A Comprehensive Review on Different Types of PCM Used in BTMS

1. Introduction

1.1. Background and Significance

The rapid electrification of transportation systems has positioned electric vehicles (EVs) as the cornerstone of sustainable mobility, with the global EV market projected to expand at a compound annual growth rate (CAGR) of 23.1% from 2023 to 2030 [8]. This exponential growth is driving unprecedented demand for advanced battery thermal management solutions, as lithium-ion batteries—the dominant energy storage technology in EVs—exhibit significant sensitivity to operating temperatures. Research has demonstrated that these batteries experience 3–8% capacity degradation for every 10°C increase above their optimal temperature range (typically 20–40°C), highlighting the critical need for precise thermal regulation [9,10]. Traditional active cooling systems, such as liquid or air cooling, while effective, introduce substantial weight penalties (5–15% of total battery pack mass) and consume 3–5% of the battery's total energy output [11]. These limitations have spurred intense interest in passive cooling alternatives, particularly phase change materials (PCMs), which offer energy-efficient thermal management without moving parts or significant parasitic power losses.

1.2. PCM Fundamentals

Phase change materials represent a paradigm shift in thermal energy storage, capable of storing 5–14 times more thermal energy per unit volume than conventional sensible heat materials through isothermal phase transitions [12]. This exceptional energy density arises from the latent heat absorbed or released during phase changes (typically solid-liquid transitions), enabling PCMs to maintain nearly constant temperatures during operation. The three primary PCM categories—inorganic, organic, and composite materials—each exhibit distinct thermophysical properties that dictate their suitability for battery thermal management systems (BTMS).

1.3. Inorganic PCMs

Inorganic PCMs, particularly salt hydrates like calcium chloride hexahydrate (CaCl₂·6H₂O), offer compelling advantages including high thermal conductivity (0.5–1.5 W/mK) and substantial latent heat capacity (180–300 kJ/kg) [13]. However, these materials are plagued by technical challenges such as supercooling (where liquids remain metastable below their freezing point by 5–15°C), phase segregation (non-uniform distribution of components during cycling), and corrosive tendencies that can compromise battery components [14].

1.4. Organic PCMs

Organic PCMs, encompassing paraffin waxes (C₁₈–C₂₈ alkanes) and fatty acids, address many of these limitations through excellent chemical stability, minimal supercooling (<2°C), and compatibility with battery materials [15]. Their principal drawback lies in relatively low intrinsic thermal conductivity (0.1–0.3 W/mK), which can impede heat dissipation rates during high-power operation [16].

1.5. Composite PCMs

Composite PCMs have emerged as a sophisticated solution, combining the advantageous properties of both material classes. For instance, paraffin-expanded graphite composites demonstrate thermal conductivity enhancements of 10–30 times (reaching 2–8 W/mK) while maintaining shape stability with less than 3% leakage after 1000 thermal cycles [17,18]. These engineered materials achieve this performance through carefully designed microstructures where the graphite matrix provides continuous thermal pathways while the paraffin serves as the energy storage medium.

Hybrid Systems and Safety Enhancements

Hybrid cooling systems that integrate PCMs with active methods (e.g., air or liquid cooling) have shown exceptional promise. Studies indicate that these systems can maintain battery temperatures within a narrow range of ±1.5–2°C, while reducing energy consumption by up to 50% compared to standalone active cooling. Furthermore, fire-retardant PCM composites and salt hydrate/polyurethane foam combinations have demonstrated the ability to delay thermal runaway propagation by up to 15 minutes, significantly enhancing safety in high-stress scenarios.

2. Review

Table 1. Analysis of PCM Materials and Characteristics.

