Flexible Phase Change Materials Research Articles

Flexible phase change composite based on loading paraffin into cross-linked CNT/SBS network for thermal management and thermal storage

Phase change materials (PCM), which can release and absorb a large amount of latent heat during phase change, have aroused great interest in the field of energy storage. However, the inherent brittleness of PCM was the trickiest problem in practical applications such as flexible electronic devices and smart textiles. To obtain flexible PCMs, current methods based on physical blending of PCMs and flexible polymers tend to cause uneven composites and leakage of core materials. Here, we report an intrinsically flexible phase change composite with high enthalpy (147.63 J/g), which can be bent and even twisted at room temperature. Thanks to the sulfur crosslinkers, PW is filled uniformly in the cross-linked interpenetrating network formed by styrene butadiene styrene (SBS) and carbon nanotubes (CNTs). Meanwhile, the addition of 2 wt% CNT nearly doubled the elongation, and the maximum stress was also increased to 1.47 MPa. This work will give insight on rational design of intrinsically flexible PCMs for electronic devices thermal management and solar-thermal energy storage.

Multifunctional Phase Change Composites Based on Elastic MXene/Silver Nanowire Sponges for Excellent Thermal/Solar/Electric Energy Storage, Shape Memory, and Adjustable Electromagnetic Interference Shielding Functions.

Multifunctional phase change materials (PCMs) are highly desirable for the thermal management of miniaturized and integrated electronic devices. However, the development of flexible PCMs possessing heat energy storage, shape memory, and adjustable electromagnetic interference (EMI) shielding properties under complex conditions remains a challenge. Herein, the multifunctional PCM composites were prepared by encapsulating poly(ethylene glycol) (PEG) into porous MXene/silver nanowire (AgNW) hybrid sponges by vacuum impregnation. Melamine foams (MFs) were chosen as a template to coat with MXene/AgNW (MA) to construct a continuous electrical/thermal conductive network. The MF@MA/PEG composites showed a high latent heat (141.3 J/g), high dimension retention ratio (96.8%), good electrical conductivity (75.3 S/m), and largely enhanced thermal conductivity (2.6 times of MF/PEG). Moreover, by triggering the phase change of the PEG, the sponges displayed a significant photoinduced shape memory function with a high shape fixation ratio (∼100%) and recovery ratio (∼100%). Interestingly, the EMI shielding effectiveness (SE) can be adjusted from 12.4 to 30.5 dB by a facile compression-recovery process based on shape memory properties. Furthermore, a finite element simulation was conducted to emphasize the advantage of the MF@MA/PEG composites in the thermal management of chips. Such flexible PCM composites with high latent heat storage, light-actuated shape memory, and adjustable EMI shielding functions exhibit great potential as smart thermal management materials in military and aerospace applications.

Experimental investigation of form-stable phase change material with enhanced thermal conductivity and thermal-induced flexibility for thermal management

Form-stable phase change material (PCM) has become the preferred material in the field of thermal management. However, the practical application of form-stable PCM is restricted by low thermal conductivity, strong rigidity, and complicated production. In this work, a facile strategy is successfully proposed to prepare a novel form-stable PCM, which is composed of paraffin (PA), styrene-ethylene-propylene-styrene (SEPS), and expanded graphite (EG). Here, SEPS acted as supporting material not only prevents leakage of liquid PA but also provides thermal-induced flexibility property. Moreover, EG takes a positive part in improving heat transfer and shape stability. The thermal conductivity and enthalpy of PA/SEPS/EG composite are measured as high as 1.340 W m−1 K−1 and 207.02 kJ kg−1, respectively. Simultaneously, the composite PCM performs excellent leakage-proof and realizes good flexibility under external force without fracture. It is worth mentioning that the flexible PCM can reduce thermal contact resistance between battery and PCM under steady state. As a result, the battery temperature could be maintained about 43 °C by PA/SEPS/EG composite in the form of interference fit. Therefore, these results imply that the flexible composite PCM with excellent integrated properties has promising prospects for applications in thermal management.

