What is battery preheating

[WapCar] Battery preheating refers to a technology used to enhance the battery temperature as soon as possible when "starting" the new engine vehicles, especially the pure electric vehicles, so that it can enter the optimal working temperature.

Why do we need battery preheating technology

Whether it is the lithium iron phosphate battery or the ternary lithium battery, in the low temperature environment, it will be affected by the activity of positive and negative material and the decrease of electrolyte conductivity. From the result, the charging time will increase correspondingly, and at the same time the electricity of the battery will be more difficult to be fully charged. During the using process, the "power down" speed of the power battery pack will be obviously increased. Therefore, in order to solve the above problem, engineers developed the battery preheating system and thermal management system. By adjusting the temperature of the battery pack, the effect of the ambient temperature on it is reduced.

What are the preheating technologies   

At present, the preheating methods of pure electric vehicle battery packs can be divided into two types: inner heating and outer heating. The former mainly uses the additional heating device to enhance the battery mode as soon as possible, while the latter uses alternating current to directly stimulate the internal chemical substances of the battery to heat the battery itself.

Outer heating

1. Thermistor heating: place the temperature sensing element near the battery pack, and let it serve as the source of heat.

According to the different state of the pure electric cars, the energy source of the preheating structure is slightly different. For example, when the car owner is charging, the battery management system will monitor the battery status, which includes the temperature of the battery. When the physical connection of the charging gun is completed, if the temperature of the battery pack is too low, it will use the electric energy provided by the charging pile to enter the preheating mode. If the temperature of the battery pack is too low during driving, the energy source is the power battery pack.

In addition to the above-mentioned method of using thermistor to preheat the power battery pack, the current mainstream electric vehicles preheating method on the market is also electric heating film heating. Although there are obvious differences in the structural design between them, essentially they both use electric heating devices to generate heat to achieve the purpose of increasing the temperature of the battery pack.

2. Liquid cooling temperature control: it can direct the overall thermal mangement requirements of the power battery pack by cooling it at high temperatures and heating at low temperatures.

Generally speaking, the liquid cooling temperature control system mainly includes the cold heat exchanger, heating device, coolant circulation line and liquid circulation power source. It uses the cold heat exchanger or heating device to control the increase or decrease of the power battery, various car companies will make adjustments according to the products' battery pack layout and needs.

Generally speaking, the liquid cooling temperature control system can ensure that after the electric vehicle is driven, the temperature reaches the set interval throughout the whole process, and there is no need or a small amount of use of the power battery to provide energy for the temperature control system. After the preheating is completed, compared with the thermistor heating method, its effect can remain longer.

Inner heating

The above two preheating systems are currently the mainstream temperature control methods on the market, whether using the thermistor or the liquid cooling with a more complex structure, they both need to consume a certain amount of electrical energy. Recently, scientists have discovered that reasonable use of the AC system designed by Tesla can achieve the purpose of heating the battery. Specifically, a small part of alternating current is directly applied to the positive and negative battery within a certain frequency range, and the chemical substances inside the battery are stimulated to generate heat by themselves in the form of charging and discharging in a short period of time. 

However, these methods have not been extensively verified at this stage, and it is still unknown whether they will cause damage to the battery.