Accurate Modeling of Li-ion Cells Applied to LiFePO4 and NMC Chemistries

Lithium-ion (Li-ion) based batteries are now commonly used in many applications such as electric vehicles, utility-scale storage, and even consumer electronics. However, to maximize the power utilization and optimize runtime voltage-current (V-I) characteristics of these cells, it is imperative to accurately predict the behavior of these batteries for varying load profiles. In this work, we explicitly model Li-ion cells using the 2RC model implemented through the modified block in MATLAB/Simulink. The 2RC model parameters are extracted with a relaxation time of only six minutes. The model was tested (through measurements of six cells) for two Li-ion cell chemistries (NMC and LiFeP04) in three packages (18650, 32650, and 26650) and varying capacities (1500 mAh to 6000 mAh) with high accuracy. The root mean square error between experimental and modeled results ranges from 0.3 ‐ 0.7 % even with varying load profiles, which is key in the accurate performance modeling of these cells. This work will, therefore, be very useful in modeling Li-ion cells and battery pack for a wide variety of applications with diverse usage profiles.