Evaluation of accuracy for Bernardi equation in estimating heat generation rate for continuous and pulse-discharge protocols in LFP and NMC based Li-ion batteries

Accurate prediction of heat generation in Li-ion batteries during real driving conditions is essential for an efficient thermal management system. In this study, we verify the applicability of a commonly-used heat generation estimator (i.e., Bernardi equation) in Li-ion batteries. The real-world drive cycles comprise of intermittent discharge pulses as opposed to continuous discharge. Therefore, we consider both continuous and pulse-discharge protocols, and compare the heat generation evaluated through Bernardi equation and direct in-situ measurements. It is observed that for continuous discharge, Bernardi equation predicts the heat generation rate with reasonable accuracy. However, the equation substantially overestimates the heat generation under pulse-discharge protocol (realistic scenarios). The heat generation analysis is performed on two leading Li-ion battery chemistries, i.e., LiFePO4 (LFP) and LiNi0.8Mn0.1Co0.1O2 (NMC). Direct measurement shows deviations from the Bernardi equation to be as high as 26% and 49% for LFP and NMC cells, respectively, under high-rate discharge pulses. For the sake of accurate measurement of heat generation, specific heat capacities of Li-ion cells are evaluated with a combined experimental–numerical approach. The heat generation is examined at different cell temperatures and depth of discharge (DoD) levels, and their individual effects on heat generation are analyzed.