Innovative Battery Thermal System Balances Extreme Temperatures
A new battery thermal management system (BTMS) developed by researchers at Jinan University and Tsinghua University is addressing one of the most persistent challenges in electric vehicle (EV) performance: maintaining optimal battery temperature in both extreme cold and extreme heat. The research, published in Energy Storage Science and Technology, introduces a flexible, modular design that adapts to seasonal conditions, significantly improving battery longevity, safety, and usability in harsh climates.
As global EV adoption accelerates, ensuring reliable performance across diverse environmental conditions has become a critical engineering priority. Lithium-ion batteries, the dominant power source for modern electric vehicles, are highly sensitive to temperature fluctuations. In high heat, they risk thermal runaway—a dangerous chain reaction that can lead to fires or explosions. In subzero conditions, their capacity plummets, charging becomes difficult, and internal resistance increases, often rendering vehicles inoperable without lengthy preheating. Traditional thermal management systems typically prioritize either cooling or heating, forcing compromises in performance during seasonal extremes. This new approach, led by Liu Songyan and Professor Wang Weiliang of Jinan University’s International Energy School, in collaboration with Professor Lü Junfu from Tsinghua University’s Key Laboratory of Thermal Science and Power Engineering, proposes a dual-mode solution that dynamically shifts function based on ambient conditions.
The core innovation lies in a removable thermal storage module. During winter months, this module—composed of phase change materials (PCM) and insulating aerogel—is installed around the battery pack. It acts as a thermal buffer, preserving heat generated during driving and slowing the rate at which the battery cools when the vehicle is parked in freezing temperatures. In summer, the same module is removed, transforming the system into a high-efficiency cooling setup that combines PCM, heat pipes, and forced air convection to rapidly dissipate heat. This physical reconfiguration avoids the inherent conflict in conventional systems, where insulation that helps in winter impedes heat dissipation in summer, and vice versa.
The research team employed advanced computational fluid dynamics (CFD) simulations using Star CCM+ software to model and validate the system’s performance. Their model included four lithium-ion battery cells, two types of phase change materials (designated PCM1 and PCM2), flat heat pipes, and an aerogel insulation layer. The design was constrained to fit within typical EV battery pack dimensions, with all added layers—PCM, insulation, and heat pipes—kept to a minimal 3 mm thickness to avoid increasing the overall footprint. PCM2, used in the winter module, was selected for its phase change range between 10 °C and 21 °C, allowing it to store and release latent heat effectively during typical cold-weather operation. PCM1, used year-round in the cooling configuration, has a higher phase change range of 35 °C to 42 °C, making it ideal for absorbing excess heat generated during high-power discharge in warm conditions. The heat pipes, modeled with a high thermal conductivity of 8,000 W/(m·K), serve as efficient thermal conduits, rapidly transferring heat between the batteries and the PCM layers.
Simulations focused on two critical operational scenarios: battery behavior after use in deep cold, and thermal performance during high-rate discharge in hot conditions. For the cold-weather tests, the battery pack was initialized at 25 °C, simulating a vehicle that had just been driven, and then allowed to cool in an ambient environment of -20 °C. The results were striking. With the full thermal management system—including PCM2, heat pipes, and the aerogel insulation—the battery temperature remained above 0 °C for up to 17 hours after a 3C discharge, and for 14.2 hours after a 1C discharge. This is a dramatic improvement over unmanaged batteries, which dropped below 0 °C in just 1.5 hours under the same conditions. Compared to using PCM alone, the new system extended the sub-zero threshold time by nearly threefold. The research team emphasized the critical role of the aerogel insulation layer, noting that removing it reduced the effective insulation time by 1.7 hours, underscoring its necessity in the design.
This extended thermal retention has profound practical implications. For EV owners in cold climates, it means the vehicle can be parked overnight and started the next morning without the need for energy-intensive preheating. Preheating not only consumes electricity, reducing overall range, but also requires time, diminishing the convenience of EV ownership. By maintaining the battery within its optimal operating window, the system preserves battery health, prevents lithium plating during charging, and ensures full power delivery at startup. The study’s authors point out that for typical daily driving patterns, a 14- to 17-hour window of thermal protection is more than sufficient to cover overnight parking, making the technology highly relevant for real-world use.
The simulations also revealed excellent temperature uniformity within the battery pack. Even during extended cooling periods, the maximum temperature difference between cells never exceeded 5 °C, well within the safety margin for lithium-ion batteries. Uneven temperatures can lead to accelerated degradation in the hottest cells and inefficient use of the battery’s total capacity. The combination of heat pipes and PCM ensures that heat is distributed and absorbed evenly, preventing localized hot spots and contributing to longer battery life.
