Expanded Graphite Matrix Research Articles

Experimental study of phase transition heat of composite thermal energy storage materials paraffin wax/expanded graphite

In this paper, the effect of the expanded graphite (EG) matrix on the phase transitions enthalpy of phase change material (PCM) is studied experimentally. For this purpose, the paraffin wax (PW) containing EG (up to 6.5 wt%) was explored in terms of the effective heat capacity and a diffuse phase transitions enthalpy difference over the 25–65 °С temperature range. Composite PCMs PW/EG was prepared using a new method and were inherent in high pores fill factor. The main advantage of the proposed method is preliminary vacuuming of the PW and EG with subsequent mixing and sonication under vacuum. The EG choice was based on the hypothesis that the EG matrix contributes to modifying the PW internal structure due to the PW molecules' adsorption on the EG surface during PCM cooling and solidification. Consequently, a significant change in PW/EG caloric properties vs. pure PW was observed. The EG presence in PW reverses the enthalpy hysteresis in the heating-cooling cycle vs. pure PW. The enthalpy difference during PW heating and melting in the range of 30–60 °С is higher than during its cooling and solidification: 336.2 J∙g−1 vs. 214.9 J∙g−1. On the contrary, the enthalpy difference of melting for PW/EG of 3.6 wt% in the range 30–60 °С was 171.2 J∙g−1 vs. 273.8 J∙g−1 during solidification. The obtained results are explained by the different dynamics of processes of PW melting and solidification in EG matrix pores. The presence of the 3.2–6.5 wt% of EG in PW contributes to an increase in solidification enthalpy difference in the range 30–60 °C on 27–33 % vs. pure PW. A decrease in the melting enthalpy difference for PW/EG on 44–50 % vs. pure PW was recorded in the range of 30–60 °C. In addition, thermal conductivity was measured to confirm the advantages of PW/EG as PCM. Thermal conductivity for PW/EG with EG content of 3.6 and 6.5 wt% at 25 °C was 8.9 and 9.6 times higher than for pure PW. Similarly, 8.8 and 10.9 times thermal conductivity increase was observed at 65 °C. The composite PCM containing 3.6 wt% of EG in PW obtained by developed method can be recommended as a rational composition in benefit of the thermal conductivity and caloric properties for utilization in high-performance TES systems.

Research on Expanded Graphite Matrix Phase Change Composites

As a new functional material, expanded graphite has many excellent properties such as light weight, low density. non-toxic and harmless, high and low temperature resistance, environmental protection and energy saving. With the continuous progress of science and technology and scientific research, expanded graphite composite materials such as expanded graphite are continuously used in various research fields. For example, absorb environmental pollution, sealing materials, flame retardant materials, shielding interference materials, etc. In this paper, the microstructure, excellent properties of EG, the preparation of EG matrix composites, and the research and development of graphitization for special applications of expanded graphite and expanded graphite matrix are reviewed. Through these studies and reviews, it is hoped that some inspiration can be given to the research on the direction of expanded graphite matrix composites, which will help to explore new fields in the future.

Thermal energy storage composites with preformed expanded graphite matrix and paraffin wax for long-term cycling stability and tailored thermal properties

