Composite Phase Change Materials Research Articles

Developing a flame-retardant flexible composite phase change material to realize both temperature control and thermal runaway prevention for lithium-ion battery pack

Exploring a facile solution to controlling the operating temperature within the range between −25 °C and 60 °C and the temperature difference between batteries less than 5 °C as well as preventing thermal runaway for battery packs, is significant, but remains challenging. Herein, a flame-retardant flexible composite phase change material was developed and applied for both the temperature control and thermal runaway prevention of battery packs. Specifically, a flame-retardant coating comprising 70 % polydimethylsiloxane as a binder was first investigated to determine the optimal mass ratio of 3:1 for the blend of expandable graphite and ammonium polyphosphate. The flame-retardant flexible composite phase change material was then produced by applying the optimal coating at a loading of 15 % on a flexible composite phase change material that was obtained from incorporating an ethylene propylene diene monomer with a mass fraction of 40 % into an 80 % paraffin/20 % expanded graphite composite. The flame-retardant flexible CPCM not only exhibited the highest flame-retardant rating of V-0, a significant latent heat capacity and good thermal reliability, but also demonstrated improved thermal conductivity and enhanced mechanical properties in tensile strength, bending, and compression as compared with the uncoated counterpart. The flame-retardant flexible composite phase change material achieves better temperature control performance for a battery pack compared to the material without a flame-retardant coating. Moreover, the flame-retardant flexible composite phase change material effectively prevents thermal runaway propagation within a battery pack. These favorable characteristics demonstrate the considerable potential of the flame-retardant flexible CPCM for battery thermal management in electric vehicles.

Hectorite aerogel stabilized NaCl solution as composite phase change materials for subzero cold energy storage

Inorganic phase change cold storage materials have garnered significant interest in cold chain transportation due to their high energy storage density. Nevertheless, practical applications have been hindered by inherent limitations such as high supercooling and susceptibility to phase separation. To address these challenges, this study devised 3D-Hectorite/sodium chloride (NaCl) composite phase change cold storage materials by utilizing 3D-Hectorite aerogel to adsorb NaCl solution, effectively mitigating the issue of phase separation common in such materials. Additionally, various concentrations of nucleating agents such as SrCl2·6H2O, borax, and diatomite were introduced for step cooling curve tests, establishing 0.03% diatomite as the optimal concentration for nucleation, reducing the supercooling of the NaCl solution to 1.1 °C. The results showed that the latent heat and thermal conductivity of 3D-Hectorite/NaCl were 215.30 J/g and 0.6315 ± 0.013 W/mK, respectively. The phase transition temperature could be adjusted in the range of -33~0 °C by changing the concentration of NaCl to meet the different temperature requirements. Furthermore, exceptional cyclic stability was observed even after subjecting the material to ten dissolution-solidification cycles. Analyzing the temperature change of the air inside the insulation bag showed that, compared with ice, 3D-Hectorite/NaCl can be applied to meet lower cooling temperature requirements, demonstrating good prospects for its application in cold chain transportation.

Development of a novel composite phase change material based on paints and brick for energy storage applications in agricultural greenhouses

