Mechanical Property Evolution of Silicon Composite Electrodes Studied by Environmental Nanoindentation

• Published in: Advanced energy materials 2018-04, Vol.8 (10), p.n/a
• Main Authors: Wang, Yikai, Zhang, Qinglin, Li, Dawei, Hu, Jiazhi, Xu, Jiagang, Dang, Dingying, Xiao, Xingcheng, Cheng, Yang‐Tse
• Format: Article
• Language: English
• Subjects: Degradation; Electrodes; Evolution; Lithium-ion batteries; Mechanical properties; Modulus of elasticity; Nanoindentation; Polyvinylidene fluorides; Porosity; Si composite electrode; Silicon; State of charge; state of charge (SOC)
• ISSN: 1614-6832; 1614-6840
• DOI: 10.1002/aenm.201702578

Mechanical degradation is largely responsible for the short cycle life of silicon (Si)‐based electrodes for future lithium‐ion batteries. An improved fundamental understanding of the mechanical behavior of Si electrodes, which evolves, as demonstrated in this paper, with the state of charge (SOC) and the cycle number, is a prerequisite for overcoming mechanical degradation and designing high capacity and durable Si‐based electrodes. In this study, Young's modulus (E) and hardness (H) of Si composite electrodes at different SOCs and after different cycle numbers are measured by nanoindentation under both dry and wet (liquid electrolyte) conditions. Unlike electrodes made of Si alone, E and H values of Si composite electrodes increase with increasing Li concentration. The composite electrodes under wet conditions are softer than that under dry conditions. Both E and H decrease with the cycle number. These findings highlight the effects of porosity, liquid environment, and degradation on the mechanical behavior of composite electrodes. The methods and results of this study on the mechanical property evolution of Si/polyvinylidene fluoride electrodes form a basis for exploring more effective binders for Si‐based electrodes. Furthermore, the evolving nature of the mechanical behavior of composite electrodes should be taken into consideration in future modeling efforts of porous composite electrodes. Young's modulus and hardness of Si composite electrodes vs the state of charge (SOC) and cycle number are measured by nanoindentation under both dry and wet conditions. In contrast to Si films, Young's Modulus (E) and hardness (H) of Si composite electrodes increase with increasing Li concentration. E and H values at the same SOC decrease with increasing cycle number.