A team from the University of Tokyo and the Tokyo Institute of Technology has synthesized a new pyrophosphate compound (Li2FeP2O7) by a conventional solid-state reaction for use as a cathode material in Li-ion batteries. 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.
The new pyrophosphate Li2FeP2O7 thus offers the highest voltage among the known Fe-based phosphate cathodes, they noted in a Communication in the Journal of the American Chemical Society.
The material showed steady capacity retention upon cycling. However, they found, the initial charge curve showed a different shape from that of subsequent cycles, possibly due to the irreversible structural change. About 40% of the initial capacity can be delivered in 1 h (1C rate), and about 20% even in 6 min (10C rate), suggesting that such electrodes could sustain respectable rate capabilities, they observed.
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.—Nishimura et al.
Shin-ichi Nishimura, Megumi Nakamura, Ryuichi Natsui, and Atsuo Yamada (2010) New Lithium Iron Pyrophosphate as 3.5 V Class Cathode Material for Lithium Ion Battery. J. Am. Chem. Soc., Article ASAP doi: 10.1021/ja106297a