The Importance of Battery Thermal Management Systems in Electric Vehicles

The electric vehicle (EV) market is experiencing an unprecedented surge in growth. According to the International Energy Agency (IEA), global electric car sales rose to 3.1 million in 2020,a 41% increase compared to 2019.

As this market expands, we see several technological advancements, including battery capacity, charging rates, range, high-performance traction motors, and wide bandgap semiconductors. Lithium-ion batteries have emerged as the preferred choice for powering electric vehicles (EVs) due to their long cycle life, high energy density, low discharge rate, high specific power, and other benefits. However, these advancements have also highlighted a significant concern: the risk of thermal runaway in EVs, leading to explosion. There is a growing need for effective battery thermal management systems, to maintain the temperature of lithium-ion batteries in Electric Vehicles.

Let's take a closer look at why battery thermal management is so vital in electric vehicles. Continue reading to learn more about the same.

Understanding the Functioning of Lithium-Ion Batteries & the Importance of Temperature Control

Lithium-ion batteries are complex systems comprising several modules, each containing a set of cells. These cells have a positive and negative terminal, called the anode and cathode. The anode is typically carbon, while the cathode comprises a metal oxide, such as lithium cobalt oxide. Both the anode and cathode play a critical role in storing lithium ions.

The electrodes in a lithium-ion battery is immersed in an electrolyte, a liquid that transports positively charged lithium ions from the anode to the cathode during charging and from the cathode to the anode during discharging. The movement of these ions is a crucial aspect of the battery's operation. A separator separates the two terminals, preventing the flow of negative and positive electrons within the battery while allowing ions to pass through.

When a lithium-ion battery charges, positively charged lithium ions move from the positive electrode to the negative electrode via the electrolyte, the separator prevents the flow of electrons within the battery, so electrons travel through the external circuit to reach the negative electrode.

A thermal management system is essential to prevent thermal runaway and control the heat in lithium-ion batteries.

Thermal Management System in EVs

The thermal management system regulates the excessive heat in battery packs, improving electric vehicles' performance.

The primary role of the BTMS (Battery Thermal Management System) is to keep the battery temperature within safe limits in order to avoid thermal runaway. It employs several mechanisms, such as insulating, cooling, heating, and so on, to guarantee that the battery pack operates efficiently. The cooling function minimises excessive heat in the battery pack, keeping the temperature within the permitted range and limiting the adverse effect on surrounding cells.

Types of Thermal Management Systems

The increasing demand for electric vehicles puts pressure on manufacturers to design batteries with a proper thermal management system that ensures high levels of safety. Thermal runaway, caused by electrical, mechanical and thermal abuse, can be significantly reduced by incorporating a proper cooling system, selecting a good battery design and using efficient battery materials. 

The design of electric vehicle batteries is limited by prescribed temperature ranges within which they can operate efficiently. If the temperature exceeds the specified capacity, the batteries may experience reduced performance, overheating, or even thermal runaway. 

Different Battery Cooling Methods

Several cooling methods are used to maintain the temperature of electric vehicle batteries within safe operating limits. These methods include:

• Air Cooling

Air cooling is a straightforward and cost-effective method for cooling electric vehicle batteries. This method transfers heat from the battery pack as air flows over its surface. It offers heating, cooling, and ventilation functions per the battery pack's requirement. Air cooling is one of the oldest and most widely used methods, utilising natural and forced convection methods depending on the air intake. While this method is commonly used for stationary battery energy storage systems, it is less efficient than liquid cooling for high-performance electric vehicles.

• Liquid Cooling

Liquid cooling is one of the electric vehicles' most efficient and safe methods for cooling battery packs. Compared to air cooling, liquid coolants have higher heat conductivity and heat capacity, which enables them to transfer and store more energy. This method is preferred for high-performance and high-power applications where heat dissipation is critical. However, liquid coolants require a closed-loop system with proper seals and maintenance to prevent leakage.

There are two types of liquid cooling systems used in electric vehicle battery packs:

• Direct cooling system:

  Battery cells, such as mineral oil, are directly submerged in a liquid coolant with low or no conductivity. However, a new type of coolant may be needed for this system.

• Indirect cooling system:

  Like glycol and water, the liquid is pumped through metal pipes surrounding the battery cells. This system is more efficient and offers better safety by isolating the battery module from its surroundings. The efficiency of this cooling system depends on the shape of the battery pack.

• Refrigerant Cooling

The refrigerant direct cooling system is a popular method used to cool electric vehicle batteries, offering higher cooling rates compared to liquid glycol cooling methods. In this system, a refrigerant is circulated through the battery to cool or heat it. Different coolant materials are utilized for cooling and heating functions. This method is known for its efficiency and is commonly used to maintain safe operating temperatures for electric vehicle batteries.

• Heat Pipes-Based System

The heat pipe method is highly effective for cooling electric vehicle batteries, using devices with extremely high thermal conductivity. This method ensures better heat dissipation and provides better temperature uniformity, particularly with prismatic and pouch batteries due to their shape and large contact surfaces. The heat pipe method works by utilizing the temperature gradient between the evaporation and condensation of the working fluid to transfer heat away from the battery cells.

• Phase Change Material

The phase change material (PCM) method involves heat absorption during the phase transition from solid to liquid. However, it doesn't significantly reduce the battery pack's temperature since the phase change material is ineffective in transferring heat away from the battery. Therefore, the PCM method is often combined with air or liquid cooling systems to provide better thermal stability for battery packs. This combination of techniques helps to maintain the temperature of the battery pack within a safe and optimal range, thus improving the performance and lifespan of the battery.

In addition to the cooling methods mentioned earlier, other ways, such as hybrid battery thermal management systems and thermoelectric coolers, are available in the market. With the increasing demand for electric vehicles, safety concerns have driven significant technological developments in thermal management systems to ensure efficient cooling arrangements and maintain optimal temperatures.

Conclusion

The primary objective of a battery thermal management system is to ensure the efficient operation of the battery, thereby enhancing its performance and extending its lifespan. Battery safety has become a top priority. The EV industry is experiencing rapid growth and demand for higher capacity and charge/discharge rates. A robust BTMS is necessary to ensure faster charge rates, improved driving performance, and, most importantly, battery safety.

If you're interested in the field of thermal management systems in electric vehicles, pursuing a relevant course could help you acquire the necessary knowledge and skills.

As the electric vehicle industry expands, the demand for professionals with expertise in BMS is expected to rise. Pursuing a battery thermal management course could help you acquire the necessary skills and knowledge to become a valuable asset to the industry.

Skill-Lync offers a comprehensive course on battery thermal management for electric vehicles. Talk to our experts to know and get a free demo.