Stabilization of the cubic, fast-ion conducting phase of Li 7 La 3 Sn 2 O 12 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 Li 7 La 3 Zr 2 O 12 (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 Al 3+ or Ga 3+ . Despite prior attempts, the stabilization of the cubic phase of isostructural Li 7 La 3 Sn 2 O 12 (LLSO) by doping on the Li sites has up to now not been realised. Here, we report a novel cubic fast-ion conducting Li 7 La 3 Sn 2 O 12 -type phase stabilized by doping Ga 3+ 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.