标题：Dynamic study of (De)sodiation in alpha-MnO2nanowires
作者：Yuan, Yifei ;Ma, Lu ;He, Kun ;Yao, Wentao ;Nie, Anmin ;Bi, Xuanxuan ;Amine, Khalil ;Wu, Tianpin ;Lu, Jun ;Shahbazian-Yassr, Reza
作者机构：[Yuan, Yifei ;He, Kun ;Yao, Wentao ] Department of Materials Science and Engineering, Michigan Technological University, 1400 Townsend Drive, Houghton 更多
摘要：In this report, the electrochemical sodiation and desodiation in single crystalline alpha-MnO2nanowires 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 Na0.5MnO2as a result of tunnel degradation, and ends with the Mn2O3phase. The inserted Na+can be partially extracted out of the sodiated products, and the following cycles are dominated by the reversible conversion reaction between Na0.5MnO2and Mn2O3. The Mn valence evolution inside a cycling coin using alpha-MnO2nanowire electrode also exhibits partially reversible characteristic, agreeing well with the in situ TEM analysis. The sodiation is compared with lithiation in the same alpha-MnO2nanowires. Both Na+and Li+interact with the tunneled structure via a similar tunnel-driven intercalation mechanism before Mn4+is reduced to Mn3.5+. 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+.
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