Modification/Novelty	Remark	Key Numerical Findings	Type of Study	Method Used	Reference
Hydrated salt with nucleating agents	Improved thermal stability for building applications by preventing phase separation.	Latent heat: ~150–250 kJ/kg; Temp. range: 20–80°C	Experimental	DSC analysis	[44]
Salt hydrates with thickening agents	Reduced supercooling in salt hydrates, enhancing reliability for thermal storage.	Organic PCM latent heat: 100–200 kJ/kg; Melting pt: 20–60°C	Review	Literature survey	[45]
Eutectic salt mixtures	High energy density and tailored melting points for diverse applications.	Paraffin wax: 200–250 kJ/kg; Salt hydrate: ~170–280 kJ/kg	Review	Comparative analysis	[46]
Metal-based PCM encapsulation	Enhanced thermal conductivity using metal matrices, ideal for rapid heat transfer.	Thermal conductivity typically < 0.5 W/m·K	Experimental	Thermal cycling	[47]
Graphite-enhanced salts	Improved heat transfer via graphite additives, reducing charging/discharging times.	Paraffin: Latent heat = 200–220 kJ/kg; Conductivity ~0.2–0.5 W/m·K	Review	Numerical modeling	[48]
Fatty acid eutectics	High latent heat and stability, suitable for solar energy storage.	Latent heat range: 150–250 kJ/kg	Experimental	DSC/TGA	[49]
Palmitic acid with carbon fibers	Enhanced conductivity while maintaining high energy storage capacity.	Latent heat = 186.8 kJ/kg; Melting pt = 63.3°C	Experimental	Heat flux method	[50]
Binary fatty acid mixtures	Tunable melting points for customized thermal management solutions.	Heat of fusion: 150–200 kJ/kg	Experimental	Thermal analysis	[51]
Polymer-PCM microcapsules	Shape stabilization prevents leakage and improves handling.	Microencapsulation size: 1–100 μm	Review	Microscopy/SEM	[52]
Nanoencapsulated paraffin	Leakage prevention via nanocapsules, enabling durable PCM integration.	Capsule size: ~300 nm; Latent heat: ~220 kJ/kg	Experimental	Emulsion polymerization	[53]
Ag nanoparticle doping	High thermal conductivity (4× enhancement) with minimal PCM loading.	Conductivity ↑ to 0.87 W/m·K; Latent heat: 135.8 kJ/kg	Experimental	TEM/XRD	[54]
Graphene aerogel support	Lightweight & stable composite with efficient light-to-thermal conversion.	Conductivity ↑ 5.19 W/m·K; Latent heat ~200 kJ/kg	Experimental	FTIR/Raman	[55]
Graphite nanoplates	Reduced supercooling and improved heat diffusion in PCMs.	Conductivity ↑ from 0.2 to 1.5 W/m·K	Experimental	Laser flash analysis	[56]
CNT-enhanced perlite/PCM	High energy retention (96%) after 1000 thermal cycles.	Conductivity ↑ by ~400%; Stability for 200 cycles	Experimental	Hot disk method	[57]
Expanded graphite matrix	No leakage and 80% higher conductivity than pure paraffin.	Conductivity ↑ 10x; Latent heat: ~170–190 kJ/kg	Experimental	SEM/DSC	[58]
Attapulgite clay support	Shape-stabilized PCM with 90% latent heat retention.	Latent heat: 154.2 kJ/kg; Melting pt: 24.6°C	Experimental	XRD/TGA	[59]
In situ Cu doping	3× higher conductivity than pure PEG/SiO₂ composites.	Conductivity ↑ to 0.56 W/m·K; Latent heat: ~90 kJ/kg	Experimental	Laser flash method	[60]
Activated carbon support	High absorption capacity (70 wt% PCM) with no leakage.	Conductivity ↑ 3.5x; Latent heat: ~155 kJ/kg	Experimental	BET/DSC	[61]
Expanded graphite composite	Stable performance over 500 melt-freeze cycles.	Conductivity ↑ from 0.24 to 2.32 W/m·K	Experimental	Thermal cycling	[62]
Cement-based PCM composite	Building-integrated thermal storage with 30% energy savings.	Latent heat: ~163.1 kJ/kg; Thermal cycle stability: >100 cycles	Experimental	Thermal simulation	[63]
Ternary acid/expanded perlite	High capacity (145 J/g) and stable up to 100°C.	Latent heat: ~162.8 kJ/kg; Form-stable	Experimental	DSC analysis	[64]
Metal foam integration	Rapid charging (2× faster) due to enhanced conductivity.	Conductivity ↑ to 4.2 W/m·K	Experimental	Infrared thermography	[65]
Seasonal solar storage	Year-round usability with 85% solar energy efficiency.	Latent heat: ~200 kJ/kg; Low leakage	Experimental	Thermal cycling	[66]
Microencapsulated n-eicosane	Leak-proof design with 98% encapsulation efficiency.	Capsule size: 1–10 µm; Latent heat = 247 kJ/kg	Experimental	SEM/DSC	[67]
Cellulose matrix	Biodegradable PCM with 120 J/g latent heat.	Melting pt: ~38.5°C; Latent heat: 134.5 kJ/kg	Experimental	FTIR/TGA	[68]
Mesoporous silica	High loading capacity (75 wt%) without leakage.	Conductivity ↑ ~3x; Good shape stability	Experimental	BET/DSC	[69]
Electrospun fibers	Flexible PCM textiles for wearable thermal regulation.	Melting range: ~32–43°C; Fiber diameter: ~300 nm	Experimental	SEM/TGA	[70]
PEG/cellulose blend	Biocompatible fibers for medical thermal therapy.	Fiber diameter: 300–800 nm; Latent heat: ~80–120 kJ/kg	Experimental	Electrospinning	[71]
PMMA microencapsulation	Long-term stability (>5 years) under thermal cycling.	Capsule size: 10–50 µm; Latent heat: ~200–240 kJ/kg	Experimental	SEM/DSC	[72]
Sol-gel encapsulation	High durability against oxidation and moisture.	Particle size: 100–600 nm; Latent heat: ~210 kJ/kg	Experimental	TEM/DSC	[73]

Table 1. Analysis of PCM Materials and Characteristics.

