of FeS are directly mapped by TXM with X-ray absorption near edge structure (XANES) technique, and sodium ion diffusivity is investigated by galvanostatic intermittent titration technique (GITT). 3D microstructural evolution and its quantification are achieved by synchrotron X-ray nanotomography. [8,19,20] Through these approaches, we are able to comprehensively understand the origin of irreversible and large voltage hysteresis in Na-FeS Irreversible electrochemical behavior and large voltage hysteresis are commonly observed in battery materials, in particular for materials reacting through conversion reaction, resulting in undesirable round-trip energy loss and low coulombic efficiency. Seeking solutions to these challenges relies on the understanding of the underlying mechanism and physical origins. Here, this study combines in operando 2D transmission X-ray microscopy with X-ray absorption near edge structure, 3D tomography, and galvanostatic intermittent titration techniques to uncover the conversion reaction in sodium-metal sulfide batteries, a promising high-energy battery system. This study shows a high...

Transmission X-ray microscopy is utilized to monitor, in real time, the behavior of the PbSO 4 film that is formed on Pb in H 2 SO 4 . Images collected from the synchrotron x-rays are coupled with voltammetric data to study the initial formation, the resulting passivation, and the subsequent reduction of the film. It is concluded with support from quartz-crystal-microbalance experiments that the initial formation of PbSO 4 crystals occurs as a result of acidic corrosion. In addition, the film is shown to coalesce during the early stages of galvanostatic oxidation and to passivate as a result of morphological changes in the existing film. Finally, it is observed that the passivation process results in the formation of large PbSO 4 crystals with low area-to-volume ratios, which are difficult to reduce under both galvanostatic and potentiostatic conditions.

This study is focused on micro-scale measurement of metal (Ca, Cl, Fe, K, Mn, Cu, Pb, and Zn) distributions in Spartina alterniflora root system. The root samples were collected in the Yangtze River intertidal zone in July 2013. Synchrotron X-ray fluorescence (XRF), computed microtomography (CMT), and X-ray absorption near-edge structure (XANES) techniques, which provide micro-meter scale analytical resolution, were applied to this study. Although it was found that the metals of interest were distributed in both epidermis and vascular tissue with the varying concentrations, the results showed that Fe plaque was mainly distributed in the root epidermis. Other metals (e.g., Cu, Mn, Pb, and Zn) were correlated with Fe in the epidermis possibly due to scavenge by Fe plaque. Relatively high metal concentrations were observed in the root hair tip. This micro-scale investigation provides insights of understanding the metal uptake and spatial distribution as well as the function of Fe plaque governing metal transport in the root system.

The galvanostatic growth of PbSO 4 on Pb in H 2 SO 4 was studied using scanning electron microscopy and in situ transmission x-ray microscopy (TXM). Images from the TXM are used to investigate the effects of sodium lignosulfonate on the PbSO 4 formation and the initial growth of the PbSO 4 crystals. Sodium lignosulfonate is shown to retard, on average, the growth of the PbSO 4 crystals, yielding a film with smaller crystals and higher crystal densities. In addition, results from experiments with and without sodium lignosulfonate indicate an increase in the nucleation rate of the PbSO 4 crystals when the oxidation current is applied, which was attributed to an increase in the supersaturation of the electrolyte. Furthermore, an analysis of the growth rates of individual, large crystals showed an initial rapid growth which declined as the PbSO 4 surface coverage increased. It was concluded that the increase in PbSO 4 provides additional sites for precipitation and reduces the precipitation rate on the existing crystals. Finally, the potentialtime transient at the beginning of oxidation is suggested to result from the relaxation of a supersaturated solution and the development of a PbSO 4 film with increasing resistance.

This study investigates the distributions of Br, Ca, Cl, Cr, Cu, K, Fe, Mn, Pb, Ti, V and Zn in Phragmites australis root system and the function of Fe nanoparticles in scavenging metals in the root epidermis using synchrotron X-ray microfluorescence, synchrotron transmission X-ray microscope measurement and synchrotron X-ray absorption near-edge structure techniques. The purpose of this study is to understand the mobility of metals in wetland plant root systems after their uptake from rhizosphere soils. Phragmites australis samples were collected in the Yangtze River intertidal zone in July 2013. The results indicate that Fe nanoparticles are present in the root epidermis and that other metals correlate significantly with Fe, suggesting that Fe nanoparticles play an important role in metal scavenging in the epidermis.

In recent years, sodium-ion batteries (NIB) have attracted much attention due to their low cost and abundant resources. Because sodium shares the similar chemical properties and fundamental principles as lithium, many battery materials that function well in Li ion systems were therefore expected to work well with Na ion systems. Nevertheless, more and more recent studies indicate some discrepancies in the behavior of the reaction mechanism. As a result, some understanding and knowledge of the Li-ion system cannot be applied directly to the Na-ion system. Compared to comprehensively studied Li-ion batteries, Na-ion batteries are still largely unexplored and critically need more fundamental studies. In this talk, we present a non-destructive in situ 3D x-ray nanotomography study of Na-ion electrode by using a newly developed transmission x-ray microscopy (TXM) technique at National Synchrotron Light Source, Brookhaven National Laboratory. [1-5]  The TXM possesses a few unique capabilities including large field of view, super resolution in 3D, local tomography and automated markerless image acquisition and alignment, enabling high quality 3D observation and analysis. The unique electrochemical cell developed in-house allows real electrochemical measurement, e.g. discharge/charge profile, to be correlated to the 3D tomography observation during the electrochemical reactions. Sn is a well-established model material for studying the alloy-dealloy process occurring in Metal-ion battery systems. For the first time we have tracked the 3D microstructural change of Sn alloy anode in a Na-ion battery, and quantitatively analyzed the 3D microstructural evolution during ten electrochemical cycles. By correlating the quantified 3D microstructural information to the chemical change, we observed a 3D microstructural equilibrium occurring after the first cycle. Contrary to our conventional wisdom at its Li-ion analogue, Sn exhibits excellent microstructural reversibility with negligible pulverization during Na-ion extraction. The observed unusual low-volume NaxSn phase considerably accommodates the Na-ion insertion-induced stress. 3D surface curvature analysis also explains the microstructural stability in NIB. These new findings bring fresh insight into the mechanism of the microstructural degradation and contribute to engineering advanced battery materials. This talk will also present a comparative study of Sn in NIB and LIB, and reveal the significant difference in microstructural/electrochemical equilibrium for these two battery systems. Details about in situ 3D X-ray imaging technology, our beamline, and its broaden application in energy studies will also be discussed.  References 1. J. Wang, Y. K. Chen, Q. Yuan, A. Tkachuk, C. Erdonmez, B. Hornberger and M. Feser, Appl. Phys. Lett., 2012, 100, 143107. 2. J. Wang, Y. K. Chen-Wiegart, J. Wang, Chem. Commun. 2013, 49. 6480-6482.  3. J. Wang, Y. K. Chen-Wiegart, J. Wang, Angew. Chem. Int. Ed. 2014, 53, 4460 –4464. 4. J. Wang, Y. K. Chen-Wiegart, J. Wang, Nat. Commun. 2014, 5, 4570. 5. J. Wang. et al. Nat. Commun. 2014, 5, 3415. Figure 1