Résumé
The next generations of Li- and Na-ion batteries will rely on the development of new sustainable, low-cost and safe positive electrode materials. To this end, we explored the world of minerals with an emphasis on spotting structures having the prerequisites for insertion and deinsertion of alkaline ions. From this survey, we embarked on the investigation of bimetallic sulfates derived from the bloedite mineral and having the general formula AxM(SO4)2*nH2O (A = Li, Na, M = 3d transition metal and n = 0, 4). These systems present rich crystal chemistry, undergoing phase transitions upon heating and removal of water. The new structures were determined by combining X-ray, neutron and electron diffraction techniques. We have also shown that lithium-based compounds LixM(SO4)2 present interesting antiferromagnetic properties resulting from their peculiar structures, which solely enable super-super-exchange interactions. Finally, and more importantly, we identified among the isolated compounds three iron-based sulfates, namely Na2Fe(SO4)2*4H2O, Na2Fe(SO4)2 and Li2Fe(SO4)2, which present attractive electrochemical properties against both lithium and sodium. With a potential of 3.83 V vs. Li+/Li0, the new marinite phase Li2Fe(SO4)2 displays the highest potential ever observed for the FeIII+/FeII+ redox couple in a fluorine-free iron-based inorganic compound, only rivaled by the triplite form of LiFeSO4F.