Harvesting solar energy, preventing hot spots in electronics, transport of temperature-sensitive materials, and capture and repurposing of thermal energy require a latent heat thermal energy storage (TES) system to store/discharge heat repeatedly. For the practical application of phase change material (PCM) composites within TES systems, reliable thermal performance throughout its operational lifetime is essential. Nevertheless, the reliability of thermal conductivity in multi-phase composites over relevant numbers (>103) of melt/freeze cycles has barely been studied, particularly for composites containing fillers for thermal conductivity enhancement. Here, we introduce a preform-type expanded graphite (EG)/paraffin wax composite possessing highly robust heat transfer and storage properties even after 10,000 melt/freeze cycles. To achieve such excellent reliability, comparative studies on the combined influence of fabrication process, particle size, EG vol%, binder amount, and compaction on both magnitude and robustness of thermal conductivity were undertaken. Our parametric study has yielded a trade-off between thermal conductivity and latent heat. Based on our modeling, 20 vol% EG approaches the case where all EG particles are well-connected thermally while 10 vol% EG is close to loosely connected fillers in the matrix. Thermal conductivity of our paraffin composites containing 20 vol% EG (25.1 W·m−1·K−1) is highest among other EG/paraffin composites without aligned EG in the literature. After 10,000 thermal cycling, negligible conductivity fading was observed for the 10 vol% EG composite, while reduction in latent heat remained within 10% for all 10, 14, 17 and 20 vol% EG samples. We anticipate this work provides insight on suitable recipe for desirable magnitude and robustness of thermal conductivity of EG/paraffin composites.

Transient Finite Element Simulation of a Lithium-Ion Battery Pack Thermal Management System Based on Latent Heat System Materials

High-intensity use of lithium-ion battery packs can lead to overheating. When heat generated from battery use exceeds the rate at which its surroundings dissipate the heat, thermal runaway occurs. 12-cell and 84-cell assemblies of lithium-ion NCR18650B batteries exceeded the manufacturer maximum temperature after a discharge at constant power, 1P. To passively regulate the temperature of the battery packs, a phase-change material was used as a latent heat system, transferring heat from the cells to the material during operation. Utilizing ANSYS, finite element analysis simulations were performed to show the advantage of an expanded graphite matrix infiltrated with paraffin wax. Material properties of the mixture were studied with differential scanning calorimetry and an ideal mixture of 25% EG and 75% PureTemp 60 paraffin wax was found. The results verified that the mixture significantly lowered the temperature of the cells; providing a cost efficient, accessible solution to counter increased operating temperatures.

Characterisation and sorption behaviour of LiOH-LiCl@EG composite sorbents for thermochemical energy storage with controllable thermal upgradeability

• Binary lithium-based salt hydrates hierarchical inclusion in the matrix. • Temperature lift is over 20℃ accompanied by high energy density. • Energy capacity decreases with the discharging temperature. • Over 95% of the original energy capacity is maintained after 20 cycles. Considering the eminent benefits of high energy storage density (ESD) and long-term energy storage ability with ignorable heat losses, thermochemical energy storage (TCES) in salt hydrates is a potential technology to bridge the gap between supply and demand for renewables in domestic heating. The development of thermochemical material is currently the primary concern. In this work, the composite sorbents consisting of expanded graphite (EG) and varying mass ratios of LiOH and LiCl are synthesised and characterised, and the thermochemical behaviours such as sorption kinetics and sorption isotherms are also investigated. The results suggest the salts are uniformly dispersed in the EG matrix in the form of hierarchical micro-nano scale particles, and the salt contents of samples are over 60 wt%, which in favour of the enhancements of vapour sorption property and ESD. By regulating the mass ratio of LiOH and LiCl, the composite sorbents (LiOC@EG) can achieve thermal upgrade with different temperature requirements, i.e., 35–45℃ for space heating and 45–55℃ for domestic hot water (DHW) production, accompanied by high volumetric ESD (over 200 kWh/m 3 ) benefiting from the reaction enthalpy. Besides that, the effects of regenerative temperature and vapour pressure on the water uptake and ESD of the sorbent are revealed. The cyclability results indicate that more than 95% and 96% of the original ESDs are retained after 20 dehydration-hydration cycles for the samples of LiO2C1@EG and LiO3C1@EG, suggesting good stability of the composites. The developed composite sorbents provide new insights into the fields of long-term energy storage and heat upgrade with high energy density.

