Electric Vehicle Battery Thermal Management Using Hybrid Heat Pipe-Cold Plate Cooling System

Battery thermal management systems (BTMSs) ensure that lithium-ion batteries (LIBs) in electric vehicles (EVs) are operated in an optimal temperature range to achieve high performance and reduce risks. A conventional BTMS operates either as an active system that uses forced air, water or immersion cooling, or as a complete passive system without any temperature control. Passive systems function without any active energy supply and are therefore economically and environmentally advantageous. However, today’s passive BTMSs have limited cooling performance, which additionally cannot be controlled. To overcome this issue, an innovative BTMS approach based on heat pipes with an integrated thermal switch, developed by the Fraunhofer Cluster of Excellence Programmable Materials (CPM), is presented in this paper. The suggested BTMS consists of switchable heat pipes which couple a passive fin-based cold plate with the battery cells. In cold state, the battery is insulated. If the switching temperature is reached, the heat pipes start working and conduct the battery heat to the cold plate where it is dissipated. The environmental benefits of this novel BTMS approach were then analysed with a Life Cycle Assessment (LCA). Here, a comparison is made between the suggested passive and an active BTMS. For the passive system, significantly lower environmental impacts were observed in nearly all impact categories assessed. It was identified as a technically promising and environmentally friendly approach for battery cooling in EVs of the compact class. Furthermore, the results show that passive BTMS in general are superior from an environmental point of view, due their energy self-sufficient nature.

Because of their high energy density and long cycle life, lithium-ion batteries are commonly employed in electric cars. As battery performance and life are highly dependent on temperature, it is critical to maintain the optimum temperature range. A battery thermal management system (BTMS) is critical for controlling the thermal behaviour of the battery. Air cooling, liquid cooling, direct refrigerant cooling, phase change material (PCM) cooling, and heat pipe cooling are all BTMS strategies. Heat pipes come in a variety of sizes and configurations that can be employed in the BTMS and many studies have proven the feasibility of using heat pipe as the electric vehicles’ BTMS. However, there are many aspects of the design and configuration of the heat pipe that could affect the overall thermal performance of the heat pipe BTMS such as its length, diameter, evaporator and condenser lengths, tilt angle, types of heat pipes and working fluids. In this work, a numerical study was conducted to investigate the effect of heat pipe’s diameter, number of heat pipes and the types of heat pipes on the thermal performance of the heat pipe BTMS. The diameter of the heat pipe varies between 6 – 12 mm, the number of heat pipes varies from 2 – 10 and the type of heat pipe considered in this work is straight heat pipe. The thermal performance of the heat pipe is measured by the maximum battery temperature and the thermal resistance at different battery heat generation rate in the range of 10 - 30W. The simulation model was validated against experimental data and results indicate excellent agreement between simulation and experimental data. Simulation results shows that the greater the diameter, the lower is the battery temperature. By increasing the heat pipe’s diameter, the battery temperature can be reduced by at least 10% or 3.4°C. Temperature reduction of at least 12.7% was observed when the number of heat pipes used in the BTMS increases.

Hierarchical thermal modeling and surrogate-model-based design optimization framework for cold plates used in battery thermal management systems

