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Solid-state ionic conduction is significantly influenced by bottleneck sizes, which impede ion diffusion within solid lattices. Using aberration-corrected scanning transmission electron microscopy and multislice electron ptychography, we directly observed that increased La occupancy in the perovskite solid electrolyte Li0.5La0.5TiO3correlates with reduced bottleneck sizes formed by four oxygen atoms connecting neighboring A-site cages. This correlation was also confirmed in local aperiodic regions, where smaller bottleneck sizes due to increased La occupancies affect the directionality and dimensionality of the Li+ion conductivity. Furthermore, while prior studies have focused on averaged Li+ion diffusion across different bottleneck areas or chemical environments, by devising a molecular dynamics (MD)-based methodology, we quantify the diffusivity of Li+ions through specific bottleneck regions. Atomistic simulations, including nudged elastic band calculations and this MD-based methodology, revealed that larger bottleneck sizes correlate with smaller local migration barriers and higher local diffusivity. This study elucidates the relationship among local chemistry, lattice structure, and Li+ion transport, providing insights for the design of advanced oxide solid electrolytes.

Enhancing the power of lithium ion batteries necessitates an understanding of the molecular processes governing Li+ion transfer across the electrode–electrolyte interface. Here, employing enhanced sampling molecular dynamics simulations, we investigated the driving force and thermodynamic barrier of Li+ion adsorption onto Li0.5CoO2(104) electrode in LiClO4-, LiPF6-, and LiTFSI-based EC/EMC (3:7) electrolytes. The weaker cation–anion pairing in LiTFSI compared to LiClO4was found to enhance the driving force for adsorption from −0.48 eV in LiClO4to −1.26 eV in LiTFSI for an electrode–electrolyte interface with zero cation coverage, which was accompanied by an increased thermodynamic barrier from 0.33 eV in LiClO4to 0.43 eV in LiTFSI at an equilibrium surface coverage of Li+ions. The hindered diffusivity of the solvent molecules in the electric double layer (EDL) at the electrode–electrolyte interface was the main contributor to the thermodynamic barrier for ion transport. The entropic component of the thermodynamic barrier was found to be more than 1 order of magnitude smaller for ClO4–compared to TFSI–, which can be attributed to the presence of more ClO4–than TFSI–in the EDL, causing more structural changes in the EDL. The strong dependence of the entropic component of the thermodynamic barrier on the EDL structure enables its decoupling from the enthalpic components (e.g., ion-pairing that can be tuned independently) and thus can be used to control the kinetics of the interfacial transport. This work provides a fundamental understanding of the thermodynamic and kinetic parameters involved in Li+ion adsorption, which is a crucial step in the performance of Li+ion batteries.