Numerical and Experimental Investigation of Thermal Behaviour for Fast Charging and Discharging of Various 18650 Lithium Batteries of Electric Vehicles

Abstract

Fast charging and discharging are keen focus areas of electric vehicles (EVs) in order to reduce vehicle down time and support the variable load requirement. In EVs, mainly lithium batteries with various chemistry such as NCA (nickel cobalt aluminum oxides), LTO (lithium titanate oxide), LFP (lithium iron phosphate), LNO (lithium nickel oxide) and NMC (nickel manganese cobalt oxides) are used as energy storage system. Performance of lithium batteries varies with the chemistry and temperature of batteries along with surrounding conditions. More heat is generated during fast charging and discharging of batteries which lead to high temperature rise and further impact the performance, life and safety of batteries. Thus, it’s essential to study the thermal behaviour for fast charging and discharging of various lithium batteries to provide desired thermal management system for safety and better performance. In this paper, the thermal characteristics of various 18650 lithium batteries including NCA, NMC and LFP are investigated experimentally and numerically from slow charging and discharging loading rate of 0.5C to fast charging and discharging loading rates of 1.5C and 2.5C at different surrounding temperature of 27°C and 45°C. In the numerical investigation, the internal resistance of the batteries is first measured experimentally at various SOCs and battery temperatures, and then the battery surface temperature is determined using an appropriate numerical method for solving the energy balance equation. From slow to fast loading rates at varying ambient temperatures, the numerical study approach presented in this work estimates the battery surface temperature with at least 90% accuracy for the whole duration of the load cycle. The thermal assessment of NCA, NMC, and LFP batteries in this work can help to determine battery management system operating strategies and, ultimately, to develop an appropriate thermal management system.