Interstitial Li plus and Li plus Migrations in the Li2+XC1-XBXO3 Solid Electrolyte

Herein, based on powder and single-crystal diffractions of the samples synthesized, and density functional theory (DFT) calculations, we investigated the crystal structure of the Li2+xC1-xBxO3 (LCBO) solid solution ss1 (Li2CO3 phase, 0 <= x < 0.35) electrolyte. Besides the Li1 site, three interstitial lithium sites [Li2 (8f), Li3 (8f), and Li4 (8f)] are observed. Most of the Li+ are located at site Li1 with the occupancy (occLi1) > 0.80(1) and the occLi1 decreases as x increases [occLi1 = 0.92(1), 0.82(1), and 0.82(1) in Li2.1C0.9B0.1O3, Li2.2C0.8B0.2O3, and Li2.3C0.7B0.3O3, respectively]. The interstitial Li+ occupy the site Li2 with occLi2 + occLi1 approximate to 1.0 and Li3, Li4 sites. We carried out theoretical calculations/optimizations to check the energy-preferred structural geometry; Li1 is the most energy-preferred site in both Li2CO3 and Li9C3BO12. We also investigated the ionic conductivity and Li+ migrations of Li2+xC1-xBxO3 ss1. The continuous -Li3-s1-Li2-s2-Li1-s3-Li3- one-dimensional (1D) pathway (through s1-s3 saddle sites) shows the lowest barrier energy (0.094-0.29 eV). The 1D paths are then connected by the saddle sites s4 (0.31 eV) and s5 (0.48 eV) with a higher barrier energy to form a curved two-dimensional (2D) migration pathway in the a-c plane, and are connected by Li4 through the saddle site s8 (0.49-0.55 eV) to form a three-dimensional (3D) framework migration pathway. The Li+ migration is dominated by the -Li3-s1-Li2-s2-Li1-s3-Li3- 1D pathway at T <= 75 degrees C and by 1D, 2D, and 3D pathways at T >= 100 degrees C.

Automated summary

In this study, the crystal structure and ionic conductivity of the Li2+xC1-xBxO3 solid solution were investigated using experimental and theoretical methods. Multiple lithium sites were observed, and the migration pathways of lithium ions at different temperatures were explored.