Development of the inorganic composite phase change materials for passive thermal management of Li-ion batteries: Application

In this study, two inorganic phase change materials (PCM) were tested to be used for thermal control of lithium-ion batteries. Paraffin wax was used as a reference material. To increase thermal conductivity, the PCMs were impregnated into the expanded graphite matrix, forming composite PCM (CPCM). Four types of Li-ion battery packs were manufactured to show the difference in performance between the packs with various CPCMs and No-CPCM.Electrical cycling studies at ambient temperature showed that at C/2 discharge the No-CPCM pack surpasses 35 °C, while all CPCM packs remain around 30 °C, demonstrating similar behavior. At 1C discharge, No-CPCM pack reaches 49 °C, whereas the CPCM packs do not exceed 40 °C. At 2C discharge, the No-CPCM pack overpassed the safety limit of 65 °C and was stopped before completing the first discharge. The CPCM packs successfully completed the cycling. Studies performed at 45 °C demonstrate a similar trend, but with higher peak temperatures. Nail penetration testing proved that the inorganic CPCMс inhibited the pack from self-accelerated degradation, successfully prevented thermal runaway propagation and potential explosion. Low cost and incombustibility make inorganic PCMs а viable alternative to the organic PCMs, with a positive impact on environmental and economic issues.

Study on the microwave absorbing properties of Fe nanoparticles prepared by the HEIBE method in expanded graphite matrix composites

Recent findings reveal that expanded graphite (EG) composite with metal nanoparticles has an excellent performance in the field of absorbing materials. The N-dope broken EG/FeNPs (NBEG/Fe) composites with sandwich structure and low graphitization degree were prepared through hydrothermal reaction. The doping N element further enhances the electrical conductivity of EG, the purpose is to be consistent with the high permeability of the core-shell Fe/Fe3O4 nanoparticles (FeNPs), which can effectively improve the matching impedance. The experimental results in the 2–18 GHz range prove that NBEG/Fe has better absorption performance than pure EG and BEG/Fe, and by changing the content of FeNPs, the purpose of effectively absorbing electromagnetic microwaves in different frequency bands can be achieved. With only 10% addition of NBEG/Fe, when the matching frequency is 15.67 and 4.51 GHz, and the matching thickness is 1.42 and 5.40 mm, the reflection loss (RL) of NBEG/Fe reaches −56.75 and −43.3 dB, the RL value of NBEG/Fe has also reached an effective absorption bandwidth of 3.92 GHz (RL ≤ 20.0 dB) in the interval 4.06–10.64 GHz. In particular, the RL value of NBEG/Fe in the S-band (at 3.74 GHz) reaches −40.3 dB at a thickness of 6.5 mm. Moreover, under the matching frequency and matching thickness good absorption performance (RL<−20.0 dB) from 2.00 GHz to 18.00 GHz is obtained.

Synthesis and Characterization of Magnetic Expanded Graphite Material (EG@CoFe2O4) Through Sol-Gel Processing

The development of novel materials is indispensable to industrial development due to their instrumental role in medical and decontamination applications. Expanded graphite (EG) possesses a number of advantages including pore structure, non-toxicity and ease of recoverability, making it suitable materials for a wide array of possibilities in many fields. In this paper, a material composite based on expanded graphite (EG) and cobalt ferrite (CoFe2O4) was successfully prepared by the direct sol-gel process. The obtained EG@CoFe2O4 was then characterized using a number of analysis techniques including scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray (EDX) and Fourier transform infrared spectroscopy (FT-IR). The results indicated successful impregnation of CoFe2O4 into the EG matrix. The as-synthesized EG@CoFe2O4 is also uniform and possessed good crystallinity. The isotherm of the obtained EG@CoFe2O4 material seems to follow the typical type IV isotherm and the pore size of the materials ranged from 2-55 nm.

