Analysis of the FePO4 to LiFePO4 phase transition

The electrochemical phase transformation of carbon coated nanophase (60-70 nm) FePO4 to LiFePO4 was investigated by use of the Avrami-Johnson-Mehl-Eroofev equation. The analysis at three temperatures showed an Avrami exponent equal to one. Based upon reinterpretation and in agreement with recent microstructural evidence, a two-dimensional growth mechanism for the phase transformation is proposed in which the new phase grows in a direction perpendicular to the direction of lithium ion transport. Furthermore, the relatively low value of the activation energy for the phase transformation of 13 kJ/mol suggests that the phase transition is controlled by lithium ion diffusion along the phase boundary.