EIS-Based Hysteresis Modelling of LFP Cells

Based on recent advances in non-equilibrium thermodynamics, a new approach to the modelling of the hysteresis of LiFePO
4
is proposed. A method for characterising the hysteresis based on electrochemical impedance spectroscopy (EIS) is presented, which allows to reduce the characterization time from multiples weeks to few days. The results show that hysteresis in LiFePO
4
is a very slow relaxation process strongly correlated with prior works results in crystalline phase transitions. An Electrical Circuit Model (ECM) of the cell is then extracted by using the distribution of relaxation times (DRT) on the EIS profile of the cell. The extracted DRT parameters show good agreement at low frequencies with previous thermodynamic studies. The performances of the ECM is compared with state of art physics-based ECM (without hysteresis compensation) and show an RMSE reduction of four fold under dynamic cycling.