Thermal management of supercapacitors: a review of thermal challenges, management strategies, future directions

1 Introduction

Supercapacitors (SCs) complement batteries in energy storage systems, boasting exceptional power delivery, rapid charging, and long cycle life (Satpathy et al., 2020; Satpathy et al., 2019; Djerioui et al., 2019). As show in Figure 1a, they occupy an intermediate position on the Ragone plot between traditional capacitors and batteries, making them well-suited for applications demanding high bursts of power, such as electric vehicles, power grid, wind power, solar, aerospace and defence, and portable electronics, as illustrated in Figure 1b (Ellabban et al., 2014; Chu and Majumdar, 2012; Li et al., 2022; Adalati et al., 2022; Libich et al., 2018; Akkinepally et al., 2023). However, like batteries, supercapacitors are highly sensitive to temperature fluctuations, albeit through distinct degradation mechanisms, and therefore careful thermal design and operation (Mars, 2011). Understanding how temperatures affect supercapacitor performance underscores the need for proactive thermal management and implementing effective thermal management strategies (Akkinepally et al., 2023).

The thermal challenge facing SCs is rooted in Joule heating, where internal heat is generated due to the equivalent series resistance (ESR) of the electrolyte and electrode materials during charge and discharge cycles. Recent work by Li et al. (2025) has identified a negative Joule heat effect in supercapacitor modules under specific operating conditions–specifically, during high-frequency charge-discharge cycles at low current densities in multi-cell modules, adding a layer of complexity to thermal behavior prediction. This phenomenon is discussed further in Section 4 in context of heat generation modeling. This internal heat buildup can elevate the temperature of the supercapacitor, affecting its performance in various ways. High temperatures accelerate degradation of the electrolyte and electrode materials, leading to faster self-discharge, reduced efficiency, and potential safety hazards such as electrolyte decomposition, gas evolution, or in extreme cases thermal runaway (Yang H. et al., 2018; Li et al., 2015; Wu et al., 2022). Conversely, low temperatures hinder performance by reducing ionic conductivity in the electrolyte, thereby increasing ESR and limiting accessible capacitance (Zhang J. et al., 2018; Fly et al., 2021).

To address these thermal challenges and unlock the full potential of supercapacitors, various thermal management strategies have been developed (Voicu et al., 2019; Soltani et al., 2019). Air cooling, a simple and cost-effective approach, utilizes convective heat transfer. However, its effectiveness is limited by low convective heat transfer coefficients and strong dependence on ambient temperature (Xia et al., 2014; Hirano et al., 2014). Liquid cooling offers superior heat removal but adds complexity and weight to the system and introduces sealing and leaking-management requirements (Karimi et al., 2021a). Heat pipes provide a passive alternative, utilizing phase change of a working fluid for heat transfer. Phase Change Materials (PCMs) are another promising approach (Karimi et al., 2020; Jaguemont et al., 2019; Chen K. et al., 2021; Bamdezh et al., 2020). These materials absorb latent heat during melting, attenuating temperature excursions and protecting the supercapacitor during high-power operation. Beyond these established techniques, researchers are exploring advanced materials with higher thermal stability for both electrodes and electrolytes. Such materials may reduce, though are unlikely to fully eliminate the need for active thermal management in some application scenarios.

Selecting the optimal thermal management strategy depends on factors like application context, power density, size constraints, and cost. A holistic approach that considers both device design and thermal management is crucial for maximizing supercapacitor performance and reliability across diverse applications. By effectively managing temperature, researchers and engineers can extend operational lifetime, maintain rated performance across temperature extremes, and broaden the range of viable SC applications. Recent studies on battery thermal management systems have provided valuable insights that can be adapted for supercapacitor applications, particularly in the design of cooling plates (Zhuang et al., 2021), liquid cooling with composites PCMs (Zhao et al., 2020), and innovative liquid-cooling plate concepts (Akbarzadeh et al., 2021).

The literature on supercapacitors (SCs) is extensive, with most articles focusing on state estimation (Zhang L. et al., 2018), fractional order modeling (Zou et al., 2018), industrial applications (Muzaffar et al., 2019; Lin et al., 2016), electrode materials, electrolytes (Widyantara et al., 2022; Stettner and Balducci, 2021), and reliability (Chen Y. et al., 2021; Liu S. et al., 2020; Roy et al., 2021). There is a relative scarcity of review publications specifically addressing thermal modeling and thermal management systems for SCs. Previous studies have focused on specific aspects, without proving a cohesive treatment of thermal challenges faced by SCs (Kumar et al., 2018). Recent reviews by Zhang L. et al. (2018), Taurbekov et al. (2023), Rashidi et al. (2022), and Zhou et al. (2023) have touched on thermal modeling advances but do not provide an integrated analysis linking temperature-dependent material behavior, thermal effects on performance, and system-level thermal management strategies–the gap this review addresses.

The paper employs a systematic approach to thoroughly examine the thermal characteristics of supercapacitors as shown in Figure 2. An overview of these energy storage devices is given in Section 1. The architecture of supercapacitors and methods for evaluating their performance are covered in detail in Section 2. Section 3 examines the effects of temperature on key components including electrolytes, electrodes, and separators. In Section 4, the impact of temperature on performance metrics including self-discharge rate, capacitance retention under extreme temperatures, aging mechanisms, and the phenomenon of thermal runaway (Section 4.4) is discussed. The passive and active techniques for managing and dissipating heat produced during supercapacitor operation are covered in Section 5. Section 6 identifies critical research gaps and outlines future directions. Section 7 concludes by summarizing important findings and identifying open research challenges.

1.1 Innovation and novelty

This review paper systematically analyses the influence of temperature and thermal management strategies on the performance of supercapacitors. It provides a detailed analysis of how temperature affects key supercapacitor performance parameters including self-discharge, aging, resistance, and capacitance. The paper addresses temperature-dependent behavior, including methodologies for accurate temperature measurement across wide operating ranges. The review also presents state-of-the-art thermal management techniques tailored for supercapacitors, including active and passive cooling approaches, and material modifications for improved thermal conductivity. By evaluating the effectiveness of these thermal management strategies, the review aims to inform the optimization of supercapacitor performance and longevity under varying thermal conditions. The increased use of supercapacitors in temperature-sensitive applications including renewable energy systems, electric vehicles, and high-power density devices requiring extended cycle life is supported by the thermal insights and design guidance synthesized in the review.

1.2 Literature search methodology

To ensure a systematic and reproducible selection of source material, the literature search was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) framework. Searches were performed in the Web of Science, Scopus, and Google Scholar databases using the following primary keyword combinations: “supercapacitor thermal management,” “supercapacitor temperature effects,” “electrochemical double layer capacitor cooling,” “supercapacitor heat pipe,” “supercapacitor phase change material,” “supercapacitor aging temperature,” “lithium-ion capacitor thermal management,” and “supercapacitor electrolyte thermal stability.” Searches were not restricted by date but prioritized publications from 2014 to 2025 to reflect the current state of the art; seminal earlier works were included where they established foundational concepts.

