The increasingly urgent global dema

The increasingly urgent global demand for more efficient energy storage techniques calls upon further improvements of the present lithium (ion) batteries for heavy-duty applications, including powering electric vehicles and integrating alternative energy technologies into the grid.1–4 However, the conventional electrolytes based on organic liquids with a dissolved Li salt pose severe obstacles to this cause; the ammable organic liquids give rise to serious safety issues (especially in large-sized batteries), and the undesired electrolyte–electrode side reactions reduce the battery life.2–4 These limitations have stimulated an intense research interest in inorganic Li-ion-conducting solid electro-lytes, since they do not present safety issues like leakage or explosion and are also sufficiently stable for a long cycle life.2–4 Beyond that, the solid electrolytes with an appropriate electro-chemical window may enable the use of the Li metal anode, which possesses the highest possible capacity for Li batteries.2 Despite these apparent advantages, the ionic conductivity of solid electrolytes is generally low, which limits their application.2