锂离子电池硅基负极材料的研究

发布时间：2018-04-19 14:19

本文选题：硅基负极 + 容量衰减　；参考：《中国科学院大学(中国科学院物理研究所)》2017年博士论文

【摘要】：硅具有非常高的脱嵌锂比容量和较低的脱嵌锂电位,因此是下一代最有潜力替代石墨大规模使用的锂离子电池负极材料。目前硅基负极材料已经少量商业化使用,然而硅基负极材料低的首次效率、巨大的体积形变及表面不稳定的固态电解质膜(SEI膜)严重限制了硅基负极材料的推广应用。针对硅基负极全电池衰减十分严重的问题,分别制作了一种石墨负极和三种不同容量硅基负极的软包电池,电化学性能显示随着硅含量的提高全电池的循环性能急剧下降。本文对四种全电池的衰减机理进行了细致研究,对经过50次循环后的电池进行拆解并用正负极极片分别组装半电池,发现正极片和负极片的半电池面容量没有明显衰减,SEM和XRD结果也从侧面证实了上述结论。对拆解后的正极半电池首次放电容量和负极半电池首次充电容量进行了对比分析,发现可迁移锂离子的损耗和电池的极化是造成硅基负极全电池迅速衰减的主要原因。ICP和EDS结果也辅助证明了上述结论。最后对全电池的d Q/d V-V和d V/d Q-Q曲线研究发现:随着全电池容量的衰减,石墨和Si Ox在电池循环过程中贡献的容量均在减小。针对硅基负极材料在脱嵌锂过程中巨大的体积形变造成的材料的破裂和不稳定的SEI膜问题,本论文采用表面为微米金字塔锥结构的硅片作为负极,研究了表面纳米孔、电解液添加剂、高充放电倍率对样品表面的裂纹和SEI膜厚度的影响。表面纳米孔的存在抑制了硅片表面在充放电过程中的裂纹,同时电解液添加剂的加入也会减小硅片表面的碎裂程度。采用表面纳米孔的样品做对比实验,发现高的充放电倍率相比低的充放电倍率会明显抑制表面SEI膜的厚度,成膜添加剂也能够在一定程度上减少SEI膜的增厚,其中VC效果最好,FEC次之。针对硅基负极材料低的首次效率问题,本论文研究了锂-联苯-二甲氧基乙烷溶液作为预锂化试剂的可能性。结果显示该溶液能够有效的提高负极材料纳米硅、硬碳、软碳的首次效率,而且并不会对材料的循环性能带来不良影响。同时测量了该溶液的电子电导率和离子电导率,并发现该溶液的总电导率遵循阿累尼乌斯定律。用该溶液与磷酸铁锂正极组装电池,得到了具有高的首次效率并能够循环的半液流电池。
[Abstract]:Because of its high deintercalated lithium specific capacity and low deintercalated lithium potential, silicon is the most promising anode material for the next generation of lithium ion batteries, which can replace graphite on a large scale.At present, silicon based negative electrode materials have been used in a small amount of commercial use. However, the low initial efficiency of silicon based negative electrode materials, huge volume deformation and unstable solid electrolyte film (SEI) seriously limit the application of silicon based negative electrode materials.One kind of graphite anode and three kinds of silicon based anode soft-clad cells with different capacities were fabricated to solve the serious problem of the decaying of silicon based negative electrode. The electrochemical performance showed that the cycling performance of the whole cell decreased sharply with the increase of silicon content.In this paper, the attenuation mechanism of four kinds of whole batteries is studied in detail. After 50 cycles, the batteries are disassembled and assembled with positive and negative electrode plates respectively.It is found that the surface capacity of the semilayer of the positive and negative plates has no obvious attenuation. The results of SEM and XRD also confirm the above conclusions from the side.The first discharge capacity of positive half battery and the first charge capacity of negative half battery are compared and analyzed.It is found that the loss of mobile lithium ion and the polarization of the cell are the main reasons for the rapid decay of the silicon based negative electrode battery. The results of ICP and EDS also prove the above conclusions.Finally, the study of the d Q / d V-V and d V / d Q-Q curves of the whole battery shows that the contribution of graphite and SiOx to the battery cycle decreases with the decrease of the total cell capacity.In order to solve the problem of the rupture and unstable SEI film caused by the huge volume deformation of silicon based negative electrode material during the deintercalation of lithium, the surface nano-pore was studied by using the silicon wafer with a micropyramidal structure as the negative electrode in this paper.The effect of electrolyte additive and high charge / discharge ratio on the surface crack and thickness of SEI film.The existence of nano-pore on the surface of the silicon wafer can restrain the crack in the process of charge and discharge, and the addition of electrolyte additive can also reduce the fragmentation degree of the silicon wafer surface.Compared with the low charge / discharge ratio, the thickness of surface SEI film can be obviously inhibited with high charge / discharge ratio, and the thickening of SEI film can be reduced to a certain extent by film forming additive.The best effect of VC is FEC.In this paper, the possibility of lithium-biphenyl-dimethoxy ethane as a prelithiation reagent is studied for the first time efficiency of silicon-based anode materials.The results show that the solution can effectively improve the initial efficiency of nano-silicon, hard carbon and soft carbon, and will not have adverse effects on the cycling performance of the materials.The electronic conductivity and ionic conductivity of the solution were also measured, and it was found that the total conductivity of the solution obeyed Arrhenius law.Using this solution to assemble the battery with lithium iron phosphate positive electrode, a high efficiency semi-liquid flow battery with high efficiency and recirculation was obtained.
【学位授予单位】：中国科学院大学(中国科学院物理研究所)
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TM912

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