Inclusion criteria required that articles (i) address thermal behavior, thermal effects on performance, or thermal management strategies in supercapacitors or lithium-ion capacitors; (ii) be published in peer-reviewed journals or conference proceedings; and (iii) be available in full text. Articles were excluded if they addressed thermal management exclusively in lithium-ion batteries without SC-specific content, or if they were duplicates of other included sources. Initial database searches returned approximately 850 records. After removal of duplicates and screening of titles and abstracts, 312 full-text articles were assessed for eligibility. Of these, 158 met the inclusion criteria and are cited in this review. Reference lists of included articles were also manually screened to identify additional relevant sources not captured by the database searches.

2 Architecture of supercapacitors

At the core of a supercapacitor are two porous electrodes made of high surface area materials such as activated carbon or carbon nanotubes (Taurbekov et al., 2023; Béguin et al., 2014). The configuration of a supercapacitor is shown in Figure 3 (González et al., 2016). These electrodes are separated by an ion-permeable separator and immersed in an electrolyte solution, typically an organic or aqueous electrolyte (González et al., 2016; Eskusson et al., 2022). When a voltage is applied, ions from the electrolyte are attracted to the oppositely charged electrodes, forming an electrochemical double layer at the electrode-electrolyte interface (Dubal et al., 2015). This double layer acts as a capacitor, storing energy electrostatically via charge separation; the high surface area of the porous electrodes allows for a large double layer capacitance (Wang et al., 2012), while the thin double layer supports rapid ion adsorption and high-power density (Pal et al., 2019). The separator prevents electrical shorting between electrodes while allowing ion transport (Pothu et al., 2021).

Supercapacitors derive their distinctive characteristics from the combination of high-surface-area electrode materials and carefully selected electrolytes. This combination yields higher energy density than conventional electrostatic capacitors and higher power density than batteries, along with extended cycle life and rapid charge-discharge capability, properties that position them as effective complements to batteries in hybrid energy storage systems. Figures 4a–c shows the structure of a supercapacitor, a typical supercapacitor module pack, and a typical supercapacitor structure integrated with a supercapacitor module (Muso and lino, 2011; Musolino et al., 2013).

3 Influence of temperature on supercapacitor components

The temperature at which supercapacitors operate plays a significant role in their components and overall performance. When ambient temperature exceeds 298 K, the estimated calendar lifetime is approximately halved for every 10 K increase in operating temperature (Liu et al., 2022). This section provides a focused overview of thermally driven changes in SC component materials and their consequences for device-level performance metrics including capacitance, ESR, and self-discharge rate under elevated and reduced temperatures.

3.1 Temperature influence on electrolytes

Electrolytes serve as the medium for ion transport between electrodes and play a crucial role in the performance of supercapacitors. They are typically composed of a solvent and dissolved ionic salt. There are three principal electrolyte classes used in supercapacitors: aqueous, organic, and ionic liquid electrolytes. The electrolyte operating temperature range is normally between approximately 233 K and 343 K for organic electrolytes; aqueous electrolytes operate over a narrower range (273–333 K), while ionic liquid electrolytes can function up to 450 K. Sage, high-energy supercapacitors based on solvent-free ionic liquid electrolytes have been demonstrated (Arbizzani et al., 2008), while solid-state flexible supercapacitors operating across wide temperatures ranges represent an emerging frontier (Chaichi et al., 2020).

• Ionic Conductivity: The ionic conductivity of electrolytes is strongly influenced by temperature. Generally, as temperature rises, ionic conductivity increases, following Arrhenius-type behavior, but may decline at very high temperatures due to electrolyte decomposition or solvent evaporation. Higher temperatures provide greater thermal energy, facilitating ion movement within the electrolyte and improving overall charge-transfer kinetics.
• Viscosity: Consistent with Walden’s rule (Yuan et al., 2018; Roe et al., 2022), as temperature increases, viscosity typically decreases. Lower viscosity allows for better ion mobility and enhanced charge/discharge rates.
• Decomposition: High temperatures can lead to electrolyte decomposition, generating gas, form unwanted reaction products, and increasing internal pressure, potentially leading to electrolyte leakage through seals or venting. This leads to degradation of performance and reliability.
• Solvent Volatility: Temperature variations can increase solvent volatility, potentially causing electrolyte evaporation and a decrease in electrolyte volume and concentration.

3.2 Temperature influence on electrodes

Supercapacitor electrodes typically comprise an active material (such as activated carbon), a binder, and a conductive agent. Carbon-based materials remain the most widely studied electrodes for supercapacitors due to their tunable properties and thermal stability (Zhang and Zhao, 2009).

• Active Materials: Temperature can influence the electrochemical behavior and energy storage capacity of active materials. Past studies have shown that graphite and carbon nanotubes are commonly used thermal conductive carbon electrode materials (Li et al., 2018; Balandin et al., 2008; Hu et al., 2006). Extensive ex situ temperature measurements of a supercapacitor under varying pressures (Table 1) have established that the electrode is the primary factor influencing the thermal resistance of supercapacitors (Hauge et al., 2014; Kötz et al., 2006). Additionally, strong thermal stability and high thermal conductivity are crucial factors in assessing the thermal efficiency of SCs. Compared to research on lithium-ion batteries at high temperatures of graphite anodes (Kumaravel et al., 2021; Roth et al., 2004; Yang K. et al., 2018; Ayadi et al., 2013; Shao et al., 2018; Niu et al., 2004), little work has been carried out on the thermal stability of carbon electrodes in SCs, excluding work on carbon-based materials (Wu et al., 2009; Li et al., 2014; Hammar et al., 2010; Linzen et al., 2005). Interconnected carbon nanosheets derived from hemp have shown ultrafast performance with high energy density (Wang H. et al., 2013), demonstrating the potential of bio-derived carbon materials.

TABLE 1. Ex-situ temperature measurements yielded the mean thermal conductivities of supercapacitor stack components (Hauge et al., 2014; Kötz et al., 2006).

Manganese dioxide (MnO₂) and ruthenium dioxide (RuO₂) are transition metal oxides that show promise as electrode materials for supercapacitors. MnO₂ exhibits good thermal stability (Pothu et al., 2021; Ragupathy et al., 2009), with a weight loss of approximately 14% when heated up to 2,000 °C, which is mainly attributed to the loss of water molecules adsorbed on the surface or incorporated within the crystal nanostructure (structural water). On the other hand, RuO₂-coated electrodes demonstrate high thermal stability (Fei et al., 2021; Kim and Kim, 2006; Shinde et al., 2017; Ma et al., 2023; El Brouji et al., 2009; Hahn et al., 2006). The heating of RuO₂ electrodes can lead to an increase in capacitance, which is potentially due to improved electron/proton transport, increased active reaction sites, or the reduced mass of active electrodes through dehydration, resulting in a higher calculated capacitance (Karmakar et al., 2018; Hu et al., 2004; Brousse et al., 2004; Bitt et al., 2012). Table 2 shows a comprehensive summary of the thermal conductivities of various electrode materials (Divakar, 2016; Qin et al., 2018).

