December 2, 2024
With extensive research being done on discovering sustainable and environmentally friendly energy sources, batteries are becoming a promising method for energy storage. Today, batteries power a wide range of devices, from small electronics to large electric vehicles (EVs). Lithium-ion batteries are particularly favored for phones and EVs due to their high energy density and long lifespan. However, when temperatures fall below or rise above a battery’s ideal operation range, it can negatively impact performance and significantly shorten the battery’s lifespan. Therefore, understanding thermal management of batteries helps ensure high performance and a long lifespan. In this blog, we will explore the concept of battery thermal management and how it impacts the efficiency and safety of battery-operated systems.
The Battery Thermal Management System (BTMS) is a concept that deals with regulating the thermal conditions of a battery system. A good BTMS keeps the battery system’s temperature within optimum levels during charging and discharging, thereby improving its performance, safety, and lifespan. Charging is the process of restoring a battery’s energy by reversing the discharge reactions, while discharging is the release of stored energy through chemical reactions.
Figure 1: Charging and discharging of batteries
In the above figure, you can see that when electrons move from the cathode (the positive node) to the anode (negative node), they increase the chemical potential energy of the system, thus charging the battery. When the electrons move in the opposite direction (ie: anode to cathode) they convert the chemical potential energy to electricity, consequently discharging the battery. Both processes generate heat. When temperatures get too high, it can cause a reduction in battery performance, accelerate degradation, and increase the risk of thermal runaway, which can lead to the battery catching fire or exploding. This makes BTMS important to control the temperature of battery systems effectively.
Temperature is one of the most critical parameters in battery systems because it impacts the battery’s performance and safety margins. Before exploring how temperature variations can be harmful, it’s important to understand how heat is generated in batteries. The electric current that flows through batteries during charging and discharging faces resistance in different materials such as electrodes and the electrolyte, current collectors, busbars, and other connections. This resistance results in the loss of some electrical energy, which is dissipated in the form of heat. The higher the current, the more heat is produced.
It is well known that batteries perform optimally in temperatures between 20 and 30°C (68 and 86°F). Within this range, chemical reactions that take place in the battery are the fastest and are the best compromise between energy, power and durability.
However, temperatures outside this range can have detrimental effects:
High Temperatures: High temperatures gradually affect the battery’s chemical processes resulting in even faster degradation or depletion of its output capacity to deliver electrical energy. In extreme conditions, the risk of thermal runaway increases, which can lead to fires or explosions.
Low Temperatures: Low temperatures are known to decrease the rate of chemical reactions occurring in the battery, hence slowing down the power flow. Therefore, this becomes an issue in applications like electric vehicles where high power output is critical to drive at high speeds and long distances.
Therefore, it is important to regulate the temperature of the battery to ensure safety, efficiency, and longevity.
Figure 2: A brief explanation of Thermal Runaway
Even though battery thermal management systems are critical components that affect the battery’s performance and safety, they come with various disadvantages:
Increased Complexity: One of the primary disadvantages of BTMS is the complexity of the manufacturing process, where precise control systems, sensors, and cooling mechanisms need to be incorporated into a compact design. This increases the risk of malfunctions and failures, requiring more frequent checkups and maintenance.
Cost Implications: To design an effective thermal management system, one needs advanced engineering expertise and sophisticated materials. The design, development and integration of BTMS causes a high initial cost.
Maintenance and Reliability costs: Maintaining an effective BTMS requires regular maintenance to ensure optimal performance. Components such as pumps, valves, heat exchangers and sensors are prone to wear and tear, hence requiring maintenance to avoid any failures or malfunction. This in turn also increases the down time, making the systems less reliable and inconvenient.
Less Effective in Low Temperatures: Battery thermal management systems have limited effectiveness in extreme temperatures. In very hot temperatures, the cooling capacities may not work effectively, while in very cold temperatures, the system might have problems heating up to optimal temperatures needed for the battery pack. Hence, it leads to reduced performance and increased energy consumption.
Potential Points of Failure: A BTMS is made up of several elements that need to be integrated for the system to be successful. Failure in any of the cooling system, sensor or control units affects thermal control, impacting the general safety and performance of the battery.
Efficiency Trade-offs: While BTMS plays a crucial role in maintaining battery health and safety, it also leads to energy consumption and efficiency trade-offs. The components of these systems such as pumps, fans and compressors consume energy. Consequently, it can impact the range and performance of the vehicle.