This study addresses challenges associated with supercooling, phase separation, and inadequate thermal properties in Na2SO4·10H2O (SSD) by expanding the application of inorganic hydrate salt phase change materials within agricultural greenhouses. A novel composite phase change material, Na2SO4·10H2O-Al2O3 (NAPCM), was successfully synthesized using the vacuum impregnation method. NAPCM was strategically incorporated into paints and hollow bricks, leading to the creation of innovative phase change paint and phase change bricks designed for efficient thermal energy storage in agricultural greenhouses. The investigation revealed the homogeneous dispersion of porous Al2O3 particles in SSD, effectively preventing phase separation in NAPCM and ensuring its durable shape stability. The interaction between SSD and porous Al2O3 remained purely physical, with porous Al2O3 acting as an effective modifier to adjust various thermal properties of SSD. Optimal mass ratio determination for the combination of paint and NAPCM particles resulted in a 9:1 ratio, ensuring the uniform distribution of NAPCM particles within the paint matrix. This achieved a particle size averaging 290.93 μm with no discernible leakage features. The phase change paint exhibited an impressive solid content of 56.62 %, demonstrating exceptional resistance to water, alkali, salt, and abrasion. In thermal plate testing, the phase change paint significantly decelerated the heating rate. Infrared thermal imaging observations depicted circular areas with temperatures notably lower than their surroundings, indicating NAPCM's ability to impede heat absorption during the heating process, thereby reducing the rate of temperature change. The phase change paint also exhibited a slower cooling rate in the cooling test. Simultaneously, phase change bricks demonstrated superior thermal insulation compared to ordinary bricks. Throughout the heat storage phase, the temperature of the phase change greenhouse wall was lower than that of an ordinary greenhouse, while in the heat release phase, it was higher. The phase change greenhouse, relative to its ordinary counterpart, demonstrated superior insulation effects, creating a warm environment conducive to plant growth. This advancement enhances the energy storage performance of agricultural greenhouses, providing a novel solution for improving energy efficiency and environmental sustainability.

Experimental investigation on the stability and heat transfer enhancement of phase change materials composited with nanoparticles and metal foams

Conventional phase change materials (PCMs) possess the challenge of low thermal conductivity, which hinders the energy exchange rate and storage efficiency. PCMs composited nanoparticles and metal foams have been a proven solution to enhance the thermal characteristics of PCMs. In this work, three enhanced PCM composites including nanoparticle/paraffin, metal-foam/paraffin and nanoparticle/metal-foam/paraffin were prepared using fusion blending and vacuum impregnation method. The effects of different nanoparticles with different mass fractions on the stability and heat storage and release characteristics of nanoparticle/paraffin were investigated. Compared with paraffin, the melting time and solidification time of nano-metal/paraffin are reduced by a maximum of 30.18 % and 43.15 %, respectively. In addition, the effect of pore density of metal foam on natural convective heat transfer process was evaluated. The results showed that the stability in descending order is as follows: nano‑aluminum, nano‑copper and nano‑silver. The optimal mass fraction of nanoparticles with good stability was 1.5 wt% (copper), 1.0 wt% (silver), 1.5 wt% (aluminum), respectively. The metal foam makes the internal temperature distribution of PCMs more uniform in the heat transfer process, while inhibiting the convective heat transfer process. With the increase of pore density, the effect on natural convection heat transfer process rises. When the PPI (pores per linear inch) of foamed metal is greater than 40, the natural convection process can be inhibited, obviously. The foam metal has a more significant effect on the heat transfer performance of nanoparticle/metal-foam/paraffin than that of the nanoparticles. The economic benefits of nanoparticle/paraffin, metal-foam/paraffin and nanoparticle and metal foam composite phase change materials are progressively decrease, with MFP being suitable for applications with high economic budgets.

Enhancing the thermal conductivity and shape stability of phase-change composites using diatomite and graphene nanoplates for thermal energy storage

The effects of mixing diatomite and graphene nanoplatelets (GNP) with xylitol were examined in this study. Form stability and thermal conductivity were also evaluated. According to the experimental results, the PCM composites exhibited a thermal conductivity of 0.403 W/mK. Melting and solidification points were determined by differential scanning calorimetry (DSC) to be 89.0 °C and 36.5 °C, respectively. To maximize the thermal characteristics of the PCM, the response surface methodology (RSM) was utilized to create prediction models for thermal conductivity based on the mass fractions of diatomite and GNP. These findings highlight the importance of understanding how the introduction of nanoparticles affects thermal properties. The prospective use of PCM in thermal energy storage is enhanced by its higher solidification enthalpy, noteworthy thermal stability, and insights into the impacts of diatomite and GNP.

