Surface Coating Constraint Induced Self-Discharging of Silicon Nanoparticles as Anodes for Lithium Ion Batteries

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• 作者：Langli Luo ; Peng Zhao ; Hui Yang ; Borui Liu ; Ji-Guang Zhang ; Yi Cui ; Guihua Yu ; Sulin Zhang ; Chong-Min Wang
• 刊名：Nano Letters
• 出版年：2015
• 出版时间：October 14, 2015
• 年：2015
• 卷：15
• 期：10
• 页码：7016-7022
• 全文大小：492K
• ISSN：1530-6992

文摘

One of the key challenges of Si-based anodes for lithium ion batteries is the large volume change upon lithiation and delithiation, which commonly leads to electrochemi-mechanical degradation and subsequent fast capacity fading. Recent studies have shown that applying nanometer-thick coating layers on Si nanoparticle (SiNPs) enhances cyclability and capacity retention. However, it is far from clear how the coating layer function from the point of view of both surface chemistry and electrochemi-mechanical effect. Herein, we use in situ transmission electron microscopy to investigate the lithiation/delithiation kinetics of SiNPs coated with a conductive polymer, polypyrrole (PPy). We discovered that this coating layer can lead to 鈥渟elf-delithiation鈥?or 鈥渟elf-discharging鈥?at different stages of lithiation. We rationalized that the self-discharging is driven by the internal compressive stress generated inside the lithiated SiNPs due to the constraint effect of the coating layer. We also noticed that the critical size of lithiation-induced fracture of SiNPs is increased from 鈭?50 nm for bare SiNPs to 鈭?80 nm for the PPy-coated SiNPs, showing a mechanically protective role of the coating layer. These observations demonstrate both beneficial and detrimental roles of the surface coatings, shedding light on rational design of surface coatings for silicon to retain high-power and high capacity as anode for lithium ion batteries.