A novel elastomeric copolymer-based phase change material with thermally induced flexible and shape-stable performance for prismatic battery module

In this study, a novel thermally induced flexible phase change material (PCM), which consists of an elastomeric block copolymer called styrene-b-ethylene-co-butylene-b-styrene triblock copolymer (SEBS), paraffin (PA) and expanded graphite (EG), is successfully prepared. Here, SEBS and EG serve as a supporting material and a thermal enhanced component. The effects related to latent heat, thermal stability, thermal conductivity and shape stability of different SEBS mass fractions are investigated and the test results reveal the good thermal performance of the PA/SEBS/EG blends. Besides, the further rheological analysis points out that the property of shape stability and thermal induced flexibility are based on the physical crosslinking mechanism between SEBS and PA. As a result, PA/SEBS/EG composite considerably reduces thermal contact resistance due to narrower gap, endowing the battery module with much better heat dissipation efficiency and temperature uniformity. The 3 C discharge of the battery module test shows that the maximum temperature of battery module using PA/SEBS/EG blend is effectively controlled within 42.2 °C, while the maximum temperature difference is below the safety threshold of 5 °C during the 5-cycling discharge and charge tests.

Polymer/expanded graphite-based flexible phase change material with high thermal conductivity for battery thermal management

Phase change materials, as smart, ideal latent heat storage, and passive technology, have become the promising option for thermal management. However, the melting leakage, poor mechanical property, and intrinsic low thermal conductivity are long-standing bottlenecks for practical applications. In this study, a synergetic method is proposed to fabricate phase change composites with excellent shape stability, flexible property, and high thermal conductivity. Here, paraffin is used as thermal energy storage material, styrene-ethylene-propylene-styrene served as supporting material provides a cross-linked network to restrict paraffin molecular and endow the composite with thermal-induced flexibility, and expanded graphite with lamellar structure constructs an interconnected thermally network. The thermal conductivities of composites reach up to 2.671–10.019 W m−1 K−1 with EG loading of 5–30 wt%. Simultaneously, the phase transition enthalpy is measured as high as 155.4–211.9 kJ kg−1, indicating that the composites have good thermal properties. In addition, the composites exhibit superior thermal management behavior by controlling the operating temperature of battery to below 50 °C under normal discharge-charge and dynamic stress test cycles. Therefore, this work offers a convenient and efficient method to synthesize scalable form-stable composite with promising performance for battery thermal management and other advanced thermal management applications.

Post COVID-19 ENERGY sustainability and carbon emissions neutrality

This review covers the recent advancements in selected emerging energy sectors, emphasising carbon emission neutrality and energy sustainability in the post-COVID-19 era. It benefited from the latest development reported in the Virtual Special Issue of ENERGY dedicated to the 6th International Conference on Low Carbon Asia and Beyond (ICLCA′20) and the 4th Sustainable Process Integration Laboratory Scientific Conference (SPIL′20). As nations bind together to tackle global climate change, one of the urgent needs is the energy sector's transition from fossil-fuel reliant to a more sustainable carbon-free solution. Recent progress shows that advancement in energy efficiency modelling of components and energy systems has greatly facilitated the development of more complex and efficient energy systems. The scope of energy system modelling can be based on temporal, spatial and technical resolutions. The emergence of novel materials such as MXene, metal-organic framework and flexible phase change materials have shown promising energy conversion efficiency. The integration of the internet of things (IoT) with an energy storage system and renewable energy supplies has led to the development of a smart energy system that effectively connects the power producer and end-users, thereby allowing more efficient management of energy flow and consumption. The future smart energy system has been redefined to include all energy sectors via a cross-sectoral integration approach, paving the way for the greater utilization of renewable energy. This review highlights that energy system efficiency and sustainability can be improved via innovations in smart energy systems, novel energy materials and low carbon technologies. Their impacts on the environment, resource availability and social well-being need to be holistically considered and supported by diverse solutions, in alignment with the sustainable development goal of Affordable and Clean Energy (SDG 7) and other related SDGs (1, 8, 9, 11,13,15 and 17), as put forth by the United Nations.