Encapsulation effectiveness and thermal energy storage performance of aluminum-graphite composite phase change materials subjected to oxide coating

The utilization of metals as phase change materials (PCMs) in high-temperature latent heat storage technology holds promising prospects, especially when integrated with concentrated solar power (CSP) systems, as it enables higher working temperatures for CSP and enhances power generation cycle efficiency. However, the practical application of metal-based phase change processes faces challenges such as liquid leakage and high-temperature corrosion, which impede their widespread implementation. In this study, aluminum (Al) is employed as the PCM, while expanded graphite (EG) is used as the matrix material. Composite PCMs with embedded structures were synthesized using powder metallurgy techniques. Notably, an oxidation pre-treatment process was employed to create an oxide layer on the surface of Al particles, thereby improving the encapsulation performance and thermal properties of the composite PCM. By increasing the oxidation pre-treatment temperature to 1100°C, the maximum encapsulation ratio was enhanced from 50 wt% to 80 wt%, and the latent heat energy storage density increased from 101.0 J/g to 188.2 J/g. Moreover, the composite PCM subjected to oxidation pre-treatment at temperatures of 670°C and above maintained a stable structure, chemical composition, and energy storage density after 50 thermal cycles. Within the temperature range of 600–700°C, the total energy storage density of the composite PCM reached 284.5 J/g. These results indicate that the oxidation pre-treatment is a promising technology in high-temperature energy storage technology.

Experimental study on the temperature control characteristics of graphite foam-based composite phase change materials

Thermal management systems are crucial for ensuring the reliable operation of electronic devices. Heat dissipation using phase change materials (PCMs) is an effective, lightweight method for devices experiencing transient high heat flow. Graphite foam (GF), known for its high thermal conductivity and low density, significantly increases thermal conductivity when combined with PCMs. However, research on the heat transfer characteristics of composite PCMs is limited. This study experimentally investigates the heat dissipation characteristics of a graphite foam-PCM (GF-PCM) composite cooling structure. It explores the impact of factors like the shell's tilt angle, acceleration, and the position of cavities (voids) between the PCM and the shell structure on the transient melting heat transfer of the cooling device under varying thermal source heat flux densities. Results show that using a pure paraffin phase change module, the temperature rise of the heat source increases with the tilt angle, and horizontal placement offers the best heat dissipation and temperature control. The position of the cavity influences heat dissipation; at 30W heating power, a cavity between the heat source and paraffin increases the temperature rise of the heat source by 19.2 %. Furthermore, cavity position is affected by acceleration; at 50W heating power and 3.6g acceleration, the cavity shifts from the top of the module to near the heat source side, increasing its final temperature by 3.7 °C. Acceleration also enhances liquid paraffin convection, significantly affecting paraffin's later melting stage. Adding graphite foam speeds up paraffin melting, reducing the temperature rise of the heat source by 42.8 %, 42.9 %, and 28.3 % at 30W, 40W, and 50W heating powers, respectively. This improvement mitigates the adverse effects of tilt angle, cavities, and uncertainties introduced by acceleration.

Epoxy resin/ aluminium hydroxide/expanded graphite synergistic effects on advancing flame retardancy, mechanical structure and thermal management of octadecanoic acid and octadecanol-based eutectic phase change materials

In the present research, a novel approach wherein a flame-retardant composite phase change material (PCMs) is devised by incorporating eutectic PCMs, epoxy resin (ER), aluminium hydroxide (ATH), and expanded graphite (EG). This innovative formulation capitalizes on the synergistic interaction between ER and ATH, alongside the porous structure of EG, resulting in a triple-layer encapsulation of the eutectic PCMs. The outcome of this formulation is marked by remarkable thermal stability, even under extreme conditions such as exposure to temperatures as high as 800 °C. Notably, one of the representative samples, denoted as S5, showcases impressive attributes with a thermal conductivity of 1.335 W∙m-1K−1 and a substantial phase change latent heat of 150.4 J∙g−1. It was observed an increase in latent heat up to 181.3 J∙g−1 after 100 heating–cooling cycles of composite PCMs. This indicates the good thermal reliability of the form-stable composite PCMs synthesized. Moreover, the composite PCMs exhibit outstanding mechanical properties, especially S5 which showed a 14.69 % and 400.12 % increase in compression strength and compression modulus compared with pure eutectic PCM (S0), respectively. Besides, the ternary composition of ER, ATH, and EG enhances the flame retardancy of the composite PCMs, yielding a substantial reduction of 67.33 % in peak heat release rate and 50.38 % in total heat release. This collaborative effect also establishes a robust defense mechanism against the rapid propagation of flames, as exemplified by the attainment of a V-0 rating in the UL-94 test. As a result, the flame-retardant ER/ATH/EG ternary-based form-stable composite PCM presents itself as a promising candidate for ensuring both safety and efficiency in thermal management applications.

