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53 articles found

E0178 – Thermodynamic and structural analyses and mechanisms of the crystallisation of multi-alkane model mixtures similar to petroleum cuts

Thermodynamic and structural analyses were carried out by X-ray diffraction and differential thermal analyses as functions of the temperature on multi-alkane samples whose distribution of mole fractions shows a shape of the 'exponential decreasing' type, as observed in petroleum cuts. Nine samples, whose number of normal-alkanes, Cns, varied from 15 up to 23, were studied with continuous distributions of mole fractions going from the C22-C36 series to the C14-C36 series: C22 and C14 corresponding respectively to the first Cns of the two terminal series and C36 is always the last Cn of each series: each mixture differed from the previous sample by the addition of a lighter C'n-1). At the solid state and according to literature, the multi-alkane samples of C22-C36, C21-C36 and C20-C36 series are in a two-phase solid thermodynamic state, C19-C36 to C15-C36, three-phase, the broader distribution C14-C36, four-phase and the mixtures with numbers of Cns<11, single-phase. Thus, the Cns crystallise in the solid phase, where the thickness of molecule layers is compatible with their own chain length. The results allow for extracting the recurring structural and thermodynamic properties for these types of mixtures during crystallisation, and to clarify the molecular mechanisms involved in the number of observed solid phases, in the order of their appearance and in their thermodynamic and structural behaviour during the course of cooling from the liquid state.
A-J. Briard, M. Bouroukba, D. Petitjean, N. Hubert, J-C. Moise, M. Dirand, Fuel 85 (2006) 764-777

E0092 – Thermoanalytical investigation of some alkaline earth hydroxide hydrates on application as latent heat storage materials

Owing to their high specific melting enthalpy and the range of the melting temperatures the alkaline-earth hydroxide hydrates Ba(OH)2.8H20 and Sr(OH)2.8H20 are promising latent heat storage materials. The investigations of the melting and solidification behaviour of Sr(OH)2.8H20 and its mixtures with Ba(OH)2.8H20, which had been performed by means of DTA and DSC methods in the closed system with a constant gross composition lead to statements on the melting temperature and specific melting enthalpy vs. concentration. Theoretical storage densities of 532 MJ/m 3 are obtained for the mixture of Ba(OH)2-8H20 and Sr(OH)2.8H20 (80/20) and a value of 655 MJ/m 3 can be achieved for Sr(OH)2.8H20. The kinetics of rehydration to the octahydrates has a great influence on the storage temperature and storage density.
R. Naumann and O. Schatz, Journal of Thermal Analysis 38 (1992) 665-671

E0073 – Thermoanalytical investigation of sodium acetate trihydrate for application as a latent heat thermal energy storage material

The thermal behaviour of sodium acetate trihydrate (NaAc. 3H20 ) was investigated by DTA, Q-TG and measurements of the solubility properties. The nucleation efficiency of Na4P207 9 10H20 for the crystallization of NaAc. 3H20 melts is not stable over lofig periods. Stratification can be ascribed to the formation of anhydrous sodium acetate in the supercooled melts. Under static heat storage conditions, NaAc- 3H20 and Na4P207 9 10H20 do not exhibit stable behaviour.
R. Naumann, Th. Fanghänel and H-H. Emons, Journal of Thermal Analysis 33 (1988) 685-688

B3315 – Experimental and numerical study of annular PCM storage in the presence of natural convection

Latent thermal energy storage (TES) systems have shown growing potential in matching the production to the demand in Concentrated Solar Power (CSP) systems. Indeed, the improved storage density and the constant temperature release of energy allow for more compact heat exchanger design and simplify system management. The shell and tubes heat exchanger is the most promising technology, owing to its low cost. However, phase change phenomena occurring during PCM melting (charge) and PCM solidification (discharge) need to be carefully controlled. To better understand the heat exchange involved in this exchanger type, an annular latent storage unit filled with paraffin RT35 is experimentally and numerically studied. A testing loop with visualisation is built to analyse the influence of the heat transfer fluid (HTF) injection side on the system. The experimental test section is modelled with CFD simulations to explain the charge and discharge results. The combined study proves that an injection side coupled with free convection heat transfer mechanism influences the evolution of the PCM melting front. To conclude, a top injection for charge and a bottom one for discharge are recommended.
Martin Longeon, Adèle Soupart, Jean-François Fourmigué, Arnaud Bruch, Philippe Marty, Applied Energy 112 (2013) 175–184

