Research Of Phenomenological Multi-Physics Model Of Square Ternary Lithium-Ion Battery Expansion Forceexpansion Displacement

With the increase of people’s awareness of environmental protection,the current situation of energy shortage and environmental pollution in the world today,the automotive industry is focusing on the development of environment-friendly and energy-saving cars,but the problems of lithium-ion batteries in new-energy vehicles today limit their further development.In order to solve some problems of the battery,this paper designs a lithium battery expansion force and displacement test bench.The reliability of the test bench is verified by finite element simulation and battery charge and discharge experiments.Based on the battery charging and discharging data obtained from the test bench,a phenomenological multi-physics model of lithium battery cells is established using parameter identification,including 1D expansion displacement model and 1D expansion force model.The research contents of this article include:(1)The hardware of each system of the lithium battery expansion force and displacement test bench is designed,and the design and development of test devices in the test system of test bench is focused on,and the advantages and disadvantages of different design schemes are compared through structural analysis;test bench data acquisition programs are written.(2)A method of equivalent lithium-ion battery expansion caused by charge and discharge during the finite element simulation is proposed,that is,the expansion of the battery caused only by temperature changes is equivalent to the expansion caused by thermo-mechanicalelectric coupling during the actual charge and discharge,and the finite element simulation verification of the test bench is completed;the reliability verification of the test bench is completed by analyzing the experimental data obtained from the test bench.(3)Based on the difference of the surface temperature change of the lithium battery,the 1D expansion displacement model is divided into two parts: lithium-ion embedding expansion displacement model and thermal expansion displacement model,and the mathematical expression of the thermal expansion displacement model is derived based on the thermal expansion theory.Based on the battery charging and discharging data,a 1D expansion displacement model is established using polynomial regression fitting.The RMSE under the 0.5C 、 1C and 2C discharge rate are 1.1296 μm,1.5528 μm,1.2381 μm and 1.5692 μm,respectively.The proposed 1D expansion displacement model can accurately predict the expansion displacement of lithium batteries at various discharge rates.(4)Based on the force balance of the lithium battery in the quasi-static process in different conditions in the test bench,the expansion displacement when unconstrained is coupled with the expansion force when restrained,and the coupling equation of the 1D expansion force model is determined.Based on the battery charging and discharging data,the LM method is used to estimate the parameters for the 1D expansion force model.The prediction result is good under conditions of different discharge rate and different preloads.The proposed 1D expansion force model can accurately predict the lithium battery expansion force change under any preload.