In the field of sustainable transportation, thermal management of lithium-ion batteries (LIBs) in electric vehicles is a key research area that is crucial for improving energy system efficiency and ensuring safety. Battery thermal management systems (BTMSs) play a decisive role in maintaining LIBs within the optimal temperature range, helping to optimize battery performance and extend lifespan. This field faces significant challenges, mainly related to the overheating and temperature changes of LIBs, which can affect the safety and performance of batteries, accelerate their aging and reduce energy storage capacity, and in extreme cases, even lead to thermal runaway (TR) and fire or explosion risks.
The progress of BTMSs has shown significant advantages in electric vehicles, such as providing more accurate and uniform temperature regulation, improving battery efficiency and reliability; The innovation of phase change materials (PCMs) and other BTMS technologies has improved heat dissipation and TR prevention, increasing the safety and energy density of batteries; The study of thermal generation in LIBs is becoming increasingly important, especially its impact on battery performance and safety; There are currently multiple innovative methods for thermal management of electric vehicles, but there are still key challenges that require further in-depth research.
1.Thermal management of lithium-ion batteries
The thermal management of LIBs is crucial for their efficient and safe operation, especially in applications such as electric vehicles and energy storage systems. There are three types of thermal management: active, passive, and hybrid systems, each with unique characteristics suitable for different applications and requirements.
Active system: using mechanical or electrical means (such as pumps and fans) to regulate battery temperature, including air and liquid cooling methods, has good heat dissipation effect, but increases system power consumption, reduces overall battery efficiency, and is more complex and costly in design.
Passive systems: using technologies such as PCMs and heat pipes, rely on natural processes such as conduction and convection for heat transfer, do not require additional energy, have higher energy efficiency and simpler design, but may face challenges when dealing with high heat loads or extreme temperatures, and some materials (such as PCMs) may have low thermal conductivity and leakage after melting.
Hybrid system: Combining active and passive methods, such as integrating PCMs with air or liquid cooling systems, can improve temperature control while avoiding high energy consumption of fully active systems, but requires careful design and advanced engineering to achieve the optimal balance between energy efficiency and thermal management effectiveness.
Choosing a suitable thermal management system requires consideration of factors such as battery size, lifespan, and charge discharge rate. New materials such as nano PCMs and advanced cooling and heating technologies are improving the efficiency and safety of these systems, helping to increase the adoption of batteries in various applications, reduce costs, and encourage the use of cleaner and more sustainable energy sources. In addition, the integration and compatibility of these systems with the overall EV or storage system design is also a challenge. Many studies have proposed various design improvements to enhance the efficiency of BTMSs.
There are significant challenges in BTMSs, especially under harsh operating conditions. A key limitation is the low thermal conductivity of PCMs, which leads to uneven temperature distribution within battery cells and has adverse effects on the performance and efficiency of LIBs. In extreme cases, such as discharge rates above 1 ° C or ambient temperatures above 35 ° C, this problem can be exacerbated, and the temperature difference between individual cells may be less than 3 ° C, which has a significant impact on the performance and durability of LIBs.
In addition, current BTMSs also have substantial limitations, especially in fast charging scenarios and high ambient temperatures, which may lead to low thermal management efficiency and increased risk of TR.
2.Innovation in cooling methods for battery management systems
The progress of refrigeration technology is significant in both single-phase and multi-phase fields. Single phase refrigeration design is simple, but its heat transfer capacity is relatively limited compared to multiphase technology. In single-phase cooling, new nanofluids have been explored to improve thermal conductivity and heat transfer efficiency. Immersive cooling systems also have good thermal regulation efficiency. In multiphase refrigeration, traditional refrigerants such as HFCs and HCFCs have an impact on the environment. Therefore, exploring new dielectric fluids with lower boiling points is crucial to extend battery life and improve battery safety by introducing thermal management models.
Innovations in materials and structures are changing thermal efficiency, such as using PCMs to maintain battery temperature within a safe range but with low thermal conductivity, which can be addressed by introducing highly conductive metal matrices and adding metal nanoparticles or porous materials; Microchannel cooling plates can effectively manage the temperature of battery packs, but production is complex and costly; The hybrid structure combines the advantages of passive and active cooling systems, but increases weight and complexity; Innovative materials such as graphene can improve heat dissipation, but the production cost is high. Despite significant progress in improving thermal efficiency, there are still challenges such as cost optimization, manufacturing process simplification, and effective integration that require continued research and development to address these challenges and fully leverage the advantages of advanced technology.
3.Challenges of lithium-ion batteries under extreme conditions
At room temperature: below 10% SoC, the battery temperature is relatively stable. When the 4C (12A) stage begins, the temperature rises to 54 ° C. This temperature rise has attracted significant attention at the battery pack level, emphasizing the need for precise charging strategies to mitigate overheating risks and ensure the safety and long-term operational integrity of the battery pack. Ultimately, achieving safe and fast charging for these batteries requires a balance between the required SoC level and effective temperature management strategies to avoid thermal runaway.
Extreme temperature test: Rapid charging test at extreme temperatures (-10 ° C, 10 ° C, 45 ° C, and 60 ° C), record the temperature change Δ T of the rapid charging test for comparison. That is a good method for comparing different temperature tests with different initial temperatures.
High temperature test results: For high temperature testing, it is clear that 45 ° C is most beneficial for fast charging, as the high current stage lasts longer than other high temperatures. When the temperature drops to ambient temperature (25 ° C), the high current phase is shortened due to the higher resistance compared to 45 ° C. At 60 ° C, the constant current (CC) stage is shorter than at 45 ° C, which may be attributed to the increased resistance caused by accelerated aging in this environment.
The extreme test conditions of 60 ° C resulted in a significant increase in resistance, which is related to the growth of the solid electrolyte interface (SEI) layer on the graphite negative electrode. The increased cycling temperature will lead to an increase in lithium coating during the cycling process, resulting in the detection of deposits on the graphite electrode. Therefore, the rapid charging test at 60 ° C may have triggered lithium deposition on the anode, increasing internal resistance.
Low temperature test results: In low temperature environments, the high current stage is significantly affected. At 10 ° C and below, due to higher internal resistance, the CC stage is shorter than at 25 ° C. Specifically, at -10 ° C, the current curve initially decreases, but there is a brief increase as charging continues. This is due to the evolution of resistance: at the beginning of the fast charging test, the resistance is relatively high, and as the battery temperature increases, the resistance decreases, resulting in the observed current curve. Overall, low temperature conditions are not conducive to fast charging, meaning it takes twice as long to charge to 80% at 10 ° C. Therefore, a pre-treatment thermal management strategy should be developed to optimize fast charging in this environment.
4.Construction
This article focuses on the fundamental aspects of sustainable and safe development of lithium-ion batteries, particularly in key applications such as electric vehicles and energy storage systems. The crucial importance of battery thermal management systems in maintaining LIBs within the optimal temperature range, optimizing their performance, and extending their lifespan was emphasized. Including overheating and temperature changes, this may compromise the safety and performance of the battery, accelerate its aging, and reduce its energy storage capacity.