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Synthesis and rate performance of monolithic macroporous carbon electrodes for lithium-ion secondary batteries

机译：锂离子二次电池单片大孔碳电极的合成及倍率性能

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摘要

Three-dimension ally ordered macroporous (3DOM) materials are composed of well-interconnected pore and wall structures with wall thicknesses of a few tens of nanometers. These characteristics can be applied to enhance the rate performance of lithium-ion secondary batteries. 3DOM monoliths of hard carbon have been synthesized via a resorcinol-formaldehyde sol-gel process using poly(methyl methacrylate) colloidal-crystal templates, and the rate performance of 3DOM carbon electrodes for lithium-ion secondary batteries has been evaluated. The advantages of monolithic 3DOM carbon electrodes are: 1) solid-state diffusion lengths for lithium ions of the order of a few tens of nanometers, 2) a large number of active sites for charge-transfer reactions because of the material's high surface area, 3) reasonable electrical conductivity of 3DOM carbon due to a well-interconnected wall structure, 4) high ionic conductivity of the electrolyte within the 3DOM carbon matrix, and 5) no need for a binder and/or a conducting agent. These factors lead to significantly improved rate performance compared to a similar but non-templated carbon electrode and compared to an electrode prepared from spherical carbon with binder. To increase the energy density of 3DOM carbon, tin oxide nanoparticles have been coated on the surface of 3DOM carbon by thermal decomposition of tin sulfate, because the specific capacity of tin oxide is larger than that of carbon. The initial specific capacity of SnO2-coated 3DOM carbon increases compared to that of 3DOM carbon, resulting in a higher energy density of the modified 3DOM carbon. However, the specific capacity decreases as cycling proceeds, apparently because lithium-tin alloy nanoparticles were detached from the carbon support by volume changes during charge-discharge processes. The rate performance of SnO2-coated 3DOM carbon is improved compared to 3DOM carbon.
机译：三维有序大孔（3DOM）材料由相互连接的孔隙和壁结构组成，壁结构的壁厚为几十纳米。这些特性可以用于增强锂离子二次电池的倍率性能。使用聚甲基丙烯酸甲酯胶体晶体模板，通过间苯二酚-甲醛溶胶-凝胶工艺合成了硬质碳3DOM整体，并评估了锂离子二次电池3DOM碳电极的倍率性能。整体式3DOM碳电极的优点是：1）锂离子的固态扩散长度约为几十纳米，2）由于该材料的表面积大，用于电荷转移反应的活性部位很多， 3）由于良好互连的壁结构，3DOM碳具有合理的电导率； 4）3DOM碳基质中电解质的高离子电导率； 5）不需要粘合剂和/或导电剂。与相似但非模板化的碳电极相比，与由球形碳和粘合剂制成的电极相比，这些因素可显着提高倍率性能。为了增加3DOM碳的能量密度，由于氧化锡的比容量大于碳的比容量，所以通过硫酸锡的热分解将氧化锡纳米颗粒涂覆在3DOM碳的表面上。与3DOM碳相比，涂覆SnO2的3DOM碳的初始比容量增加，从而导致改性3DOM碳的能量密度更高。但是，比容量随着循环的进行而降低，这显然是因为在充电-放电过程中，锂锡合金纳米颗粒由于体积变化而从碳载体上脱离。与3DOM碳相比，涂覆SnO2的3DOM碳的速率性能得到改善。

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