For real applications of all-solid-state batteries (ASSBs) to be realized, understanding and control of the grain boundaries (GBs) are essential. However, the in-depth insight into the atomic-scale defect stabilities and transport of ions around GBs is still far from understood. Here, a first-principles investigation on the promising garnet Li7La3Zr2O12 (LLZO) solid electrolyte (SE) GBs is carried out. The study reveals a GB-dependent behavior for the Li-ion transport correlated to the diffusion network. Of particular note, the Σ3(112) tilt GB model exhibits a quite high Li-ion conductivity comparable to that in bulk, and a fast intergranular diffusion, contrary to former discovered. Moreover, the uncovered preferential electron localization at the Σ3(112) GB leads to an increase in the electronic conductivity at the GB, and the Li accumulation at the coarse GBs is revealed from the negative Li interstitial formation energies. These factors play important roles in the dendrite formation along the GBs during Li plating in the LLZO|Li cell. These findings suggest strategies for the optimization of synthesis conditions and coating materials at the interface for preventing dendrite formation. The present comprehensive simulations provide new insights into the GB effect and engineering of the SE in ASSBs.
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