Crystal Structure Engineering Enables Enhanced Ionic Conductivity in LAGP Solid‐State Electrolytes

Solid-state lithium batteries (SSLBs) have emerged as promising energy storage systems, offering superior safety and energy density compared to conventional liquid electrolyte-based lithium-ion batteries. Among solid-state electrolytes, NASICON-type lithium aluminum germanium phosphate (LAGP) has attracted significant attention due to its exceptional air stability and wide electrochemical window. However, its practical ionic conductivity remains substantially below theoretical predictions. This study demonstrates a crystal structure engineering strategy using γ-Al₂O₃ instead of conventional α-Al₂O₃ as the aluminum source. The weaker Al─O bonds and higher reactivity of γ-Al₂O₃ facilitate increased Al³⁺ incorporation into the LAGP framework, enhancing free Li⁺ concentration at M2 sites and boosting bulk ionic conductivity. Furthermore, γ-Al₂O₃ addition reduces AlPO₄ impurities and improves morphological uniformity, thereby optimizing grain boundary conductivity. The optimized γ-Al₂O₃-derived LAGP achieves a threefold enhancement in lithium-ion conductivity, reaching 6.04 × 10^-4 (total) and 2.77 × 10^-3 S cm^-1 (intracrystalline), representing a significant advancement in solid electrolyte performance.