Fabrication of MoS2 loaded on expanded graphite matrix for high-efficiency pH-universal hydrogen evolution reaction

As a promising electrocatalyst for hydrogen evolution reaction (HER), molybdenum disulfide (MoS2) owns inadequate edge active sites and inferior conductivity which restricts its effective application. In this study, the expanded graphite matrix (EGM) cathode was fabricated by tableting worm-like expanded graphite (EG), acetylene black and poly tetra fluoroethylene (PTFE) emulsion, and MoS2 grew on EGM via a hydrothermal synthesis process, subsequently employed for the HER process. Benefiting from the superior conductivity and sufficient exposure of edge active sites on the rough structure of EGM, MoS2/EGM exhibits a small overpotential of 230 mV (j = 10 mA cm−2), a low Tafel slope of 77 mV·dec−1 and a lower value of charge transfer resistance (Rct, 0.919 Ω cm2). The improvement of HER performance of MoS2/EGM could be due to the participation of the EGM as a highly conductive substrate. Excellent electrochemical durability of MoS2/EGM was attested by the cyclic voltammetry and the amperometric (i−t) measurements. This work may have the potential to develop a promising path to design advanced electrode materials for HER.

Scaled prototype of a tantalum target embedded in expanded graphite for antiproton production: Design, manufacturing, and testing under proton beam impacts

This study presents a further step within the ongoing R&D activities for the redesign of the CERN's Antiproton Decelerator Production Target (AD-Target). A first scaled target prototype, constituted of a sliced core made of ten Ta rods -8 mm diameter, 16 mm length- embedded in a compressed expanded graphite (EG) matrix, inserted in a 44 mm diameter Ti-6Al-4V container, has been built and tested under proton beam impacts at the CERN's HiRadMat facility, in the so called HRMT-42 experiment. This prototype has been designed following the lessons learned from previous numerical and experimental works (HRMT-27 experiment) aiming at answering the open questions left in these studies. Velocity data recorded on-line at the target periphery during the HRMT-42 experiment is presented, showing features of its dynamic response to proton beam impacts. Furthermore, x-ray and neutron tomographies of the target prototype after irradiation have been performed. These non-destructive techniques show the extensive plastic deformation of the Ta core, but suggest that the EG matrix can adapt to such deformation, which is a positive result. The neutron tomography successfully revealed the internal state of the tantalum core, showing the appearance of voids of several hundreds of micrometers, in particular in the downstream rods of the core. The possible origin of such voids is discussed while future microstructure analysis after the target opening will try to clarify their nature.

Preparation of expanded graphite/polyethylene glycol composite phase change material for thermoregulation of asphalt binder

Phase change materials (PCMs) have been widely applied as heat storage and thermal regulation units in many areas. However, the utilization of PCMs in asphalt pavements for thermal regulation is still limited because of the low thermal conductivity and melted phase leakage of the common used solid-liquid PCMs. The aim of this paper was to prepare a shape-stabilized expanded graphite (EG)/polyethylene glycol (PEG) composite phase change material (EG/PEG) with high thermal conductivity, and to verify its feasibility of regulating temperatures of asphalt binder. EG and PEG were selected as supporting material and working substance respectively. The EG/PEG composites and their modified asphalt binders were fabricated respectively by vacuum adsorption and physical blending process. X-ray diffraction (XRD) and differential scanning calorimeter (DSC) analyses indicated that the crystallization ability and phase change behavior of PEG was hindered by the increase of EG in the composites. The nitrogen adsorption analyses revealed that the EG matrix had an adsorptive limitation to PEG. The aforementioned results indicated that the maximum mass ratio of EG and PEG in the composites without any leakage during the melting period was 1:7. This conclusion was also proved by scanning electron microscopy (SEM) and Fourier transform infrared (FT-IR) spectrum. The thermogravimetric analyses (TGA) verified the viability of EG/PEG composites during the hot mixing process of asphalt mixture. The thermal analysis experiments indicated that the thermal conductivity and compatible stability of asphalt binder were improved by adding EG/PEG composites, and the thermal regulation effects of EG/PEG composites on the asphalt binder was verified by a thermocouples proved.

