Microwave鈥揌ydrothermal Crystallization of Polymorphic MnO2 for Electrochemical Energy Storage

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• 作者：Kunfeng Chen ; Young Dong Noh ; Keyan Li ; Sridhar Komarneni ; Dongfeng Xue
• 刊名：The Journal of Physical Chemistry C
• 出版年：2013
• 出版时间：May 23, 2013
• 年：2013
• 卷：117
• 期：20
• 页码：10770-10779
• 全文大小：583K
• 年卷期：v.117,no.20(May 23, 2013)
• ISSN：1932-7455

文摘

We report a coupled microwave鈥揾ydrothermal process to crystallize polymorphs of MnO₂ such as 伪-, 尾-, and 纬-phase samples with plate-, rod-, and wirelike shapes, by a controllable redox reaction in MnCl₂鈥揔MnO₄ aqueous solution system. MnCl₂鈥揔MnO₄ redox reaction system was for the first time applied to MnO₂ samples under the coupled microwave鈥揾ydrothermal 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鈥揔MnO₄ aqueous system. The present results indicate that MnCl₂鈥揔MnO₄ reaction system can selectively lead to 伪-, 尾-, and 纬-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 伪- > 纬- > 尾-MnO₂ upon their tunnel structures, the intercalation鈥揹eintercalation reactivity of these MnO₂ cathodes follows the order 纬- > 伪- > 尾-phase, and the conversion reactivity of these MnO₂ anodes follows the order 纬- > 伪- > 尾-phase. MnCl₂鈥揔MnO₄ reaction system can also lead to the mixed-phase MnO₂ (尾- and 纬-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.