LAUSR

Lithium iron phosphate (LiFePO4) has been demonstrated as a commercially important cathode material for lithium-ion batteries due to its large theoretical capacity (~170 mAh/g), superior stability and cyclability [1]. Theoretically, LiFePO4 and FePO4 are the only two stable phases in bulk equilibrium condition, indicating that interfaces exist between these two phases during lithiation and delithiation processes. However, for high-rate battery applications, size reduction, carbon coating and doping are essential modifications to improve their low ionic and electronic conductivities. Among various methods, reducing the size to nanoscale can effectively lead to increase of reaction rate and meanwhile may modify the reaction mechanisms [2]. Although enormous studies of nanosized LiFePO4/FePO4 have been reported, the phase transformation through either solid-solution or two-phase mode still remains elusive [3, 4]. Here, we report the structural change in LiFePO4 nanoflakes during reversible electrochemical reactions using in situ transmission electron microscopy (TEM) techniques.