TABLE 2. Comparative thermal conductivity study of electrode materials with distinct compositions (Divakar, 2016; Qin et al., 2018).

ACN: acetonitrile; MWCNT: multiwalled carbon nanotube; PTFE: polytetrafluoroethylene; TEABF₄: tetraethylazanium tetrafluoroborate; OLC: onion-like carbon.

In addition, polymers with electrical conductivity, such as polypyrrole, exhibit favorable thermal stability properties. In summary, the thermal stability of electrodes is influenced not only by the thermal stability of the electrode materials themselves but also by the thermal stability of the binders. This is because binders and electrode materials are often in direct contact with each other. In the next section, the thermal stability of binders will be discussed to provide a comprehensive understanding of the overall thermal stability of electrodes in supercapacitors.

• Binders: Common binder materials include polymeric substances like polyvinylidene fluoride (PVDF) and carboxymethyl cellulose (CMC). The operational temperature range of the electrodes can be limited by the binder’s melting temperature. To enhance the electrochemical performance of the electrodes, carbonization of the electrodes/binders at temperatures exceeding 873 K under an inert atmosphere has been proposed. This process potentially improves performance by creating modifications in the porous structure due to binder decomposition and enhancing electrical conductivity. Additionally, the choice of binder materials impacts the thermal conductivity of the electrodes. For instance, polymer binders used in coating carbon nanotube networks can form conductive substrates with nanometer-level thickness, leading to improved thermal conductivity of the electrodes. Thermal stability and thermal conductivity are two key aspects when considering the influence of binders on supercapacitors. In the context of binders, higher thermal conductivity is generally desired. This facilitates efficient heat dissipation within the SC, reducing temperature gradients that can negatively affect performance and lifespan. Temperature can affect the binding properties and stability of binders. High temperatures can soften or melt binders, potentially leading to delamination or reduced adhesion between the active material and current collectors.
• Current Collectors: Current collectors are typically made of metals like aluminum or copper; carbon-based collectors (e.g., carbon cloth, graphitic nanometals on carbon fibre) are also used, particularly in flexible SC applications. Temperature influences the electrical conductivity and thermal expansion properties of current collectors, and differential thermal expansion between the current collector and the electrode coating can contribute to interfacial delamination at temperature extremes (Divakar, 2016).
• Lignin: Lignin is a natural polymer derived from plant materials and has been explored as a potential binder or carbon precursor in supercapacitor electrodes. The influence of temperature on lignin-based electrodes can vary depending on specific characteristics, such as amount of oxygen atoms and carbonization. A proper amount of oxygen atoms in lignin leads to increased electrolyte ion adsorption for supercapacitors and interactions with other electrode components. Higher temperatures can impact the stability and thermal decomposition behavior of lignin (Zhu et al., 2020). It may undergo degradation or morphological changes, affecting the overall performance and structural integrity of the electrode (Guizani et al., 2023).

3.3 Temperature influence on separators

Separators are ion-permeable membranes positioned between the anode and cathode that allow rapid ion transport while preventing electronic conduction between the electrodes. High temperatures can cause the separator to degrade or lose its structural integrity, leading to short circuits or reduced performance, and an eventual thermal runaway (Qin et al., 2018; Sun et al., 2023). At low temperatures, below approximately 243 K, the mobility of ions is greatly reduced, primarily through increased electrolyte viscosity and reduced ionic conductivity, which limit ion transport through the separator pores (Qin et al., 2018; Sun et al., 2023). With that in mind, temperature variations can impact the porosity and pore structure of the separator, affecting ion transport and diffusion through the pores. This can influence the overall capacitance and charge/discharge rates of the SC.

4 Influence of temperature on supercapacitor performance

The performance of supercapacitors is significantly influenced by temperature variations. Isothermal calorimetry has been employed to measure time-dependent heat generation rates in individual supercapacitor electrodes (Munteshari et al., 2018), while studies on ionic liquid-based EDLCs have quantified the effect of temperature on irreversible and reversible heat generation rates (Likitchatchawankun et al., 2020).

4.1 Influence of temperature on self discharge

Supercapacitors exhibit a phenomenon called self-discharge, where they gradually lose their voltage over time after being charged to a set voltage and left in open-circuit conditions-that is with no external load connected. Operating temperatures of SCs have considerable influence on the rates of self-discharging. At elevated temperatures, ions exhibit increased mobility, resulting in increased leakage current and consequently higher rates of self-discharge (Ayadi et al., 2013). Numerical investigations by Atayo et al. (2025a) have provided insights into the charge transfer mechanisms that govern self-discharge behavior under varying thermal conditions. The relationship between leakage current and temperature is modeled using the Arrhenius equation (Equation 1):

I l e a k a g e = A e x p − E a R T (1)

Where E _*a* represents the activation energy. For processes controlled by faradaic mechanisms, the activation energy typically ranges between 40 − 80 k J m o l − 1, whereas for diffusion-controlled processes, it falls within 16 − 20 k J m o l − 1. Moreover, as the type of reaction at the interfaces between the two electrodes and the electrolyte may vary, the impact of temperature might not be uniform across both electrodes (Conway, 2013). Charged SCs store energy in a higher Gibbs free energy state; the tendency to self-discharge is the thermodynamic driving force towards the lower-energy discharged state (Niu et al., 2004). Self-discharge rate is an indicator of SC health and affects usable capacity over time. The rate is typically highest immediately after charging, before declining towards a quasi-steady-state value. Aged SCs exhibit higher self-discharge rates than new devices, reflecting accumulated electrode and electrolyte degradation. The estimation of melting points of organic compounds used in electrolytes (Yalkowsky and Alantary, 2018) is also relevant for understanding phase behavior at low temperatures.

4.2 Influence of temperature on aging

Supercapacitor aging and performance loss are significantly influenced by temperature. High temperatures not only accelerate breakdown reactions but also increase chemical reactivity (Yang K. et al., 2018). An increase of approximately 10 K above the rated operating temperature leads to a twofold reduction in estimated calendar lifetime, consistent with the Arrhenius-based degradation rule introduced in Section 3 (Linzen et al., 2005; Ma et al., 2023; Kötz et al., 2010). In a high-temperature operation, the following SC aging mechanisms are proposed:

• Pressure evolution: High temperatures can cause the electrolytes in supercapacitors to degrade thermally and electrochemically, releasing by-products including H₂, CO, and other organic gases as a result. In the electrolyte space, these gases gather and raise the pressure. Controlling internal pressure is essential for safe operation and requires appropriate cell design, including pressure-relief venting mechanisms (Hahn et al., 2006). In practice, the safety valve may release internal pressure before a 20% capacitance loss is reached, which is the conventional end-of-life threshold for SCs (El Brouji et al., 2009). Furthermore, hazardous chemicals that are emitted into the atmosphere could be dangerous. For instance, aqueous electrolytes driven above their electrochemical stability window (approximately 1.2–1.4 V for water-based systems) cause electrolysis, evolving H₂ and O₂ which can accumulate as a pressure and ignition hazard (Brousse et al., 2004).
• Increase in pore resistance: Electrode and electrolyte-interface-breakdown processes are accelerated by high temperature. The porous electrode surface is blocked by the solid decomposition products produced by the oxidative decomposition of the carbon electrode and electrolyte. As a result, the electrodes’ effective surface area is decreased, which lowers capacitance. After conducting porosimetry experiments on old electrodes, Bittner et al. found that the reduction in capacitance is predominantly caused by the obstruction of pores with dimensions similar to those of the solvated ions (Bitt et al., 2012).
• Increase in Equivalent Series Resistance (ESR) and Joule heating: Joule heating accelerates electrochemical degradation, which in turn increases ESR, generating more Joule heating, a positive feedback cycle that progressively elevates internal temperature and accelerates aging (Kötz et al., 2006).
• Appearance of oxides: The current collectors start to deteriorate at high temperatures, increasing the contact resistance between them and the electrode. According to electrochemical impedance spectroscopy measurements, this results in greater ESR values (Kim et al., 2020; Oz et al., 2017).
• Evaporation in electrolytes: Weight loss occurs when temperature exceeds the boiling point, allowing for tracking electrolyte evaporation. Acetonitrile (ACN)-based supercapacitors have experienced a reported weight loss of approximately 25% after 12,000 s at 3 V and 343 K, a condition that exceeds the recommended operating voltage for most commercial ACN-based devices and therefore represents an accelerated stress test rather than normal operation (Hahn et al., 2006; Park et al., 2019).
• Overvoltage: Power cycling with constant current causes a voltage increase due to aging at higher temperatures, in turn causing further aging in charging and capacitors (Bohlen et al., 2007).

4.3 Performances in extreme temperatures

Advancements in supercapacitor technology are crucial for extreme temperature power storage systems in space-based avionics, electric aircraft, unmanned aerial vehicles, and electric cars. SCs require excellent performances in extreme temperatures for capacitance and ESR, with recent advancements addressing these challenges. The most recent developments in SC performance at extremely low and extremely high temperatures are covered in this section.

4.3.1 Performance in extremely low temperatures

High-power energy storage systems are crucial for electronic devices, cold-cranking engines, and hybrid electric vehicles in polar regions. Peak power systems such as space-related electronics require operating at temperatures as low as 218 K or below. Energy storage systems operating at low temperatures must aim to minimize system weight and streamline thermal management setups to enhance specific energy in power sources (Fly et al., 2021; Li et al., 2017; Zhou et al., 2015).

4.3.2 Performance in extremely high temperatures

High-temperature performance in power supplies (greater than 393 K) is crucial in various industries, such as military, space, and oil drilling. Stability of the electrolytes is a limiting factor for supercapacitors to operate at high temperatures (Lin et al., 2011). Organic electrolytes are unsuitable for ultra-high-temperature operation primarily due to their relatively low boiling points, flammability, and the risk of toxic decomposition product evolution above their electrochemical stability windows. Organic electrolytes in commercial SCs may cause issues in hybrid vehicles where the average peak temperature is about 333 K, due to the narrowing electrochemical stability window. Ionic liquid electrolytes are increasingly used in high-temperature applications owing to their negligible vapor pressure, wide electrochemical stability windows, and high thermal stability, with some remaining stable above 450 K. (Armand et al., 2010). By avoiding instances of thermal runaway and pressure buildup during operation at high temperatures, this ensures thermal reliability. Inorganic fillers like clay have been added to improve high-temperature thermal stability, permeability, and active surface area (Borges et al., 2013). Overcharging is the worst-case scenario in SCs, causing pressure build-up and potential leakage of gas and electrolyte (Huang et al., 2019). EDLCs are generally considered less susceptible to thermal runaway than lithium-ion batteries because they lack the highly exothermic self-propagating reactions associated with lithium intercalation chemistry. However, as discussed in Section 3.4, thermal runaway remains a concern in SCs under conditions of damage, overcharge, or manufacturing defects, particularly in devices using flammable organic electrolytes (Yao et al., 2023).

4.4 Performance metrics for supercapacitors

Supercapacitor performance under thermal stress is typically characterized by changes in capacitance (C) and equivalent series resistance (ESR). Commercial EDLCs have capacitances up to 12,000 F, cell voltages of 2.3–2.75 V, and cycle lives exceeding one million cycles under mild conditions (González et al., 2016; Kötz and Carlen, 2000). Temperature-dependent variations in C and ESR (Gualous et al., 2003) and self-discharge behavior (Diab et al., 2009) are particularly relevant for aging studies. Modeling efforts for ultracapacitors in automotive systems (Lee et al., 2008) and novel stack arrangements for improved heat transfer (Voicu et al., 2022) contribute to the broader knowledge base.

4.5 Thermal runaway

Thermal runaway is a significant concern in supercapacitors, primarily due to issues with thermal stability, or in instances where supercapacitors undergo damage, mishandling, or suboptimal manufacturing processes. It refers to a self-reinforcing thermal escalation within the SC cell, which becomes extremely difficult to arrest once initiated. This phenomenon occurs when the internal temperature of the device reaches a threshold at which exothermic electrolyte decomposition begins. This reaction generates additional heat, further elevating the temperature and instigating subsequent chemical reactions, leading to a continuous rise in temperature (Wu et al., 2022; Mali and Tripathi, 2022). During thermal runaway, the temperature within the battery cell escalates rapidly, resulting in the sudden and forceful release of stored energy. This chain reaction produces exceedingly high temperatures.

Therefore, the associated hazards are fire and explosion. In supercapacitors using acetonitrile-based electrolytes, thermal runaway can produce toxic decomposition products including acetonitrile vapor, hydrogen cyanide, and nitrogen oxides. Devices using propylene carbonate electrolytes produce carbon dioxide and carbon monoxide upon decomposition. These hazards differ substantially from those associated with lithium-ion battery thermal runaway and must be assessed separately in safety analyses. Studies on thermal stability of supercapacitors in HESS for lightweight electric vehicles have provided practical insight into safe operations (Mali and Tripathi, 2022).

5 Thermal management systems

Thermal management systems regulate supercapacitor temperature, maintaining consistent and lower temperatures in the pack (Shahjalal et al., 2021). However, these systems increase the size, weight, and cost, and reduce effective capacity while impacting reliability from additional components like pumps and fans (Shahjalal et al., 2021; Mirk et al., 2012). In many commercial SC applications, active cooling is not required below approximately 333 K; however, the threshold depends on the specific duty cycle, cell chemistry, and module configuration. Cooling systems are categorized as active or passive (Divakar, 2016). Active systems remove heat through forced convection (air or liquid cooling), while passive systems rely on mechanisms such as phase change materials (PCMs), heat pipes, or enhanced thermal conductivity materials to buffer temperature excursions and promote temperature homogeneity within the pack (He and Zhang, 2022). Passive systems consume no parasitic electrical energy during operation, which is a significant advantage in energy-limited applications. Implementing cooling systems enables temperature control but has tradeoffs like increased size and reduced capacity, which must be balanced. Table 3 provides an overview of thermal management schemes in SCs. A critical review of thermal management models and solutions for lithium-ion batteries (Wang et al., 2016) provides a useful framework that can be adapted for supercapacitor applications.

