硅碳负极锂离子电池性能研究

RESEARCH ON PERFORMANCE OF LITHIUM ION BATTERIES BY USING SILICON/CARBON COMPOSITE AS ANODE

易婷婷

11749103

硕士

材料学

徐政和(Zhenghe Xu)

2019-06-01

2019-07-12

哈尔滨工业大学

深圳

锂离子电池的发展是电动汽车行业发展的关键一步，为了适应电动汽车行业的发展，亟需制备高能量密度且稳定性好的电极材料。传统的锂离子电池负极材料为石墨，能量密度低。硅基负极具有最高的理论能量密度，是目前最有潜力商业化应用的材料，但是硅基负极材料也存在一些问题，阻碍了其商业化应用。其主要存在的问题首先是硅基负极材料在充放电过程中形成锂硅合金造成的巨大膨胀,容易造成硅基材料的粉碎；其次硅材料本身的导电性比较差，不利于电子的传输迁移；最后由于负极材料表面在形成固体电解质膜，固体电解质膜既可以传输锂离子，又可以阻断电解液与内层硅材料的接触，减少副反应，但是锂硅合金形成时膨胀会破环固体电解质膜。为了解决这些问题，本文介绍了一种新型的硅碳复合负极材料的合成制备方法。具体为利用重油在不同溶液体系下的选择吸附，使用溶剂过渡法制备硅基负极的前驱体，研究了制备过程中各个因素对于所制备材料的性能影响。实验证明可以通过调控溶剂体系的溶剂特性来得到具有不同结构和机械性能的表面包覆层。而不同特性的表面包覆层会对硅碳复合负极锂离子电池的循环稳定特性产生较大的影响。另外通过调控热处理温度，能够在纳米硅表面形成结构差异化的包覆层，实现温度对结构的调控。利用溶剂过渡法，通过调控溶剂特性和制备过程当中不同的参数，得到了高性能的锂离子电池，经400圈充放电循环后，其剩余容量为1450 mAh·g-1，保持率约为92.9%，平均充放电循环容量损失在万分之二以下。本文中所制备的硅基负极材料为硅碳复合材料，其中表面碳层在微观条件下不同区域具有不同的模量分布，可细分为高弹性模量区和低弹性模量区，即得到了一种全新的包覆层。这种包覆层具有良好的机械性能，可以有效的防止内部硅材料在膨胀过程中破裂粉化。此种包覆层不仅可以应用在硅基负极表面，亦可以与其他容易发生膨胀的材料形成复合材料，有效的缓冲膨胀。

The development of lithium ion batteries is vital to the promotion of electronic vehicle. In order to keep pace with the development of electronic vehicle, electrode material with high performance and good stability should be researched. The traditional material used in anode of lithium ion batteries is graphite, which has a low energy density and cannot meet the demand of electronic vehicle. Silicon-based material is much promising compared to graphite because its high theoretical capacity. However, there are several problems that inhibits the commercialization of silicon-based material. The first one is that the formation of lithium-silicon alloy accompanying with the huge expansion, which will easily destroy the silicon material. Another problem is that the poor conductivity of silicon material. This will inhibit the transfer and diffusion of lithium ions. The last problem is that the solid electrolyte interface formed on the surface of silicon material is very important to maintain the stability of electrode. This solid electrolyte interface will enable the lithium ion transfer and prevent the electrolyte from reacting with the silicon material. The solid electrolyte interface can also reduce the side reaction between electrolyte and silicon. However, the huge expansion during charging and discharging will destroy the solid electrolyte interface. In order to solve these problems, a new approach is proposed to synthesize a kind of silicon/carbon composite. The principle we use in this thesis is to drive asphaltene onto the surface of silicon by changing the property of the solution. The performance effected by different parameters in the synthesis procedure were investigated. It has been proved that the structure and mechanical property of the coating-layer could be modified by adjusting the property of the solvent while the cycling performance of silicon/carbon anode is dependent on the structure and mechanical property of the coating layer. In another word, the cycling performance of silicon/carbon could be optimized by changing the solvent property. Furthermore, the mechanical property of coating layer on nano-silison would be adjusted by changing the temperature of heat treatment. Plenty of batteries were assembled to test the electrochemistry performance of synthesized material. High-performance batteries were obtained by using this approach. One of our best batteries can maintain 92.9% reversible capacity after cycling for 400 cycles in 0.2 C current density, the capacity los was 0.02% per cycle. The carbon in the silicon/carbon composite is different from other carbon materials reported before. The elastic modulus was different from area to area. In a micro horizon, some area can be defined as hard area while others are defined as soft area. This coating layer can prevent the cracking of inner material and enhance the stability of batteries. This kind of coating layer can be used not only in lithium ion batteries, but can also be applied to other kinds material by compositing together, which could effectively buffer the expansion.

锂离子电池 硅基负极 高性能 固体电解质膜 重油

lithium ion batteries silicon-based anode high-performance solid electrolyte interface heavy oil

中文

联合培养

南方科技大学

易婷婷. 硅碳负极锂离子电池性能研究[D]. 深圳. 哈尔滨工业大学,2019.