Flexible Phase Change Materials Research Articles

Flexibility, malleability, and high mechanical strength phase change composite films for solar-thermal and electro-thermal energy storage

Phase change materials (PCMs) are widely used in a range of energy storage applications due to high latent heat absorption and release capacities during phase change processes. There is still a lot to be done to resolve the inherent leakage, stiffness problems, and poor solar-thermal and electrical-thermal conversion capacities of PCMs to functionalize them. Here, a novel solid-solid phase change material (IGPCM) is created using block copolymerization. The IGPCM has a tunable enthalpy (from 58.16 to 99.60 J g−1) by adjusting the molecular weight of the PEG. The obtained IGPCM10K has high toughness (479.1 MJ/m3), excellent bending and malleability. Since IGPCM10K suffers from poor thermal conductivity, photo responsiveness, and electro-thermal conversion, carbon nanotubes (CNT) can be added to our IGPCM10K in a simple way to improve these issues. The thermal conductivity of IGPCM10K-CNT-3 is improved by 55.6 % compared to IGPCM10K. The photothermal conversion efficiency is 84.9 % at 300 mW/cm2. The electrothermal conversion efficiency is 82.3 % at 12 A. The prepared flexible PCM composites have super toughness, high enthalpy, excellent thermal conductivity, and photo-thermal and electro-thermal conversion capabilities, which will show great potential in future applications.

All‐Climate Thermal Management Performance of Power Batteries Based on Double‐Layer Flexible Phase Change Materials

AbstractThermal management systems for power batteries based on phase change materials (PCM) are limited by low heat transfer efficiency, leakage issues, and high rigidity, and most of them cannot meet the needs of all‐climate thermal management. A double‐layer flexible phase change material (FPCM) sleeve structure for all‐climate thermal management is proposed in this study for the first time. Innovations in both material and design have enhanced the adaptability of the thermal management system. The outer layer FPCM achieves high thermal conductivity (4.23 W m−1 K−1) and electrical conductivity (0.95 S m−1), the inner layer FPCM achieves insulation (22.76 MΩ) and flexibility, the thermal contact resistance (TCR) between the double‐layer sleeve structure and the battery are measured to be only 0.15 °C W−1, significantly improved thermal management performance. Experimental results show that at 30 °C ambient temperature, 5 C discharge, the system reduces the maximum temperature by 14.5 °C, from 61.4 to 46.9 °C, compared to natural convection. Additionally, during heating, the system achieves heating rates of 7.0, 8.3, and 8.7 °C min−1 at −20, −10, and 0 °C, respectively, extending battery discharge duration by 32.5%, 65.9%, and 33.6%.

Neuron-Inspired Flexible Phase Change Materials for Ambient Energy Harvesting and Respiration Monitoring.

The global energy crisis and climate change pose unprecedented challenges. Wearable devices with personal thermoregulation and energy harvesting hold great promise for achieving energy savings and human thermal comfort. Here, inspired by neurons, a novel phase change material (PCM) is reported for efficient energy harvesting and respiratory monitoring via a self-assembly strategy. The use of gum arabic (GA) enabled the encapsulation of polyethylene glycol (PEG) and the targeted distribution of carboxylated multi-walled carbon nanotubes (cMWCNTs) simultaneously in poly (ethylene vinyl acetate) (EVA) matrix. The material exhibits an outstanding toughness value of 14.88MJ m-3 and high elongation at a break of 565.67%, exhibiting remarkable flexibility. The material with sufficient melting enthalpy (71.11 J g-1) demonstrates high photothermal conversion efficiency (95.27%) under 808nm laser irradiation (105mW cm-2). In addition, due to the synergistic effect of GA and PEG, especially the formation of microdome structures on the surface, the material demonstrates ultrasensitive humidity responsiveness for respiratory monitoring with high precision, excellent repeatability, and fast response/recovery time (50.4/50.5ms). Notably, it shows great potential for moisture-electric generators (MEGs) with the function of non-contact sensing. This material opens the path toward next-generation wearable devices in energy conversion and health monitoring.

