Abstract
Owing to the attractive energy density, high reversibility, and long product lifetime, Li-ion technology has conquered portable electronics[1-3] and now promises to accelerate the integration of environmentally friendly electric vehicles into the marketplace. While the most intensive research efforts started with investigations of oxide-based cathodes, many polyanionic compounds (namely olivine LiFePO4) have emerged as possible cathode systems for sustainable highvolume production.[4] Therefore, in an attempt to increase the energy density of these polyanionic compounds, we have exploited the concept of the inductive effect to enhance the voltage of the battery by replacing PO4 tetrahedra by SO4 tetrahedra. Recently, we discovered a new class of Li-based fluorosulfate materials, among which the tavorite phase of LiFe- SO4F turns out to be an attractive 3.6 V insertion compound.[ 5] Mindful of the close structural relationship between the precursor and target phases, we have characterized a broad family of fluorosulfates using a robust variety of lowtemperature synthetic approaches.[6-9] Practically unknown two years ago, this family (AMSO4F; A=Li or Na, M=Mn, Fe, Co, Ni, or Zn) presently consists of no less than 20 members, many of which present a rich crystal chemistry in combination with interesting electrochemical properties. In addition to the typical LiFeSO4F tavorite phase we have recently reported the existence of two new polymorphs in this family of compounds: triplite LiMnSO4F[10] and sillimanite LiZnSO4F.[11, 12]