Effects of stack pressure on the equivalent circuit model of lithium-ion batteries

The stack-level mechanical pressure is inevitable in battery pack and it has a significant effect on battery characteristics. However, parameters variation of equivalent circuit models (ECMs) caused by stack pressure has seldom been considered. For the first time, the effect of stack pressure on ECM is investigated in detail with commercial Li[NiCoMn]O₂ (NMC) cells and LiFePO₄ (LFP) cells in this paper. The changes in model parameters and their influence on model accuracy are evaluated through a test procedure including capacity tests, a modified Hybrid Pulse Power Characteristic test, and the dynamic current test. The results of the comprehensive experiments show that all the parameters of ECM vary significantly with stack pressures. Voltage errors in model simulations suggest that the pressure-induced parameter differences reduce the model accuracy. To further demonstrate the effects, the SOC estimation is carried out, which indicate the negative impact of such parameter variations on model application. These results are instructive for the application of the ECM in battery management.