Abstract:
The transfer diffusion properties of lithium ions play an important role in the charge and discharge rate of lithium ion batteries (LIBs). In this article, we used non-equilibrium molecular dynamics (NEMD) simulation to mimic lithium ions migration behavior in graphite, MoS
2 and their composites (G/MoS
2 ) during charging process. Assisted by equilibrium molecular dynamics (EMD) simulation and quantum mechanics simulation, we investigated the relationship of the diffusion time, diffusion coefficient and adsorption energy of lithium ions, and examined the influences of layers spacing and edge structures of graphite and MoS
2 on lithium ions diffusion. It was shown that transport diffusivity varied from the self-diffusivity by 5—7 orders of magnitudes, which indicated that the self-diffusion coefficient based on EMD could not properly describe the LIBs charging and discharging processes. The results also indicated that lithium ions had the highest diffusion rate when the layers spacing of graphite and MoS
2 were 0.42 nm and 0.75 nm, respectively. The promoting effect of graphite edge structure on lithium diffusion was: C−OH > C−F > C= O > C−H. On the other hand, we compared the diffusion time of lithium ions when the edges of MoS
2 were Mo atom and S atom, it was found that the difference between them was not significant. For G/MoS
2 composites, we studied six kinds of composite structures, the analysis results showed that lithium ions had the fastest diffusion rate and the largest diffusion coefficient in the 1+1 composite structure. Therefore, the more homogeneous the composites are, the faster the diffusion will be.