Modification/Novelty	Remark	Key Numerical Findings	Type of Study	Method Used	Reference
Hydrated salt with nucleating agents	Improved thermal stability for building applications by preventing phase separation.	Latent heat: ~150–250 kJ/kg; Temp. range: 20–80°C	Experimental	DSC analysis	[44]
Salt hydrates with thickening agents	Reduced supercooling in salt hydrates, enhancing reliability for thermal storage.	Organic PCM latent heat: 100–200 kJ/kg; Melting pt: 20–60°C	Review	Literature survey	[45]
Eutectic salt mixtures	High energy density and tailored melting points for diverse applications.	Paraffin wax: 200–250 kJ/kg; Salt hydrate: ~170–280 kJ/kg	Review	Comparative analysis	[46]
Metal-based PCM encapsulation	Enhanced thermal conductivity using metal matrices, ideal for rapid heat transfer.	Thermal conductivity typically < 0.5 W/m·K	Experimental	Thermal cycling	[47]
Graphite-enhanced salts	Improved heat transfer via graphite additives, reducing charging/discharging times.	Paraffin: Latent heat = 200–220 kJ/kg; Conductivity ~0.2–0.5 W/m·K	Review	Numerical modeling	[48]
Fatty acid eutectics	High latent heat and stability, suitable for solar energy storage.	Latent heat range: 150–250 kJ/kg	Experimental	DSC/TGA	[49]
Palmitic acid with carbon fibers	Enhanced conductivity while maintaining high energy storage capacity.	Latent heat = 186.8 kJ/kg; Melting pt = 63.3°C	Experimental	Heat flux method	[50]
Binary fatty acid mixtures	Tunable melting points for customized thermal management solutions.	Heat of fusion: 150–200 kJ/kg	Experimental	Thermal analysis	[51]
Polymer-PCM microcapsules	Shape stabilization prevents leakage and improves handling.	Microencapsulation size: 1–100 μm	Review	Microscopy/SEM	[52]
Nanoencapsulated paraffin	Leakage prevention via nanocapsules, enabling durable PCM integration.	Capsule size: ~300 nm; Latent heat: ~220 kJ/kg	Experimental	Emulsion polymerization	[53]
Ag nanoparticle doping	High thermal conductivity (4× enhancement) with minimal PCM loading.	Conductivity ↑ to 0.87 W/m·K; Latent heat: 135.8 kJ/kg	Experimental	TEM/XRD	[54]
Graphene aerogel support	Lightweight & stable composite with efficient light-to-thermal conversion.	Conductivity ↑ 5.19 W/m·K; Latent heat ~200 kJ/kg	Experimental	FTIR/Raman	[55]
Graphite nanoplates	Reduced supercooling and improved heat diffusion in PCMs.	Conductivity ↑ from 0.2 to 1.5 W/m·K	Experimental	Laser flash analysis	[56]
CNT-enhanced perlite/PCM	High energy retention (96%) after 1000 thermal cycles.	Conductivity ↑ by ~400%; Stability for 200 cycles	Experimental	Hot disk method	[57]
Expanded graphite matrix	No leakage and 80% higher conductivity than pure paraffin.	Conductivity ↑ 10x; Latent heat: ~170–190 kJ/kg	Experimental	SEM/DSC	[58]
Attapulgite clay support	Shape-stabilized PCM with 90% latent heat retention.	Latent heat: 154.2 kJ/kg; Melting pt: 24.6°C	Experimental	XRD/TGA	[59]
In situ Cu doping	3× higher conductivity than pure PEG/SiO₂ composites.	Conductivity ↑ to 0.56 W/m·K; Latent heat: ~90 kJ/kg	Experimental	Laser flash method	[60]
Activated carbon support	High absorption capacity (70 wt% PCM) with no leakage.	Conductivity ↑ 3.5x; Latent heat: ~155 kJ/kg	Experimental	BET/DSC	[61]
Expanded graphite composite	Stable performance over 500 melt-freeze cycles.	Conductivity ↑ from 0.24 to 2.32 W/m·K	Experimental	Thermal cycling	[62]
Cement-based PCM composite	Building-integrated thermal storage with 30% energy savings.	Latent heat: ~163.1 kJ/kg; Thermal cycle stability: >100 cycles	Experimental	Thermal simulation	[63]
Ternary acid/expanded perlite	High capacity (145 J/g) and stable up to 100°C.	Latent heat: ~162.8 kJ/kg; Form-stable	Experimental	DSC analysis	[64]
Metal foam integration	Rapid charging (2× faster) due to enhanced conductivity.	Conductivity ↑ to 4.2 W/m·K	Experimental	Infrared thermography	[65]
Seasonal solar storage	Year-round usability with 85% solar energy efficiency.	Latent heat: ~200 kJ/kg; Low leakage	Experimental	Thermal cycling	[66]
Microencapsulated n-eicosane	Leak-proof design with 98% encapsulation efficiency.	Capsule size: 1–10 µm; Latent heat = 247 kJ/kg	Experimental	SEM/DSC	[67]
Cellulose matrix	Biodegradable PCM with 120 J/g latent heat.	Melting pt: ~38.5°C; Latent heat: 134.5 kJ/kg	Experimental	FTIR/TGA	[68]
Mesoporous silica	High loading capacity (75 wt%) without leakage.	Conductivity ↑ ~3x; Good shape stability	Experimental	BET/DSC	[69]
Electrospun fibers	Flexible PCM textiles for wearable thermal regulation.	Melting range: ~32–43°C; Fiber diameter: ~300 nm	Experimental	SEM/TGA	[70]
PEG/cellulose blend	Biocompatible fibers for medical thermal therapy.	Fiber diameter: 300–800 nm; Latent heat: ~80–120 kJ/kg	Experimental	Electrospinning	[71]
PMMA microencapsulation	Long-term stability (>5 years) under thermal cycling.	Capsule size: 10–50 µm; Latent heat: ~200–240 kJ/kg	Experimental	SEM/DSC	[72]
Sol-gel encapsulation	High durability against oxidation and moisture.	Particle size: 100–600 nm; Latent heat: ~210 kJ/kg	Experimental	TEM/DSC	[73]

