Systematic Study of the Effect of Cycle Number and Crystal Structure on Si Anodes

MD simulations were employed to model the behavior of single crystal lithium electrodes and polycrystalline silicon anodes. The results suggest that a higher number of cycles leads to notable volume expansion of the silicon electrode, resulting in decreased capacity, cycle performance, and structural stability. The transformation of the silicon crystal structure from diamond to amorphous is influenced by the degree of lithiation and desulfurization.

Abstract

This paper shows that the number of cycles and the crystal structure play an important role in the capacity and cycling ability of lithium-ion batteries. However, the detailed dynamics and continuity of the capacity decay mechanism caused by the number of cycles and crystal structure need to be further understood at the nanoscale. Molecular dynamics simulation was used to examine the microstructure development and deformation behavior of the Si anode in an electric field. The results show that the increase of the number of cycles leads to a large expansion of the volume of the Si electrode, which further leads to the loss of capacity and the decrease of cycle capacity, as well as the decrease of structural stability. The formation of Si crystal structure from diamond structure to amorphous depends on the depth of lithiation and desulfurization. Due to the presence of a large number of nanoscale voids, the Si anode has undergone volume expansion. The transformation associated with nanogap nucleation caused by the involuntary diffusion process is driven by more cycles, resulting in irreversible capacity loss of lithium-ion batteries. The analysis model shows that the stress caused by diffusion is not only related to the position of the Si anode, but also to the cycle time.

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