Potential and Current Distributions in Planar Electrodes of Lithium-Ion Batteries

Two-dimensional distribution of potential and current density in planar electrodes of pouch-type lithium-ion batteries are investigated numerically and analytically. A concentration-independent polarization expression, obtained experimentally, is used to mimic the electrochemical performance of the battery. By numerically solving the charge balance equation on each electrode in conjugation with the polarization expression, the battery behavior during constant-current discharge processes is simulated. The numerical analysis shows that reaction current density between the electrodes remains approximately uniform during most of the discharge process, i.e., when depth-of-discharge varies from 5% to 85%. This observation suggested simplifying the electrochemical performance of the battery such that the charge balance equation on each electrode can be solved analytically to obtain closed-form solutions for potential and current density distributions. The analytical model shows fair agreement with experimental and numerical data at modest computational cost. The model is applicable for both charge and discharge processes, and its application is demonstrated for 20 Ah and 75 Ah prismatic lithium-ion batteries. The analytical model is used to describe electrical conduction in the electrodes, and to investigate the effects of tab design on voltage drop. It is demonstrated that constriction/spreading resistance in current collectors of the considered battery is fairly small; about 10% of the total cell resistance but it is larger than the contribution of bulk resistance which is about 3%. The model confirms that constriction/spreading increase with: decrease in the aspect ratio of the current collector, decrease in the tab width, and increase in the tab eccentricity.