A novel flexible phase change material with well thermal and mechanical properties for lithium batteries application

Battery thermal management and battery collision prevention are very important for the safe operation of batteries of electric vehicles. This study proposes a novel flexible phase change material (PCM) with both battery thermal management and anti-collision performance. Experiments were conducted to test the thermophysical properties and battery thermal management performance of PCM. Under 3C discharge, the battery thermal management system (BTMS) of the material can control battery temperature and the temperature difference of 45.7 °C and 1.7 °C, respectively. Moreover, the battery drop experiment and simulation were also performed to evaluate the anti-collision performance of flexible PCM. The results show that the PCM has a good impact buffering effect. The battery can reduce the stress of the battery shell and core by 96.3% and 41.9%, respectively, than the system without the flexible PCM when dropped from a height of 1 m.

Flexible phase change materials obtained from a simple solvent-evaporation method for battery thermal management

In the advanced battery thermal management (BTM) strategy of phase change material (PCM) cooling, composite PCM (CPCM) is commonly obtained by a melting-blending method, which requires a preparation temperature as high as 150–200 °C to melt the polymer component. Herein, we prepare a new kind of flexible CPCM (FCPCM) through a simple solvent-evaporation method under room temperature by carefully selecting an ethylene-vinyl acetate (EVA) copolymer as the flexible polymer component. As prepared, the obtained EVA-based FCPCM possesses suitable thermo-physical properties and an excellent flexibility at room temperature, which can effectively reduce the thermal contact resistance, and therefore delivers an outstanding temperature-control performance in BTM applications. For example, during a harsh cyclic working environment, the battery module cooled by EVA-FCPCM plates shows a much lower maximum temperature and temperature difference at 50.0 and 3.7 °C, respectively, 8.1 and 4.8 °C lower than the battery module cooled by traditional rigid CPCM plates, respectively. This new and mild strategy adopting solvent-evaporation instead of melting-blending is believed to greatly simplify the preparation procedure, and thereby promotes the engineering applications.

Light-actuated shape memory and self-healing phase change composites supported by MXene/waterborne polyurethane aerogel for superior solar-thermal energy storage

A flexible water-borne polyurethane (WPU)/MXene aerogel was applied as a supporting scaffold to confine polyethylene glycol (PEG) to fabricate photo-driven and flexible phase change material (PCM) composites. Firstly, the WPU@MXene aerogels with superior resilience were prepared via directional freeze-drying method. Secondly, the porous WPU@MXene aerogels were encapsulated with PEG by vacuum impregnation. The obtained WPU@MXene/PEG PCM composites possessed excellent dimension retention (98%@70 °C) along with high phase change enthalpy value (154.6 J g-1). Thanks to the three-dimensional interconnected structure and excellent photo absorption ability of MXene, the PCM composites showed superior solar-thermal energy conversion and storage capability. Additionally, combining the elasticity of the WPU@MXene aerogels and the solid-liquid phase change of PEG ensured that the PCM composites realized excellent light-actuated shape memory and self-healing functions. This study enriches the way for developing flexible and multifunctional PCM composites, as well as shows enormous potential applications for the efficient utilization of solar energy.

Structural analysis and mechanical properties of thermal battery by flexible phase change materials [P.C.M.