This table provides a categorized overview of PCM types—inorganic, organic, and composite—with details on their materials, methods used, thermal behaviour, advantages, and limitations. It aims to highlight key differences in performance and practicality for thermal energy storage and battery thermal management systems. The comparative analysis of materials used as phase change materials (PCMs) for thermal energy storage in building applications reveals that organic PCMs like paraffins and fatty acids are preferred due to their chemical stability, non-corrosiveness, and wide melting temperature ranges. Inorganic PCMs, such as salt hydrates, offer higher latent heat values but face issues like phase separation and subcooling. Recent developments in composite PCMs, such as those using expanded graphite, carbon nanotubes, and metal foams, significantly enhance thermal conductivity while maintaining structural integrity.

Encapsulation techniques and shape-stabilized composites have advanced the practical usability of PCMs by preventing leakage and improving heat transfer performance. Additionally, fatty acid eutectics and biocompatible materials are emerging as sustainable and tunable solutions for targeted temperature applications.

Comparison of Latent Heats of different PCM Materials

Table 2. Latent Heat of different PCM Materials.

Serial Number (Sr No.)	PCM Materials	Latent Heat
1	Hydrated salt with nucleating agents	250 kJ/kg
2	Salt hydrates with thickening agents	200 kJ/kg
3	Eutectic salt mixtures	250 kJ/kg
4	Graphite-enhanced salts	220 kJ/kg
5	Fatty acid eutectics	250 kJ/kg
6	Palmitic acid with carbon fibers	186.8 kJ/kg
7	Binary fatty acid mixtures	200 kJ/kg
8	Polymer-PCM microcapsules	200 kJ/kg
9	Nanoencapsulated paraffin	220 kJ/kg
10	Ag nanoparticle doping	135.8 kJ/kg
11	Graphene aerogel support	200 kJ/kg
12	Expanded graphite matrix	190 kJ/kg
13	Attapulgite clay support	154.2 kJ/kg
14	In situ Cu doping	90 kJ/kg
15	Activated carbon support	155 kJ/kg
16	Cement-based PCM composite	163.1 kJ/kg
17	Ternary acid/expanded perlite	162.8 kJ/kg
18	Seasonal solar storage	200 kJ/kg
19	Microencapsulated n-eicosane	247 kJ/kg
20	Cellulose matrix	134.5 kJ/kg
21	PEG/cellulose blend	120 kJ/kg
22	PMMA microencapsulation	240 kJ/kg
23	Sol-gel encapsulation	210 kJ/kg

Table 2. Latent Heat of different PCM Materials.

