Abstract
Strain rate sensitivity has been widely recognized as a significant feature of the dynamic mechanical properties of lithium-ion cells, which are important for their accurate representation in automotive crash simulations. This research sought to improve the precision with which dynamic mechanical properties can be determined from drop tower impact testing through the use of a diaphragm to minimize transient shock loads and to constrain off-axis motion of the indenter, specialized impact absorbers to reduce noise, and observation of displacement with a high speed camera. Inert pouch cells showed strain rate sensitivity in an increased stiffness during impact tests that was consistent with the poromechanical interaction of the porous structure of the jellyroll with the liquid electrolyte. The impact behaviour of the inert pouch cells was similar to that of an Expanded Polypropylene foam (EPP), with the exception that the inert pouch cells did not show hysteretic recovery under the weight of the indenter. This suggests that the dynamic mechanical behaviour of the inert pouch cells is analogous to a highly damped foam.
Highlights
At the time of writing, cost effective finite element modelling of vehicle impact in the absence of a supercomputer is typically limited to several millions of elements [1,2]
Despite the complexity of multi-physics in the jellyroll [11,12,13], a notable consensus has arisen within a growing body of research that structural properties can be adequately approximated in solid mechanical terms for the practical finite element simulation of lithium-ion cells [6,14,15,16,17,18,19]
This is approximately 2% of the load at peak displacement observed in the force-displacement curve for the pouch cells shown in Figure 6d and this represents a much
Summary
At the time of writing, cost effective finite element modelling of vehicle impact in the absence of a supercomputer is typically limited to several millions of elements [1,2]. For full vehicle crash simulations, it may only be computationally efficient to represent individual lithium-ion cells with several thousands of elements, which is insufficient to model all of the layers of the jellyroll [3]. Homogenization techniques have included representative volume elements [4,5,6], material models validated with empirically derived engineering constants [7] and estimation of globalized properties from individual layers [8]. These ‘macroscopic’ approaches contrast with ‘microscopic’ or ‘detailed’ modelling, which seeks to represent individual layers in the jellyroll as separate entities [9]. The through-thickness compression of jellyrolls has been observed to occur with a negligible in-plane
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