TABLE 3. Overview of thermal management schemes in supercapacitors.

Thermoelectric cooling operates via the Peltier effect and requires continuous external electrical power input; it is therefore classified as an active technique regardless of the system context in which it is deployed. When integrated with passive components such as heat sinks or PCMs, the overall system may be considered hybrid, but the thermoelectric element itself remains an active device.

5.1 Passive thermal management

Passive thermal management methods are techniques used to control and dissipate heat in supercapacitors without the use of mechanically driven components such as fans or pumps. These methods rely on conduction, natural convection, radiation, and in the case of phase change materials and heat pipes, latent heat transfer to transfer heat away from the SC cells and module. In this section, we explore different passive thermal management methods and how they enhance cooling in SCs.

5.1.1 Heat pipe cooling systems

Heat pipes (HPs), a passive cooling technology, use a closed two-phase thermodynamic cycle to dissipate heat. The liquid medium in the pipe evaporates when heated, absorbing thermal energy. The vapour condenses on the cooler side, releasing latent heat, which is then transferred to the environment via the condenser surface (Yue et al., 2021). HPs enable significant heat transfer with near-isothermal operation, enabling efficient heat removal from SC modules (Thakur et al., 2020). Studies show that, by quickly removing heat, HP cooling reduces peak cell temperature by 7.5%–11.7% and increases capacitance retention by approximately 2.1% compared to natural convection (Karimi et al., 2021b). Variations such as vapor chambers with integrated fin structures have also been investigated for enhanced thermal spreading in cylindrical cell formats (Liu et al., 2019). However, HPs have disadvantages, including space constraints and requirements for specific cell geometries to ensure adequate thermal contact between the HP and cell surfaces (Thakur et al., 2020). Hybrid thermal management systems (HTMSs) combine HPs and phase change materials to address the limitations of each approach individually. The PCM stores latent heat while the HP provides continuous heat transport once the PCM’s latent heat capacity is exhausted, preventing uncontrolled temperature rise during sustained high-power operation (Chen K. et al., 2021; Karimi et al., 2021c). Experiments show that a HTMS achieves approximately 35% lower peak cell temperature and 86% lower temperature non-uniformity than cooling with PCMs only (Karimi et al., 2021c). Research on nanofluid-based pulsating heat pipes has shown potential for further improving the thermal conductance of these passive systems (Chen and Li, 2020). Figure 5 illustrates the HP cooling system employed for the lithium-ion capacitor. Heat sinks provide extra surface area for heat transfer but are insufficient as a standalone cooling solution in high-power SC applications, where heat flux densities exceed the capacity of passive fin-and-surface conduction alone (Shahjalal et al., 2021). Despite their technical challenges, including low intrinsic thermal conductivity and the risk of PCM leakage upon melting, PCM systems are generally less costly than HP-based solutions and can provide better temperature uniformity within the SC module than air-cooled approaches (Jaguemont et al., 2019). In summary, hybrid passive thermal management systems that combine HPs and PCMs exploit the complementary strengths of both, the HP’s high thermal conductance and the PCM’s latent heat buffering capacity, to achieve more reliable temperature control than either method alone.

5.1.2 Phase change materials (PCM) cooling systems

Phase change materials (PCMs) are passive thermal management systems that absorb and release latent heat during solid-to-liquid phase transitions, enabling temperature buffering without active components. In SC applications, PCMs integrated around or between cells act as thermal buffers, limiting peak temperature rise during high-power discharge cycles (Karimi et al., 2020; Jaguemont et al., 2019). During high-power SC operation, PCMs absorb excess thermal energy as latent heat, preventing sharp temperature excursions; during rest or low-power periods, the stored heat is released as the PCM re-solidifies. Ideal PCMs for SC thermal management have melting points of 303–333 K, high latent heat capacity, and a narrow melting range. Paraffin wax is a widely used PCM candidate owing to its low cost, chemical stability, non-toxicity, and tunable melting point across the range of interest (Jaguemont et al., 2019). Other PCM candidates are chlorobenzene/bromobenzene mixtures and stearic acid (Jaguemont et al., 2018; Yuan et al., 2014). High-temperature PCMs, such as Na₂CO₃-Li₂CO₃ eutectics, have been explored for applications requiring thermal stability above 700 K, though these are more common in concentrated solar power that in SCs (Jiang et al., 2017). In addition, PCMs can delay the onset of thermal runaway in defective or abused cells by absorbing the initial heat generated before the self-reinforcing exothermic reaction is triggered (Talele et al., 2024; Al-Masri et al., 2024).

PCM cooling is advantageous for its simplicity, and passive temperature regulation compared to air and liquid systems that require external energy and maintenance (Xia et al., 2017; Arora, 2018). SC cells or modules can be embedded within or surrounded by PCM, which absorbs heat during high-power operation to maintain temperatures within the target range, as illustrated in Figure 6a (Gan et al., 2020). Paraffin wax is widely used for its low cost, stability, and durability but has low intrinsic thermal conductivity (typically 0.1–0.3 W m^-1 K⁻¹), which limits the rate at which heat can be transferred into and out of the PCM (Thakur et al., 2020). To overcome this limitation, thermal conductivity enhancement strategies such as metal foam infiltration, fin structures, or conductive mesh inserts have been investigated. Studies incorporating metal foam-PCM composites have demonstrated significant improvements in heat dissipation during fast charging (Kumar et al., 2026), while composites paraffin with fin structures has been shown to reduce peak temperatures and improve temperature uniformity (Wang et al., 2017). Flame-retardant composite PCMs have also been developed to address safety concerns associated with organic PCM flammability (Zhang et al., 2020). Tubular phase change material unit have been proposed as a novel strategy for constructing battery thermal management modules (Wu et al., 2021), a concept that could be adapted for cylindrical supercapacitor cells. Studies have examined paraffin-based PCM cooling for lithium-ion capacitors (LICs), adding aluminum (Al) mesh to improve heat conduction within the PCM matrix surrounding the LIC cells, as shown in Figure 7b. This PCM-Al system keeps temperatures lower than with pure PCM cooling, as shown in Figure 7c.

Subsequent studies have optimized PCM thickness to balance heat capture, temperature control, cost, and weight. Thinner PCMs result in higher peak cell temperatures during high-power operation, which can accelerate electrolyte degradation and reduce calendar lifetime. For specific LIC module configuration studied in (Karimi et al., 2020), a PCM layer thickness of approximately 7 mm was identified as the optimum. In summary, jointly optimizing PCM layer thickness and thermal conductivity (for example, through conductive filler addition or metal mesh integration) is essential to achieving effective temperature control within the practical constraints of module mass, volume, and cost.

5.2 Active thermal management

Active cooling involves using a cooling mechanism, such as a fan or refrigerant, to dissipate heat from the supercapacitor. This technique is useful in high-temperature environments where passive cooling may not be sufficient. This method involves air cooling and liquid cooling methods as explained in detail below.

