Effect of local structural disorder on lithium diffusion behavior in amorphous silicon
Wenwen Li, Yasunobu Ando
Abstract
Lithium-ion batteries with amorphous silicon ($a$-Si) anodes exhibit very high theoretical energy capacity, with the lithium kinetic transport having the most crucial effect on the battery performance. In this study, the lithium diffusion pathways in a series of large-scale $a$-Si models (512 atoms) with various extents of structural order are calculated using the machine learning interatomic potential. Then, the Li diffusion behavior in different atomistic environments is estimated from the transient state theory. The Li diffusion activation energy is observed to be lower (higher) in an ordered (disordered) local environment. The activation energy varies within the range of 1.21--1.46 eV, which agrees well with experimental measurements, 1.38--1.46 eV. Our simulations also show that Li diffusion is enhanced at higher Li concentration, which is consistent with experimental observations. The effects of structural disorder and Li concentration can be explained by the ``trap'' mechanism. Finally, we show that the sources of Li diffusion traps are dangling bonds and large voids in the $a$-Si matrix with the help of first-principles calculations. Our work provides insight into the Li diffusion mechanism, which is beneficial for improving the performance of $a$-Si anodes for lithium-ion batteries. In addition, we demonstrate the significant dependence of the ion transport behavior on the local atomic environment, which will be useful for future theoretical studies of technologically important amorphous materials beyond Si.