B3304 – Thermodynamic investigation of a solid–solid phase change material: 2-Amino-2-methyl-1,3-propanediol by calorimetric methods

An important solid–solid phase change heat storage material (PCM) 2-amino-2-methyl-1,3-propanediol was investigated by calorimetric methods. The molar heat capacities of the compound were measured in the temperature range from 78 to 405 K by means of a small sample automated adiabatic calorimeter. A solid–solid and solid–liquid phase transitions were found at T = 351.598 K and 380.633 K, respectively, from the experimental Cp–T curve. The molar enthalpies and entropies of these transitions were determined to be 24.33 ± 0.02 kJ mol?1, 69.20 ± 0.07 J K?1 mol?1 for the solid–solid phase transition and 4.01 ± 0.01 kJ mol?1, 10.52 ± 0.01 J K?1 mol?1 for the solid–liquid phase transition, respectively. The thermodynamic functions (HT ? H298.15) and (ST ? S298.15), were derived from the heat capacity data in the temperature range of 78–405 K with an interval of 5 K. A precise oxygen-bomb combustion calorimeter was used to obtain the standard molar enthalpy of combustion and the standard molar enthalpy of formation, (C5H11NO2, cr) = (?3326.25 ± 0.52) kJ mol?1 and (C5H11NO2, cr) = (?213.37 ± 0.86) kJ mol?1. DSC and TG tests were performed to investigate the solid–solid and solid–liquid phase transition behaviors and its thermostability. The results were in agreement with those obtained from heat capacity measurements, which indicated that 2-amino-2-methyl-1,3-propanediol possesses typical solid–solid phase change material characteristics, such as, suitable transition temperature, high transition enthalpy and good thermal stability.
Tong Bo, Tan Zhi-Cheng, Liu Rui-Bin, Meng Chang-Gong, Zhang Jing-Nan, Energy Conversion and Management 51 (2010) 1905–1910

B3303 – Hexamethylene dilauroyl, dimyristoyl, and dipalmytoyl amides as phase change materials for thermal energy storage

Hexamethylene dilauroyl, dimyristoyl, and dipalmytoyl amides have been produced as solid–liquid phase change materials via condensation of hexamethylene diamine with the respective acyl chlorides (lauroyl chloride, myristoyl chloride, and palmytoyl chloride) and were characterized by FT-IR, NMR, DSC, and TG analysis. Hexamethylene dilauroyl, dimyristoyl, and dipalmytoyl amides crystallized due to structural symmetry and flexibility of long alkyl groups. They were characterized by DSC and FT-IR spectroscopy before and after thermal cycling to determine their thermal reliability. Phase change enthalpies were found 110.1 and ?103.3 J g?1 for hexamethylene dilauroyl amide (N,N?-hexamethylene didodecanamide), 116.9 and ?110.4 J g?1 for hexamethylene dimyristoyl amide (N,N?-hexamethylene ditetradecanamide), and 144.5 and ?140.5 J g?1 for hexamethylene dipalmytoyl amides (N,N?-hexamethylene dihexadecanamide) by DSC. The endurance of hexamethylene dilauroyl, dimyristoyl, and dipalmytoyl amides was studied by TG analysis.
Gülcin Canik, Cemil Alkan, Solar Energy 84 (2010) 666–672

B3280 – Experimental assessment of heat storage properties and heat transfer characteristics of a phase change material slurry for air conditioning applications

A new microencapsulated phase change material slurry based on microencapsulated Rubitherm RT6 at high concentration (45% w/w) was tested. Some heat storage properties and heat transfer characteristics have been experimentally investigated in order to assess its suitability for the integration into a low temperature heat storage system for solar air conditioning applications. DSC tests were conducted to evaluate the cold storage capacity and phase change temperature range. A phase change interval of approximately 3 °C and a hysteresis behaviour of the enthalpy were identified. An experimental set-up was built in order to quantify the natural convection heat transfer occurring from a vertical helically coiled tube immersed in the phase change material slurry. First, tests were carried out using water in order to obtain natural convection heat transfer correlations. Then a comparison was conducted with the results obtained for the phase change material slurry. It was found that the values of the heat transfer coefficient for the phase change material slurry were higher than for water, under identical temperature conditions inside the phase change interval.
Bogdan M. Diaconu, Szabolcs Varga, Armando C. Oliveira, Applied Energy 87 (2010) 620–628

