Sensitivity Analysis of an Electrochemical Model of Li-ion Batteries and Consequences on the Modeled Aging Mechanisms

The growing number of electrified vehicles remains particularly constrained by the performance of the energy storage system, which is a complex and expensive component in the vehicle. Li-ion batteries seem to be the best candidates due to their suitable performances for plug in or full electric vehicle application. However, the aging phenomena in those batteries will have a direct impact on the autonomy, power and maintenance costs of the vehicle and are not yet clearly understood. For automotive industry, this kind of information is critical in determining the performance and durability of the battery in traction applications. For that reason, there is an urgent need of validated predictive models for the long term behavior of those electrochemical components, ensuring an optimal battery sizing on one hand, and a proper energy management onboard on the other hand.

The aging of a Li-ion battery is mainly due to a modification of its electrochemical properties which will lead to a loss of capacity (decrease of the autonomy) and an increase of its internal impedance (loss of power). A simplified electrochemical model has already been developed at IFP Energies Nouvelles^[1] taking into account the loss of cyclable lithium due to the growth of the Solid electrolyte Interphase (SEI) and the modification of the porosity of the graphite electrode as aging mechanisms. This model allows us to estimate the evolution of the performance (power and autonomy) of a Graphite/LiFePO₄-based battery as if it was used on a typical hybrid or electric vehicle. In order to ensure the reliability of this model, a sensitivity analysis based on Zhang et al. work^[2] has been performed to find out the impact of the variation of each parameters on the model output (Voltage, Temperature) and determine the optimal testing conditions for this model calibration.

Moreover, the discrepancies observed during the validation of our properly calibrated model with experimental data highlighted an additional capacity loss due to another aging mechanism than SEI growth. According to our previous research and to the literature, we decided to add a mechanical stress based mechanism involving cracking into the electrode that leads to a loss of active materials or enhances the loss of lithium inventory. Therefore, specific experiments inducing stress during intercalation of lithium ions in the negative electrode have been carried out to gather data to identify parameters of the new mechanism added to our model. Afterwards, the behavior of this new aging model will be validated on dynamic PHEV duty profiles to ensure its good reliability.

References

[1]          E.Prada, Di Domenico D., Creff Y., Bernard J., Sauvant-Moynot V. et al., J.Electrochem.Soc. 160 (2013) A616-A628.

[2]          L.Zhang, Lyu C., Hinds G., Wang L., Luo W. et al., J.Electrochem.Soc. 161 (2014) A762-A776.