SiOC陶瓷纳米结构的设计、调控及其储锂性能研究

The low theoretical capacity of graphite anode material limits the further improvement of specific energy for lithium ion batteries. In this regard, it is necessary to explore novel anode materials with higher reversible capacity and long-cycle stability. SiOC ceramics are composed of mixed SiOxC4-x (0≤x≤4) units and free carbon phase, and this special structure makes it of great interest for application as anodes in lithium ion batteries. However, the initial coulombic efficiency of SiOC anodes is lower than 50%. On the issues of low initial reversible capacity and coulombic efficiency, the tuning of SiOC nanostructure and lithium storage performance are studied. SiOC nanoparticles are synthesized by sol-gel method with organically modified silicon alkoxides as precursor, and the oxygen-enriched units are decreased by KOH etching and magnesiothermic reduction reaction, which are favorable for the improvement of the reversible capacity of SiOC ceramics. XRD, SEM and TEM techniques will be used to characterize the physical properties of the synthesized materials. By combining electrochemical performance of SiOC materials, the structure-activity relationship between the physical properties and the electrochemical performance is established, and the lithium storage mechanisms of different active sites are discussed. Furthermore, the specific capacity and cyclic stability of SiOCs could be further enhanced by synthesis of SiOC@C and Sn/SiOC composites as anodes in lithium ion batteries.

石墨负极由于低的理论比容量限制了锂离子电池比能量的进一步提高。开发新型负极材料，提高比容量和循环稳定性是锂离子电池负极材料研究的重要课题。SiOC陶瓷由SiOxC4-x（0≤x≤4）与自由C相组成，其特殊的结构组成在锂离子电池负极材料的研究中备受关注，但是SiOC的首圈库伦效率低于50%。针对SiOC负极材料的首圈可逆容量与充放电效率较低的问题，本项目从SiOC陶瓷的纳米结构与储锂性能关系入手，以有机硅氧烷为溶胶凝胶前驱体，实现SiOC纳米材料的合成与结构调控，通过KOH刻蚀以及镁热还原反应降低富氧结构单元，提高SiOC的可逆容量。采用XRD、TEM、NMR等测试手段，对合成的材料进行结构表征，结合SiOC材料的电化学性能测试，建立材料结构与性能之间的构效关系，分析SiOC各结构单元的储锂机理。在此基础上，合成SiOC@C、Sn/SiOC复合材料，进一步改善材料的比容量和循环稳定性。

石墨负极由于低的理论比容量限制了锂离子电池比能量的进一步提高。开发新型负极材料，提高比容量和循环稳定性是锂离子电池负极材料研究的重要课题。SiOC陶瓷由SiOxC4-x（0≤x≤4）与自由C相组成，其特殊的结构组成在锂离子电池负极材料的研究中备受关注。项目从SiOC陶瓷的结构调控入手，通过对多聚糖微球的表面处理，研究表面羟基与羧基对SiOC陶瓷结构的影响。尽管表面含氧官能团增加了SiOC陶瓷的富氧结构，羧基使SiOC完全转变为SiO2。将SiOC陶瓷用作锂离子电池负极材料，研究结构与储锂性能之间的构效关系。采用溶胶凝胶法合成SiOC陶瓷，并对其进行KOH刻蚀处理。KOH刻蚀不仅与SiOC陶瓷中的富氧结构单元反应，而且对自由C有活化作用，产生纳米级的孔隙结构，增加材料的比表面积，改善电化学性能。纳米尺寸的孔、SiOxC4-x结构以及自由C对电化学性能的提高有协同作用，但是自由C对可逆容量的贡献高于SiOxC4-x结构及比表面积。在此基础上，以SnCl2为前驱体合成了Sn/SiOC复合材料。加入SnCl2不仅降低了SiOC陶瓷中的富C结构单元，而且增加了自由C表面的含氧官能团。在热处理过程中SnO2与自由C发生碳热还原反应生成Sn。碳热还原反应的程度与Sn纳米颗粒的尺寸随着Sn/Si比的增加而增加。电化学性能表明均匀分散的Sn纳米颗粒、SiOxC4-x结构单元与自由C有利于电化学性能的提高，其中自由C对可逆容量的贡献高于Sn与SiOxC4-x结构。因此，Sn/SiOC复合材料的储锂容量要低于SiOC陶瓷。另外，以SiO2/SiOC复合材料为前驱体，采用NaOH刻蚀设计了富C结构的蜂窝状SiOC陶瓷，研究结果表明SiOxC4-x微结构对材料的可逆容量贡献较大。