An ancient B.T.M. with P.C.M. was controlled through the issues of high inflexibility of phase change material, leakage problems and very low conductivity in thermal energy. This research paper reports a facile batter thermal management and creativity along with induced non-rigid phase change material composites. This battery model can be determined by the flexible phase change material composites along with an intervention due to the recovery in shape and non-rigidity of flexible phase change components. This assemble was modelled to be efficient and compact without any requirement for grease. A constant state reveals various stages of phase change material which has various properties in thermal efficiency. A unified state was linked with the recovery shape of flexible phase change components, which can cause a low resistance in FCPCM and battery. Battery thermal management demonstrates the perfect process of thermal control power. If the battery was discharged from 90 to 10% of charge, then the temperature of flexible phase change components depends upon battery thermal management. It was 44.5 °C during the 3.5 °C rate, which was 29.8 °C lower than no phase change material. It also reveals low-temperature oscillation inside the long-time process and range of heat of recovered phase change material. The performance of battery thermal management and its flexibility will give perceptions of passive battery thermal management systems.

Flexible Phase Change Materials for Electrically-Tuned Active Absorbers.

Phase change materials (PCMs), such as GeSbTe (GST) alloys and vanadium dioxide (VO2 ), play an important role in dynamically tunable optical metadevices. However, the PCMs usually require high thermal annealing temperatures above 700 K, but most flexible metadevices can only work below 500K owing to the thermal instability of polymer substrates. This contradiction limits the integration of PCMs into flexible metadevices. Here, a mica sheet is chosen as the chemosynthetic support for VO2 and a smooth and uniformly flexible phase change material (FPCM) is realized. Such FPCMs can withstand high temperatures while remaining mechanically flexible. As an example, a metal-FPCM-metal infrared meta-absorber with mechanical flexibility and electrical tunability is demonstrated. Based on the electrically-tuned phase transition of FPCMs, the infrared absorption of the metadevice is continuously tuned from 20% to 90% as the applied current changes, and it remains quite stable at bending states. The metadevice is bent up to 1500 times, while no visible deterioration is detected. For the first time, the FPCM metastructures are significantly added to the flexible material family, and the FPCM-based metadevices show various application prospects in electrically-tunable conformal metadevices, dynamic flexible photodetectors, and active wearable devices.

Structural Analysis and Mechanical Properties of Thermal Battery by Flexible PCM

An ancient BTM with PCM was controlled through the issues of high inflexibility of phase change material, leakage problems and very low conductivity in thermal energy. This research paper reports a facile batter thermal management and creativity along with induced non-rigid phase change material composites. This battery model can be determined by the flexible phase change material composites along with an intervention due to the recovery in shape and non-rigidity of flexible phase change components. This assemble was modeled to be efficient and compact without any requirement for grease. A constant state reveals various stages of phase change material which has various properties in thermal efficiency. A unified state was linked with the recovery shape of flexible phase change components which can cause a low resistance in FCPCM and battery. Battery thermal management demonstrates the perfect process of thermal control power. If the battery was discharged from 90 to 10% of charge, then the temperature of flexible phase change components depends upon battery thermal management. It was 44.5°C during the 3.5°C rate which was 29.8°C lower than no phase change material. It also reveals low-temperature oscillation inside the long-time process and range of heat of recovered phase change material. The performance of battery thermal management and its flexibility will give perceptions of passive battery thermal management systems.

An intrinsically flexible phase change film for wearable thermal managements

Phase change materials (PCMs) involving significant amounts of latent heat absorbing and releasing at a constant transition temperature have been extensively utilized for thermal management of electronic devices. However, it is still a great challenge to apply thermal management for wearable devices using PCMs due to their solid rigidity and liquid leakage. Although considerable efforts have been dedicated to constructing flexible composite PCMs by physically blending bulk PCMs with different flexible polymers, design and fabrication of intrinsically flexible PCM films still remain unexplored. Herein, we report an intrinsically flexible PCM film with apparent solid-solid phase transition performance, outstanding self-support and shape-conformable property for wearable thermal management. Remarkably, the as-obtained PCM film behaves adjustable phase transition enthalpy and temperature in the region from about (5 to 60)°C, long-term cycling stability up to 1000 cycles, highly mechanical flexibility and remarkable shape tailorability and foldability. Notably, such flexible PCM films are easily integrated into wearable devices with a flexible graphene film as thermal source, revealing superior temperature control behaviors, together with unprecedented electro-thermal and photo-thermal energy conversion performance. The intrinsically flexible PCM film developed in this work is holding great potential for next-generation flexible thermal management electronics.