Adsorption and decomposition of dimethyl methylphosphonate (DMMP) on expanded graphite/metal oxides

Composites based on expanded graphite (EG) and metal oxides (MOs) were prepared by an explosive combustion and blending method. A metal oxide (Ag2O, CuO or ZnO)-containing phase was employed as a component with reactive functionality, which was supported on EG as a component with adsorptive functionality. The physical properties of the EG/MO composites were examined using SEM and FTIR spectroscopy, the results of which indicated that the MOs were incorporated in the EG matrix after impregnation. Solid state magic angle spinning (MAS) 1H, 31P and cross polarization (CP) MAS 13C NMR studies of the EG/MO composites were performed after adsorption of dimethyl methylphosphonate (DMMP). The FTIR and NMR data showed that the initial uptake occurred through both molecular and reactive adsorption. Molecular adsorption occurred by van der Waals interaction of M(Zn, Cu, Ag)⋯OP and hydrogen-bond formation to isolated hydroxyl groups. Reactive chemisorption appeared to occur through interaction with both Lewis acid sites and active oxygen species present on the MO surface. The FTIR and NMR results exhibited a trend of reactivity towards DMMP in the order Ag2O > ZnO > CuO, which indicated stronger interaction between the Lewis acid sites and the phosphoryl O atom of DMMP for Ag2O as compared with ZnO and CuO, with concomitant formation of surface-coordinated DMMP and bridge-bonded OPO phosphorus oxide species.

Preparation and thermal performance of form-stable expanded graphite/stearic acid composite phase change materials with high thermal conductivity

Thermal energy storage plays an important role in improving the working reliability and utilization efficiency of renewable energy systems. Thermal energy storage includes sensible heat storage, latent heat storage using phase change material (PCM) and thermochemical heat storage. In comparison with sensible heat storage, latent heat storage has the distinct advantages of its high energy storage density and stable temperature during the energy storage and release processes. However, low thermal conductivity of PCM is the common drawback for various latent heat energy storage systems. The purpose of the research is to enhance the thermal conductivity of PCM by developing new form-stable composite phase change materials using expanded graphite matrix. Firstly, a preparation method “heating adsorption of liquid SA into expanded graphite (EG) matrix and compressing stable-shape composite” is employed to synthesis form- stable composite phase change material. Twenty samples with different EG contents and packed densities are prepared using stearic acid (SA) as phase change material and two kinds of EG with different dilatation as porous matrix. Secondly, the microstructures, thermal properties and thermal stabilities of different EG/SA samples are tested to analyze the influence of the dilatation of expanded graphite on the thermal performance of form-stable composite phase change materials. Moreover, EG/SA form-stable heat storage units with different EG contents and packed densities are fabricated to analyze the thermal storage/release performance through heating/cooling experiment. The microstructures of EG and EG/SA samples are observed using scanning electron microscopy (SEM) and the results show there exist obvious differences between two kinds of EG and SA distribution in the samples. The EG/SA samples with high dilatation EG are even more uniform because the high dilatation EG has larger pore size and pore volume. The data obtained from differential scanning calorimetry (DSC) show the addition of EG and compressing operation have negligible effect on the latent heat and slightly increase the phase transition temperature of pure SA. The form-stable EG/SA composite PCMs have lower supercooling degree than pure SA. LFA447 flash thermal diffusivity instrument is used to evaluate the effect of EG’s dilatation on the thermal conductivity of EG/SA samples. The results show that the use of high dilatation EG is more effective to improve the thermal conductivity of form-stable EG/SA composite PCMs when packed density is large. The radial thermal conductivity of form-stable 20 wt.%EG/SA phase change composite with packed density of 950 kg m−3 is as high as 19.6 W m−1 K−1 when high dilatation EG is utilized. This figure is more than 110 times higher than that of pure SA. Finally, the thermal stability of EG/SA samples is conducted by repeating the charging and discharging processes of SA. These samples prepared by high dilatation EG have better thermal stability than the samples prepared by low dilatation EG. The EG with high dilatation can assure the uniform distribution of SA inside EG/SA sample and thus prevent the leakage of liquid SA during the phase change transformation process due to its dilated microstructure. The heating/cooling test results show that the heat storage/release time of EG/SA composite units is about 1/8–1/4 of that of pure SA unit, and this means the heat transfer can be significantly enhanced. It suggests that the form-stable EG/SA composite phase change materials prepared by high dilatation EG has good comprehensive performance due to its high thermal conductivity, good thermal stability and no leakage problem.

