Stabilization of the cubic, fast-ion conducting phase of Li₇La₃Sn₂O₁₂ garnet by gallium doping

All-solid-state batteries present promising high-energy-density alternatives to conventional Li-ion chemistries, and Li-stuffed garnets based on Li₇La₃Zr₂O₁₂ (LLZO) remain a forerunner for candidate solid-electrolytes. One route to access fast-ion conduction in LLZO phases is to stabilize the cubic LLZO phase by doping on the Li sites with aliovalent ions such as Al³⁺ or Ga³⁺. Despite prior attempts, the stabilization of the cubic phase of isostructural Li₇La₃Sn₂O₁₂ (LLSO) by doping on the Li sites has up to now not been realised. Here, we report a novel cubic fast-ion conducting Li₇La₃Sn₂O₁₂-type phase stabilized by doping Ga³⁺ in place of Li. 0.3 mole of gallium per formula unit of LLSO were needed to fully stabilize the cubic garnet, allowing structural and electrochemical characterizations of the new material. A modified sol-gel synthesis approach is introduced in this study to realise Ga-doping in LLSO, which offers a viable route to preparing new Sn-based candidate solid-electrolytes for all-solid-state battery applications.