Li2Fe(SO4)2 as a 3.83 V positive electrode material

We report on the preparation and electrochemical characterization of Li2M(SO4)(2) (M=Co, Fe), where the Fe-based phase was previously unknown. Both compounds can be made at low temperatures (<320 degrees C) and the Fe-based phase displays an open circuit voltage of 3.83 V vs. Li+/Li-0 for the Fe3+/Fe2+ redox potential. This corresponds to the highest voltage ever obtained for the Fe3+/Fe2+ redox couple in an iron-based, fluorine-free compound and is only matched by the triplite phase of LiFeSO4F. While the theoretical capacity of 102 mA h g(-1) will likely limit the commercial prospects for this phase, knowledge of the structure will provide useful insight into the structural origin of these increased potentials. (C) 2012 Elsevier B.V. All rights reserved.