Porous carbon network-based composite phase change materials with heat storage capacity and thermal management functions

Porous carbon network-based phase change composites have been widely used in energy storage and thermal management related fields. At present, the demand of energy crisis for photothermal energy storage and the prevention and management of thermal abuse of electronic equipment constantly promote the development of carbon-based composite phase change materials (PCMs). Therefore, a series of new composite materials filled with PCMs and polyethylene glycol (PEG) and added with flame-retardant magnesium hydroxide were developed, which makes the composites show certain flame-retardant ability in high-temperature environments. The results show that the thermal conductivity increases from 0.25 to 0.94 W/m·K, and the latent heat of phase change remains at 142.7 J/g. In addition, due to the capillary effect caused by the synergistic effect of multi-pore carbon (MPC) structure and cellulose macromolecular chain, the composite material has good shape stability, which effectively prevents the leakage behavior of PCMs during solid-liquid phase change. Moreover, the absorbance of the composite material can reach 1.28 L/(g cm) in the ultraviolet–visible light range of 200 nm–800 nm, and its photothermal conversion efficiency can reach 90.8 %. Therefore, this material has a broad application prospect in the thermal management of electronic equipment and photothermal energy storage devices.

Preparation and characterization of eicosane-paraffin/expanded graphite/polyurethane as form-stable composite phase change materials with wide phase change temperature range

Phase change materials (PCMs) with wide phase change temperature range, high latent heat, good thermal conductivity, and shape stability are essential for applications such as solar energy conservation and thermal management of electronic devices. Form-stable composite PCMs (FSCPCMs) with a broad phase change temperature range of 18–65 °C were successfully developed by using a mixture of eicosane and paraffin mixture along with cross-linking polyurethane as PCM, expanded graphite as thermally conductive filler and supporting material. The prepared FSCPCMs demonstrated excellent thermal stability and thermal conductivity with a latent heat up to 142.5 J/g. In conclusion, the synthesized FSCPCMs exhibit promising potential for practical applications in thermal energy storage.

An energy saving strategy on the composite phase change material and spiral liquid cooling channel for battery thermal management

In order to ensure the safety and stability of the cooling system during the operation of the battery thermal management system combined with composite phase change material cooling and liquid cooling, it is usually necessary to continuously pump cooling water. It inevitably caused that the latent heat of composite phase change material could not be fully released and extra pump power was consumed. In the study, five different energy saving strategies were proposed and the energy efficiency ratio was defined to evaluate their cooling effects and energy saving. The effect of energy saving strategies on energy consumption of liquid cooling and latent heat utilization of composite phase change material was analyzed. The results show that III and V can meet their cooling requirements and have a high energy efficiency ratio. The screw pitch and cooling water flow rate in these two modes were investigated. The results show that the increase in screw pitch reduces the heat transfer efficiency, resulting in an increase in Tmax and ΔTmax, and ΔTmax exceeding the maximum range. Diminishing the cooling water flow will precipitate a rise in battery temperature, enabling the CPCM to operate at its maximum capacity and consequently decreasing ΔTmax. As a cooling water flow of 20 ml/min in III and V all can satisfy the cooling requirements. Additionally, the III was also competent when the cooling water temperature was raised from 25 °C to 35 °C.