Flexible phase change materials with enhanced tensile strength, thermal conductivity and photo-thermal performance

Phase change materials are most potential candidates for storing solar thermal energy with large enthalpy and high exergy. However, the intrinsic drawback such as poor optical absorptive capacity, low thermal conductivity and poor tensile strength restrict the thermal efficiency of phase change materials. To overcome drawback, expanded graphite is used to encapsulate the paraffin then thermoplastic elastomer is used to mix with the powders with twin-screw extrusion technology. The highly flexible phase change composite shows a melting enthalpy of 124.6 J g−1 and a thermal conductivity of 2.2 W m−1 K−1 with 70% of expanded graphite/paraffin. The tensile strength of 2.1 MPa and a breaking elongation of 220%. This flexible phase change composite demonstrates good photo-thermal energy charging/discharging property and shows much larger exergy than traditional fluids in the solar thermal energy systems.

An innovative battery thermal management with thermally induced flexible phase change material

Traditional battery thermal management (BTM) with phase change material (PCM) is constrained by the problems of leakage, low thermal conductivity and high rigidity of PCM from the assembly perspective. Herein, we report an innovative and facile BTM with thermally induced flexible composite PCM (FCPCM). In this design, battery could be clinched to the FCPCM with an interference fit because of the thermally induced flexibility and shape recovery of FCPCM. Such an assembly is designed to be compact and efficient with no need for thermal grease. The steady-state measurement results show that different phase states of PCM have different thermal interface properties. The integration associated with the shape recovery of FCPCM could cause a low thermal contact resistance between battery and FCPCM. As a result, the constructed passive BTM exhibits an excellent thermal control performance. When the battery is discharged from 100% to 0% charge state, the maximum temperature of FCPCM based BTM is 43.4 °C during 2.5C discharge rate, which is 28.8 °C lower than No PCM. For the conditions of dynamic stress test and charge–discharge cycle, it shows lower temperature fluctuation within the acceptable range and the long-time function of latent heat of PCM could be recovered. With these prominent performances, the BTM performed here with respect to assembly methods and process flexibility will provide insights into the passive BTM system.

Study of using enhanced heat-transfer flexible phase change material film in thermal management of compact electronic device

Strict internal space limit of compact electronics makes it hard to use cooling tubes for the forced convection or phase change materials (PCMs) block to thermal control. In this paper, two types of high thermal conductive flexible phase change material (FPCM) with latent heat of 160.2 J/g and 153.1 J/g were developed into film morphology with the thickness of 0.4 mm, and were used to manage heat dissipation of the compact electronics. The experimental results show that temperature of the analog chip controlled by FPCM film is indeed lowered with a maximum drop of 14.3 ℃. The promotion of FPCM’s thermal conductivity increases the effective thermal control time but still is insufficient to the heat dissipation along the inplane direction inside electronics. Therefore, the graphene film with plane thermal conductivity of 1500 W/m·K is employed to fabricate the composite heat-diffusion FPCM film to enhance transverse heat transfer. The result shows the latent heat capacity utilization rate of the FPCM film and heat diffusion area along the inplane direction are significantly increased with the extension of thermal control time by 32.4% at 3.2 W. These results are expected to provide a strong basis for the implementation and optimization of phase change thermal management technique in compact electronic device.

Flexible phase change filament with ionic liquid core

ABSTRACTA flexible phase change filament with core‑sheath structure was successfully prepared by post‐filling of a polypropylene (PP) hollow fiber. The ionic liquid (IL) 1‐butyl‐4‐methylpyridinium hexafluorophosphate was chosen as core component, while copper decorated muscovite (Cu‐MVT) was synthesized via in situ reduction and used as the refining additive for the IL. Results from differential scanning calorimetry demonstrated that the encapsulation ratio of the flexible phase change filament reached 93% with a fusion latent heat of 52.7 J/g at 48.3 °C. Supercooling of the ionic liquid was suppressed effectively as shown by the crystallization in the cooling step due to the addition of Cu‐MVT. The flexible phase change material with core‑sheath structure also showed good thermal stability, durability, and mechanical property under the protection of the sheath polymer material. It is evident that the phase change filament possesses promising characteristics for thermal energy storage and thermoregulation. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47830.

