Sodium-ion batteries (SIBs) have attracted tremendous attentions in recent years due to the abundance and wide distribution of Na resource on the earth. However, SIBs still face the critical issues of low energy density and unsatisfactory cyclic stability at present. The enhancement of electrochemical performance of SIBs depends on comprehensive and precise understanding of the underlying sodium storage mechanism. Although extensive transmission electron microscopy (TEM) investigations have been performed to reveal the sodium storage property and mechanism of SIBs, a dedicated review on the in situ TEM investigations of SIBs has not been reported. In this review, recent progress in the in situ TEM investigations on the morphological, structural, and chemical evolutions of cathode materials, anode materials, and solid-electrolyte interface during the sodium storage of SIBs is comprehensively summarized. The detailed relationship between structure/composition of electrode materials and electrochemical performance of SIBs has been clarified. This review aims to provide insights into the effective selection and rational design of advanced electrode materials for high-performance SIBs.
Recent advances in scanning transmission electron microscopy have enabled atomic-scale focused, coherent, and monochromatic electron probes, achieving nanoscale spatial resolution, meV energy resolution, sufficient momentum resolution, and a wide energy detection range in electron energy-loss spectroscopy (EELS). A four-dimensional EELS (4D-EELS) dataset can be recorded with a slot aperture selecting the specific momentum direction in the diffraction plane and the beam scanning in two spatial dimensions. In this paper, the basic principle of the 4D-EELS technique and a few examples of its application are presented. In addition to parallelly acquired dispersion with energy down to a lattice vibration scale, it can map the real space variation of any EELS spectrum features with a specific momentum transfer and energy loss to study various locally inhomogeneous scattering processes. Furthermore, simple mathematical combinations associating the spectra at different momenta are feasible from the 4D dataset, e.g., the efficient acquisition of a reliable electron magnetic circular dichroism (EMCD) signal is demonstrated. This 4D-EELS technique provides new opportunities to probe the local dispersion and related physical properties at the nanoscale.
即使在像差校正电镜方兴未艾之时,材料的微观结构分析也面临残余像差、带轴偏离、表面损伤和辐照损伤等问题,不仅使电镜的空间分辨率近年来一直徘徊在 0.5 Å左右,而且制约了微观结构分析的可靠性和精度.电子叠层(electron ptychography)是结合扫描透射电镜和相干衍射成像的一种计算成像方法,具有高空间分辨、高相位精度、高剂量效率等特点.电子叠层包括数据采集和数值重构两个阶段.在数据采集阶段,通过像素化探测器记录电子束在样品上二维扫描时每个位置的二维衍射图,形成所谓的四维扫描透射电镜数据集(four-dimensional scanning transmission electron microscopy,4D-STEM).在数值重构阶段,通过合适的算法从这些数据集中提取样品的振幅和相位.相比像差校正减小透镜像差对成像质量的影响而言,电子叠层可以消除这种影响,实现零像差成像,近乎完美地重现样品的真实结构.作者从材料微观结构分析面临的主要问题出发,简要介绍电子叠层的基本原理和算法,并通过应用实例介绍电子叠层的主要特点.
瞬时液相焊接(TLP连接)是一种极具应用价值的高温合金连接和修复方法.本文对1 230℃ 下使用Ni-Cr-B中间层对镍基高温合金Mar-M247进行瞬时液相焊接的接头进行了显微结构表征,研究了由非等温凝固区(NSZ)、等温凝固区(ISZ)和扩散影响区(DAZ)组成的接头组织和沉淀相析出行为.研究结果表明:NSZ中析出相主要为M23(C,B)6和γ/γ'组成的共晶组织,其中伴生少量块状MC碳化物;与NSZ相邻的ISZ则由γ/γ'相组成;DAZ中的主要析出相为颗粒状和针状M5B3型硼化物,并伴生少量长直鱼骨状和不规则块状的M5B3型硼化物.更长的焊接保温时间会更有利于等温凝固过程,对样品进行焊后热处理可使接头组织更加均匀.
本文探讨了硫氧镁水泥(MOS)的微观结构和力学性能.结果发现硫氧镁水泥具有较高的力学性能,这得益于硫氧镁水泥的孔径主要分布在纳米量级上,几乎没有有害大孔,以及棒状的水化产物堆积交叉.MOS水泥主要由未完全反应氧化镁和水化产物5 Mg(OH)2·MgSO4·7H2O(5·1·7相)组成,5·1·7相微观形貌为微米级的棒状结构.
