Thermal management of Li-ion batteries using phase change materials: Recent advances and future challenges

Lithium-ion (Li-ion) batteries have become the dominant energy storage technology across a wide range of applications including electric vehicles, renewable energy storage systems, and portable consumer electronics [1]. Compared to other rechargeable battery chemistries such as lead-acid, nickel‑cadmium, and nickel-metal hydride, Li-ion batteries offer unparalleled advantages in terms of high energy density, high power density, high cell voltage, low self-discharge, and a lack of memory effect [2]. These characteristics make Li-ion batteries well-suited for providing the high energy and power capacities required for all-electric powertrains in vehicles, storing intermittent renewable energy, and enabling extended runtimes for portable devices [3]. The high cell voltage of Li-ion batteries also allows battery packs to achieve the electrical potentials needed using fewer cells [4]. Moreover, Li-ion batteries have high energy efficiency during charge/discharge cycles and low maintenance requirements compared to other rechargeable batteries [5]. These features have facilitated the widespread adoption of Li-ion batteries and their emergence as the battery of choice for energy storage across transportation, grid, and consumer applications. With continuous improvements in energy density, power, safety, and costs driven by research innovations and manufacturing improvements, Li-ion batteries are projected to continue dominating the battery market in the foreseeable future [6].

However, Li-ion batteries face significant limitations due to their sensitivity to operating temperatures which need to be maintained within a relatively narrow range typically between 15 and 35 °C for most cases. Temperatures beyond this range can lead to accelerated degradation of the battery performance and lifespan [7]. In particular, exposure to excessive heat can cause faster aging and irreversible capacity fade as the cycle life is reduced. High temperatures also increase the risks of thermal runaway, which occurs when the internal battery temperature continuously rises due to exothermic chemical reactions, eventually leading to fire or explosion [8]. The thermal runaway phenomenon has been responsible for product recalls in consumer devices and safety incidents in electric vehicles using Li-ion batteries [9]. Fig. 1 displays the vacant battery cells alongside an automobile damaged by fire [10].

Additionally, low temperatures can reduce battery capacity and power delivery [11]. Thus, maintaining the battery temperature within the optimal operating range is critical for ensuring safe usage without catastrophic failures, achieving the rated life cycle, and extracting the maximum performance. Effective thermal management systems that can accurately regulate battery temperatures during charging, discharging, and storage are therefore essential complements to Li-ion batteries across all applications. Sophisticated cooling strategies need to be employed to ensure that heat from internal resistance and entropic heating during operation are dissipated. Thermal management system design is a crucial enabler for secure, reliable, efficient, and optimal functionality of Li-ion batteries [12].

Various cooling methods have been explored for addressing these issues, including air cooling, liquid cooling, phase change materials (PCMs), and combinations thereof. Air cooling utilizes either forced convection with fans/blowers or natural convection to remove heat from the battery. Forced air cooling offers higher heat transfer rates but requires power for fans and blowers [13,14]. Natural convection simplifies the system but provides limited cooling capabilities. Air cooling methods suffer from low heat capacity and insufficient heat transfer rates at high heat loads. Liquid cooling leverages the higher specific heat of liquids to absorb heat either through direct contact or indirect contact using heat exchangers [15]. Direct liquid cooling methods include cooling channels embedded in the electrodes or immersing the battery in the coolant. Indirect liquid cooling involves cold plates or tube, plate, or shell-and-tube heat exchangers. Liquid cooling provides superior heat dissipation but suffers from risks of internal coolant leakage causing short circuits and corrosion. Pumping power requirements, weight, complexity, and potential coolant incompatibility are other disadvantages [16].

PCMs have recently emerged as a promising thermal management solution for lithium-ion batteries, offering unique advantages compared to traditional air or liquid cooling methods. PCMs possess high latent heat storage capacity such that they can absorb and release large amounts of heat during phase transitions between solid and liquid states [17,18]. This allows PCMs to passively absorb heat from the battery when temperature rises near the melting point, thereby maintaining the temperature relatively constant, close to the phase change temperature [19]. Appropriately selected PCM melting points allow the battery to be kept within its optimal operating range. PCMs continue absorbing heat without a significant temperature rise during the melting process until all material completes phase transition [20]. Unlike sensible heat absorption in traditional materials, this latent heat process enables significantly higher heat storage capacity in a lightweight, compact structure [21]. PCM-based cooling is entirely passive without needing any pumping power, fans or blowers [22]. The passive nature also enhances reliability and reduces maintenance requirements. Additionally, PCMs can help mitigate thermal runaway issues by absorbing the heat during uncontrolled exothermic reactions, preventing further temperature escalation [23]. The key downside is their low thermal conductivity, which restricts heat transfer rates. The low thermal conductivity hinders both the heat absorption from the battery and its rejection to the ambient, thereby reducing the PCM’s effectiveness for battery cooling applications with high heat generation rates or rapid cycling [24]. This necessitates enhancing techniques to improve the thermal conductivity of PCMs for battery thermal management.

Fig. 2 provides a comprehensive statistical overview of the research landscape from a survey of 767 papers related to PCMs in lithium-ion batteries, highlighting the global and multidisciplinary nature of this field, also showing that there has been a remarkable surge in the number of research and review papers focusing on PCM as a battery thermal management system since 2014. These illustrations, sourced from SCOPUS, provide valuable insights into the scope, trends, and interdisciplinary collaborations in PCM research for Li-ion batteries, highlighting the dynamic and evolving nature of this scientific research domain.

This review provides a comprehensive overview of PCM-based cooling technologies for Li-ion batteries. While several studies have covered various thermal management strategies, this review goes deeper into PCM-based techniques. Various types of PCMs are categorized and discussed including their enhancements, and their combination with other cooling methods. By also exploring real-world applications of these systems, the aim is to offer a practical understanding of their benefits and challenges. Using machine learning and optimization techniques, potential areas of improvement are identified along with suggested directions for future studies in this field.

The structure of this review is as follows: First, PCM fundamentals and characteristics are introduced. Then PCM enhancement strategies, hybrid cooling systems, optimization methods, and additive manufacturing are discussed, with particular emphasis on assessing limitations of current PCM cooling approaches to highlight avenues for continued innovation. In conclusion key findings are summarized and promising research directions within this rapidly evolving field are proposed.