Microwave-Hydrothermal Crystallization of Polymorphic MnO2 for Electrochemical Energy Storage
Microwave-Hydrothermal Crystallization of Polymorphic MnO2 for Electrochemical Energy Storage
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DOI：
10.1021/jp4018025
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发表时间：
2013-05-23
影响因子：
3.7
通讯作者：
Xue, Dongfeng
中科院分区：
文献类型：
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作者：
Chen, Kunfeng;Noh, Young Dong;Xue, Dongfeng
报道了一种在MnCl 2-KMnO 4水溶液体系中，通过可控的氧化还原反应，微波水热法制备α-、β-和γ-等多晶型MnO 2的方法。首次将MnCl 2-KMnO 4氧化还原反应体系应用于微波水热耦合条件下制备的MnO 2样品，该体系具有反应时间短、结晶度高、电化学性能好等优点。为了比较，我们还在我们设计的MnCl_2-KMnO_4水溶液体系中单独进行了水热反应和微波反应。目前的研究结果表明，MnCl 2 KMnO 4反应体系可以选择性地导致α，γ相MnO 2，和作为结晶MnO 2样品可以显示出有趣的电化学性能的锂离子电池和超级电容器。电化学测试结果表明，晶化态MnO 2超级电容器的法拉第反应性顺序为α- > γ- > β-MnO 2，阴极的嵌脱反应性顺序为γ- > α- > β-相，阳极的转换反应性顺序为γ- > α- > β-相。MnCl 2-KMnO 4反应体系也可导致混合相MnO 2（β-和γ-MnO 2），其可为锂离子电池提供更好的阳极性能。本工作加深了对物理化学中化学反应可控合成、晶体结构选择、电化学性能改善、电化学反应性等方面的基本认识，以及它们之间的相互关系。
We report a coupled microwave hydrothermal process to crystallize polymorphs of MnO2 such as alpha-, beta- and gamma-phase samples with plate-, rod-, and wirelike shapes, by a controllable redox reaction in MnCl2-KMnO4 aqueous solution system. MnCl2-KMnO4 redox reaction system was for the first time applied to MnO2 samples under the coupled microwave hydrothermal conditions, which shows clear advantages such as shorter reaction time, well crystallized polymorphic MnO2, and good electrochemical performances as electrode materials for lithium ion batteries. For comparison, we also did separate reactions with hydrothermal only and microwave only in our designed MnCl2 KMnO4 aqueous system. The present results indicate that MnCl2 KMnO4 reaction system can selectively lead to alpha-, and gamma-phase MnO2, and the as-crystallized MnO2 samples can show interesting electrochemical performances for both lithium ion batteries and supercapacitors. Electrochemical measurements show that the as crystallized MnO2 supercapacitors have Faradaic reactivity sequence alpha- > gamma- > beta-MnO2 upon their tunnel structures, the intercalation deintercalation reactivity of these MnO2 cathodes follows the order gamma- > alpha- > beta-phase, and the conversion reactivity of these MnO2 anodes follows the order gamma- > alpha- > beta-phase. MnCl2-KMnO4 reaction system can also lead to the mixed phase MnO2 (beta- and gamma-MnO2), which can provide better anode performances for lithium -ion batteries. The current work deepens the fundamental understanding of several aspects of physical chemistry, for example, the chemical reaction controllable synthesis, crystal structure selection, electrochemical property improvement, and electrochemical reactivity, as well as their correlations.