Research On Mechanical Properties Of Lithium-ion Power Battery For Electric Vehicles

Battery is the core component of electric vehicle.Its performance directly determines the recharge mileage,cycle life and safety characteristics of electric vehicle.Among many kinds of power batteries used in electric vehicles,lithium-ion batteries have been widely used,mainly due to their high energy density,low self-discharge rate and high environmental protection.However,as an energy storage device of electric vehicles,lithium-ion batteries store a lot of energy.When they are impacted by external force,they are prone to fire and explosion,which seriously threaten people's safety.Therefore,it is necessary to study the mechanical properties of lithium-ion battery.In this paper,the mechanical behaviors of lithium-ion power battery cell for electric vehicle were studied by experimental and numerical methods,taking lithium iron phosphate battery as an example,as follows:(1)In order to study the static and dynamic compression characteristics of representative volume element specimen of battery inner core,in-plane and out-of-plane constrained compression tests were carried at different loading speeds,respectively.The test results show that the deformation behavior of the specimen under in-plane compression mainly include buckling,plastic hinge and corresponding shear band formation and the densification of the materials.The nominal stress-strain curves obtained from tests were very similar to the compressive mechanical response of porous foam material.The mechanical responses of the specimens under static and dynamic compression had significant difference,which was mainly reflected by obvious stress enhancement and the change of deformation mode of the specimens.In the out-of-plane compression test,the mechanical response of specimens under static and dynamic compression had no obvious difference.Then,the deformation process and the dynamic effect were analyzed based on experimental results.(2)In order to study the mechanical properties of batter y cell under more working conditions by numerical simulation,a finite element model of the battery core was established.Firstly,the characteristics of several modeling methods for battery inner core were briefly described,and the homogenization finite element model of representative volume element of battery inner core was established based on the research aims of this paper.Then,local extrusion tests were conducted under in-plane and out-of-plane directions to verify the validity of the finite element model,respectively.By comparing the experimental results with the simulation results,it was found that although the deformation and force-displacement curves of the specimens had some errors,the overall consistency was good.The result could meet the research aim and verified the validity of the model.(3)Combining with the homogenization model of cell core,the mechanical response of battery cell under local extrusion in two directions of in-plane and out-of-plane was analyzed by numerical simulation method,respectively.Furthermore,the mechanical failure of battery cell and short-circuit failure of battery cell were reasonably analyzed.In addition,the effects of the shape,size of the loading head and the thickness of the aluminum alloy shell on the mechanical response of the cell were also studied.The numerical simulation results show that the size,shape and shell thickness of the indenter had great influence on the mechanical response of the cell when the cell was extruded locally in-plane or out-of-plane,respectively.