Preparation and characterization of an inorganic magnesium chloride/nitrate/graphite composite for low temperature energy storage

In this study, an inorganic mixture of 40wt% MgCl2·6H2O and 60wt% Mg(NO3)2·6H2O was impregnated into two types of the expanded graphite (EG): EG flakes and EG matrix. Different methods of preparation usually used in the organic composite preparation, such as direct blending, vacuum impregnation, ultrasonic impregnation and immersion were applied in this work. Considering the samples with EG matrix, it can be concluded that the optimal result of the encapsulation and ΔH ratio can be reached with the experimental time of 1, 3 and 4h using the vacuum, ultrasound and immersion methods, respectively. Moreover, the percentage of encapsulation increases with the experimental time and with the EG percentage for the EG matrix and for the EG flakes, respectively. Concerning the supercooling phenomena, the results show that the presence of EG reduces the difference between fusion and crystallization temperature for up to 65%, acting as а nucleating agent. The resulting composite samples (CPCM) were proved to have good latent heat and a significant reduction of the supercooling effect, which eliminates the need to use nucleating agents, that are essential for pure PCM of 40wt% MgCl2·6H2O and 60wt% Mg(NO3)2·6H2O. Moreover, using EG suppresses significantly the melting time which indicates the heat transfer enhance of the mixture. This circumstance could allow to empower the utilization of the mentioned mixture in different fields of thermal energy storage at low temperature.

Preparation and characterization of expanded graphite/metal oxides for antimicrobial application

Composite materials based on expanded graphite (EG) and metal oxide (MO) particles was prepared by an explosive combustion and blending method. The objective of the study was to develop EG impregnated with metal oxide particulates (Ag2O, CuO and ZnO) and evaluate the level of protection the materials conferred against biological agents. The physical properties of the EG/MO composites were examined using SEM, EDX and XRD spectroscopy, and the results indicated that the MO particles were incorporated into the EG matrix after impregnation. The antimicrobial activities of the EG/MO composites against Gram-positive bacteria, Gram-negative bacteria and Bacillus anthracis were investigated using zone of inhibition, minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC) and plate-counting methods. EG/Ag2O exhibited a stronger antibacterial activity than EG/CuO and EG/ZnO, with a MIC of 0.3mg/mL and a MBC of 0.5mg/mL. To the best of our knowledge, few studies have demonstrated that EG/MO composites can inhibit the growth of Bacillus anthracis-adhered cells, thus preventing the process of biofilm formation. Nanoscale metal oxides display enhanced reactive properties toward bacteria due to their high surface area, large number of highly reactive edges, corner defect sites and high surface to volume ratio.

Novel solvent-thermal preparation of a SnO2 nanoparticles/expanded graphite multiscale composite with extremely enhanced electrical performances for Li-ion batteries

A novel SnO2 nanoparticles (NPs)/expanded graphite (EG) multiscale hybrid composite was prepared via an elaborately designed solvent-thermal reaction and the following anneal treatment. A mixed solvent system of acetone-H2O with volume proportion of 3:1 was employed for the solvent-thermal reaction in order to realize moderate hydrolysis rate of Sn4+ and favorable wettability between solvent molecules and EG surface. Acetone played a very positive role for the uniform nucleation and crystal growth of SnO2-NPs, which could be proved by the ultrafine sizes of 3–6nm and well-crystallized texture of SnO2-NPs, as well as their homogeneous anchor on the surface of EG. As an anode material for Li-ion batteries, the SnO2-NPs/EG composite exhibited excellent long-term cycling stability, e.g. decay-free reversible capacity of 976mAhg−1 after 100 cycles, and good rate capability (>400mAhg−1 at 2000mAg−1). The extraordinary electrochemical performances arise from the structural advantages of the composite: the ultrafine SnO2-NPs with high dispersity on conductive EG matrix supply not only large quantity of accessible active sites for lithium-ion insertion but also good conductivity and short diffusion length for lithium ions. These results suggest the SnO2-NPs/EG composite would be a promising candidate as anode material for next-generation LIBs.