Restrictions on Vehicle Design and Packaging Constraints: The BTMS requires various components such as heat exchangers, pumps, fans, sensors that must be carefully placed. This creates restraints on design flexibility and packaging.
Despite these disadvantages, the positive impact of the BTMS on battery performance and safety outweighs the drawbacks.
There are three main types of battery thermal management systems: active cooling systems, passive cooling systems, and combined or hybrid cooling systems. All three types have their own strengths and applications.
Figure 3: Types of Battery Thermal Management Systems
Active Cooling: Active cooling systems work in parallel to an external cooling system such as fan, pump or compressor for cooling the battery. This method is very efficient in regulating battery temperature, which is critical for applications of high power such as electric vehicles. There are two chief varieties of active cooling techniques: air cooling and liquid cooling.
Passive Cooling: There are some buildings that do not require devices for cooling systems because they radiate heat in natural ways. These systems are usually made of materials that possess certain thermophysical characteristics such as high thermal conductivity so that heat can be released through convection. The passive cooling systems, though more basic and affordable, may not be as efficient for applications which need precise thermal control.
Hybrid Systems: These systems incorporate both passive and active cooling to combine efficiency and cost effectiveness. The most widely used battery systems today, like electric vehicles and renewable energy storage systems, require high performance and high reliability, so hybrid systems are often employed for these applications.
Of all active cooling methods, air cooling and liquid cooling are the most applied methods in battery thermal management systems.
Air Cooling: Air cooling uses fans or blowers to circulate air across the battery cells and components in a bid to reduce heat. This method is relatively simple and low-cost but often cannot deliver adequate cooling for high-power dissipation devices and or in high operating temperatures. Air cooling is still applied to portable electric apparatuses and some automobile industry products which have relatively low power capability.
Liquid Cooling: In liquid cooling systems, a coolant fluid is circulated through pipes or channels around the battery pack to absorb heat. Since liquids have higher conductivity and heat capacity as compared to air, liquid cooling is better than air cooling. This is especially the case in high-power density applications. This method is also applied in electric vehicles and in large scale battery storage systems.
Thermal conductivity, which is a measurement of a material’s ability to transfer heat, impacts the rate at which heat is transferred from the battery cells to the coolant. Heat capacity represents the ability of a coolant to absorb before the temperature of the coolant rises. These thermophysical characteristics help define the performance of a cooling system.
Phase Change Materials: Phase change materials (PCMs) are substances that can absorb or release latent heat when they change their state from solid to liquid or vice versa. This unique property makes them ideal for use in battery thermal management systems. By placing PCMs with battery cells, it absorbs excess heat when the cell temperature rises and releases stored heat when the temperature drops, helping maintain an optimal operating temperature.
Heat Pipe: A heat pipe uses phase-change technology to transfer heat from one part of the battery pack to the other. These systems are highly efficient in transferring heat over short distances making it a great alternative for compact battery packs.
Air Jet Impingement: This is a method where high-velocity air jets are added to the battery pack to enhance convective heat transfer. The jets are added to the bottom of battery packs or individual cells, creating high intensity localized cooling. This is most suitable for applications with limited space, where other options won’t fit.
Advanced Liquid Cooling Systems: While the traditional liquid cooling systems use single-phase liquid as a coolant, advanced liquid cooling systems use two-phase coolant or coolants that evaporate, which significantly increases the rate of heat transfer. The vapor then condenses back to liquid state, releasing the absorbed heat and completing the cooling system.
Manufacturers and researchers are continually working to refine the cooling systems to address the disadvantages of existing systems with the idea of enhancing the performance, safety and longevity of the battery packs.
Battery thermal management is important to ensure the battery energy storage systems function optimally, safely and last longer and especially in high end applications such as electrical vehicle and renewable energy storage. The benefits of a well-designed BTMS include increased performance, longer battery life and reduced safety hazards that arise when batteries are stored in regions with either too high or too low temperatures.
Thermal management, is the ability to control the thermal environment of a device or system to maintain a desired range of temperature. This can be associated with a number of approaches and tools to help reduce excessive heat or even maintain isolation of temperatures.
Battery thermal management is a technique of controlling the temperature of battery system to remain as safe and optimum as possible. This refers to the ability of the battery to be cooled with different techniques and systems like the actively or passively cooled ones during charging as well as discharging cycles.
The best temperature is around 20-30 °C that is the most suitable for the batteries of an electric vehicle (EV). Sustaining this range of temperature ensures that the battery delivers optimal performance, operates at optimal efficiency and has its durability preserved.
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