Conclusions
A quasi-static mechanical test program on commercial cylindrical
Lithium ion cells has been carried out, in order to assess the
deformability until initiation of an internal short circuit. A macromechanical
finite element model of the cell, suitable for standard
crash simulations, has been set up, using an element mesh size of
approximately 5 mm. The material model properties for the steel
housing have been obtained from tensile tests, and the material
properties for the jelly roll have been calibrated from one of the cell
tests, namely the radial crushing load case. The classical stressbased
fracture criterion after Mohr and Coulomb has been utilised
for fracture modelling of the jelly roll, which is considered
isotropic in the present study. It is shown that the MohreCoulomb
criterion correctly predicts both the punch displacement to fracture,
and also the correct different fracture locations for every load
case. The predicted fracture locations correspond to the observed
locations of the internal short circuits of the cells. The testing
demonstrated that the cells could withstand considerable deformation
prior to the onset of an internal short circuit.
Future research should involve the experimental characterisation
and numerical simulation of the individual jelly roll
components (anode, separator and cathode) and their interaction
during mechanical loading. Fracture analysis of the separator on
a meso-scale could inspire the development of improved macroscale
models and criteria suitable for industrial applications.
ConclusionsA quasi-static mechanical test program on commercial cylindricalLithium ion cells has been carried out, in order to assess thedeformability until initiation of an internal short circuit. A macromechanicalfinite element model of the cell, suitable for standardcrash simulations, has been set up, using an element mesh size ofapproximately 5 mm. The material model properties for the steelhousing have been obtained from tensile tests, and the materialproperties for the jelly roll have been calibrated from one of the celltests, namely the radial crushing load case. The classical stressbasedfracture criterion after Mohr and Coulomb has been utilisedfor fracture modelling of the jelly roll, which is consideredisotropic in the present study. It is shown that the MohreCoulombcriterion correctly predicts both the punch displacement to fracture,and also the correct different fracture locations for every loadcase. The predicted fracture locations correspond to the observedlocations of the internal short circuits of the cells. The testingdemonstrated that the cells could withstand considerable deformationprior to the onset of an internal short circuit.Future research should involve the experimental characterisationand numerical simulation of the individual jelly rollcomponents (anode, separator and cathode) and their interactionduring mechanical loading. Fracture analysis of the separator ona meso-scale could inspire the development of improved macroscale
models and criteria suitable for industrial applications.
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