Stable and reliable PEG/TiO2 phase change composite with enhanced thermal conductivity based on a facile sol-gel method without deionized water

Some shortcomings exist in organic phase change materials, including leakage susceptibility, low thermal conductivity, and preparation complexity. Herein, polyethylene glycol/titanium dioxide shape-stabilized composite phase change material (PEG/TiO2 ss-CPCM) was fabricated by facile sol-gel method without deionized water using tetrabutyl titanate (TBOT) as precursor. In this composite, not adding deionized water prolonged the gelation time, allowing PEG to bind as much TiO2 as possible and enhancing energy storage capability; TiO2 acted as the supporting framework to maintain the material's shape stability and enhance thermal conductivity. The melting and crystallization phase change enthalpies of prepared PEG/TiO2 ss-CPCM were 128.3 J/g and 113.1 J/g with an encapsulation efficiency of 74.14 % when PEG: TBOT = 1.5: 1. After repeating 300 thermal cycles, the phase change enthalpy remained almost constant. Besides, the thermal conductivity of PEG/TiO2 ss-CPCM was 1.22 times that of PEG, and the potential for thermal management applications. The advantages (energy storage capability, shape stability in thermal environments, thermal reliability, and thermal management) of the PEG/TiO2 ss-CPCM prepared by facile synthesis, not only propose a phase change material with excellent thermal properties and shape stabilization but provide a green and feasible strategy for the fabrication of PEG/TiO2 composite phase change materials utilizing the sol-gel method.

Preparation and Application of Composite Phase Change Materials

With the popularity of lithium-ion batteries, thermal runaway accidents occur frequently. The importance of thermal management was becoming increasingly prominent. In this paper, a new composite phase change material (CPCM) was developed and applied to the thermal management of lithium-ion batteries. The chemical and microstructure of the material were deeply analyzed by scanning XRD and SEM. The thermal stability of the material was tested by using DSC and TG techniques. The thermal conductivity was exhaustively analyzed. The experimental results showed that CPCM containing 9% Aluminum phenylphosphinate exhibits optimal thermal storage performance and flame retardant efficiency, which effectively delayed and reduced the risk of thermal runaway in lithium batteries.

Experimental and parametric analysis of a novel hybrid thermal management strategy for cylindrical lithium‐ion cells

AbstractThis paper reports on a novel hybrid thermal management strategy. It uses secondary coolants (air and liquid) to withdraw heat simultaneously from the composite phase change material, resulting in increased heat extraction capability of the composite phase change material and improved thermal environment of the battery module. The significance of this strategy is that the fluid used in the liquid cooling stays stationary. Comprehensive experimental and numerical studies are performed, and parametric studies are conducted to reduce the volume of the phase change material, size of the air duct, and airflow Reynolds number. The numerical results showed that the maximum temperature was limited to 27.8°C, and a high‐temperature uniformity of 0.4°C was obtained. Furthermore, the required volume of the composite phase change material is reduced by ~50%. Additionally, beyond a 6 mm height of the air duct, the reduction in maximum pressure drop is not significant enough, and it is considered the optimal height, and a Reynolds number of 1950 is considered the optimal airflow Reynolds number. Therefore, the proposed thermal management concept for the battery module can sustain the thermal environment needed for the effective operation of Lithium‐ion batteries.

Novel MoS2/montmorillonite hybrid aerogel encapsulated PEG as composite phase change materials with superior solar-thermal energy harvesting and storage