In high-temperature scenarios, the system’s performance is equally impressive. When the thermal storage module is removed, the remaining components—PCM1, heat pipes, and air cooling—work in concert to manage heat. The team simulated discharge rates of 1C, 2C, and 3C, representing typical driving, aggressive acceleration, and fast charging scenarios, respectively. Without any thermal management, battery temperatures soared to 49.5 °C, 61.4 °C, and 73.2 °C after discharge, with the 3C rate pushing temperatures dangerously close to 80 °C. Such high temperatures not only increase the risk of thermal runaway but also accelerate chemical degradation, permanently reducing battery capacity.
In contrast, the proposed thermal management system drastically reduced peak temperatures. After 1C, 2C, and 3C discharges, the maximum temperatures were lowered by 34%, 42%, and 48% respectively compared to the unmanaged case. This significant reduction brings the battery pack well within safe operating limits, even under high-stress conditions. The system’s effectiveness is enhanced by the phase change process of PCM1. As the battery heats up, PCM1 absorbs large amounts of heat as it melts, providing a powerful buffering effect that slows the rate of temperature rise. This latent heat absorption is far more effective than materials that rely solely on sensible heat (temperature change without phase transition).
An additional refinement tested in the study was the integration of cooling fins into the system. The researchers found that adding fins further improved heat dissipation, particularly at higher discharge rates. At 1C, 2C, and 3C discharges, the maximum temperature was reduced by an additional 4.8%, 5.4%, and 6.7% respectively compared to the same system without fins. The cooling effect of the fins becomes more pronounced as the discharge rate increases, which is precisely when thermal management is most critical. This is because higher discharge rates generate more heat, creating a larger temperature gradient that drives more effective convective cooling from the finned surfaces.
However, the study also noted a trade-off: while fins improved overall cooling, they slightly increased the maximum temperature difference within the battery pack by 12% to 23% at the end of discharge. This is attributed to localized cooling effects near the fins, which can create small thermal gradients. Despite this, the absolute temperature differences remained within safe limits, and the substantial benefit of lower peak temperatures outweighs the minor increase in non-uniformity. The research suggests that future designs could optimize fin placement and geometry to minimize this effect while maximizing heat transfer.
The modular, reconfigurable nature of this system offers several advantages beyond pure performance. First, it is energy-efficient. Unlike active heating systems that consume battery power to generate heat, the winter mode is entirely passive, relying on stored thermal energy and insulation. This preserves driving range. Second, it is cost-effective and scalable. The materials used—PCM, aerogel, and copper heat pipes—are commercially available and can be integrated into existing battery pack designs with minimal modification. Third, it enhances safety by preventing both extreme cold and extreme heat, the two primary triggers for battery degradation and failure.
The implications of this research extend beyond individual vehicle performance. As cities and nations push for electrified transportation to meet climate goals, ensuring that EVs are practical and reliable in all regions is essential. Cold-weather performance has been a major barrier to EV adoption in northern latitudes, where concerns about range loss and startup reliability persist. A system that effectively solves the winter thermal challenge could accelerate adoption in these markets. Similarly, in hot climates, where air conditioning and battery cooling place a heavy load on the electrical system, an efficient passive cooling strategy can improve overall energy efficiency and reduce strain on the grid.
The work also contributes to the broader field of thermal energy storage and management. The use of phase change materials for passive thermal regulation is a growing area of research, with applications in buildings, electronics, and renewable energy systems. This study demonstrates a sophisticated integration of PCM with heat pipes and insulation, showcasing how multiple passive technologies can be combined to achieve superior performance. The validation through detailed CFD modeling adds robustness to the findings and provides a framework for further optimization.
From a manufacturing and service perspective, the removable module introduces a new paradigm. It suggests a maintenance or seasonal service routine where the thermal module is swapped by a technician or even by the owner, much like changing seasonal tires. This could become a standard part of annual vehicle servicing in regions with distinct seasons. It also opens the possibility for modular battery packs that can be customized for different climate zones at the point of sale.
While the current study is based on simulation, the results are highly promising and pave the way for experimental validation and prototype development. The next steps will likely involve building a physical test rig to confirm the thermal performance under real-world conditions, including dynamic driving cycles, varying ambient temperatures, and long-term cycling to assess durability. Integration with a vehicle’s battery management system (BMS) will also be crucial, allowing the BMS to monitor temperature and potentially provide alerts or recommendations for module installation or removal.
In conclusion, the thermal management system proposed by Liu Songyan, Wang Weiliang, Peng Shiliang, and Lü Junfu represents a significant step forward in battery technology. By elegantly solving the conflicting demands of winter insulation and summer cooling through a simple, modular design, it addresses a fundamental limitation of current EVs. The system’s ability to keep batteries above 0 °C for up to 17 hours in -20 °C conditions and to reduce peak temperatures by nearly half during high-power discharge demonstrates its potential to enhance safety, extend battery life, and improve user convenience. As the automotive industry continues to innovate, solutions like this one—rooted in sound engineering principles and practical application—will be key to unlocking the full potential of electric mobility.
Liu Songyan, Wang Weiliang, Peng Shiliang, Lü Junfu, Energy Storage Science and Technology, doi: 10.19799/j.cnki.2095-4239.2024.0369