Li Ion Diffusion Mechanisms in the Crystalline Electrolyte γ-Li[sub 3]PO[sub 4]

Solid state lithium ion electrolytes are becoming increasingly important in batteries and related technologies. We have used first-principles modeling techniques based on density functional theory and the nudged elastic band method to examine possible Li ion diffusion mechanisms in idealized crystals of the electrolyte material . In modeling the Li ion vacancy diffusion, we find direct hopping between neighboring metastable vacancy configurations to have a minimal migration barrier of . In modeling the Li ion interstitial diffusion, we find an interstitialcy mechanism, involving the concerted motion of an interstitial Li ion and a neighboring Li ion of the host lattice, that can result in a migration barrier as low as . The minimal formation energy of a Li ion vacancy-interstitial pair is determined to be . Assuming the activation energy for intrinsic defects to be given by , the calculations find for ionic diffusion in crystalline , in good agreement with reported experimental values of .