A Liquid Cooling System For Thermal Management Of Lithium-Ion Battery Packs

01. Background

In recent years, the development of electric vehicles (EVs) has accelerated significantly due to growing concerns about fossil fuel consumption and carbon emissions from tailpipes.
Lithium-ion batteries are currently the most widely used power source for electric vehicles due to their high energy density, low self-discharge rate, low maintenance requirements, long cycle life, and lightweight, and compact structure. However, the performance of lithium-ion batteries is greatly affected by the operating temperature. The ideal operating temperature range for lithium-ion batteries is 25 ~ 40℃, and the maximum temperature difference between different batteries is less than 5℃. Operating at either low or high temperatures will result in battery performance degradation, shorter lifespan, and even thermal runaway.
Therefore, an excellent Battery Thermal Management System (BTMS) is necessary to ensure the safe and efficient operation status of Li-ion batteries.

According to the different cooling strategies, thermal management system for electric vehicles can be categorized into passive cooling system, active cooling system, and hybrid system combining passive and active.
In passive cooling systems, there is no additional power consumption, but they also cannot control the cooling system to change the cooling rate.
Special materials or heat dissipation structures are implemented on the surface of the lithium-ion battery to achieve a high heat transfer capability between the battery and the external environment. Typical examples include natural air convection, phase change materials (PCM), and heat pipes.

Passive air cooling has a very low cooling capacity and is not suitable for cooling high-energy density Li-ion batteries.
PCMs, which are capable of storing and releasing large amounts of energy during thawing, have received increasing attention in recent years. The main advantages of loading PCM into BTMS are that good cell temperature uniformity and flexible geometry can be achieved. However, the low thermal conductivity of PCM hinders the heat dissipation rate of the battery, which is a serious concern under high-rate charging and discharging conditions.
Therefore it is very important to develop a battery thermal management system for new energy trams with excellent thermal performance.

02. Results

Recently, Prof. Yu Feng's team at Harbin Institute of Technology (HIT) has made new progress on liquid-cooled battery thermal management systems (BTMS).
The common linear flow channel structure leads to serious temperature distribution non-uniformity. The team proposed a new tapered-channel heat sink with multiple channels to improve the battery temperature uniformity and reduce the power consumption of the battery cooling system. The team analyzed and compared the maximum cell temperature and temperature difference, temperature inhomogeneity distribution parameters, and power consumption performance of eight different designs. Also, the effect of the delayed cooling strategy on the temperature uniformity of the liquid cooling system was analyzed.
The results show that the cooling performance of BTMS system can be improved by using a conical channel heat sink structure while increasing the number of channels improves the thermal performance at the cost of increased power consumption.
The tapered flow structure with three channels has the best cooling performance and reduces power consumption by 86.3% from the base within the cell temperature and temperature difference limits.
In addition, the delayed cooling scheme is not a good strategy for ev thermal management system because it accumulates large temperature differences in a short period. These results have important implications for the design of advanced liquid-cooled BTMS.
The research results are presented as "A manifold channel liquid cooling system with low-cost and high-temperature uniformity for lithium-ion battery pack thermal The research results were published in Thermal Science and Engineering Progress under the title of "A manifold channel liquid cooling system with low-cost and high temperature uniformity for lithium-ion battery pack thermal management".

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