Si is an attractive negative electrode material for lithium ion batteries due to its high specific capacity (~3600 mAh/g). However, the huge volume swelling and shrinking during cycling leads to several coupled issues at the material/electrode/cell level, including fracture of Si particles, unstable solid electrolyte interphase (SEI), and low Coulombic efficiency.<br/>SEI is a passivation layer formed on the electrode surface to ensure the long-term cyclability of silicon based electrode. The understanding of the relationships between the structure and properties of SEI is crucial for pinpointing the capacity fading mechanisms, and designing high performance/durable electrode coatings, particularly for the high capacity electrode materials. On the other hand, Surface modification on electrode has been reported to be an effective way to improve the cycling stability, coulombic efficiency, and abuse tolerance. However, less work has been done to fundamentally understand its role on the formation of solid electrolyte interphase (SEI) and lithium transport. In this work, for the first time, we were able to unveil the mechanical properties of SEI formed on silicon using laser acoustic wave (LAW) method, and correlated the SEI Young’s modulus with its composition. Furthermore, we tailored the mechanical and chemical properties of SEI and investigated their impact on cycling behaviors of Si electrodes. We found that more inorganic components in SEI led to higher elastic modulus and provided better mechanical protection and higher cycle efficiency. We further developed surface coating as the artificial SEI, not only to stabilize the interface between electrolyte and electrode, but also to mitigate the mechanical degradation of electrode and improve the cycling stability.

Toward high cycle efficiency of high energy density lithium ion batteries

249th National Meeting (2015)

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