Kinetic study of the electrochemical FePO4 to LiFePO4 phase transition

The electrochemical phase transformation of carbon-coated nanophase (60-70 nm) FePO4 to LiFePO4 has been investigated by use of the Avrami-Johnson-Mehl-Eroofev equation. The analysis shows an Avrami exponent equal to 1, which is indicative of one-dimensional growth. The analysis does not support the conventional shrinking core model for the electrochemical conversion of FePO4 to LiFePO4. Analysis of the Avrami exponent reveals that the phase transformation is not controlled by diffusion but by a phase boundary reaction. Measurements at different temperatures allowed for an estimate of the activation energy, which was found to be about 13 kJ/mol for the electrochemical FePO4 to LiFePO4 transformation.