Experimental study on the effects of integrating phase change material with a solar updraft tower

AbstractThe solar updraft tower power plant presents a promising renewable energy solution but faces limitations in thermal efficiency and energy production during nonsunny hours. This study addresses a critical gap in the literature by investigating the integration of latent heat storage systems utilizing paraffin wax as phase change materials (PCMs) to enhance solar updraft tower (SUT) performance. Two identical small‐scale SUTs were constructed, both using the same tank configuration; however, the PCM device was filled with paraffin wax as a PCM, while the non‐PCM device contained only atmospheric air. Three scenarios were explored, featuring varying PCM tank heights of 2, 4, and 6 cm (the full capacity of the PCM tank). Results indicated that, from 3 p.m. until sunset, the PCM‐integrated SUT in Case 3 (with 6 cm of PCM) achieved the best performance, with an average absorber temperature rise of 25°C, compared with 12°C for the non‐PCM device. During the same period, the average air velocity at the tower neck, where a wind turbine could be installed, was 1.21 m/s for the PCM device, versus 0.82 m/s for the non‐PCM device. Notably, the nocturnal operating time extended significantly with PCM use, rising from 90 min for the 2 cm case to 125 min for the 6 cm case. In contrast, the non‐PCM device exhibited no operational time after sunset. This research not only demonstrates the effectiveness of PCM in improving the thermal performance and operational longevity of SUTs but also introduces a novel tank configuration that allows for flexible PCM integration, representing a significant advancement in the development of more efficient SUT systems.

Flexible AIE/PCM composite fiber with biosensing of alcohol, fluorescent anti-counterfeiting and body thermal management functions

Alcohol sensing plays a critical role in medical detection and personal health management. AIE materials with high sensitivity, selectivity and fast response have been widely used in biosensing, but their application in the field of alcohol sensing still needs further research and development. Furthermore, developing flexible phase change materials (PCMs) is significant for the research of human-body thermal management. In this study, a kind of flexible polyacrylonitrile (PAN)/polyvinylpyrrolidone (PVP)/polyethylene glycol (PEG)/Py-CH (pyrene-based AIE molecule)/SiO2@h-BN composite fiber textile (PAB) with alcohol sensing performance, writable fluorescence property, and human body thermal management function has been prepared via electrospinning technique. The PAN/PVP fiber matrix successfully integrated AIE fluorescent sensing material and PCM into a multi-functional composite with great shape stability. Owing to the introduction of novel pyrene-based Py-CH with AIE characteristic, this innovative textile exhibited wonderful fluorescent properties, including sensitive alcohol fluorescence sensing, writable fluorescence performance and variable temperature fluorescence. Furthermore, proposed PAB textile delivered a high energy storage density of 87∼90 J/g, excellent thermal reliability, great comprehensive mechanical flexibility and enhanced thermal conductivity for flexible human body thermal management. Hence, this flexible multifunctional AIE/PCM composite sensing textiles can be widely used in alcohol sensing, fluorescence anti-counterfeiting and flexible body thermal management.

Design of flexible polyethylene glycol-based phase change materials by crystal structure regulation

The design of flexible phase change materials (FPCMs) with polyethylene glycol (PEG) as phase change components remains a great challenge due to high crystalline structure makes for high thermal energy storage ability yet deteriorates mechanical toughness. Herein, the preparation strategy of FPCMs was developed by introducing crystal structure regulators (CSRs) in PEG-based FPCM networks in a form of covalent linkages. The hydroquinone CSR had the strongest ability of crystal structure regulation over FPCMs compared to the three other used CSRs. The FPCMs had tuneable phase change temperatures (−2.0 °C–49.7 °C) and enthalpies (40.7 J g−1 to 109.3 J g−1) depending on the number-average molecular weight (Mn = 4000 Da, 6000 Da) of PEGs used as well as the content and type of CSRs, further enabling tuneable mechanical stress (0.59–15.61 MPa) and strain (5.74%–505.86 %). Compared with the pristine PEGs, the FPCMs yielded excellent shape stability, thermal stability and thermal reliability. The flexibility and phase change properties endowed the FPCMs with excellent self-adaptability and shape memory function. The innovative strategy towards FPCMs highlights the application potential on individual wearable temperature-controlled devices.

