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How do we manage heat when designing custom battery packs?

clock6 mins Read
calendar 14/03/2023

Heat management is an important part of maintaining a batteries peak performance in any battery pack. When we’re prototyping your custom battery pack it is important to identify how we can passively or actively manage the temperature of the battery. Our engineers will decide what actions they will take to effectively manage heat in your custom battery pack. This all depends on how your custom battery pack will be used and where it will be used.

Why do large format batteries face heat management problems?

Before we create a large format battery pack, we must understand why a large battery pack could face heat management issues. Once we have an understanding of why, we can then develop solutions in order to prevent them. In some cases, the thermal mass of a battery pack will be the reason why it faces heat management issues. A typical lithium-ion battery generally specifies 0.2C – 0.5C for charging. At this slow charge rate most lithium-ion cells do not generate a great deal of heat. However, once a battery requires a charging rate of 1C or above then the thermal mass of the pack will increase causing difficulties heating up or cooling down. Once a battery achieves these charging rates, heat generated becomes a critical part of the whole process.

Where does this heat come from?

Once we have understood why the batteries face heat management problems, its important to understand where the actual heat within the pack comes from. Li-ion cells typically have an internal resistance (IR) in the 80- to 100-mΩ range and are realistically heat sources when the charge or discharge current is near or exceeds the maximum for the cell. Both the Charge and discharge cycles of operation can and will generate significant heat through electrochemical reactions and IR. In basic terms Lithium Ions traveling from anode to cathode and vice versa during charge and discharge face resistance in the form of the separator, the chemical reaction through charging is endothermic (absorbs heat), the chemical reaction during discharge is exothermic (generates heat).

Why does the generated heat cause an issue?

The resultant heat generated can and often will remain inside the cells or pack, causing the cells to degrade faster than usual. The same can be said of discharging at above the specified rates indicated on the data sheets. Managing the heat effectively during charging helps reduce cells damage substantially. The acceptable temperature region for Lithium-ion batteries is normally −20 °C ~ 60 °C. Both low temperature and high temperature that are outside of this region will lead to degradation of performance and irreversible damages, such as lithium plating and thermal runaway. Alexander Battery Technologies can achieve effective heat management through proper prototyping, design and engineering of the battery. This will then lead to our batteries being both safe and reliable when used in their specified application.

How can we reduce the heat passively?

After initially discussing the specifications of your battery our engineers will apply the most effective method to reduce heat in your large battery pack. They will be able to choose from a number of methods to passively cool large format batteries, however these do tend to be application specific. Air cooling & heat sinks are a common method where there is sufficient airflow due to its simple operating system. Methods based upon the heat pipe principal, can be either refrigerant or water-based, these act in relation to both the principles of Phase change and thermal conductivity. Phase change materials combined with heat absorbent fillers can also be an effective passive BTMS (battery thermal management system). However, in real terms Air cooling is not sufficient to remove heat from a large-format lithium-ion battery.

How can we reduce heat actively?

Again, there are numerous ways for our engineers to actively cool large format batteries or large battery packs from forced air cooling to electrolyte immersion cooling. More commonly single cooing plate designs with polar mounted cells are used for both SESS (Static Energy Storage Systems) and EV (Electric Vehicles) applications. Double cooling plates where cells are sandwiched between the two are less common but are a good alternative. Both are indirect fluid cooling systems and require additional components to circulate and in turn cool the coolant. The same methodology can be used with refrigerant gasses but again external components are generally required and systems can become very complicated with external heat exchangers, pumps and delivery systems. Direct liquid cooling systems where the coolant is in direct contact with the cell, generally use electrolyte or oils to transfer heat away, these systems are similar if not more complicated than the indirect variant, heavy and bulky.

What are the best methods?

Air is by far the simplest method either by ducting external air into the battery or relying on simple convection and managing the loading on the battery. However ambient air doesn’t remain a constant temperature and if the air temperature increases above the battery temperature you are effectively heating the battery therefore the risk of overheating increases especially in high-power applications.

Liquid cooling is the most common method in EV however this is more complicated than air cooling requiring more components and control. There is also the consideration of how then the fluid is cooled either passively or actively, passively you face similar issues to air cooing, actively the system becomes even more complicated. In static ESS systems, indirect liquid cooling is also a popular option whereby the cooling can be provided by adiabatic chilled water systems that are essentially free cooling to control the temperature.

Immersion cooling again whereby the fluid is in direct contact with the cells is an effective way to cool large format batteries, some would say it is the best method overall but this method has its downsides, firstly it is expensive, it adds weight and has a heat capacity if we start to get into circulating the cooling fluid and/or cooing this actively then we get into very expensive and complicated systems.

Our commitment to our customers

At Alexander Battery Technologies our engineers keep their finger on the pulse in respect of new developments in heat management of high-power battery systems, we work closely with our customers in determining the right solution for the application, technology is advancing rapidly and with new development printed electronics thin film heaters combined with temperature and pressure sensors means that we can offer our customer’s the best solution for their application.

Conclusion

Heat management is crucial when it comes to keeping the battery pack working at optimal capacity for the duration required. Our highly skilled engineers have a variety of both active and passive methods to keep your batteries heat in control no matter what environment or charging state, this is why many companies chose to develop their own bespoke custom battery packs. If you wish to get in touch with us about developing your own custom battery pack, please contact us.

Author

Andy Taylor

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