Lithium ion (Li-ion) batteries are low cost and have a high energy density and a small volume. Thus, battery packs comprised of multiple Li-ion batteries have become the dominant energy source for electric vehicles (EV) and hybrid electric vehicles (HEV), and have contributed to their current popularity, as has fast-charge technology, which is also used in EVs and HEVs. However, due to the high power requirement of EVs and HEVs under high-speed operating conditions or fast charging conditions, Li-ion battery packs suffer from high temperatures if no appropriate thermal management system is installed, leading to battery performance degradation and even thermal runaway [1]. The energy efficiency, safety, and life of power batteries, such as lithium-ion batteries, are very sensitive to temperature, and the performance and stability of Liion batteries are reduced in the abnormal temperature range [2]. The temperature change of batteries is usually inevitable because they are affected by environmental conditions and release heat by a series of chemical reactions during charging and discharging. Therefore, it is essential to develop a smart thermal management system that maintains the proper temperature range for power batteries. In this talk, key technologies for a smart thermal management system of power batteries for electric vehicles and energy storage system will be presented. The key technologies are based on our recent findings that utilize multiscale micro/nanostructured surfaces for integrated wicks [3]. These surfaces manipulate the nucleation site density that controls the heat transfer coefficient and critical heat flux for the evaporator of a heat spreader [4, 5]. The multiscale micro/nanostructured wick design and micro/nano multiscale structure fabrication techniques are crucial for controlling the capillary flow and evaporation that improve the effective thermal conductivity of the thermal management system for power batteries. We presented a novel technique for the thermal management of power batteries utilizing ultrathin heat spreaders. Temperature significantly affects the energy efficiency, safety, life, and performance of a lithium-ion battery pack in electric vehicles (EVs). Therefore, controlling the temperature of the battery pack within a certain range has become a challenge in the development of EVs, especially in fast charging with high charge rates (C-rates). An ultrathin thermal ground planebased battery thermal management system was developed, which utilized 0.4 mm thick ultrathin thermal ground planes and cooling fans as a heat sink. The thermal performance of the novel battery thermal management system was experimentally investigated at 2.2 C to 4 C FC regimes under environmental temperatures from 10 ℃ to 50 ℃. The battery thermal management system was able to maintain a mean surface temperature of 55Ah lithium iron phosphate (LiFeO_4, LFP) batteries below 42.7 ℃ even at a 4 C charge rate and achieve good surface temperature uniformity in all cases. At an ambient temperature as high as 50 ℃, the battery thermal management system can still maintain the mean battery surface temperature under 57.3 ℃. The temperature rise, temperature uniformity, and thermal resistance gained improvements of up to 23.3%, 28.4%, and 62.6%, respectively, compared to a battery thermal management system with the same dimensions as copper heat spreaders. The effects of different pores densities of the mesh in the ultrathin thermal ground plane were also studied. The battery thermal management system showed brilliant performance in controlling the temperature of the battery pack, which was capable of being a viable solution for high-power battery thermal management in EVs.

An experimental study of heat pipe thermal management system with wet cooling method for lithium ion batteries

Performance simulation of a heat pipe and refrigerant-based lithium-ion battery thermal management system coupled with electric vehicle air-conditioning

This study emphasises lithium-ion batteries, which have been the subject of extensive research due to their wide range of benefits, including extended life cycle, minimal discharge, and high energy density. However, the temperature sensitivity of the batteries presents a notable obstacle that can negatively impact their performance and longevity when operating under extreme conditions. To overcome this challenge, implementing an effective battery thermal management system (BTMS) is imperative. Battery thermal management is crucial for ensuring the safety and longevity of lithium-ion batteries, especially in high-demand applications like electric vehicles. This comprehensive review explores a variety of BTMS technologies, including air-cooling methods, liquid-cooling techniques, heat pipes, and PCM materials. While air-cooled BTMS is a safe and straightforward design, its lower heat capacity and thermal efficiency limit its use to low-capacity batteries. However, forced air-cooled BTMS is an excellent solution for high charging/discharging rates, as air flows through channels within the battery packs to optimize cooling. Liquid-cooled BTMS also shows promise, although designers must ensure the sealing cover is secure to prevent leaks. Heat pipes (HP) offer a unique approach to controlling battery temperature, while Phase change materials (PCM) thermal management is notable for its ability to absorb significant heat by latent heat. Hybrid cooling combines fins, nanofluids, PCM, and microchannels-based cooling and can significantly enhance battery performance under high charging/discharging rates. Furthermore, lithium-ion batteries are extensively used in various applications, including the Electric vehicle industry. Keeping the lithium-ion battery temperature within the optimal range is important and is accomplished by a suitable BTMS. Different methods, such as air cooling, Liquid cooling, Heat pipe, and PCM materials, are used in BTMS. An effective thermal management system and efficient battery model are absolutely necessary. Each of the techniques in BTMS has its own benefits and drawbacks. The effectiveness of thermal management configurations and methods can vary. Thus, evaluating performance and optimal configuration is crucial before implementation.

Recent developments in the passive and hybrid thermal management techniques of lithium-ion batteries

Optimization of an air-based thermal management system for lithium-ion battery packs