Serial Number (Sr No.)	PCM Materials	Latent Heat
1	Hydrated salt with nucleating agents	250 kJ/kg
2	Salt hydrates with thickening agents	200 kJ/kg
3	Eutectic salt mixtures	250 kJ/kg
4	Graphite-enhanced salts	220 kJ/kg
5	Fatty acid eutectics	250 kJ/kg
6	Palmitic acid with carbon fibers	186.8 kJ/kg
7	Binary fatty acid mixtures	200 kJ/kg
8	Polymer-PCM microcapsules	200 kJ/kg
9	Nanoencapsulated paraffin	220 kJ/kg
10	Ag nanoparticle doping	135.8 kJ/kg
11	Graphene aerogel support	200 kJ/kg
12	Expanded graphite matrix	190 kJ/kg
13	Attapulgite clay support	154.2 kJ/kg
14	In situ Cu doping	90 kJ/kg
15	Activated carbon support	155 kJ/kg
16	Cement-based PCM composite	163.1 kJ/kg
17	Ternary acid/expanded perlite	162.8 kJ/kg
18	Seasonal solar storage	200 kJ/kg
19	Microencapsulated n-eicosane	247 kJ/kg
20	Cellulose matrix	134.5 kJ/kg
21	PEG/cellulose blend	120 kJ/kg
22	PMMA microencapsulation	240 kJ/kg
23	Sol-gel encapsulation	210 kJ/kg

Graph 1.Comparison of Latent Heat.

Table 2. Experimental and Review-based Configurations in PCM Research.

PCM Type	Configuration / Composite	Modification / Novelty	Key Findings	Methods Used	Model	Reference
Organic (Paraffin)	Paraffin integrated with copper foam	Enhanced thermal conductivity through copper foam integration	Improved heat dissipation and temperature uniformity in battery modules	Thermal performance testing		[1]
Organic (Paraffin)	Paraffin combined with NiTi Shape Memory Alloy (SMA)	Smart BTMS with SMA-actuated switching mechanism	Reduced battery temperature rise by 4.63°C at 3C and 6.1°C at 5C discharge rates	Electrochemical-thermal modeling		[2]
Composite (Paraffin + Graphite)	Composite PCM with graphite fins	Integration of graphite fins to enhance thermal conductivity	Achieved better cooling performance and temperature uniformity in EV batteries	CFD simulation and thermal analysis		[3]
Composite (Paraffin + Metal Foam)	PCM integrated with metal foam structures	Use of metal foam to improve heat transfer rates	Enhanced thermal management across various environmental temperatures	Thermal cycling tests		[4]
Composite (Paraffin + EG)	Liquid cooling combined with composite PCM containing EG	Segmented layout with varying EG contents for optimized heat transfer	Reduced maximum temperature and temperature difference; improved cooling efficiency	CFD modeling		[5]
Various PCMs	Review of PCMs in BTMS for electric and hybrid vehicles	Comprehensive analysis of different PCM materials and their applications	Identified suitable PCMs for various BTMS configurations; highlighted challenges and future directions	Literature survey		[6]
Composite (Paraffin + Graphene Oxide)	PCM enhanced with graphene oxide nanoparticles	Improved thermal conductivity through graphene oxide addition	Achieved better thermal regulation and battery performance	Thermal analysis and simulations		[7]
Inorganic (Calcium Chloride Hexahydrate)	Inorganic composite PCM for medium-temperature storage	Development of stable inorganic PCM for thermal storage applications	Demonstrated effective thermal storage capabilities with improved stability	Synthesis and characteristic analysis		[8]
Inorganic (Calcium Chloride Hexahydrate)	Composite PCM for high-power battery cooling	Focus on leakage prevention and thermal stability	Enhanced thermal management with improved safety features	Thermal performance evaluation		[10]
Inorganic (Magnesium Nitrate Hexahydrate)	PCM for thermal management of LiFePO₄ batteries	Application of magnesium nitrate hexahydrate as PCM	Effective temperature control and improved battery safety	Thermal analysis and battery testing		[11]

Table 2. Experimental and Review-based Configurations in PCM Research.

PCM Type	Configuration / Composite	Modification / Novelty	Key Findings	Methods Used	Model	Reference
Organic (Paraffin)	Paraffin integrated with copper foam	Enhanced thermal conductivity through copper foam integration	Improved heat dissipation and temperature uniformity in battery modules	Thermal performance testing		[1]
Organic (Paraffin)	Paraffin combined with NiTi Shape Memory Alloy (SMA)	Smart BTMS with SMA-actuated switching mechanism	Reduced battery temperature rise by 4.63°C at 3C and 6.1°C at 5C discharge rates	Electrochemical-thermal modeling		[2]
Composite (Paraffin + Graphite)	Composite PCM with graphite fins	Integration of graphite fins to enhance thermal conductivity	Achieved better cooling performance and temperature uniformity in EV batteries	CFD simulation and thermal analysis		[3]
Composite (Paraffin + Metal Foam)	PCM integrated with metal foam structures	Use of metal foam to improve heat transfer rates	Enhanced thermal management across various environmental temperatures	Thermal cycling tests		[4]
Composite (Paraffin + EG)	Liquid cooling combined with composite PCM containing EG	Segmented layout with varying EG contents for optimized heat transfer	Reduced maximum temperature and temperature difference; improved cooling efficiency	CFD modeling		[5]
Various PCMs	Review of PCMs in BTMS for electric and hybrid vehicles	Comprehensive analysis of different PCM materials and their applications	Identified suitable PCMs for various BTMS configurations; highlighted challenges and future directions	Literature survey		[6]
Composite (Paraffin + Graphene Oxide)	PCM enhanced with graphene oxide nanoparticles	Improved thermal conductivity through graphene oxide addition	Achieved better thermal regulation and battery performance	Thermal analysis and simulations		[7]
Inorganic (Calcium Chloride Hexahydrate)	Inorganic composite PCM for medium-temperature storage	Development of stable inorganic PCM for thermal storage applications	Demonstrated effective thermal storage capabilities with improved stability	Synthesis and characteristic analysis		[8]
Inorganic (Calcium Chloride Hexahydrate)	Composite PCM for high-power battery cooling	Focus on leakage prevention and thermal stability	Enhanced thermal management with improved safety features	Thermal performance evaluation		[10]
Inorganic (Magnesium Nitrate Hexahydrate)	PCM for thermal management of LiFePO₄ batteries	Application of magnesium nitrate hexahydrate as PCM	Effective temperature control and improved battery safety	Thermal analysis and battery testing		[11]