Room-temperature flexible phase change material with high emissivity and high enthalpy for building energy saving

Summer heatwave events become more and more frequent, building cooling load continues to rise, and the traditional cooling method using air conditioning consumes a lot of energy. New technologies and materials with high efficiency, energy saving and low cost are urgently needed to solve the problem of high energy consumption in buildings. In this paper, by combining phase change storage technology with passive cooling technology of sky radiation, a new type of high-emission flexible composite phase change material (CPCM) was prepared using polypropylene hollow fiber (PP hollow fiber), Styrene-Ethylene-Butylene-Styrene (SEBS) and paraffin wax (PA). The prepared CPCM with excellent thermophysical properties, including a latent heat of 175.19 J/g, room temperature flexibility, the contact angle of the hydrophobic test of 129.15°, and the infrared emissivity of the atmospheric window of 0.942. The cooling experiment results show that the maximum temperature difference between CPCM and the environment is 2.6 °C lower than the ambient temperature. In addition, the simulation results show that the external surface temperature of the CPCM roof can be reduced by 23.15 K at the highest compared with a common roof, and the maximum energy saving can reach 13.24 W/m2. Compared with the high emissivity roof without CPCM, the external surface temperature is further reduced by 0.47K, the delay time is 50min, and the maximum energy saving can reach 0.76 W/m2. It's worth getting excited that CPCM can delay the opening time of air conditioning for 10 days. In addition, the application efficiency of cities in typical climate regions is simulated, and outstanding energy-saving efficiency is obtained, among which the maximum saving energy in Guangzhou is as high as 20.16 W/m2. The successful preparation of the novel CPCM material provides a new direction for the development of radiation-cooling technology.

Distribution strategy of flexible phase change materials for pouch battery thermal management considering temperature non-uniformity

Flexible composite phase change materials (CPCMs) have been extensively studied in the thermal management of cylindrical lithium-ion batteries and proven to have a good cooling effect. However, passive cooling of pouch lithium-ion batteries with severe uneven temperature distribution has not received the attention it deserves. The thermal management of pouch battery based on passive cooling of flexible PCMs considering the heat-generating structure of pouch batteries needs to be further studied. Herein, CPCMs with different thermal conductivity were prepared, and four different distribution modes of CPCMs, including partial coverage and complete coverage, were applied to thermal management of pouch battery. Results indicated that the maximum temperature (Tmax) and maximum temperature difference (ΔTmax) can be kept separately within 35 °C and 5 °C in the passive thermal management of a single battery except upper coverage at discharge rate of 5C, and the middle coverage (case B) showed excellent temperature control in partial coverage cases. Equally noteworthy was that the increase in thermal conductivity increased the ΔTmax in partial coverage cases, while showing the opposite trend for full coverage (case ABC). Furthermore, only passive cooling of pouch battery pack did not meet the safety requirements under the discharge rate cycle of 5C. Under the active–passive combination mode, case B can control the Tmax (32.22 °C) and ΔTmax (4.69 °C) within a safe range, which was superior to case ABC (Tmax = 35.53 °C, ΔTmax = 5.04 °C). This conclusion provides technical support for the pouch battery to seek economic, stable and efficient thermal management.

Synergistic performance enhancement of lead-acid battery packs at low- and high-temperature conditions using flexible phase change material sheets

