Si基锂离子电池负极纳米材料的表面改性

Because of its high theoretical lithium capacity, Si has been considered as the most promising anode material for the next generation high energy lithium-ion battery. In this project, we are going to synthesize Si based nanostructure-graphene composites, and then improve the electrochemical properties of the anode composites via surface modification of the Si based nanostructures. Firstly, ultrathin SiO2, SiC or SiN films will be produced on surface of the Si based nanostructures via surface chemical reactions of Si with oxygen, carbon or nitrogen contained gases. These ultrathin films not only reduce the side reactions of Si based electrode resulting from the reducing contact of the Si based nanostructures with the electrolyte but also limit the volume change of the Si based nanostructures during lithiation/delithiation processes. By this way, it will effectively improve the electrical contact between the Si based electrode and electrolyte and inhibit the cracking of the Si based nanostructures then maintain their high lithium capacity. Secondly, Si-Ge alloy nanostructures will be synthesized to modify the low lithium ion diffusion rate and high bulk resistance of Si with the good physical properties of Ge and finally improve the electrochemical properties of the Si based electrode.

由于它的高锂离子理论容量，Si纳米材料被认为是新一代高能锂离子电池的理想负极材料。本项目我们将制备Si基纳米结构－石墨烯复合材料，同时通过Si基纳米材料的表面改性来提升这些锂离子负极材料的电化学性能。首先使用化学反应法在Si表面形成一层均匀超薄的Si化合物（比如：SiO2、SiC或SiN）薄膜，该薄膜不仅通过减少Si电极和电解液的接触来减少电极副反应又能有效抑制Si电极在嵌/脱锂离子过程中产生的体积变化。这样就能通过有效地改善电极／电解液界面的同时解决Si电极本身在嵌/脱锂离子过程中产生的机械裂化来保持电池材料的锂离子容量。然后将通过Si与Ge合金，用Ge的物理特性来改善Si本身的高电阻和低锂离子扩散速率的缺陷，从而整体提高Si基纳米材料的电化学活性。

本项目的主要目的是拟通过表面修饰Si纳米材料来提高其电化学储锂能力。在实际实验中首先我们通过化学气相沉积和等离子体辅助化学气相沉积方法制备石墨烯薄膜，同时了解石墨烯形成机理。然后在Si纳米线上通过等离子体辅助化学气相方法沉积石墨烯薄膜，形成Si@石墨烯核壳结构。实验结果表明Si纳米线表面修饰石墨烯后大大提高了其作为锂离子电池负极材料的电化学性能和循环寿命。接着我们研究了锂原子在氢修饰Si原子簇的吸附和表面扩散的情况。同时基于该基金的支持我们还合成高性能石墨烯/氧化物锂离子电池负极复合材料，然后通过表面改性进一步增强这些电极材料的电化学性能。在石墨烯/氧化物复合物电极上修饰一层薄的三氧化二铝保护层可以提高电极的循环寿命，这是由于该惰性氧化物层能很好地保护了电极材料在循环过程中的完整性。基于对以后研究兴趣，我们还合成了金属有机框架化合物，并了解其光学以及电化学性质。

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