5.2.1 Air cooling systems

Air cooling is a popular cost-effective active cooling option for SC modules, despite the relatively low thermal conductivity of air (approximately 0.026 W m^-1 K⁻¹ at ambient conditions). Its two main types are natural air convection and forced air convection. Natural convection cooling relies on buoyancy-driven airflow around SC cells to remove heat by convection. While simple and requiring no auxiliary power, it achieves low heat transfer coefficients and is therefore limited in its thermal management capacity (Bashir et al., 2018). Natural convection is primarily employed in low-power or laboratory-scale SC characterization studies rather than in high-power commercial applications. Forced air convection, in which fans or blowers drive airflow over SC cells, achieves significantly higher heat transfer coefficients than natural convection by reducing the thickness of the thermal boundary layer at cell surfaces (Ianniciello et al., 2018).

Forced air convection is the most widely implemented active cooling approach for SC modules, offering greater heat dissipation capacity and operational reliability than natural convection while avoiding the sealing and leak management requirements of liquid cooling. However, achieving uniform airflow distribution across all cells in a multi-cell module requires careful duct geometry design, which remains a significant engineering challenge. Research focuses on optimizing SC spacing, airflow direction, and fan placement to improve temperature uniformity. Recent studies on on-board supercapacitor boxes have demonstrated that optimized air-cooled heat dissipation structures can significantly reduce maximum cell temperatures (Hu et al., 2024). Innovations such as uniform flow distribution plates have been shown to improve temperature uniformity in air-cooled cylindrical cell arrays (Suryavanshi and Ghanegaonkar, 2025). Xia et al. designed cooling channels with parallel and series connections for SC module packs (Xia et al., 2014). Air intake in the middle and side exits enabled airflow across each cell to remove heat. This limited maximum temperature differences to 5 K across the module. Hybrid cooling configurations (combining parallel and series airflow paths), prevent localized hot-spot clustering and reduce effective coolant path lengths, thereby mitigating inter-cell temperature non-uniformity. In summary, forced convection outperforms natural convection, but requires meticulous duct design to provide uniform airflow and temperature control across capacitors (Wang K. et al., 2013; Lee et al., 2014).

Voicu et al. (2015) investigated forced air convection cooling of a staggered SC module architecture under 70 A charge/discharge cycling. A horizontal cell spacing of 1.25 times the cell diameter was identified as optimal, improving heat removal while reducing module footprint and fan power requirements. Column-resolved temperature analysis showed that the first column (at the air inlet) experienced the least cooling at inlet velocities up to 0.36 m/s, while the downstream columns experienced progressively warmer inlet air due to thermal absorption along the flow path - indicating that the maximum cell temperature is likely to occur in the final column rather than at the inlet (Voicu et al., 2015). In summary, research on staggered architectures and arranged modules aims to optimize cooling performance through spacing and airflow design.

Zhang et al. designed an air-cooling system for a supercapacitor electric bus cabin, adding 138 mm × 48 mm deflectors to account for outdoor air ingress effects (Zhang et al., 2017). Here, cooling air moved from the passenger area to the underside cabin vents. At 8.33 m/s (equivalent to 30 km/h), the redesigned enclosure temperature was reduced by 10 K relative to the baseline configuration, demonstrating improved SC module cooling.

Soltani et al. computationally and experimentally studied air cooling of a 12-cell lithium-ion capacitor (LIC) module (Soltani and Beheshti, 2021). Combining factors like fan location, air speed, and cell spacing optimized temperature uniformity, reduced peak cell temperature, and minimized parasitic fan energy consumption, as illustrated in Figures 8a,b. A right-side fan and left-side air vent increased air-cell contact area, improving heat transfer, as shown in Figure 8. Longitudinal airflow arrangements with fin configurations have also been shown to enhance cooling performance and temperature uniformity in battery modules, a principle directly applicable to SC pack design (Alzwayi and Paul, 2025). Optimal cooling effectiveness and minimum fan energy consumption were achieved at a cell spacing of 5 mm, supported by simulations and experiments with a maximum deviation of 2 K between predicted and measured temperatures, as shown in Figures 7, 8, with the corresponding LIC air cooling system illustrated in Figures 9.

5.2.2 Liquid cooling systems

Liquid cooling systems are a common active cooling approach using water, glycol-water mixtures, or other engineered coolants to transfer heat. Liquid cooling is more effective than air cooling due to the significantly higher thermal conductivity and volumetric heat capacity of liquid coolants compared to air - water, for instance, has a thermal conductivity approximately 25 times greater than air at ambient conditions. Direct contact methods immerse cells directly in a dielectric coolant, while indirect methods use thermally conductive plates, cold plates, or fin structures to transfer heat to circulating coolant, as illustrated in Figures 10a,b (Xia et al., 2014; Voicu et al., 2015). Direct cooling provides uniform temperatures providing intimate thermal contact across the entire cell surface, reducing localized temperature gradients; however, the requirement for a dielectric coolant, the risk of coolant contamination, and the associated system complexity and cost limit its practical adoption. Indirect cooling uses conductive components like copper or aluminum cold plates to create efficient heat flow paths to the coolant (Liu et al., 2017). Higher coolant flow velocity increases the convective heat transfer coefficient at the cold plate–coolant interface, while coolants with higher thermal conductivity and specific heat capacity improve overall heat dissipation per unit mass flow rate. The prismatic supercapacitor geometry is particularly compatible with cold plate insertion between adjacent cells, as shown in Figure 10c (Xia et al., 2014). Studies on liquid cooling plates with variable contact surfaces (Wang et al., 2020a; Rao et al., 2017) and phase change material nano-emulsion-based liquid cooling (Wang F. et al., 2020) has demonstrated enhanced thermal performance in battery systems. Additionally, integrated systems combining mini-channel liquid cooling and air cooling (Chen et al., 2021c; Yang et al., 2020) offer operational flexibility that could benefit supercapacitor modules.

Studies have examined the factors governing liquid cooling performance in SC and LIC applications, with a key advantage being the ability to maintain lower and more uniform cell surface temperatures than air cooling. Lithium-ion capacitors (LICs) are particularly sensitive to elevated temperatures; reference (Karimi et al., 2021a) reports an upper operating limit of 313 K for the specific LIC configuration studied, beyond which performance and longevity are significantly compromised. To address this, liquid cooling systems employ increased coolant flow velocity to raise the convective heat transfer coefficient at the cell–coolant interface, thereby enhancing heat dissipation rate. In the system examined in (Karimi et al., 2021a), a coolant inlet temperature of 303 K was adopted, representing a balance between maintaining the LIC below its upper operating limit and avoiding the need for sub-ambient coolant conditioning. Maintaining the coolant at 303 K may require a radiator or chiller depending on ambient conditions. Table 7 provides a comparative analysis of liquid, air, and PCM cooling performance metrics for SC applications. Novel liquid-cooling strategies coupling with graphene-modified silica gel (Lv et al., 2019) represent emerging directions for enhancing thermal conductivity in cooling media (Lebrouhi et al., 2022). Further insights into thermal management systems for energy storage devices, including supercapacitors and LIC cells, are summarized in Table 8. This comprehensive analysis provides a detailed comparison of various cooling strategies, emphasizing their effectiveness, limitations, and suitability for different operational conditions. The findings underscore the importance of advanced cooling solutions, such as liquid cooling, in maintaining optimal performance and preventing thermal degradation in energy storage systems.

