K2Fe3(SO4)3(OH)2(H2O)2: A new high-performance hydroxysulfate cathode material for alkali metal ion batteries

With advantages of safety benefits, high stability and tunable redox potentials, polyanionic electrode materials, especially sulfates draw lots of interests. Exploring general cathodes for alkali ion (Li, Na and K) battery is of great importance to understand the effect of ion size on materials' electrochemical performance. Here, we report on a new K2Fe3(SO4)(3)(OH)(2)(H2O)(2) sulfate as a promising cathode material for rechargeable alkali-ion batteries. Regardless of employing Li ions or large radius Na ions and K ions, the material manifests comparable capacities (similar to 100 mA h.g(-1)) along with excellent rate behaviors (70 mA h.g(-1) at 10C) and long lifetimes (similar to 100% after 100 cycles at 1C). In addition, K2Fe3(SO4)(3)(OH)(2)(H2O)(2) cathode delivers different electrochemical performances with three alkali ions, which is beneficial to understand the fundamental aspects of the reaction mechanisms. This work not only enriches the crystal chemistry of sulfate family, but also proposes a new design strategy to other K-based polyanionic compounds as cathode materials for Li ions and Na ions batteries.