Phase change materials (PCMs) offer significant advantages in energy conversion and storage by facilitating the storage and release of thermal energy during phase transition processes. However, challenges such as leakage during PCM phase transitions and poor light absorption properties have constrained their application in the field of photothermal energy storage. In this study, Montmorillonite (Mt) and molybdenum disulfide (MoS2) has been used to design and synthesize hybrid aerogels (MoS2/Mt) boasting high mechanical strength and excellent photothermal conversion performance. These aerogels are then used to encapsulate polyethylene glycol (PEG) to prepare composite PCMs with outstanding solar-thermal conversion and storage performances. The results show that the synthesized MoS2/Mt-PEG composite PCMs exhibit high enthalpies of melting and solidification of 169.16 J/g and 170.78 J/g, respectively, while the aerogel supporting material has a high compressive modulus of 1.96 MPa. Moreover, the composite material displayed excellent thermal stability and leakage resistance after undergoing 30 melting-cooling cycles. Furthermore, the incorporation of MoS2 imparted outstanding light absorption properties to the MoS2/Mt-PEG composite, resulting in a high light absorption and photothermal conversion-storage efficiency of 93.4 % and 96.47 %, respectively. Synthesized composite PCMs also demonstrate outstanding performance in solar-thermal-electricity conversion, achieving a voltage output of 458 mV under illumination conditions and maintaining a sustainable voltage output even after removing the light source. Thus, the composite PCMs prepared in this work can meet the requirements of high enthalpy, effective leakage prevention, efficient solar-thermal conversion and solar-thermal-electricity conversion performance, thereby presenting potential applications in practical solar energy collection, conversion, and storage.

Preparation and Performance of Inorganic Hydrated Salt-Based Composite Materials for Temperature and Humidity Regulation

In this work, it was first proposed to combine hydrated salt phase change materials (PCMs) with humidity control materials to prepare the temperature and humidity control material. The composite PCM was prepared by absorbing Na2HPO4·12H2O with colloidal silicon dioxide, and diatomite was selected as the humidity control material. The humidity performance tests found that diatomite had good moisture absorption/desorption capacity and excellent moisture buffering capacity. The supercooling degree tests showed that Na2SiO3·9H2O as nucleating agent effectively reduced the supercooling degree, and the addition of deionized water improved the water loss problem of composite PCMs. The DSC tests showed that the enthalpy and melting temperature of composite PCMs were 153.1 J/g and 28.9°C, respectively. By placing the temperature and humidity control material in different humidity, it was found that the moisture content of diatomite affected the thermal properties of composite PCMs. Diatomite could not only transfer moisture to hydrated salts but also absorb moisture from hydrated salt. The application performance tests of the temperature and humidity control material in the room model showed that it could simultaneously regulate indoor temperature and humidity. Overall, this temperature and humidity control material was more suitable for environments with high relative humidity such as greenhouses.

Adjustment of phase change temperature using KCl to develop composite phase change materials based on super absorbent polymer as carrier for use in building energy conservation

In the present work, a Na2HPO4·12H2O–KCl/SAP composite phase change material (CPCM) adapted to the comfortable indoor temperature of the human body has been successfully prepared. The CPCM was developed by physical mixing of Na2HPO4·12H2O (DSP) as the main PCM, KCl as temperature regulator and super absorbent polymer as carrier. In addition, the CPCM was characterized by various techniques, and its thermal properties were analyzed. The results showed that the phase change temperature (Tm) of DSP could be adjusted from 35.8 °C to 32.7 °C by KCl and the DSP-KCl mixture containing 4 % KCl had a high enthalpy value (241.5 kJ kg−1). The cooling curve test found that adding 0.75 % nano-α-Al2O3 as nucleating agent could greatly reduce the supercooling degree of DSP-KCl mixture to 3.39 °C. Adding 14 % SAP into the mixture can solve the leakage and reduce the supercooling degree and thermal conductivity. The resulting CPCM with 14 % SAP added had appropriate Tm (26.9 °C), high enthalpy value (153.5 kJ kg−1), low supercooling degree (1.34 °C) as well as thermal conductivity (0.3079 W K−1 m−1) and excellent thermal reliability. These results indicated that the CPCM was suitable for the field of building energy conservation.

Phase Engineered Composite Phase Change Materials for Thermal Energy Manipulation.

