American Chemical Society, Chemistry of Materials, 14(26), p. 4178-4189, 2014
DOI: 10.1021/cm5012845
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To enhance the safety, cost, and energy d. of Li-ion batteries, significant research efforts have been devoted to the search for new pos. electrode materials that exhibit high redox potentials and are composed of low-cost, earth abundant elements. Sulfate chem. has yielded promising results for iron-based polyanionic electrode materials using the FeIII+/FeII+ redox couple, including the recent discovery of a monoclinic marinite Li2Fe(SO4)2 phase (3.83 V vs. Li+/Li0). Here, we report the ball-milling synthesis and electrochem. properties of a new orthorhombic polymorph of Li2Fe(SO4)2, which rapidly and reversibly reacts with lithium through a two-step redox process (3.73 V and 3.85 V vs. Li+/Li0) with an overall sustained capacity of about 90 mAh/g. Using similar synthesis conditions, the cobalt-, zinc-, magnesium- and nickel-based orthorhombic analogs were also obtained, though no electrochem. activity was obsd. for these phases. Overall, our results demonstrate that polymorphism can play a crucial role in the search for new battery electrode materials and emphasize the need to understand and master synthetic control. [on SciFinder(R)]