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首页> 外文期刊>Solid state ionics >Mass and charge transport in hierarchically organized storage materials. Example: Porous active materials with nanocoated walls of pores
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Mass and charge transport in hierarchically organized storage materials. Example: Porous active materials with nanocoated walls of pores

机译：在按层次组织的存储材料中进行质荷运输。示例：具有纳米涂层孔壁的多孔活性材料

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To enhance the kinetics of poorly conducting cathode materials for Li batteries, the authors have proposed a number of strategies based on crushing the active material into nanopowder and embedding the powder into a carbon-based web or coating. Using the well-elaborated example of LiFePO4, we demonstrate that the same goal can be achieved with a different approach where the active material remains in a form of large (I 20 gm) single crystals. Instead of crushing the material, we make it porous-with average pore size around 50 nm and pore surface area of 25 m(2)/g. The walls of the pores (but also the outer surfaces of crystals) are covered with ca. 1-nm-thick carbon film. Most surprisingly, such a unique nanoarchitecture can be prepared using a simple sol-gel based procedure including a single heat treatment. The crucial part is the selection of appropriate carbon precursor, For example, citric acid decomposes quite vigorously into gases and solid carbon at temperatures up to ca. 450 degrees C. This range matches exactly the first solidification of LiFePO4. Thus, the evolving gases can create an interconnected web of pores while the solid parts (carbon) are deposited simultaneously on the walls of pores. We further show that a carbon content of less than 3% is already sufficient for surpassing the percolation threshold with respect to surface conductivity of carbon. Using more carbon can decrease the rate performance so a fine balance is required in this respect. Most importantly, carbonization at a temperature of slightly less than 700 degrees C is sufficient to achieve a composite conductivity of the order of 10(-2) S cm(-2)-more than sufficient for good cathode kinetics. In the end, we show new evidence that the phase that is responsible for high conductivity of LiFePO4-C composites is indeed the carbon phase. (c) 2006 Elsevier B.V. All rights reserved.
机译：为了增强锂电池导电不良的正极材料的动力学性能，作者提出了许多基于将活性材料压碎成纳米粉并将粉末嵌入碳基纤维网或涂层的策略。使用精心设计的LiFePO4的例子，我们证明了使用不同的方法可以实现相同的目标，其中活性材料仍以大（I 20 gm）单晶形式存在。不用压碎材料，而是使它具有多孔性，平均孔径约为50 nm，孔表面积为25 m（2）/ g。孔的壁（也包括晶体的外表面）被约。 1纳米厚的碳膜。最令人惊讶的是，可以使用基于简单的基于溶胶-凝胶的方法（包括一次热处理）来制备这种独特的纳米结构。至关重要的部分是选择合适的碳前体，例如，柠檬酸在高达约200℃的温度下会剧烈分解为气体和固体碳。 450摄氏度。此范围与LiFePO4的第一次固化完全匹配。因此，不断散发的气体可以形成相互连接的孔网，而固体部分（碳）同时沉积在孔壁上。我们进一步表明，相对于碳的表面电导率，小于3％的碳含量已经足以超过渗滤阈值。使用更多的碳会降低速率性能，因此在这方面需要保持良好的平衡。最重要的是，在略低于700摄氏度的温度下碳化足以实现10（-2）S cm（-2）数量级的复合电导率，这足以满足良好的阴极动力学要求。最后，我们显示出新的证据，表明负责LiFePO4-C复合材料高电导率的相实际上是碳相。 （c）2006 Elsevier B.V.保留所有权利。

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