This table summarizes various experimental and review studies involving PCM materials in combination with heat transfer enhancements such as metal foams, nanoparticles, and hybrid systems. It includes the type of PCM, modification approach, method used, resultant impact, and the nature of the study (Experimental or Review).reveals a strong emphasis on enhancing thermal conductivity and safety via composite formulations. Metal and carbon-based foams (aluminium, copper, graphite) are effective in improving heat transfer and reducing peak battery temperature. Nanoparticle-infused systems demonstrate substantial gains in conductivity and reliability. Review studies affirm that hybrid approaches combining structure + PCM yield promising results for real-world deployment.

3. Discussion

The analysis of these research studies on phase change materials (PCMs) for battery thermal management systems reveals several significant findings. Organic PCMs like paraffin, when combined with materials such as expanded graphite, demonstrate excellent temperature reduction capabilities, lowering battery temperatures by 8°C at high 3C discharge rates. Composite PCMs show particular promise, with paraffin/aluminum foam combinations improving heat dissipation by 50% and carbon nanotube-enhanced PCMs achieving thermal conductivities up to 4.7 W/mK for faster heat transfer. Hybrid systems that integrate PCMs with active cooling methods, such as forced air or mini-channel cooling, stand out for their superior performance, maintaining temperature uniformity within ±1.5-2°C while reducing energy consumption by 50% compared to conventional active cooling alone.

Safety enhancements represent another critical advantage of PCM applications, with fire-retardant composites successfully delaying thermal runaway propagation by 15 minutes in experimental tests. Flexible PCM solutions, including salt hydrate/PU foam composites, address packaging challenges by maintaining structural integrity under deformation while preventing leakage. From a practical implementation perspective, PCM/aluminum tube hybrid designs offer scalable solutions for electric vehicle battery packs, though challenges remain in optimizing costs and weights for commercial viability.

3.1. Conclusion on PCM Applications in Battery Thermal Management Systems

The analysis of current research demonstrates that phase change materials (PCMs) offer significant advantages for battery thermal management systems (BTMS) in electric vehicles and energy storage applications. Organic PCMs, particularly paraffin-based composites, have shown excellent thermal regulation capabilities, with studies reporting temperature reductions of up to 8°C at high 3C discharge rates (Ling et al., 2014). Composite PCMs enhanced with materials like expanded graphite or aluminum foam have demonstrated 50% improvements in heat dissipation compared to conventional systems (Rao et al., 2011).

Hybrid cooling systems that combine PCMs with active cooling methods represent a particularly promising approach. Research by Sabbah et al. (2008) and Ling et al. (2015) has shown these hybrid systems can maintain exceptional temperature uniformity (±1.5-2°C) while reducing energy consumption by 50% compared to traditional active cooling alone. For safety-critical applications, fire-retardant PCM composites have proven effective at delaying thermal runaway propagation by 15 minutes or more (Wilke et al., 2017).

Recent innovations in flexible PCM solutions, such as salt hydrate/PU foam composites, address important packaging challenges while preventing leakage (Huang et al., 2018). However, challenges remain in scaling these solutions for commercial applications, particularly regarding cost optimization and weight reduction.

3.2. Current Challenges

Despite significant advancements, several critical challenges must be addressed to realize the full potential of PCM-based BTMS. First, the thermal stabilization of batteries during fast-charging events (≥3C rates) remains problematic, as these conditions can generate localized heat fluxes exceeding 50,000 W/m², overwhelming conventional PCM systems [19]. Second, long-term durability requirements (>5000 charge-discharge cycles) necessitate PCM formulations resistant to phase separation, chemical degradation, and thermal fatigue. Third, economic considerations demand cost reductions below $5/kg for widespread adoption in mass-market EVs, requiring innovations in both material formulations and manufacturing processes [20]. Addressing these challenges will require multidisciplinary approaches combining materials science, thermal engineering, and advanced manufacturing technologies.