5.3 Comparative analysis of thermal management systems and selection framework

A comparative analysis of the thermal management studies summarized in Tables 4-8, when viewed through the lens of supercapacitor and lithium-ion capacitor operation, reveals a distinct progression from simple forced convection to hybrid phase change strategies tailored for high power transient loads. The foundational work on supercapacitor specific modules, catalogued in Table 8, establishes the baseline performance expectations for air-cooling systems. The experimental and simulation efforts of Voicu et al. (2019) and Soltani et al. (2019) demonstrate that for lithium ion capacitor and supercapacitor modules, optimal forced air cooling is highly sensitive to geometric spacing and flow velocity, with optimal cell spacing identified at one point two five times the cell diameter and an effective air speed of 5 m per second. These parameters achieve a balance between minimizing pressure drop and maximizing convective heat transfer across the cylindrical cell surfaces. However, the limitation of air cooling for high power supercapacitor applications, specifically its inefficiency under sustained high rate cycling, is evident when contrasted with the liquid cooling data from Karimi et al. (2021a), where a controlled flow rate of one hundred milliliters per minute and a precise inlet temperature of 30 °C were necessary to manage the heat generated within a single lithium ion capacitor cell. This underscores the need for more aggressive thermal management as power density scales within the module.

TABLE 4. Battery and hybrid supercapacitor thermal management studies with transferable applicability to SCs.

TABLE 5. Hybrid supercapacitor systems with non-uniform thermal distribution.

TABLE 6. Battery/LIC thermal management studies (non-uniform distribution) with transferrable applicability to SCs.

PCM, refers to phase change materials used for thermal management.

TABLE 7. Comparative analysis of different thermal management systems.

TABLE 8. Research summary of thermal management for supercapacitor and LIC cells (2014–2025).

The integration of phase change materials into supercapacitor and lithium-ion capacitor modules, as detailed in Table 8 and further contextualized by the transferable hybrid architectures in Table 5, addresses the specific thermal capacitance deficit identified in purely active cooling systems. The work of Jaguemont et al. (2019) and Karimi et al. (2020) specifically validates phase change material application on lithium-ion capacitor modules, highlighting that while the addition of an aluminum mesh enhances effective thermal conductivity, the optimal phase change material thickness for balancing cost against thermal buffering performance is approximately 7 mm. This finding is critical for supercapacitor pack designers who must operate within tight volumetric constraints. The limitation of phase change material only systems, namely, the low intrinsic thermal conductivity cited in Table 7, is directly countered by the high conductivity composite approach described by Cao et al. (2020) in Table 5, where an expanded graphite composite achieving ten point 8 W per m K provides a validated pathway for maintaining supercapacitor temperature uniformity during the peak shaving events characteristic of regenerative braking. This is complemented by the honeycomb cooling geometry from Zhuang et al. (2021) shown in Table 6, which achieves uniform temperature distribution solely through architecture independent of cell chemistry, making it directly applicable to cylindrical supercapacitor packs where minimizing variation in equivalent series resistance is paramount for extending operational life.

The most effective thermal management for supercapacitors, however, emerges from the hybrid systems detailed in Table 8, specifically the combined phase change material and heat pipe configuration investigated by Karimi et al. (2021c). This approach directly leverages the latent heat capacity of phase change materials to absorb high magnitude short duration thermal pulses while utilizing heat pipes for efficient transport to a distal heat sink. The reported outcomes, a thirty five percent reduction in peak temperature and an eighty six percent reduction in temperature nonuniformity within the lithium-ion capacitor module, represent a substantial improvement over single method approaches and align precisely with the duty cycle demands of supercapacitor applications characterized by high power bursts followed by lower power rest periods. A practical selection framework for supercapacitor thermal management therefore centers on the power profile of the application. For low-cost maintenance sensitive installations where power bursts are infrequent, the staggered air-cooling parameters established by Voicu et al. (2019) in Table 8 remain a valid and easily implemented benchmark. For modules subjected to continuous high rate cycling or rapid charge discharge transients, the liquid and phase change material hybrid methodology, informed by the flow rate optimization of Karimi et al. (2021a) and the composite conductivity enhancements of Cao et al. (2020), offers a validated and chemistry agnostic template for ensuring supercapacitor longevity and performance stability without the complexity risks associated with full immersion battery thermal management systems.

Based on our comprehensive analysis shown in Table 9, we propose a decision-making framework to guide researchers and engineers in selecting the optimal thermal management approach for specific supercapacitor applications:

TABLE 9. Multi-parameter comparison of thermal management approaches.

5.4 Hybrid systems analysis

Review of the available literature on hybrid SC thermal management systems identifies three promising combinations, as discussed below:

• PCM-Heat Pipe Hybrids: Combine the temperature uniformity advantages of PCMs with the rapid response and high heat transfer capabilities of heat pipes. 35% lower peak cell temperatures and 86% reduction in temperature non-uniformity compared to PCM-only cooling (Karimi et al., 2021c). Thermal uniformity performance of hybrid systems using PCM and cooling plates arranged in honeycomb patterns (Zhuang et al., 2021) further illustrates the potential of geometric optimization.
• PCM-Enhanced Forced Air Systems: Integrate phase change materials into forced-air cooling channels to buffer temperature fluctuations while maintaining system simplicity. Studies have reported improvements in cooling effectiveness with reduced temperature excursions compared to forced air alone.
• Liquid-Air Dual Mode Systems: Offer operational flexibility by switching between liquid cooling (for high-power transients) and air cooling (during steady-state or low-power operation), potentially reducing overall parasitic energy consumption compared to continuously active liquid cooling.

6 Research gaps and future directions

The synthesis presented in this review identifies the following specific research gaps and corresponding future directions.

