Safety Analysis Of Bottom Crash Of Vehicle Power Battery Pack

Short-circuit failure caused by partial extrusion of vehicle power battery pack is a typical condition with high risk in crash accident of electric vehicle.Especially,the power battery pack is often arranged at the bottom of the body floor,and safety standard design has not yet been formulated.Low ground clearance causes more serious crash accidents.Therefore,the research on the bottom crash safety of the power battery pack is of great significance and practical value for improving the protection safety of the bottom of the power battery pack and the safety of the electric vehicle.Firstly,based on the in-depth analysis of vehicle-related road-debris accident data,the key features of road debris are simplified and extracted,the geometric parameter structure model of road debris is established,and the kinematics model of bottom crash of vehicle power battery pack is constructed to objectively reflect the response of power battery pack bottom crash.Next combined with finite element simulation and punch test,the deformation failure mechanism of thin plate under mechanical loading is discussed.Based on the theory of strain hardening material,two simple expressions of critical failure displacement and maximum loading force are derived,which are applied to the failure prediction analysis of the bottom structure of the vehicle power battery pack.Then the compression test and battery disassembly observation of the lithium-ion phosphate battery with rectangular aluminium shell are carried out.It is found that the change characteristics of macro-mechanical response,deformation failure mode and damage of the battery core are highly consistent.The deformation failure mechanism and short circuit reasons at different stages of battery are analyzed.The material parameters and short-circuit failure parameterization are provided for the finite element model of lithium-ion battery.The mechanical parameters characterizing the short-circuit failure of the battery are obtained: the compression deformation of the battery is safe within 4.5 mm,the potential short-circuit risk is between 4.5 mm and 6.0 mm,and the short-circuit failure of the battery is more than 6.0 mm.Finally,the homogenized layered finite element model of lithium-ion batteries is applied to the bottom crash of vehicle power battery pack.The deformation failure of power battery pack and the crash safety of internal Structures such as shell,inner frame and so on,are analyzed comprehensively.The results show that the inner structures of lower shell,plastic frame,upper cover and inner frame are extruded and deformed in varying degrees,and the lower shell is subjected to the most serious impact.The bottom of the shell is broken and perforated,which results in the battery module contacting with road debris directly on the road,and aggravates the deformation and failure of the battery.It is found that the maximum compression deformation of the battery is 8.5 mm,which is far beyond the safe threshold of the deformation of the battery.The structure of the power battery pack has potential safety hazards.The optimum design of the battery pack shell is carried out.It is found that the double plate structure and foam sandwich structure can effectively protect the battery and improve the crash safety of the vehicle battery pack.The mechanical response characteristics of lithium-ion batteries under compression load and the results of internal short-circuit failure analysis,the safety analysis of bottom crash of vehicle power battery pack and the proposed optimization scheme of battery pack structure have guiding significance and practical value for improving the impact safety of vehicle power battery pack.