Engineering Excellence: Creating a Liquid-Cooled Battery Pack for Optimal EVs Performance
(Last Updated On: 08/06/2023)
Engineering Excellence: Creating a Liquid-Cooled Battery Pack for Optimal EVs Performance
As lithium battery technology advances in the EVS industry, emerging challenges are rising that demand more sophisticated cooling solutions for lithium-ion batteries. Liquid-cooled battery packs have been identified as one of the most efficient and cost effective solutions to overcome these issues caused by both low temperatures and high temperatures. In this blog post, Bonnen Battery will dive into why liquid-cooled lithium-ion batteries are so important, consider what needs to be taken into account when developing a liquid cooled pack system, review how you can design your own such system with best practice methods and products, evaluate what types of cold plates currently exist on the market today suitable for use in EVs applications, analyze testing requirements for verification purposes of any newly designed solution—all to help project managers better understand how they can best develop a liquid-cooled battery pack when implementing their projects within an EVS environment. Let’s get started!
1. Why do we need Liquid-cooled Lithium-Ion Battery Pack?
Electric vehicles require higher energy density to achieve longer range. The increase of energy density results thermal load increase to battery pack. In addition, to achieve big battery capacity, the number of battery cells in a single vehicle increases. This, however, causes the gap between the battery cells to decrease due to the layout space and weight requirements of the vehicle. This leads to a reduced heat dissipation space. In such circumstance, natural heat dissipation and forced air cooling can no longer meet batteries’ cooling needs under high-rate charging and discharge condition. To ensure the safety and service life of the lithium-ion battery system, it is necessary to develop a high-efficiency liquid cooling system that maintains the battery’s temperature within an appropriate range.
2. Why do lithium-ion batteries fear low and high temperatures?
When the lithium-ion battery is in a low-temperature environment, the activity of the active material in the battery is low, the internal resistance and viscosity of the electrolyte are high, and the ion diffusion speed is slow. If the charging and discharging power of the battery is not limited, lithium ions inside the battery will be precipitated, causing the irreversible attenuation of the battery capacity, and it will bury a safety hazard for the use of the battery.
When the lithium-ion battery is in a high-temperature environment, the side reactions of the battery increase, which leads to the continuous consumption of lithium ions during the cycle, and the battery capacity decays rapidly. If a large amount of heat generated by a violent chemical reaction occurs in the battery and accumulates quickly in the battery, it may cause the battery to burn violently and explode. When the temperature difference between the battery cells is too large, it will cause the performance and capacity decay rate of each battery cell in the battery module to be inconsistent, thus affecting the overall performance of the battery system.
3. What needs to be considered to develop a liquid-cooled lithium-ion battery pack?
The development content and requirements of the battery pack liquid cooling system include:
1) Study the manufacturing process of different liquid cooling plates, and compare the advantages and disadvantages, costs and scope of application;
2) Develop a liquid cooling system with a more flexible flow channel design and stronger applicability, which is convenient for BATTERY PACK design;
3) Develop a liquid cooling system with a higher heat transfer efficiency. When cooling, the cooling rate is not less than 0.2°C/min, and when heating, the heating rate is not less than 0.3°C/min;
4) Develop a liquid cooling system with better temperature uniformity. During the cooling process, the maximum temperature difference of the battery pack does not exceed 5°C, and during the heating process, the maximum temperature difference of the battery pack does not exceed 8°C;
5) Develop a liquid cooling system with high reliability, with a pressure resistance of more than 350kPa and a service life of 10 years;
6) The total flow resistance of the liquid cooling system should within 20~30kPa;
7) The liquid cooling system needs safety guarantees such as leakage risk control, insulation protection, and flame-retardant requirements.
4. How to design your liquid cooled battery system?
In order to design a liquid cooling battery pack system that meets development requirements, a systematic design method is required. It includes below six steps.
1) Design input (determining the flow rate, battery heating power, and module layout in the battery pack, etc.);
2) Carry out flow field simulation, thermal field simulation, and vibration simulation of the liquid cooling system, and correct the digital model by the simulation results;
3) Sample making (machining) of the liquid cold plate, and conducting thermal performance and type tests;
4) Revise the design plan, proof twice, and conduct a thermal performance and type test;
5) Structural review of the entire liquid cooling system and risk assessment for mass production;
6) Determine the structural form of a liquid cooling system that can be mass-produced.
5. What’s the requirement for a liquid cold plate?
There are generally four key requirements for liquid cold plates:
1) Large cooling power;
2) High reliability, ensuring a sealed cold plate;
3) Precise heat dissipation design to avoid excessive temperature differences in the system;
4) Strictly control the weight of the cold plate to avoid a cooling system that seriously reduces the energy density of the whole system.
6. What types of liquid cold plates are in the current EVs market?
At present, liquid cooling plates in the EV market include the following types:
1) Harmonica tube liquid cold plate
Harmonica tube-type liquid cooling plate has low cost, lightweight, simple structure, and high production efficiency. However, due to its single flow channel, small contact area, and thin pipe wall, its heat exchange effect is normal and its load-bearing capacity is poor.
2) Stamped liquid cooling plate
The stamped liquid cooling plate has the advantage of arbitrarily designed flow channels, a large contact area, an efficient heat transfer effect, excellent production efficiency, superior pressure resistance, and strength. However, it needs to do tooling thatthe cost is high. Also, it has strict requirements for flatness, making it difficult to install.
3) Inflatable liquid cooling plate
The inflatable liquid cooling plate has the advantages of low cost, efficient heat transfer effect, and high production efficiency. However, due to its soft material, it has relatively shortcomings in pressure resistance and strength.
4) Parallel flow tube liquid cooling belt
The parallel flow tube liquid cooling belt has a good heat exchange effect and is suitable for cylindrical cells. However, its cost is high due to its complex structure.
5) Profile plus friction stir welding
This kind of liquid-cooled plate formed by joining profiles through friction stir welding has the advantages of high reliability, superior load-bearing capacity, high surface smoothness, and a good heat exchange effect. However, due to its thick thickness and complicated processing methods, the cost is high, the weight is heavy, and it occupies a lot of space.
7. Liquid cold plates test verification
In order to verify the performance and safety reliability of the liquid-cooled plate, three aspects of testing must be carried out:
2. Thermal performance test 1) Cooling performance test 2) Heating performance test
3. Type test 1) Low-temperature sealing test 2) Pressure drop test 3) Static pressure strength test 4) Blasting test 5) High and low-temperature resistance test 6) Pressure-alternating test 7) Vibration test 8) Salt spray test 9) Internal corrosion tests
With the variety of factors to consider and the complexity of designing a liquid-cooled battery pack for EVs projects, it is understandable why you may feel overwhelmed or uncertain. Bonnen Battery has a dedicated team and decades of industry experience in liquid-cooled battery packs. We have guided customers around the world in lithium-ion battery implementation and provided help with engineering, scale up production and test verification as well as our exclusive supportive services. Our comprehensive approach helps ensure projects run smoothly from concept to completion. Contact us today to discuss how we can help you develop your liquid-cooled battery pack system projects successfully. Together, we can explore creative solutions that meet the specific needs of your lithium-ion application while adhering to safety regulations. Let’s take a step towards making lithium-ion batteries more efficient and reliable than ever before!
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