Dynamic polarization effect and lithium-ions distribution non-uniformity coupling heat generation characters inside lithium-ion cell with battery cell design

Abstract

Electrode structure sizes including negative electrode volume fraction ε_s,n, positive electrode volume fraction ε_s,p, negative electrode particle radius r_p,n and positive electrode particle radius r_p,p are key design parameters of lithium-ion cell. To assess the impacts of electrode structure sizes on heat generation, polarization effect expressed by over-potential and lithium-ions diffusion in lithium-ion cell, an electrochemical-thermal coupling model with battery cell design was presented for a numerical investigation at charge rate 1C and ambient temperature 25 °C. The results indicate that when volume fraction or particle radius of electrode increases, total heat generation power q_tot increases. Increasing ε_s,p increases over-potential η peak of negative electrode, while decreases η of positive electrode in the middle and late stage of charge. η of negative electrode at r_p,n = 7 μm increases by 150 % compared to that at r_p,n = 3 μm. η of positive electrode at r_p,p = 5.5 μm increases by 240 % compared to that at r_p,p = 1.5 μm. Increasing ε_s,n increases and decreases respectively the lithium-ion concentration gradients grad_ce of negative electrolyte and positive electrolyte. While increasing ε_s,p increases grad_ce in the whole cell. When ε_s,n or ε_s,p increases from 0.3 to 0.7, lithium-ion concentration difference between surface and center of electrode particle Δc_s decreases by 35 % or 60 %. If r_p,n increases or r_p,p decreases, Δc_s of negative and positive electrodes increases and decreases respectively. Lithium-ion cell considering battery thermal management system was numerically studied at charging rate of 3C and initial cell temperature of 35 °C. When working medium temperature decreases or heat transfer coefficient increases, lithium-ion diffusion coefficient and redox reaction rate decrease, thus q_tot, η, grad_ce and Δc_s all increase.