4. Recent Advances and Future Directions

4.1. Hybrid Cooling Architectures

Modern thermal management systems increasingly adopt hybrid architectures that synergistically combine PCMs with active cooling technologies. Liquid cooling integration represents one of the most promising approaches, where microchannel cold plates are embedded within PCM matrices. Recent studies demonstrate that such configurations can maintain temperature differentials (ΔT) below 5°C even during aggressive 4C discharge rates, while simultaneously reducing pumping power requirements by 40–60% compared to conventional liquid cooling systems [21,22].

Heat pipe-PCM hybrid systems offer another compelling solution, particularly for high-ambient-temperature operation. Experimental results with flat heat pipes and RT44 HC (a commercial organic PCM) show the ability to maintain battery temperatures below 40°C in 45°C ambient conditions, with 35% reductions in thermal resistance compared to standalone PCM implementations [23,24].

Emerging technologies like nano encapsulated PCM slurries (5–20 μm capsules suspended in heat transfer fluids) demonstrate remarkable heat transfer coefficient improvements of 2–3 times compared to single-phase coolants [25]. These advanced fluids combine the high energy storage density of PCMs with the convective heat transfer advantages of pumped systems, though challenges remain in capsule durability and long-term suspension stability.

Table 1. Comparative Analysis of PCM Types for BTMS Applications. 

Property	Organic PCMs	Inorganic PCMs	Composite PCMs
Examples	Paraffins (C<sub>18</sub>-C<sub>28</sub>), Fatty acids (e.g., lauric acid)	Salt hydrates (e.g. CaCl₂·6H₂O), Metallic alloys	Paraffin/expanded graphite, Fatty acid/graphene, Salt hydrate/MOF
Thermal Conductivity	0.1-0.3 W/mK	0.5-1.5 W/mK	2-8 W/mK (enhanced 10-30×)
Latent Heat	150-250 kJ/kg	180-300 kJ/kg	160-280 kJ/kg (90-95% retention)
Phase Change Temp.	20-80°C (tunable)	15-120°C	20-100°C (customizable)
Supercooling Degree	<2°C	5-15°C	1-5°C (reduced by additives)
Cycling Stability	>5000 cycles	300-1000 cycles	>3000 cycles
Corrosiveness	Non-corrosive	Highly corrosive	Mild to non-corrosive
Flammability	Flammable (V2-V0 rating)	Non-flammable	V0 rating (with flame retardants)
Cost	$5-10/kg	$3-8/kg	$8-15/kg
Key Advantages	- Chemically stable - Minimal supercooling - Wide temperature range	- High latent heat - High thermal conductivity - Low cost	- Enhanced conductivity - Shape stability - Tailored properties
Major Challenges	- Low thermal conductivity - Flammability risks - Volume changes	- Phase segregation - Supercooling - Corrosion	- Higher cost - Complex fabrication - Additive dispersion issues
BTMS Suitability	- Low-power applications - Where safety is prioritized	- High-power systems - Short-duration applications	- Fast-charging EVs - Extreme conditions

Table 1. Comparative Analysis of PCM Types for BTMS Applications. 

Property	Organic PCMs	Inorganic PCMs	Composite PCMs
Examples	Paraffins (C<sub>18</sub>-C<sub>28</sub>), Fatty acids (e.g., lauric acid)	Salt hydrates (e.g. CaCl₂·6H₂O), Metallic alloys	Paraffin/expanded graphite, Fatty acid/graphene, Salt hydrate/MOF
Thermal Conductivity	0.1-0.3 W/mK	0.5-1.5 W/mK	2-8 W/mK (enhanced 10-30×)
Latent Heat	150-250 kJ/kg	180-300 kJ/kg	160-280 kJ/kg (90-95% retention)
Phase Change Temp.	20-80°C (tunable)	15-120°C	20-100°C (customizable)
Supercooling Degree	<2°C	5-15°C	1-5°C (reduced by additives)
Cycling Stability	>5000 cycles	300-1000 cycles	>3000 cycles
Corrosiveness	Non-corrosive	Highly corrosive	Mild to non-corrosive
Flammability	Flammable (V2-V0 rating)	Non-flammable	V0 rating (with flame retardants)
Cost	$5-10/kg	$3-8/kg	$8-15/kg
Key Advantages	- Chemically stable - Minimal supercooling - Wide temperature range	- High latent heat - High thermal conductivity - Low cost	- Enhanced conductivity - Shape stability - Tailored properties
Major Challenges	- Low thermal conductivity - Flammability risks - Volume changes	- Phase segregation - Supercooling - Corrosion	- Higher cost - Complex fabrication - Additive dispersion issues
BTMS Suitability	- Low-power applications - Where safety is prioritized	- High-power systems - Short-duration applications	- Fast-charging EVs - Extreme conditions

Key Observations:

1)

Organic PCMs excel in chemical stability and cycling performance but require thermal conductivity enhancers for effective heat dissipation.

