New Lithium Iron Pyrophosphate as 3.5 V Class Cathode Material for Lithium Ion Battery

A new pyrophosphate compound Li2FeP2O7 was synthesized by a conventional solid-state reaction, and its crystal structure was determined. Its reversible electrode operation at ca. 3.5 V vs Li was identified with the capacity of a one-electron theoretical value of 110 mAh g−1 even for ca. 1 μm particles without any special efforts such as nanosizing or carbon coating. Li2FeP2O7 and its derivatives should provide a new platform for related lithium battery electrode research and could be potential competitors to commercial olivine LiFePO4, which has been recognized as the most promising positive cathode for a lithium-ion battery system for large-scale applications, such as plug-in hybrid electric vehicles.