Thermal management of lead-acid batteries includes heat dissipation at high-temperature conditions (similar to other batteries) and thermal insulation at low-temperature conditions due to significant performance deterioration. To address this trader-off, this work proposes a thermal management solution based on flexible phase change materials (PCMs) with moderate thermal conductivity and other favourable properties including high specific heat capacity and high latent heat. A novel type of flexible PCM sheets is prepared with paraffin, olefin block copolymers (OBC) and expanded graphite using the co-melting method. The flexible PCM sheets are attached to a common type of lead-acid battery packs (12 Ah, dimensions of 151 × 98 × 97 mm) and thermal management performance is experimentally investigated at –10 °C and 40 °C as low- and high-temperature conditions, respectively, along with 25 °C as a baseline case for comparison purposes. Thermal properties of the battery packs such as temperature regulation and electric properties including charge/discharge capacities and rates are studied synchronously based on a standard high-performance battery detection facility. The results indicate that at –10 °C condition, the PCM sheet enhances thermal insulation of the battery pack and significantly promotes the service temperature during the charging processes. Compared with a benchmark pack attached with an encapsulated sheet, the charge and discharge capacities of the PCM-attached pack are improved by 3.7% and 5.9%, respectively. At 40 °C condition, phase transition of the PCM sheet restrains the temperature rise of the battery pack, with a maximum temperature decrease of 4.2 °C during the charging processes relative to the benchmark pack, and the temperature of the PCM-attached pack is maintained below 45 °C across 60% of the overall charge period. The overcharge and overdischarge have also been alleviated by 3.2% and 2.8%, respectively, and thus the running stability and service lifespan can be improved. The proposed PCM sheets with preferable thermal properties demonstrate potential to promote performance of lead-acid battery packs and such components are also expected to improve heat dissipation and thermal insulation in similar applications including building energy saving, thermal management of electronic chips and thermal regulation of electronic devices.

Thermally enhanced flexible phase change materials for thermal energy conversion and management of wearable electronics

The developing trend of miniaturization and integration for electronics imposes challenges of efficient heat dissipation technology, where novel materials with advanced thermal energy conversion and management are urgently needed. In this work, we propose an emerging phase change material (PCM) system with polyvinyl alcohol/expanded graphite network loading paraffin wax (PE-PW), which exhibits superb flexibility, thermal energy storage capacity and thermal conductivity. The phase change enthalpy is from 115.61 J/g to 168.93 J/g without any leakage, which can be maintained even after 500 thermal cycles. The thermal conductivity can reach 1.46 W/mK, 484% enhanced compared with that of pure PCM. Meanwhile, the thermal management test indicates that the PE-PW composites can quickly absorb and store the generated heat to achieve temperature control, thus protecting the system from overheating and indicating excellent thermal management capacity. This flexible PE-PW system has broad application prospects in the field of thermal energy conversion and management for wearable electronics.

An electric conductive wide-temperature flexible phase change material for all-climate battery thermal management

Battery thermal management with phase change materials (PCM) has been limited by leakage, low thermal conductivity and rigidity, and the inability to preheat at low temperatures. To solve these problems, a wide-temperature flexible composite PCM (FCPCM) was prepared with a high-temperature open refining method. Styrene ethylene butylene styrene (SEBS) and expanded graphite (EG) absorb paraffin (PA) onto a three-dimensional network. The FCPCM possesses good flexibility before and after phase transition. It can be bent and stretched arbitrarily at room temperature, and the shape memory function enable it can be restored to its original state after heating. The latent heat of the FCPCM-15 is 159.9 J/g and its thermal conductivity was 7.45 times higher than that of pure paraffin. The FCPCM also possesses a good volume conductivity of 92–2952 S/m and allows for uniform electrical heating. The excellent thermal and electrical performance of the FCPCM allows it to cool batteries at high temperatures and preheat batteries at low temperatures. After ten charge/discharge cycles at 30 °C, the battery pack’s temperature based on FCPCM cooling is still reduced by 3.9 °C. At a low temperature of −20 °C, the preheating rate of the battery pack can reach 12.9 °C/min, and the discharge voltage and capacity of the battery pack were increased by 15 % and 20.8 % after preheating. The FCPCM suggests a promising and practical approach way for the all-climate thermal management of batteries.