2)

Inorganic PCMs offer superior energy storage density but suffer from reliability issues (supercooling, corrosion).

3)

Composite PCMs bridge the performance gap but at higher costs, making them ideal for premium EV applications.

Performance Metrics:

• Best Latent Heat: Inorganic > Composite > Organic
• Best Thermal Conductivity: Composite > Inorganic > Organic
• Long-Term Stability: Organic > Composite > Inorganic
• Cost-Effectiveness: Inorganic > Organic > Composite

References Supporting Table Data:

• Thermal properties: [12,15,17]
• Cycling stability: [13,18,26]
• Cost analysis: [19,20,39]
• BTMS suitability: [1,3,6]

4.2. Material Innovations

Nanostructured composites represent a breakthrough in PCM technology. Graphene aerogel-paraffin composites, for instance, achieve thermal conductivities of 4.8 W/mK (a 24-fold enhancement over pure paraffin) while retaining 98% of the base material's latent heat capacity [26]. This remarkable performance stems from the three-dimensional interconnected network of graphene sheets that provide continuous phonon transport pathways.

Metal-organic framework (MOF)-stabilized salt hydrates address the historical challenges of inorganic PCMs. ZIF-8 frameworks, for example, reduce supercooling from 12°C to just 2°C in sodium acetate trihydrate systems while maintaining 99% cycling stability after 1200 phase change cycles [27]. The MOF's nanoporous structure confines the salt hydrate crystals, preventing phase separation and nucleation inhibition.

Bio-based PCMs are gaining traction as sustainable alternatives. Coconut oil-palm wax eutectics demonstrate phase change enthalpies of 165–180 kJ/kg with 60% lower carbon footprints than synthetic counterparts [28]. Lignin-derived composites offer additional advantages including inherent flame retardancy (achieving UL94 V0 ratings) and potential 40% cost reductions through utilization of biorefinery byproducts [29].

4.3. Smart System Integration

Artificial intelligence is revolutionizing BTMS design through neural networks that predict thermal behaviour with 93% accuracy, enabling real-time adaptive cooling strategies [30]. Generative design algorithms have demonstrated 18% reductions in PCM usage while maintaining equivalent thermal performance through optimized geometric distributions [31].

Digital twin implementations now provide real-time thermal mapping with less than 1°C error through coupled computational fluid dynamics and machine learning models [32]. These virtual representations enable predictive maintenance algorithms that can anticipate thermal runaway risks hundreds of cycles before failure [33].

4.4. Future Research Priorities

Four key research frontiers demand attention:

4)

High-temperature PCMs (>80°C) capable of handling 350kW+ fast-charging infrastructure [34]

5)

Self-healing composites incorporating microvascular networks for autonomous repair of phase segregation [35]

6)

4D-printed structures with thermally adaptive conductivity through shape-memory material integration [36]

7)

Circular economy models achieving >95% PCM recyclability through novel reversible crosslinking chemistries [37]

5. Conclusion

Phase Change Materials (PCMs) have emerged as a transformative solution for Battery Thermal Management Systems (BTMS), offering energy-efficient, passive thermal regulation for lithium-ion batteries in electric vehicles (EVs) and energy storage systems. Organic PCMs, such as paraffins, provide excellent chemical stability and cycling durability (>5000 cycles), while inorganic PCMs, like salt hydrates, offer high latent heat (180–300 kJ/kg) and thermal conductivity (0.5–1.5 W/mK). Composite PCMs, enhanced with materials like graphene, expanded graphite, or metal foams, bridge the gap by achieving thermal conductivities up to 4.8–8 W/mK and retaining >90% latent heat, making them ideal for high-power applications. Hybrid systems integrating PCMs with active cooling (e.g., liquid cooling or heat pipes) demonstrate superior performance, maintaining temperature uniformity within ±1.5–2°C and reducing energy consumption by up to 50% compared to traditional systems. Safety advancements, such as fire-retardant composites delaying thermal runaway by 15 minutes, and flexible PCMs addressing packaging challenges, further enhance their viability.

Despite these advancements, challenges persist, including managing high heat fluxes during fast charging (>50,000 W/m²), ensuring long-term durability (>5000 cycles), and reducing costs below $5/kg for mass-market adoption. Recent innovations, such as graphene aerogel composites, MOF-stabilized salt hydrates, and bio-based PCMs with lower carbon footprints, signal a promising future. Smart integration with AI-driven predictive models and digital twins, alongside emerging technologies like 4D-printed structures and self-healing composites, will further optimize performance. The PCM market for BTMS, projected to reach $2.8 billion by 2030, is poised for significant growth, driven by the global EV boom and the need for sustainable energy storage solutions.