Page 219 - Çevre Şehir İklim İngilizce - Sayı 3

Orhan Topal

At high temperatures, the pressure inside lithium-based battery cells
can increase, flammable gases can be released, and the cells can ignite.
A possible thermal leakage causes the whole energy in the battery to be
released as a thermal energy in an uncontrolled way, not as electrical energy
in a controlled way. In such a case, the thermal energy released in a lithium
battery can be 7 to 11 times more than the electrically stored energy. The
resulting heat accelerates the chemical reaction experienced, causing the
battery to overheat, while it becomes difficult to control a possible fire that
may also occur due to oxygen production as a result of an exothermic reaction.
It is not possible to obtain a positive result with an intervention to be made
using traditional fire extinguishing methods (Spotnitz and Franklin, 2003). In
the thermal leakages, very high temperature values are reached quickly and
this chemically causes the lithium component to ignite. Despite the airtight,
sealed structures of lithium-based batteries under normal conditions, in case
of mechanical damage or possible external fire, exposure to thermal stress may
cause the release of corrosive toxic substances and flammable components
(dust, gas or liquid).
The lithium component used in high voltage drive batteries is highly reactive
and prone to the fast auto catalytic reactions. Moreover, lithium has a relatively low
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melting point (181°C). Molten lithium inside a battery cell leads to uncontrollable
situations. In the event of fire that occur after a possible accident involving electric
& hybrid vehicles, temperatures above 200 °C may cause the electrolytes in the
battery cells to melt, and a number of different reactions may develop in the
battery cells (Spotnitz and Franklin, 2003). These reactions trigger the thermal
leakage process. On the other hand, the resulting temperature increase may
cause sparks and arcs. Another situation that is likely to occur is the possible
explosion as a result of fresh air from ventilation units located close to the high
voltage propulsion batteries containing flammable ingredient (O ) and offering
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sufficient source for ignition (Larsson et al., 2018). The temperature changes and
the accompanying reactions depend on many factors, such as the cell type and
the health status of the battery (Zhang et al., 2018; Geisbauer et al., 2020).
The increase in the reaction rate of the product obtained as a result of a
chemical reaction Thermal leakage may occur immediately after the accident
or with delay, depending on the post-accident damage status of the high
voltage propulsion battery. Along with this, sometimes there may be situations
in which it does not occur at all (Sheikh et al., 2017; Sahraei et al., 2021). In this
sense, it becomes quite difficult for emergency response teams to identify, in
particular, the possible delayed situations. Within the scope of the side crash
test conducted with the Chevrolet Volt, a type of electric vehicle, it was recorded
that the high voltage propulsion battery short-circuited and caught fire three
weeks after the determined accident scenario (Isidore, 2011; Wojdyla, 2020).

204 Journal of Environment, Urbanization and Climate