新型纳米硅碳复合负极材料的设计合成、组装及应用研究

Lithium-ion battery has become the dominant power source for consumer portable electronic devices and electric vehicles. The key issue is to develop high energy density, long cycle life, low cost and high safety lithium-ion batteries. Silicon possesses the highest theoretical capacity of all known materials and it is abundant, inexpensive, and safe. However, silicon suffers from a large volume change during Li insertion, which leads to capacity fading and poor cycle performance. So it’s always a challenging work to improve the cycle performance of the silicon anodes. In this proposal, based on our previous work, we plan to synthesize silicon-carbon nanocomposites from silica-carbon nanocomposites via a reduction approach. The internal void space generated inside the framework during the reduction process can provide sufficient voids for the volume expansion of silicon nanoparticles during Li insertion. Through structure design of the silica-carbon nanocomposites, the nanostructure of silicon-carbon nanocomposites and the formation of the solid electrolyte interface film can be well controlled. Thus the cycle performance of the silicon anodes can be improved. Furthermore, the obtained nanostructured silicon-carbon composites will be assembled to increase the tap density and volumetric capacity. The forthcoming results and conclusions of this proposal will show a low cost synthesis approach of silicon-carbon nanocomposites with understanding the reduction reaction mechanism, lay material and theoretical foundations for the applications of silicon based anodes in lithium-ion battery.

锂离子电池在便携式电子设备、电动汽车等应用中处于主导地位，开发具有高比能、长寿命、低成本、高安全的锂离子电池是发展的趋势和核心。硅是目前已知具有最高理论容量的负极材料，但由于其嵌锂时巨大的体积膨胀导致循环性能较差，限制了其实际应用。提高硅基电极的循环性能一直以来都是锂离子电池研究领域的挑战性工作。本项目拟在申请人前期工作基础上，利用镁热还原和熔融盐还原的方法将氧化硅-碳纳米复合材料还原制备硅-碳复合材料，在硅-碳复合材料骨架中产生空隙，为硅纳米颗粒在嵌锂时的体积膨胀提供足够的空间；通过对氧化硅-碳纳米复合材料的结构设计，实现对硅-碳复合材料微观结构的调控，控制硅基电极表面固体电解质界面膜的形成，从而解决硅基电极循环性能差的问题。此外，对所制备的硅-碳复合纳米材料进行进一步的组装，提高材料的振实密度，进而提高硅基电极的体积能量密度。为硅基电极在锂离子电池中的进一步应用奠定物质基础和理论基础。

锂离子电池在便携式电子设备、电动汽车等应用中处于主导地位。开发具有高比能、长寿命、低成本、高安全的锂离子电池是发展的趋势和核心。为了提高电子设备的待机时间和电动车的续航里程，开发下一代高比能锂离子电池是必由之路。锂离子电池的能量密度主要决定与其正负极材料的容量，目前商品化负极主要是石墨材料，其理论容量较低，为372 mAh/g。硅是目前已知具有最高理论容量的负极材料，理论容量可达4200 mAh/g，是商用石墨的10倍以上，此外硅是高丰度元素，价格便宜，且贮锂电位低、可以有效地避免锂枝晶的生长、提高电池的安全性。单质硅在嵌锂过程中会出现巨大的体积膨胀（~ 400%）固体电解质界面膜（SEI）不断形成-破损等问题，导致硅电极循环性能差，限制了其实际应用。提高硅基电极的循环性能一直以来都是锂离子电池研究领域的挑战性工作。本项目设计合成了yolk-shell结构硅-碳复合材料、硅-石墨烯复合薄膜材料、自支撑结构的硅-碳纤维这三种结构的硅碳复合材料，在硅-碳复合材料骨架中产生空隙，为硅纳米颗粒在嵌锂时的体积膨胀提供足够的空间，控制硅基电极表面固体电解质界面膜的形成，从而解决硅基电极循环性能差的问题。所制备的材料循环1000圈后保持1350 mAh/g，首圈库伦效率达到87%，实现了预期目标，为硅基电极在锂离子电池中的进一步应用奠定物质基础和理论基础。