The search for good solid electrolytes constitutes a major goal towards the development of safer lithium batteries. A few candidates do exist, but they suffer either from narrow electrochemical window stability or too low ionic conductivity. Herein we report the ionic-liquid-assisted synthesis of a novel LiZnSO 4 F fluorosulfate phase having a sillimanite LiTiOPO 4 -type structure, which on simply pressed samples shows a room-temperature ionic conductivity of 10 À5 -10 À7 S cm À1 together with a 0-5 V electrochemical stability window range, while ionic-liquid-free LiZnSO 4 F shows an ionic conductivity four orders of magnitude lower (10 À11 S cm À1 ). While robustly reproducible but not yet fully understood, this finding offers new opportunities to tailor inorganic composites with higher ionic conductivity. The origin of such results is demonstrated to be rooted in a surface effect associated with the grafting of a lithium-containing ionic liquid layer. This finding opens up new opportunities for the design of ceramic composites with higher ionic conductivity and should serve as an impetus for further exploiting the chemistry of ionic liquid grafting on oxides.Renewable energy sources and electric automotive transportation are popular topics in todays energy-conscious society, hence placing rechargeable batteries as one of the major technological sciences in this new century.[1] Advances in energy storage are a tribute to chemists abilities to design new and better materials. In the hunt for novel electrode materials, notions of sustainability must be considered.[2] This is the reason why LiFePO 4 , which is made of inexpensive and abundant chemical elements, has attracted the attention of the research community despite its poor conducting properties. By particle downsizing and carbon nanocoating, LiFePO 4 /C composite overcomes transport limitations and is capable of reversibly and rapidly intercalating 0.9 Li (ca. 160 mA h g À1 ) at a redox voltage of 3.43 V versus Li. Thus, it has become one of the most praised electrode materials for the next generation of rechargeable batteries for high-volume applications. [3] Further exploring the chemistry of polyanionic-based insertion electrodes, we recently synthesized, by an ionothermal process, a novel 3.6 V LiFeSO 4 F electrode showing a reversible capacity nearing 140 mA h g À1 (theoretical capacity = 151 mA h g À1 ), good rate capability, and cycling stability.[4] This fluorosulfate was found to crystallize in a tavorite structure (space group P " 1 1) with three-dimensional channels for Li diffusion as opposed to the one-dimensional channels in LiFePO 4 . Most likely, from the 3D versus 1D change in the conduction path, the use of LiFeSO 4 F powders will obviate the need for nanosizing or carbon coating, while the same cost and environmental advantages are maintained.Since our early report, we have considerably enlarged the fluorosulfate family with the discovery of AMSO 4 F (A = Li, Na and M = Co, Ni, Mn, etc.) homologues. [5] This new family of materials, pract...