Surface effected fracture behavior of nano-spherical electrodes during lithiation reaction

Degradation mechanisms that caused by repetitive insertion and extraction of the lithium ion on the electrodes can lead to a grand challenge for optimizing the design of silicon (Si) based anode with high capacity and rate capacity. However, with decreasing the electrode size into nanometer scale, the surface-to-volume ratio will become very high, meaning that surface effect will have a significant role in determining the mechanical behavior of the electrode. And these effects suppress crack nucleation and propagation, which may become a resistance to brittle fracture. In our work, we establish a theoretical model to study the diffusion induced stress (DIS) evolution and firstly discuss the crack growth by using stress intensity factor (SIF) coupled with surface effects. The results show that DIS, especially the tensile stress, would decrease noticeably due to the surface mechanism. Surface cracks will propagate when SIF is larger than the fracture toughness of materials. It can also be revealed that smaller particles exhibit higher structural integrity. Significantly, the critical nanoparticle electrode size is arrived, below which the anode will not be broken and this value is in good agreement with experimental observations. Overall, the present work maybe provides physical underpinnings for optimized structural design to mitigate the mechanical degradation in high-performance anodes for Li-ion batteries.