Li 2Fe(SO 4) 2 as a 3.83 v positive electrode material

We report on the preparation and electrochemical characterization of Li 2M(SO 4) 2 (M = Co, Fe), where the Fe-based phase was previously unknown. Both compounds can be made at low temperatures (< 320 °C) and the Fe-based phase displays an open circuit voltage of 3.83 V vs. Li +/Li 0 for the Fe 3+/Fe 2+ redox potential. This corresponds to the highest voltage ever obtained for the Fe 3+/Fe 2+ redox couple in an iron-based, fluorine-free compound and is only matched by the triplite phase of LiFeSO 4F. 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. © 2012 Elsevier B.V. All rights reserved.