Taking advantage of electric vehicles’ low pollution, the world is changing its face toward electric vehicle (EV) production. As EVs rely heavily on specialized batteries, it’s important to manage them safely and properly to prevent thermal runaway. High ambient temperatures and varied charging/discharging rates increase battery temperature. To address these challenges, Battery Thermal Management System (BTMS) come into play. This work focuses on passive cooling in BTMS, which is one of two categories of BTMS, with the other being active cooling using liquid-air systems. Passive BTMS has gained prominence in research due to its cost-effectiveness, reliability, and energy efficiency, as it avoids the need for additional components like pumps/fans. This article specifically discusses recent experimental studies regarding phase change material (PCM)-based thermal management techniques for battery packs. It explores methods for enhancing thermal conductivity in PCMs and identifies methodologies for BTMS experiments using PCMs. Also recommends the importance of optimization techniques like machine learning, temperature sensors, and state-of-charge management, to ensure accuracy and uniform temperature distribution across the pack. While paraffin wax has been a popular choice in experimental studies for its capacity to absorb and release heat during phase transitions, as a matter of its low thermal conductivity (0.2 to 0.3 Wk−1m−1) limits reaction in rapid charging/discharging of batteries. So integration with highly thermally conductive additives is recommended. Additives such as heat pipes offer superior thermal conductivity compared to expanded graphite (5 to 200 Wk−1m−1). As a result, the integration of heat pipes further reduces the temperature of battery by 28.9% in addition to the reduction of 33.6% by pure PCMs in time of high charge/discharge rates (5 C to 8 C). So high-conductivity additives correlate directly with improved thermal performance and are essential for maintaining optimal battery temperatures and overall reliability in EV battery packs.

This paper develops a self-adaptive control strategy for a newly-proposed J-type air-based battery thermal management system (BTMS) for electric vehicles (EVs). The structure of the J-type BTMS is first optimized through surrogate-based optimization in conjunction with computational fluid dynamics (CFD) simulations, with the aim of minimizing temperature rise and maximizing temperature uniformity. Based on the optimized J-type BTMS, an artificial neural network (ANN)-based model predictive control (MPC) strategy is set up to perform real-time control of mass flow rate and BTMS mode switch among J-, Z-, and U-mode. The ANN-based MCP strategy is tested with the Urban Dynamometer Driving Schedule (UDDS) driving cycle. With a genetic algorithm optimizer, the control system is able to optimize the mass flow rate by considering several steps ahead. The results show that the ANN-based MPC strategy is able to constrain the battery temperature difference within a narrow range, and to satisfy light-duty daily operations like the UDDS driving cycle for EVs.

A review on thermal issues in Li-ion battery and recent advancements in battery thermal management system

This work develops a reduced-order numerical model of a custom-built commuter electric vehicle (EV) to study the lifetime performance of EV battery packs and battery thermal management systems (BTMS). The model uses experimental battery and BTMS data collected from a commuter EV and applies drive cycles corresponding to typical highway and city driving conditions. The main advantage of this numerical modeling approach is its ability to simulate large timescales, spanning years of vehicle operation. Cell level degradation is captured, allowing for the study of battery pack longevity under a variety of temperature profiles generated by various BTMS strategies with series and parallel indirect liquid cooling configurations. Monte Carlo simulations are also used to estimate the variation in BTMS performance caused by beginning-of-life (BOL) variations and cell-to-cell thermal imbalance/spreading in the battery cells. The proposed modeling approach was demonstrated to be an effective tool in studying long timescale BTMS performance, and tradeoffs between BTMS energy consumption and pack energy retention for the case-study commuter vehicle. A 7% reduction in the mean maximum pack temperature and a 10% reduction in the mean lifetime BTMS energy consumption were achieved by tuning BTMS control parameter thresholds. However, the variability in pack energy retention greatly increased, highlighting the need to consider BOL variations and cell spreading in BTMS modeling and design.

A new design for hybrid cooling of Li-ion battery pack utilizing PCM and mini channel cold plates

The battery utilization in electric vehicles needs to be operated at its operating temperature range of $20-45^{\circ}\mathrm{C}$ to hinder several issues, including a reduction of life capacity and thermal runaway. A battery thermal management system (BTMS) is based on a phase change material (PCM) and the heat pipe is harnessed to maintain the battery temperature. In this research, the BTMS by harnessing animal fat as the PCM and a heat pipe was investigated through experimental methods. Characterization material with the T-history method and thermal performance testing with three different loads of 0,5 C, 1C, and 2 C were conducted. The Findings showed that the proposed module batteries could be applied as the BTMS in electric vehicles due to their thermal properties, which had a melting temperature of 37,18°C and latent heat of 72,71°C. The proposed BTMS could reduce the temperature by 14, 7°C at the highest load of 2 C discharge rate from three discharge loads. Moreover, the temperature differences among batteries can be retained below 5°C. In conclusion, the proposed BTMS in this research has shown the ability to harness natural resources to reduce the battery temperature in electric vehicles. Thus, this can be a promising BTMS in the future.