The impact of ionomeric active binder on Li-ion battery charge-discharge and rate capability, Part I: Electrolyte

Ionically functionalized polymers as active binders in porous electrodes of Li-ion batteries have been studied recently to improve the rate capability of thick electrodes. Li+ ion depletion and the accompanying rapid drop of electric potential act as limiting factors for thick cathodes in Li-ion batteries. We show that the incorporation of lithiated additives containing covalently bound anions, including both ionomers and nanoparticle salts, can enhance the nominal voltage and utilization of Li-ion cathodes. A mathematical model is proposed to describe the influence of the lithiated ionic additives in liquid electrolyte and is implemented. The simulation results elaborate the effect of varying ion-pair dissociability for the ionic additives. A steady state ion concentration gradient is achieved for low current density, but operation at high current density results in Li+ depletion in the electrolyte phase. The use of dissociable ionic additives can overcome this limitation and reduce the potential polarization across the electrolyte. Higher concentration of ionomer ligands can improve performance for poorly dissociable ionic additives. The model validation shows that the potential drop can be lessened when ion-pair dissociation is considered while ion mobility remains unchanged. The modeling technique can be extended to a whole battery cell.