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Li-ion batteries experience mechanical stress evolution due in part to Li intercalation into and de-intercalation out of the electrodes, ultimately resulting in performance degradation. In situ measurements of electrode stress can be used to analyze stress generation factors, verify mechanical deformation models, and validate degradation mechanisms. They can also be embedded in Li-ion battery management systems when stress sensors are either implanted in electrodes or attached on battery surfaces. This paper reviews in situ measurement methods of electrode stress based on optical principles, including digital image correlation, curvature measurement, and fiber optical sensors. Their experimental setups, principles, and applications are described and contrasted. This literature review summarizes the current status of these stress measurement methods for battery electrodes and discusses recent developments and trends.

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BACKGROUND Alkali metals are considered important chemical promoters used in Fischer–Tropsch synthesis (FTS) iron‐based catalysts. The purpose of this study is to distinguish the relative effects of alkali metals on iron based FTS catalysts. RESULTS It is found that Li and Na promoters can easily diffuse into/out the bulk of catalysts while K, Rb and Cs mostly concentrate on the catalyst surface. Alkalis also inhibited H2 adsorption, improved CO adsorption and dissociation, and suppressed the hydrogenation of carbon species on the surfaces of iron or iron carbides. Li and Na decreased the FTS activity while K, Rb and Cs largely increased the FTS activity of iron catalysts. The selectivities to methane and alkane were decreased while those to olefin and heavier hydrocarbons were increased by alkalis. Among these alkalis, potassium showed an optimal promotional effect on FTS performances. CONCLUSION The distributions of alkalis in catalysts were quite different owing to their atomic radii. The majority of Li and Na promoters diffused into the bulk of catalysts while K, Rb and Cs mostly concentrated on the catalyst surface. The selectivity of methane exhibits a parabola‐like trend with increasing atomic number of alkalis and reaches a minimum at KFeSi catalyst. © 2016 Society of Chemical Industry

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