Phase change materials (PCMs) present a dual thermal management functionality through intrinsic thermal energy storage (TES) capabilities while maintaining a constant temperature. However, the practical application of PCMs encounters challenges, primarily stemming from their low thermal conductivity and shape-stability issues. Despite significant progress in the development of solid-solid PCMs, which offer superior shape-stability compared to their solid-liquid counterparts, they compromise TES capacity. Herein, a universal phase engineering strategy is introduced to address these challenges. The approach involves compositing solid-liquid PCM with a particulate-based conductive matrix followed by surface reaction to form a solid-solid PCM shell, resulting in a core-shell composite with enhanced thermal conductivity, high thermal storage capacity, and optimal shape-stability. The core-shell structure designed in this manner not only encapsulates the energy-rich solid-liquid PCM core but also significantly enhances TES capacity by up to 52% compared to solid-solid PCM counterparts. The phase-engineered high-performance PCMs exhibit excellent thermal management capabilities by reducing battery cell temperature by 15°C and demonstrating durable solar-thermal-electric power generation under cloudy or no sunshine conditions. This proposed strategy holds promise for extending to other functional PCMs, offering a compelling avenue for the development of high-performance PCMs for thermal energy applications.

Preparation and Thermal Performances of Lauric Acid/Polyvinyl Butyral/Graphene Nanoplates Composite Phase Change Materials

In recent years, there has been significant progress in the development and application of phase change materials (PCMs) for thermal energy storage. The new lauric acid (LA)/polyvinyl butyral (PVB)/graphene nanoplates (GNP) composite phase change materials (CPCM) are prepared using the solution blending method, in which LA acts as PCM, PVB serves as support material, and GNP is used as thermally conductive enhancer. The prepared CPCM with 80 wt% LA can retain stable shape without leakage. The Fourier‐transform infrared and X‐ray diffractometer results indicate that there is no chemical reaction among the various components of the CPCM. The differential scanning calorimeter results show the CPCM3 (with 80 wt% LA and 5 wt% GNP) has melting latent heat of 134.41 KJ Kg−1 with melting temperature of 41.73 °C. The thermal conductivity tests present that thermal conductivity of CPCM3 is 0.689 W (m K)−1, which is 3.83 times that of the PCM2. The thermogravimetric analyzer results verify that the CPCM possess good thermal stability within the operating temperature range of 35–45 °C without any degradation. The thermal cycling tests indicate that CPCM have good thermal reliability. Therefore, it has promising applications in building energy conservation, solar thermal systems, thermal management, and textiles.

Development and investigation of salt based composite phase change material containing diatomite as skeleton substance by cold sintering technology for medium and high temperature thermal energy storage

This work concerns the development of a nitrate salt based form-stable composite phase change material by cold sintering technology with the employment of diatomite as skeleton substance. Such fabrication strategy has never before been reported in the literature and we demonstrate for the first time the feasibility of salt-diatomite composite production through a cold sintering process by means of sodium hydroxide solution as sintering additive. The microstructural characteristics and development mechanism, chemical and physical compatibility, mechanical strength, phase change behaviour, thermal and shape stability of the composite are investigated to reveal the structure formation and densification mechanism of salt and diatomite. The results show that the composite could be sintered at a temperature of 180 °C, far lower than that required in the traditional hot sintering approach. Due to the congruent solubility of the salt and diatomite in aqueous alkali, a rigid and dense structure induced by a so-called dissolution-precipitation process could be generated in the composite, which provides solution to accommodate the salt, endowing the composite with splendid capacity to maintain the structure stability and restrain the liquid leakage over the phase change process. An excellent chemical and physical compatibility has been achieved between the salt and other components, and over 60 wt% salt could be encapsulated in the composite by which a melting temperature around 278 °C and an energy storage density over 650 kJ/kg at a temperature range of 50–600 °C are attained. The results also reveal that the composite exhibits preeminent mechanical strength and excellent thermal cycling performance. For a given cycling temperature range of 50–500 °C, a stable macroscopic shape with a compressive strength over 210 MPa could be achieved in the composite even after 100 times of thermal cycles.