Modeling of degradation effects and its integration into electrochemical reduced order model for Li(MnNiCo)O2/Graphite polymer battery for real time applications

Abstract

Previously, a highly efficient reduced order model (ROM) for Li(MnNiCo)O2/Graphite polymer battery based on electrochemical principles has been developed for real time applications. The execution time is significantly reduced compared to that of the electrochemical thermal full order model while beginning of life of the battery with the approximately same accuracy can be predicted. However, prediction of the end of life associated with degradation effects of battery was not included. Our investigations on aging mechanisms of the Li(MnNiCo)O2 (MNC) lithium ion batteries have revealed that side reaction is the main cause among others for capacity and power fade of the battery. The production of the side reaction forms thin unsolvable layers that adhere to the surface of the graphite particles and grow as cycled, which is called solid electrolyte interphase (SEI). Growth of the SEI leads to loss of the lithium ions, loss of the electrolytes and loss of the active volume fraction. These effects are described using the Butler-Volmer kinetics and aging parameters. Particularly, electrolyte solvent diffusion described by Fick's law is integrated into the degradation model, which results in quantifying the electrolyte solvent concentration in SEI. The exchange current density of the side reaction is formulated as a function of electrolyte solvent and lithium ion concentration, which justifies the reaction rate in the aspect of reactants. In addition, temperature dependency of the model parameters is also considered by adopting the energy equations. Finally, the degradation model is incorporated into the ROM.Performances of the integrated ROM are compared with the experimental data collected from a high power pouch type lithium ion polymer battery with Li [MnNiCo]O2/Graphite chemistry.