Insight into the role of crystallinity in oxide electrolytes enabling high-performance all-solid-state lithium-sulfur batteries.

All-solid-state lithium-sulfur batteries (ASSLSBs) would be a promising candidate for the next-generation batteries due to the utilization of energy-dense electrodes and the non-flammable oxide solid-state electrolytes (SSEs), but still face great challenges such as low ionic conductivity of SSEs, poor interfacial contact and lithium (Li) dendrite propagation. Herein, we regulated the crystallinity degrees of the large-scale-fabricated Li1.5Al0.5Ge1.5(PO4)3 (LAGP) SSEs and explored the critical role of crystallinity optimization in reinforcing the basic properties of LAGP, developing a fundamental explanation for the inherent relation between the crystallinity and the performance of ASSLSBs. Benefiting from the optimized crystallinity (∼99.9 %), the large-scale-fabricated LAGP not only realizes the low surface roughness and high ionic conductivity (2.11 × 10-4 S cm-1) to improve interfacial contact and reduce resistance in ASSLSBs, but also possesses the dense internal structure with low porosity (1.49 %) to physically resist dendritic propagation and penetration. Consequently, the ASSLSB with the optimized LAGP delivers a high reversible capacity of 647.9 mAh/g even after 150 cycles at 0.1 C. This work confirms the significance of crystallinity in understanding the working mechanisms of oxide SSEs and developing future high-performance ASSLSBs.