Multilevel phase transition behavior of In2Se3-doped with Sb materials based on flexible polyimide substrate

The In2Se3-doped Sb phase change material was deposited onto a polyimide substrate using magnetron sputtering technique. A comprehensive investigation was conducted on the thermal stability, bending resistance, crystal structure, and electrical properties of this material. The findings revealed its remarkable thermal stability, data retention, and bending resilience, particularly in the In0.05Se0.19Sb0.76 film, which exhibited minimal resistance drift. The aging test confirmed the stability of the electronic structure in In2Se3-doped Sb, accompanied by reduced structural relaxation. Notably, no new crystalline phase emerged in In0.05Se0.19Sb0.76 film, but stronger In-Sb bonds were formed. Raman spectroscopy and bending tests further indicated that deformation had minimal impact on the film’s structure and surface. Utilizing the In0.05Se0.19Sb0.76 material and polyimide substrate, a flexible phase change memory device demonstrated reliable SET/RESET operations even after bending, offering three stable resistance states for multilevel storage. This enhanced the storage density, making In2Se3-doped Sb material a promising flexible phase change material with excellent performance and vast potential for applications in phase change storage, such as electronic fabrics and flexible smart wearable electronics.

Long-Lasting Heat Dissipation of Flexible Heat Sinks for Wearable Thermoelectric Devices.

Flexible wearable thermoelectric (TE) devices hold great promise for a wide range of applications in human thermal management and self-powered systems. Currently, the main challenge faced by flexible TE devices is the inadequate dissipation of heat, which hinders the maintenance of significant temperature differences over prolonged periods. Most existing heat sinks, being rigid in nature, compromise the overall flexibility of the device. Therefore, the challenge lies in maintaining device flexibility while ensuring effective heat dissipation. In this study, we developed a flexible phase-change material (FPCM) heat sink to address this issue and enhance the heat dissipation capabilities of TE devices (FPCM-TED). When used as a thermoelectric cooler (TEC), the FPCM heat sink efficiently absorbs heat from the hot end, enabling long-lasting and high-performance cooling of the TEC. This capability effectively reduces body temperature by up to 11.21 °C and can be sustained for at least 300 s. Additionally, when employed as a thermoelectric generator (TEG), the FPCM absorbs heat at the cold end, thereby increasing the temperature difference between the hot and cold ends and enhancing the output performance of the device. By integrating FPCM-TED into a fabric wristband, we successfully developed a self-powered wireless pedometer sensing system. This breakthrough lays a solid foundation for the application of wearable, smart clothing.

Experimental study on flexible flame retardant phase change materials for reducing thermal runaway propagation of batteries

The current research on phase change materials (PCM) for Battery Thermal Management Systems (BTMS) often focuses on a single characteristic, either flame retardancy or flexibility. PCM with both flexibility and flame retardancy is relatively uncommon, and studies on flexible PCMs have lacked experimental validation of their effectiveness. This study explored the optimal ratio of aluminium hydroxide (ATH)/ magnesium hydroxide (MTH)/ ammonium polyphosphate (APP), successfully creating a flexible flame-retardant PCM and applying it to battery cooling. The ratio of ATH/MTH/APP was determined as 9: 3:8, providing features such as leak resistance, high thermal conductivity, flame retardancy, and flexibility. Compared to the blank sample without flame retardants, the Peak Heat Release Rate (PHRR) and Total smoke production (TSP) of the PCM decreased by 48 % and 24.3 %, respectively. When applied to BTMS, the PCM restricted the battery's surface peak temperature and maximum temperature difference to 48.76 °C and 4.07 °C, respectively, at a discharge rate of 6C. After applying pressure to leverage flexibility, the temperature difference was further reduced to 1.76 °C, demonstrating the effectiveness of flexibility. In Thermal Runaway (TR) experiments, the PCM delayed the time triggered by TR by 84 s and reduced the maximum temperature by 92.3 °C. This work successfully combines flame retardancy and flexibility, offering valuable insights for the application of flame retardant flexible CPCM in BTMS and other relevant fields.