Characterization of Microstructure and Property for Phase Change Materials of Expanded Graphite Matrix Composite

Characterization of Microstructure and Property for Phase Change Materials of Expanded Graphite Matrix Composite

High performance form-stable expanded graphite/stearic acid composite phase change material for modular thermal energy storage

A new synthesis method is developed for preparing form-stable expanded graphite (EG)/stearic acid (SA) composite phase change material (CPCM) by using “impregnation of liquid PCM into EG matrix and then compressing into stable-shape block”. The effects of EG content and packed density on the thermal-physical property and thermal stability of form-stable EG/SA CPCM are firstly analyzed and its optimum parameters are investigated, and then an advanced form-stable modular thermal energy storage unit is manufactured and its thermal performance is evaluated. The SEM analysis shows that SA is well impregnated into graphite flakes and a regular laminar structure gradually forms with increasing packed density. The DSC analysis reveals that the CPCM nearly has no supercooling problem and the addition of EG and compressing operation have negligible effect on the phase change temperature and latent heat of SA. The form-stable CPCM has obvious anisotropic thermal conductivity and the largest difference between axial and radial thermal conductivity reaches up to 4 times. Both axial and radial thermal conductivities can be enhanced significantly by using the additive of EG, and the radial thermal conductivity is as high as 23.27W/mK. The TGA analysis indicates that the form-stable CPCM has good thermal stability within a wide range of temperature and those samples with low porosity are susceptible to liquid leakage. Experimental results show the form-stable EG/SA CPCM exhibits excellent overall thermal performance by employing the optimum parameters of 25wt.% EG content and packed density of 900kg/m3. An advanced design method for modular energy storage unit is proposed by integrating copper tubes into the form-stable CPCM, and it can be easily used to achieve different energy storage capacities by assembling different numbers of modular thermal energy storage units. It appears that the proposed new method is very effective to synthesis high-performance form-stable graphite-based CPCM in comparison with the conventional methods, and the thermal conductivity can be enhanced about 130 times higher than that of pure PCM.

Experiment and simulation of a LiFePO4 battery pack with a passive thermal management system using composite phase change material and graphite sheets

A passive thermal management system (TMS) for LiFePO4 battery modules using phase change material (PCM) as the heat dissipation source to control battery temperature rise is developed. Expanded graphite matrix and graphite sheets are applied to compensate low thermal conductivity of PCM and improve temperature uniformity of the batteries. Constant current discharge and mixed charge–discharge duties were applied on battery modules with and without PCM on a battery thermal characteristics test platform. Experimental results show that PCM cooling significantly reduces the battery temperature rise during short-time intense use. It is also found that temperature uniformity across the module deteriorates with the increasing of both discharge time and current rates. The maximum temperature differences at the end of 1C and 2C-rate discharges are both less than 5 °C, indicating a good performance in battery thermal uniformity of the passive TMS. Experiments on warm-keeping performance show that the passive TMS can effectively keep the battery within its optimum operating temperature for a long time during cold weather uses. A three dimensional numerical model of the battery pack with the passive TMS was conducted using ANSYS Fluent. Temperature profiles with respect to discharging time reveal that simulation shows good agreement with experiment at 1C-discharge rate.

The peculiarities of reduction of iron (III) oxides deposited on expanded graphite

Abstract