Fast charging will form an essential part of longer trips for EVs stopping off to top up to 80% will be crucial to keep costs of EVs down and to extend the range when needed.
Its seems quite a harsh way to charge, which could lead to excessive battery thermal cycling and eventual degradation.
Looking at the long term effects of rapid charging with regards to heating and ageing of individual cells within the battery packs and real world travel patters with the use of rapid chargers and varied temperatures is essential to understanding the replacement cycle.
In a recent study the impact of realistic fast charging on simulated battery electrical, thermal, and degradation response they found that battery degradation is minimally affected for most EVs due to the low frequency of use.
The biggest problem presented by fast charging to the battery is its effect on maximum battery temperature.
Battery temperatures can exceed safe operating limits due to repeated drive-charge sequences with short or no rests in between.
This can be controlled by using active cooling or onboard vehicle controllers limiting charging and driving activities.
In electric cars, discharging the battery generates heat; the more rapidly you discharge a battery, the more heat it generates.
Batteries work based on the principle of a voltage differential, and at high temperatures, the electrons inside become excited which decreases the difference in voltage between the two sides of the battery. Because batteries are only manufactured to work between certain temperature extremes, they will stop working if there is no cooling system to keep it in a working range.
Cooling systems need to be able to keep the battery pack in the temperature range of about 20-40 degrees Celsius, as well as keep the temperature difference within the battery pack to a minimum (no more than 5 degrees Celsius).
Which cooling system works best in Electric Vehicle batteries ?
There are a few options to cool an electric car battery, using materials, fins, air, or a liquid coolant.
There are materials available that as they absorb heat energy they change state from solid to liquid (called phase change materials), While changing phase, the material can absorb large amounts of heat with little change in temperature. Phase change material cooling systems can meet the cooling requirements of the battery pack.
We can increase surface area by designing fins to increase the rate of heat transfer. Heat is transferred from the battery pack to the fin through conduction, and from the fin to the air through convection. Fins have a high thermal conductivity and can achieve cooling goals, but they add a lot of additional weight to the pack.
Convection transfer of heat by air flow away from the battery pack can be used. As air runs over the surface, it will carry away the heat emitted by the pack.
Air cooling is simple and easy, it is not efficient and relatively crude compared to liquid cooling.
Using liquid to cool makes for a higher heat conductivity and heat capacity than air,
This performs very effectively and has advantages like compact structure and ease of arrangement.
Out of these options, liquid coolants will deliver the best performance for maintaining a battery pack in the correct temperature range and uniformity.