Modeling the Structure and Dynamics of Lithium Borosilicate Glasses with Ab Initio Molecular Dynamics Simulations

Ion transport and the associated structures in glass materials are of interest in batteries and related materials. Herein, the atomic structures and dynamics of Li+ in borosilicate glasses with high Li contents were studied using ab initio molecular dynamics (AIMD) simulations. The obtained bond distances and BO4 fractions were in good agreement with the predictions of large-scale classical molecular dynamics (CMD) simulations with the latest potentials. The boron 3-ring super structures were successfully formed in the AIMD framework, overcoming a key limitation of CMD simulations. Consequently, the structures and Li+ dynamics related to the boron 3-ring super structures were revealed by the AIMD simulations in this study. The dynamic properties of Li+ and the glass network were investigated by Li+ translation and vibration along with the libration of nonbridging O atoms. The Li+ distributions for different Li mobilities were homogeneous in the glass network regardless of the nonbridging O species. The distributions were differentiated by the type of bonding cation (Si, three- and four-coordinated B atoms, and the boron 3-ring and nonring B atoms). The coupling motion between Li+ and nonbridging O atoms is discussed based on the power spectra of Li+ vibration and O libration. The results suggest that the decoupling of motion between network atoms and Li is key to developing glasses with higher ionic conductivity.