Development of bio-based flexible phase change materials utilizing lauric acid for battery thermal management systems

Lithium-ion batteries, serving as the cornerstone of electric vehicles, generate significant thermal output during their operation. This underscores the imperative need for the implementation of an appropriate battery thermal management system (BTMS). Extensive attention has been directed towards thermal-induced flexible phase change material (FPCM) within the domain of BTMS. However, it is notable that the predominant choice in contemporary practice for FPCM in BTMS remains paraffin (PA)-based, sourced from petroleum origins. This study utilizes an environmentally friendly bio-based phase change material (PCM), lauric acid (LA), to fabricate FPCM. The FPCM is skillfully crafted through the incorporation of styrene-ethylene-propylene-styrene (SEPS) and expanded graphite (EG) as supporting materials, forming the LA/SEPS/EG composite phase change material (CPCM). The addition of EG increases the thermal conductivity of CPCM by 4.97 times and enhances the leakage resistance. Furthermore, comprehensive assessments were conducted to evaluate the thermal performance, thermally induced flexibility, heat storage, release characteristics, and cyclic stability of the fabricated FPCM. In the battery discharge tests conducted at 2C/3C/4C rates, the battery containing FPCM consistently maintained its maximum temperature below 50 °C, with a minimal temperature difference of <1 °C, showcasing excellent thermal management performance.

Flexible phase change materials based on hexagonal boron nitride (hBN) surface modification and styrene-butadiene-styrene (SBS)/low-density polyethylene (LDPE) crosslinking for battery thermal management applications

In battery thermal management (BTM), flexible phase change materials (FPCMs) emerge as highly promising substances, owing to their simple installment and low contact thermal resistance. However, FPCMs based on high thermal conductivity fillers and polymers always suffer from the enduring challenges of poor high-temperature resistance and poor filler-matrix compatibility. To solve these problems, a novel strategy is reported in this work, wherein FPCMs with excellent filler-matrix compatibility and satisfactory high-temperature resistance are synthesized by two steps: functionalizing the hexagonal boron nitride (hBN) surface and inducing the inter crosslinking between Styrene-Butadiene-Styrene(SBS) and Low-density polyethylene(LDPE). Vinyltrimethoxysilane (VTMS) molecules were introduced on the surface of raw hBN by hydroxylation and silanization surface modification to improve the compatibility of hBN with the matrix. Concluding from the results, the addition of 6.7 wt% LDPE doubled the high-temperature resistance of FPCMs, enabling them to maintain their structural integrity even at 200 °C for 1 h. The prepared FPCMs also exhibited higher thermal conductivity (increased by 20.5 %), low leakage rate (<0.6 wt% after 70 heating–cooling cycles), high enthalpy (122 J g−1), and strong adhesion (>0.1 MPa), etc. In terms of BTM performance, the FPCMs-based passive cooling BTM presents remarkable temperature control capabilities (maximum temperature reduction by 16.3 ℃) and uniform temperature performance (maximum temperature difference < 2.5 ℃). Collectively, this work will provide a promising approach for the fabrication of high-performance FPCMs in BTM and other thermal management applications for electronic devices.

Optimizing Waste Heat Conversion: Integrating Phase-Change Material Heatsinks and Wind Speed Dynamics to Enhance Flexible Thermoelectric Generator Efficiency.

Flexible thermoelectric generators (FTEGs) have garnered significant attention for their potential in harnessing waste heat energy from various sources. To optimize their efficiency, FTEGs require efficient and adaptable heatsinks. In this study, we propose a cost-effective solution by integrating phase-change materials into FTEG heatsinks. We developed and tested three flexible phase-change material thicknesses (4 mm, 7 mm, and 10 mm), focusing on preventing leaks during operation. Additionally, we investigated the impact of wind speed on the output performance of FTEGs with a flexible phase-change material heatsink. The results indicate that the appropriate flexible phase-change material thickness, when integrated with considerations for wind speed, demonstrates remarkable heat-absorbing capabilities at phase-change temperatures. This integration enables substantial temperature differentials across the FTEG modules. Specifically, the FTEG equipped with a 10 mm thick flexible phase-change material heatsink achieved a power density more than four times higher when the wind speed was at 1 m/s compared to no wind speed. This outcome suggests that integrating phase-change material heatsinks with relatively low wind speeds can significantly enhance flexible thermoelectric generator efficiency. Finally, we present a practical application wherein the FTEG, integrated with the flexible phase-change material heatsink, efficiently converts waste heat from a circular hot pipe into electricity, serving as a viable power source for smartphone devices. This work opens exciting possibilities for the future integration of flexible thermoelectric modules with flexible phase-change material heatsinks, offering a promising avenue for converting thermal waste heat into usable electricity.

