When the ambient temperature is below 0 °C, it will be very difficult to charge the lithium-ion battery, if the temperature is below 20 °C, it is hard to discharge the lithium battery.. How to solve the problem, when we use Electric Vehicle lithium battery in winter?
The problem of charging the battery at low temperature can be solved by heating the lithium ion.There are various external heating methods for lithium-ion battery, the difficulty of external heating method of lithium ion is to control the heat balance of the whole lithium battery pack.
The low temperature has a big effect on the lithium-ion battery. If the temperature is too low, the lithium battery will lose its performance and even its ability to work. To keep the lithium-ion battery working at low temperatures, the battery needs to be heated. Currently, low temperature batteries are heated in the following ways:
(1) Liquid Preheat
Liquids have higher thermal conductivity and heat capacity than air, and therefore conduct heat more efficiently, but liquid preheating systems are more complex by comparison. Depending on whether the battery is heated in contact with a heat-conducting liquid, liquid heating can be divided into two categories: 1) Non-contact heating; 2) Immersion heating. At present, non-contact liquid preheating system has been used in electric vehicle battery pack. For example, SmartPropel uses a 360V heater to heat the liquid and transfer it to a battery.
(2) Air Preheating
The air temperature control system is widely used in electric vehicles because of its simple structure and low cost. The air conditioning temperature control system works by heating the outside air through the heating system and then entering the battery for the purpose of the fan to heat the battery. Generally, air preheating is used, and the heating rate can reach 0.5-3 °C/min. The speed and temperature of the air flow will affect the effect of air preheating. Relevant studies show that the effect of increasing air velocity is more obvious than that of increasing air temperature. At the same time, the higher the air temperature, the more obvious temperature gradient will appear inside the battery, which will adversely affect the battery life. It has been used in Honda’s Insight and Toyota’s Prius models, but it still has many disadvantages, such as noise and efficiency.
(3) Preheating Of Phase Change Materials
Air preheating and liquid preheating require more complex structures inside the battery, such as pipes, pumps, and heaters, which adds to the cost and design difficulty of the battery pack. Battery pack preheating and phase change materials provide an easier way to heat and cool a battery, primarily through the heat released or absorbed by the PCMS during the phase change process, in order to solve the problem that the thermal conductivity of phase change materials (PCM) is low, which is not conducive to the rapid heat transfer to batteries, the method of joining carbon nanotubes to metal skeleton has been proposed, but the method is still in the laboratory stage, has yet to be put to practical use.
(4)Electric Heater Preheating
In the heating method of the electric heater, the electric heater is generally placed on the top or bottom of the battery, and the heat produced by the electric heater is directly transmitted to the battery. The electric heating plate is usually made of positive temperature coefficient material (PTC) . With the increase of temperature, the resistance increases, so that the temperature can be controlled automatically.
Between all above heating methods for lithium battery, the most common and effective methods is Electric heating plate. Which is high efficiency and heat the battery pack in winter quickly.Most AGV lithium battery pack and Electric Vehicle battery when have the demands to charge below -0°C or discharge below -20°C ,SmartPropel usually apply electric heating plate.