To address the issues of large volume change and low conductivity of silicon (Si) materials, carbon coatings have been widely employed as surface protection agent and conductive medium to encapsulate the Si materials, which can improve the electrochemical performance of Si-based electrodes. There has been a strong demand to gain a deeper understanding of the impact of efficient carbon coating over the lithiation and delithiation process of Si materials. Here, we report the first observation of the extended two-phase transformation of carbon-coated Si nanoparticles (Si/C) during electrochemical processes. The Si/C nanoparticles were prepared by sintering Si nanoparticles with polyvinylidene chloride precursor. The Si/C electrode underwent a two-phase transition during the first 20 cycles at 0.2°C, but started to engage in solid solution reaction when the ordered compact carbon coating began to crack. Under higher current density conditions, the electrode was also found to be involved in solid solution reaction, which, however, was due to the overwhelming demand of kinetic property rather than the breaking of the carbon coating. In comparison, the Si/C composites prepared with sucrose possessed more disordered and porous carbon structures, and presented solid solution reaction throughout the entire cycling process.

中文翻译：

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紧凑有序的碳涂层对电化学过程中硅的固态行为的影响

为了解决硅（Si）材料的大体积变化和低电导率的问题，碳涂层已被广泛用作表面保护剂和导电介质以封装Si材料，这可以改善Si基电极的电化学性能。强烈要求深入了解有效的碳涂层对Si材料的锂化和脱锂过程的影响。在这里，我们报告了电化学过程中碳包覆的硅纳米颗粒（Si / C）扩展的两相转变的首次观察。通过将Si纳米颗粒与聚偏二氯乙烯前体烧结来制备Si / C纳米颗粒。Si / C电极在前20个循环中于0.2°C经历了两相转变，但是当有序的致密碳涂层开始破裂时，开始进行固溶反应。在较高的电流密度条件下，还发现电极参与了固溶反应，但是，这是由于对动力学性能的压倒性要求而不是碳涂层的破坏所致。相比之下，用蔗糖制备的Si / C复合材料具有更多的无序和多孔碳结构，并在整个循环过程中呈现固溶反应。