Oven exposure testing is a standard benchmark that Li-ion cells
must pass to get approval for sale by the regulating bodies. These
tests are designed to ensure the safety of battery user. However,
these tests can be costly and time consuming. The development of
simulation capabilities, which can replace the physical test to a
certain extent helps both battery manufacturers and OEMs not only
in the cost cutting but also to optimize the critical parameters
which can directly influence the safety criterions. In this paper,
a numerical model of 18650 Li-ion cell in an oven test condition is
developed to study the thermal runaway, cell venting, internal
pressure, and gas flow dynamics behavior using ANSYS FLUENT
commercial software. k-ϵ Reynolds-Averaged Navier-Stokes model is
used to describe the turbulent flow out of the cells. Thermal abuse
reactions are described using by a four-equation lumped reaction
model which considers the reaction kinetics of Solid Electrolyte
Interface (SEI) decomposition, anode-electrolyte reactions,
cathode-electrolyte reactions & electrolyte decomposition. Vent
gas generation is modelled using a user defined function (UDF) and
Vent Gas release mechanism is modelled using a macro file. Vent Gas
release is designed in such a way that the flow of build-up gas
within the battery to the outer environment is allowed only when
its average pressure reaches a fixed threshold. A series of
computational fluid dynamics (CFD) simulations are conducted on
this single 18650 cell at various external Oven temperature (150C,
200C, 250C, 300C, 350C) to find out the Thermal Runaway initiation
time and the time gap between thermal runaway initiation and Vent
Valve Opening. As the rate of vent gas release is critical leading
to combustion and further catastrophic events, the valve opening,
and subsequent gas flow characteristics are critical parameters
while dealing with the thermal runaway simulations.