In this report, the electrochemical sodiation and desodiation in single crystalline alpha-MnO₂ nanowires are studied dynamically at both single particle level using in situ transmission electron microscopy (TEM) and bulk level using in situ synchrotron X-ray. The TEM results suggest that the first sodiation process starts with tunnel-based Na⁺ intercalation, experiences the formation of Na_0.5MnO₂ as a result of tunnel degradation, and ends with the Mn₂O₃ phase. The inserted Na⁺ can be partially extracted out of the sodiated products, and the following cycles are dominated by the reversible conversion reaction between Na_0.5MnO₂ and Mn₂O₃. The Mn valence evolution inside a cycling coin using alpha-MnO₂ nanowire electrode also exhibits partially reversible characteristic, agreeing well with the in situ TEM analysis. The sodiation is compared with lithiation in the same alpha-MnO₂ nanowires. Both Na⁺ and Li⁺ interact with the tunneled structure via a similar tunnel-driven intercalation mechanism before Mn⁴⁺ is reduced to Mn^3.5+. For the following deep insertion, the tunnels survive up to LiMnO₂ (Mn³⁺) during lithiation, while the sodiation proceeds via a different mechanism that involves obvious phase transition and fast tunnel degradation after Mn’s valence is below 3.5+. The difference in charge carrier insertion mechanisms can be ascribed to the strong interaction between the tunnel frame and inserted Na⁺ possessing a larger ionic size than inserted Li⁺.

中文翻译：

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α-MnO2纳米线中（去）钠盐的动态研究

在该报告中，在单结晶的α-MnO的电化学sodiation和desodiation ₂纳米线在使用原位透射电子显微镜（TEM）和体用原位同步辐射X射线级单粒子水平动态研究。TEM结果表明，第一个成膜过程始于基于隧道的Na ⁺嵌入，经历了由于隧道降解而形成的Na _0.5 MnO ₂，并终止于Mn ₂ O ₃相。插入的Na ⁺可以部分地从水合产物中提取出来，随后的循环主要由Na _0.5 MnO之间的可逆转化反应决定。₂和Mn ₂ O ₃。使用alpha-MnO ₂纳米线电极的循环硬币内部的Mn价演化也表现出部分可逆的特性，与原位TEM分析非常吻合。该sodiation与在相同的α-锂化的MnO相比₂纳米线。在Mn ⁴⁺还原为Mn ^3.5+之前，Na ⁺和Li ^+都通过类似的隧道驱动插层机制与隧道结构相互作用。对于随后的深度插入，隧道可以存活到LiMnO ₂（Mn ³⁺）在锂化过程中，而固着作用是通过另一种机制进行的，该机制涉及明显的相变和Mn价低于3.5+后快速的隧道降解。电荷载体插入机理的差异可以归结为隧道框架与插入的Na ⁺之间的强相互作用，其离子尺寸大于插入的Li ⁺。