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.