• Molecular-level degradation mechanisms: Despite extensive characterization of macroscopic performance metrics, the reaction pathways by which thermal stress converts electrolyte and electrode materials into degradation products remain poorly understood at the molecular level. The evidence motivating this gap is concrete: post-mortem porosimetry by Bitt et al. (2012) identified pore blockage by decomposition products as the dominant capacitance-loss mechanism, yet the chemical identity of those products has not been established for organic electrolyte EDLCs under thermal stress. The measurable milestone that would close this gap is identification and quantification of at least the three most abundant interfacial reaction products formed during 1,000-cycle thermal cycling between 298 K and 343 K in TEABF₄/ACN electrolyte systems, with rate constants measured by in-situ Raman spectroscopy and X-ray photoelectron spectroscopy at temperature. Until equivalent SC-specific data exist, lifetime models based on Arrhenius extrapolation cannot be validated against mechanistic degradation chemistry.
• Long-term thermal ageing under realistic operating conditions: Most reviewed ageing studies employ accelerated stress tests at constant elevated temperature or voltage. The specific gap is this: the longest SC calendar aging studies identified in this review span 12–18 months at constant stress (Kötz et al., 2010), whereas the Arrhenius rule is routinely used to project 10–15-year lifetimes, an extrapolation of nearly an order of magnitude beyond validated data. The measurable milestone would be a validated Arrhenius model with no more than ±15% error in capacitance retention prediction over a 3-year dynamic cycling protocol that replicates a published EV drive-cycle heat-generation profile (Atayo et al., 2025b). Battery aging templates (EUCAR (Ayadi et al., 2013) and IEC 62660–2) specify dynamic discharge profiles adaptable for SC thermal aging characterization.
• Standardized thermal performance evaluation protocols: The absence of agreed test protocols means that temperature reduction, capacitance retention, and ESR metrics reported across the reviewed studies are not directly comparable: for example, peak temperature reductions reported for heat pipe cooling range from 7.5% to 11.7% (Karimi et al., 2021b) and for hybrid PCM-heat pipe systems reach 35% (Karimi et al., 2021c), but these figures were obtained under different cell geometries, ambient temperatures, and power inputs, making direct comparison unreliable. A preliminary framework could specify: (a) cell geometry category (cylindrical, prismatic, pouch), (b) thermal boundary conditions (adiabatic, natural convection baseline, or defined fixed-temperature boundary), (c) charge/discharge rate expressed as multiples of rated current, (d) number of cycles before measurement, and (e) measurement timing relative to end of last discharge. This would be analogous in structure to IEC 62576, which governs SC electrical characterization, and could be developed as a complementary standard.
• Thermally conductive and electrically insulating interface materials: The specific gap motivating this direction is quantitative: the thermal interface resistance between SC cells and aluminum cold plates is estimated at 10–50 K cm²/W for commercially available silicone-based pads (Liu et al., 2017), which is comparable in magnitude to the cell-level thermal resistance itself and therefore a first-order contributor to pack-level temperature non-uniformity. No SC-specific characterization of interface material degradation under combined thermal cycling and electrolyte exposure has been reported. Emerging candidates including boron nitride-filled polymer composites (thermal conductivity 3–5 W m^-1 K⁻¹), ceramic-filled epoxy films, and graphene-reinforced elastomers have been evaluated for lithium-ion battery applications (Liu et al., 2017), not for SC module integration. The measurable milestone would be a thermal interface material demonstrating: thermal conductivity ≥3 W m^-1 K⁻¹, volume resistivity ≥10¹² Ω cm, less than 10% change in either property after 500 thermal cycles between 253 K and 358 K, and no measurable electrochemical reaction in contact with 1 M TEABF4/ACN electrolyte over 1,000 h at 333 K.
• Hybrid and adaptive thermal management systems. The reviewed literature demonstrates that hybrid PCM and heat pipe systems outperform either approach alone, but systematic design optimization frameworks for hybrid configurations are lacking. Future work should develop physics-based design tools that co-optimize PCM melting point, layer thickness, heat pipe geometry, and condenser configuration as a coupled system rather than independently. Adaptive control strategies that modulate active cooling intensity based on real-time temperature and state-of-health estimates represent a further unexplored direction. Liquid cooling with phase change materials for cylindrical cells (Cao et al., 2020) composite PCM and liquid cooling under high ambient temperature (Xin et al., 2022), and thermal management using hybrid nanofluid and non-enhanced PCM (Al-Rashed, 2022) represents promising research directions that could be translated to supercapacitor applications.
• Non-invasive in-situ temperature distribution measurement. The motivating evidence for this gap is direct: the electrode is the dominant thermal resistance in SC stacks (Table 2, (Divakar, 2016; Qin et al., 2018)), yet all thermal management studies reviewed here measure surface temperature only. Internal temperature gradients within cells, which drive the fastest-aging regions of the electrode are inferred from models rather than measured. Acoustic emission methods have detected electrolyte decomposition events in batteries in real time (Ramos et al., 2025), and the same principle applies to gas evolution in SC cells. The measurable milestone would be FBG-based internal temperature mapping of a 20-cell prismatic SC module during 5C charge-discharge cycling, with spatial resolution ≤ 5 mm and agreement with a validated 3D thermal model within ±2 K at all measurement points.

7 Conclusion

This review has examined the thermal challenges facing supercapacitors and evaluated the current state of thermal management strategies developed to address them.

Temperature exerts a pervasive influence on SC performance through multiple concurrent mechanisms. At the component level, elevated temperatures accelerate electrolyte decomposition, increase ESR through oxide formation at current collector interfaces, promote pore blocking by solid decomposition products, and raise internal gas pressure. At the system level, these effects manifest as accelerated capacitance fade, increased self-discharge rates, and reduced calendar lifetime, with the Arrhenius-based rule predicting an approximately twofold reduction in lifetime per 10 K increase above the rated operating temperature. At low temperatures, increased electrolyte viscosity and reduced ionic conductivity limit accessible capacitance and power density, creating a bidirectional thermal management challenge.

Among passive thermal management strategies, PCM-based systems offer cost-effective temperature buffering and excellent temperature uniformity, but their low intrinsic thermal conductivity (typically 0.1–0.3 W m^-1 K⁻¹) limits heat transfer rates and requires enhancement through metal mesh, foam infiltration, or fin structures. Heat pipes provide near-isothermal heat transport with no parasitic energy consumption, achieving 7.5%–11.7% reduction in peak cell temperature and 2.1% improvement in capacitance retention compared to natural convection (Karimi et al., 2021b), though their performance depends critically on cell geometry and thermal contact quality. Hybrid passive systems combining PCMs and heat pipes have demonstrated approximately 35% lower peak cell temperatures and 86% lower temperature non-uniformity than PCM-only cooling (Karimi et al., 2021c), representing the most thermally effective passive configuration identified in the reviewed literature.

Among active strategies, liquid cooling offers the highest heat removal capacity and is necessary for high-power-density applications, but introduces system complexity, sealing requirements, and parasitic energy costs. Forced air convection provides a practical intermediate solution with lower complexity, though achieving uniform airflow across multi-cell modules requires careful duct geometry optimization. The comparative analysis in Table 7 confirms that no single thermal management approach is universally optimal; selection depends on the specific combination of power density, available volume, cost constraints, and operating temperature range of the target application.

Three critical research gaps constrain further progress. First, molecular-level understanding of thermally driven electrolyte degradation mechanisms, particularly the identity and electrochemical impact of interfacial reaction products, remains incomplete. Second, standardized protocols for SC thermal performance evaluation are absent, making cross-study comparison unreliable. Third, cost-effective thermally conductive and electrically insulating interface materials optimized specifically for SC module integration are not yet commercially available.

Future work should focus on hybrid thermal management that exploits the complementary strengths of passive and active approaches, advanced electrolyte and electrode materials with extended thermal stability windows, and co-design frameworks that integrate supercapacitor architecture with cooling strategy optimization.

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Footnotes

Edited by: Omid Mahian, Xi’an Jiaotong University, China

Reviewed by: Jianfei Zhang, Xi’an Jiaotong University, China

Ram Kumar Pal, University of Central Florida, United States