Structural Failure Mechanism And Modelling Of Lithium-ion Battery Pouch Cell Under Mechanical Abuse

With the rapid development of electric vehicle market,the short circuit of lithium-ion batteries induced by mechanical abuse is of great concern in electric vehicle design.Improving crash safety of electric vehicles requires comprehensive understanding of the mechanical behavior of lithium-ion batteries under various loading conditions.In this study,experimental,analytical and numerical methods are used to provide insights into the deformation mechanisms of commercial lithium-ion pouch cells.An effective finite element model is built for predicting battery deformation.These results are important for crashworthiness design of electric vehicles.Indentation test is one of the severest loading scenarios for lithium-ion battery.The present work investigates the evolution of the damage process for a lithium-ion pouch cell under indentation.The test results indicate that the state of charge has no effect on the mechanical behavior of pouch cells unless constraints are applied.A significant inflection point on the force-indentation curve is observed before the force peak.Post-mortem examinations indicate that the characteristic change in the local slope of the curve is related to the change occurring on the anode-separator interfaces.Cracks inside active coating layer and delamination of coating from the current collectors are observed in the indentation process.A method is established to measure the adhesion strength of active material coating under different stress states.Both quasi-static and dynamic indentation tests are conducted on a lithium-ion pouch cell.The test results show strain-rate dependence of stiffness but a reduced first-peak force and deformation tolerance at high loading speed.The test results suggest that the existence of electrolyte has significant influence on the strain-rate dependence of pouch cells.Both analytical and numerical models are established to explain this fluid-structure interaction mechanism.The structural deformation drives the electrolyte to flow through the porous media of the pouch cell that includes separators and active particles of electrodes.Due to the viscosity of the electrolyte,the flow leads to considerable energy dissipation.On the macro level,the effective stiffness of the porous structure is increased,which results in the intensified deformation of the current collector.Consequently,the battery structure fractures at smaller intrusion of the punch head.For finite element simulations,both homogenized and non-homogenized models are established for predicting battery deformation under different loading conditions.To calibrate the fracture behavior of pouch cells,several failure criteria are introduced in the homogenized and non-homogenized models.The MMC model turns out to be the most satisfactory one.