Preparation of layered MnO2 via thermal decomposition of KMnO4 and its electrochemical characterizations
Preparation of layered MnO2 via thermal decomposition of KMnO4 and its electrochemical characterizations
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DOI：
10.1021/cm9801643
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发表时间：
1999-03-01
影响因子：
8.6
通讯作者：
Oh, SM
中科院分区：
文献类型：
--
作者：
Kim, SH;Kim, SJ;Oh, SM
本文报道了层状二氧化锰的制备及其在锂二次电池中阴极性能的初步结果。KMnO4粉末在250-1000℃的空气中热分解产生KalphaMnO2+ δ。γ H2O (x = 0.27-0.31, δ = 0.07-0.13, y = 0.47-0.89)，基于Mn摩尔量的产物收率为67-79%。从x射线衍射图的Rietveld细化可以判断，800℃c制备的样品具有层状结构（六边形单元胞，空间群= P6(3)/mmc, a = 2.84埃，c = 14.16埃）；其中K+离子和H2O分子位于层间的三角棱柱位（p2型结构）。与之前的发现相反，即层状MnO2在bb0 - 450℃时转变为α -/ γ -MnO2相或锰亚氧化物，即使在更高的温度下，这些杂质在这种合成中也可以忽略不计。合成的成功归功于热解介质中大量的K+离子作为柱状阳离子来稳定层状框架。此外，由于热解过程中产生了高氧化性物质，如O-2、MnO42-和MnO43-，因此没有亚氧化物转变。该材料的粉末密度高达1.36 g cm(-3)， Mn4+分数为>85%，基于单电子充放电反应的理论容量为210-230 mA h g（-1）。通过添加锰亚氧化物（Mn2O3， Mn3O4或MnO）热解KMnO4，产品收率可达bb0 98%。最后，初步的电池试验表明，这些材料具有作为锂二次电池正极材料的良好性能。
We report here the preparation of layered MnO2 and the preliminary results on its cathodic performance in Li secondary batteries. The thermal decomposition of KMnO4 powder at 250-1000 degrees C in air produces KalphaMnO2+delta.gamma H2O (x = 0.27-0.31, delta = 0.07-0.13, and y = 0.47-0.89) with a product yield of 67-79% based on the Mn molar quantity. It can be judged from the Rietveld refinement on the X-ray diffraction pattern that the 800 degrees C-prepared sample has layered structure (hexagonal unit cell, space group = P6(3)/mmc, a = 2.84 Angstrom, and c = 14.16 Angstrom); where the K+ ions and H2O molecules reside at the interlayer trigonal prismatic sites (P2-type structure). Contrary to the previous findings whereby the layered MnO2 transforms to alpha-/gamma-MnO2 phases or manganese suboxides at >450 degrees C, such impurities are negligible in this synthesis even at higher temperatures. The success of synthesis is ascribed to the high population of K+ ions in the pyrolyzing media that act as pillaring cations to stabilize the layered framework. In addition, the absence of a suboxide transition is indebted to the highly oxidizing species such as O-2, MnO42- and MnO43-, which are produced during the pyrolyzing process. The materials show a powder density as high as 1.36 g cm(-3) and the Mn4+ fraction of >85%, which gives a theoretical capacity of 210-230 mA h g(-1) based on a one-electron charge/discharge reaction. A higher product yield up to >98% is achieved by pyrolyzing KMnO4 with an addition of manganese suboxides (Mn2O3, Mn3O4, or MnO). Finally, the preliminary cell tests show that the materials give some promising features as the cathode materials for Li secondary batteries.