PerspectiveMaterials Science

Phase-transforming electrodes

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Science  27 Jun 2014:
Vol. 344, Issue 6191, pp. 1451-1452
DOI: 10.1126/science.1255819

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Lithium iron phosphate (LiFePO4) is one of the cheapest and safest materials used as the positive electrode of the lithium ion battery. Since its discovery in 1996 (1), the material has been a subject of debate regarding its outstanding performance in high-rate discharge-charge cycling applications. The surprisingly high performance is attained despite the miscibility gap (the composition range at which solutions become supersaturated and tend to separate into concentrated and dilute phases—like clear honey that partially crystallizes in the refrigerator) and phase transformation that complicates lithium insertion and extraction in this material. Such properties are typically associated with slow rates of electrical charge and discharge and even structural damage during cycling. On page 1480 of this issue, Liu et al. (2) provide experimental evidence to support new theoretical models (3, 4) that bypass the miscibility gap so that the phase transformation need not happen after all.