Coupling of flexible phase change materials and servers for improving the security of data centers in emergency situations

Data centers with high-power servers cause massive energy consumption. The service object of each server is different, and the server will change from low-load to high-load when an emergency occurs, which increases heat generation. If the heat cannot be removed timely, the temperature will rise rapidly, affecting the operation and safety of servers. A common method is to change the parameters of the cooling system, which will lead to an exponential increase in energy consumption. In this paper, novel flexible phase change material (FPCM) is used for temperature control of servers. Firstly, paraffin/styrene-ethylene-butene-styrene block copolymer/expanded graphite (PA/SEBS/EG) with high flexibility, high thermal conductivity (0.72 W∙m−1∙K−1) and high enthalpy (184.77 kJ·kg−1) was prepared. Then, PA/SEBS/EG was placed above the server, and the temperature was reduced by 3.29 °C compared to without FPCM at an inlet temperature of 26 °C, and the temperature rising rate can be reduced by above 60 %, indicating that FPCM has excellent thermal management effect. Finally, Flotherm software was used to optimize the sizes and parameters of FPCM, the results show 53 × 51 × 16 mm FPCM with 12 wt% EG can reduce the temperature of 13.74 %, 14.03 %, and 14.61 % compared to without FPCM at 1.25, 1.5, 1.75 times power, respectively, and extend 771 s to exceed 80 °C under 1.75 times power. The lifespan can be increased by 3.53 times, and the cooling demand can be reduced by 24.73 %. This study provides solutions for the safe operation and energy consumption reduction of data centers.

Tree-ring structured phase change materials with high through-plane thermal conductivity and flexibility for advanced thermal management

Phase change materials (PCMs) as one of the most promising latent heat storage materials have been applied for thermal management of electronic devices. Nonetheless, simultaneously endowing PCMs with high through-plane thermal conductivity and flexibility remains challenging. Herein, a coupling strategy combining scraping, hot compression, and roll-cutting is proposed to fabricate polydimethylsiloxane/paraffin/boron nitride (PDMS/PW/BN) composites. The BN alignment across the in-plane (x-y direction) was firstly obtained via scraping, then hot compression and roll-cutting were introduced to induce BN aligned across the through-plane (z-direction). Consequently, PW was wrapped by the cross-linked PDMS/BN network, thus forming a similar tree-ring structure to natural wood. The tree-ring structure effectively avoided the liquid leakage of PW, thus showing a high dimension retention ratio of 98 %. The vertical orientation of the BN network imparted the PCMs improved through-plane thermal conductivity of the PCMs to 2.16 W·m−1·K−1 at a BN loading of 13.0 wt%, showing a remarkable improvement of 943 % in comparison with PDMS/PW. Interestingly, the PCMs exhibited tunable thermal conductivity by triggering the melting-crystallization transition of PW. The in-situ X-ray diffraction indicated that the BN network rearrangement occurred during the phase transition. Furthermore, the good thermal management capability of PCMs was practically confirmed on working chips and via finite element simulation. This work presents a cost-effective approach for producing flexible PCMs with high through-plane thermal conductivity, which have the potential to be used in the thermal management of advanced electronics.

Flexible phase change materials for low temperature thermal management in lithium-ion batteries

The performance of Li-ion batteries can degrade dramatically at cold ambient temperatures. The excess heat generated during battery operation can be stored by PCMs and then released at low ambient temperatures to insulate the battery. However, PCMs inevitably suffer from easy leakage and poor adaptability. In this study, we prepared a novel Oct/SEBS composite PCM and applied it in a low-temperature Li-ion battery thermal management system. The prepared Oct/SEBS has good shape stability, a sufficiently high latent heat (187.7 J/g), and thermally induced flexibility properties. In addition, the BTMS containing CPCM can exhibit excellent thermal insulation performance, which can insulate the Li-ion battery for more than 30 min even at −20 °C and increase the discharge capacity from 3.78 Ah to 5.49 Ah, which is very beneficial for the operation of the Li-ion battery at low temperatures.