Abstract
Fracture in silicon anodes has fascinated the electrochemistry community for two decades, as it can result in a 80% capacity loss over the first few electrochemical cycles and is the limiting factor in commercializing such high capacity anodes. Although numerous experimental data exist illustrating severe fracture patterns and their dependence on the scale of the microstructure, no theoretical model has been able to re-produce and capture such behaviour. In this article, a multi-physics phase-field damage model is presented that can accurately capture the long standing problem of dry bed-lake crack patterns observed for Si thin film anodes. A promising aspect of the model is that, in addition to accounting for Li-ion diffusion, it can explicitly capture the microstructure, and therefore when applied to a Si film with a thickness below 100 nm no fracture was observed, which is consistent with experiments. As fracture in continuous thin films is random, micron-hole patterned Si films were also fabricated and cycled, resulting in ordered crack patterns. The proposed model was able to capture these elaborate, yet ordered, crack patterns, further validating its efficiency in predicting damage during lithiation of Si. This paves the way to using multiscale modeling for predicting the dimensions that limit and control fracture during lithiation, prolonging hence the electrode lifetime.
Highlights
Extensive experimental research has concluded that Si-based anodes are the most promising candidates for generation Li-ion batteries
This was initially assumed in Ref. [3] since a high capacity retention was obtained for such film thicknesses, but was later proven by performing scanning electron microscopy (SEM) on amorphous Si film anodes that were 100 nm and 500 nm after 10 electrochemical cycles, showing that the 100 nm film remained undamaged while the 500 nm film experienced severe fracture [4]
A phase field damage model was adopted, which allowed the fracture energy of Si to vary throughout each electrochemical cycle
Summary
Extensive experimental research has concluded that Si-based anodes are the most promising candidates for generation Li-ion batteries. The most prominent example being dry bed-lake fracture that has been observed for Si and SiSn thin film anodes [1,2]. Experimental studies have shown that Si films below a critical thickness of 100 nm did not exhibit fracture. [3] since a high capacity retention was obtained for such film thicknesses, but was later proven by performing scanning electron microscopy (SEM) on amorphous Si film anodes that were 100 nm and 500 nm after 10 electrochemical cycles, showing that the 100 nm film remained undamaged while the 500 nm film experienced severe fracture [4]. Similar observations exist for Sn [5] and Si [6] which show that damage is significantly reduced as the particle size decreases
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