Analysis of heat transfer in latent heat thermal energy storage using a flexible PCM container

Latent heat thermal energy storage (LHTES) affords superior thermal energy capacity and compactness but has limited applications due to the low thermal conductivity of phase change materials (PCMs). Several researches have focused on the improvement of heat transfer and reducing the total melting time of PCMs in LHTES system. Few researches, however, have used flexible PCM containers for this purpose. This study used a flexible elliptical container as a PCM container for improving LHTES heat transfer performance. The effects of the axis ratio (AR) and temperature difference on the thermal charging performance were numerically studied within a single container. Smaller AR values improved the heat transfer performance by promoting heat conduction and natural convection inside the containers. The enhancement rate was increased by 1.1–2.7 times for an AR range of 0.05–0.20 compared to a classic circular container (AR = 1). In addition, the elliptical container showed superior in terms of energy density reduction. Therefore, the elliptical container with optimum AR range (0.05–0.20) can be considered a suitable configuration for effective heat transfer enhancement of PCM containers.

Flexible phase change materials for thermal storage and temperature control

Flexible phase-change materials (PCMs) have great potential applicability in thermal energy storage and temperature control. A binary composite mixture comprising polyethylene glycols of solid and liquid phases (PEG2000 and PEG400, respectively) was synthesized as a PCM base material. The PEG400 liquid phase was uniformly dispersed in the PEG2000 phase-change crystal on a molecular scale, thus creating many micro- and nanocrystals of PEG2000 via polycrystalline growth from a single crystal. To retain solidity and flexibility in the composite’s melted state, hydrogel technology and low-temperature drying were applied. We prepared flexible polymer gel shaped PCMs by adding sodium stearate (NaR) to the binary fused mixture. Needle-shaped NaR crystal grains of several hundred nanometers formed three-dimensional network structures, binding the binary flexible PCM within the network structure to form a polymer gel. These geometric structures not only achieve the solid–liquid PCM structure but also maintain flexibility in both the melted and solidified states (20–80 °C). The latent heats of melting and solidification for the polymer gel were 109.7 and 107.2 J/g, accounting for 87.5% and 85.8% of the PP20 binary eutectic, respectively. The demonstrated use of polymer gels provides a new route for investigating PCMs for heat storage.

Thermal sensitive flexible phase change materials with high thermal conductivity for thermal energy storage

Application of thermal energy storage technology in practical engineering has been inhibited due to the constant strong rigidity of phase change materials (PCMs) at any given temperature. To solve this problem, a novel kind of thermal sensitive flexible PCMs was developed by using difunctional olefin blockcopolymer (OBC) replacing conventional supporting materials. Due to phase separation morphology, OBC presents physical crosslinked network and elasticity which is essential for macroscopical elastic deformation of composite. The developed PCMs based on OBC not only exhibit the same high latent capacity and stable shape as shape-stabilized PCMs, but also present thermal sensitive flexibility with the melting point of paraffin Tparaffin,m as the stimulus. Below the melting point of OBC-TOBC,m, the transformation from rigid to flexibility is reversible. The above excellent flexibility of the developed PCMs contributes to reducing thermal contact resistance and improving poor installation for conventional PCMs in energy storage field, such as in energy-storage air-conditioning and compact electron device thermal control, especially in spacecraft thermal control system. Furthermore, thermal conductivity was improved to a breakthrough level (479% of original rate) by adding 3wt.% of the maximum size of expanded graphite, which is based on the guidance of the novel calculation model on account of thermal conductivity for thermal sensitive flexible PCMs.