B3238 – Effects of copper nanowires on the properties of an organic phase change material

The effects of copper nanowires (Cu NWs) with ultra-high aspect ratio and sponge-like structure on the properties of an organic phase change material (PCM) were investigated. Tetradecanol (TD) was selected as the organic PCM. The sponge-like Cu NWs clusters were randomly dispersed in the TD matrix and were wrapped by TD to form a new kind of composite PCM. The phase change enthalpy (?H) of the composite PCMs was decreased linearly with the increasing of Cu NWs loading, while the melting speed was accelerated. The thermal conductivity of the composite PCMs was greatly enhanced by Cu NWs. The ?H of the composite PCM containing 58.9 wt% (corresponding to 11.9 vol%) of Cu NWs was 86.95 J/g, and the thermal conductivity attained to 2.86 W/m K, which was nearly 9 times higher than that of the TD. The thermal conductivity enhancement of Cu NWs on the composite PCMs showed a turning point at the Cu NWs loading of 1.5 vol%. When Cu NWs loading exceeded 1.5 vol%, the thermal conductivity of the composite PCMs increased significantly faster with the increasing of Cu NWs loading.
Ju-Lan Zeng, Fu-RongZhu, Sai-BoYu, LingZhu, ZhongCao, Li-XianSun, Guang-RongDeng, Wen-Pei Yan, LingZhang, Solar Energy Materials & Solar Cells 105 (2012) 174–178

B3226 – Pilot application of phase change slurry in a 5 m3 storage

Thermal storage can make an important contribution towards tackling the rise in energy consumption by balancing energy supply with demand. In buildings Phase Change Materials (PCMs) are increasingly being used to reduce the heating and cooling peak demand. Phase Change Slurries (PCSs) are heat transfer fluids, which consist of a latent heat component, a dispersed PCM, and a sensible heat component, a carrier fluid that provides fluidity. This combination of sensible and latent heat storage offers high heat storage capacity, while circumventing the low thermal conductivity problems associated with PCMs. The fluidity of PCSs enables pumping through pipes and the spatial separation of the heat transfer unit and storage tank. Thus PCS is an alternative to conventional single phase fluids. A new PCS was tested in a 5 m3 storage tank pilot application. Material properties, such as melting range, viscosity, density, enthalpy and particle diameter have been determined by laboratory measurements. Experimental investigations were conducted in a pilot application, in order to allow an energetic comparison of the two heat storage fluids, water as reference medium and PCS. Depending on the operation temperature range the tested PCS can store more than twice as much heat compared to water as conventional heat transfer fluid. Due to the higher viscosity the required pumping energy for PCS is around five times higher as compared with water.
Laura Vorbeck, Stefan Gschwander, Peter Thiel, Bruno Lüdemann, Peter Schossig, Applied Energy 109 (2013) 538–543

B3205 – Thermal and rheological properties of microencapsulated phase change materials

The use of microencapsulated phase change materials (MPCMs) is one of the most efficient ways of storing thermal energy. When the microencapsulated phase change material (MPCM) is dispersed into the carrier fluid, microencapsulated phase change slurry (MPCS) is prepared. Due to the relatively large surface area to volume MPCM and its large apparent specific heat during the phase change period, better heat transfer performance can be achieved. Therefore, MPCS can be used as both the energy storage and heat transfer media. This paper studies the thermal and rheological properties of a series of prepared MPCS. In the experiment: MPCS fabricated by dispersing MPCM into water with an appropriate amount of surfactant. The mass ratio of MPCM to water and surfactant was 10:90:1, 25:75:1, 35:65:1 in prepared MPCS samples, respectively. Then the thermal conductivity and specific heat of MPCS were measured by the Hot Disk. The melting/crystallizing temperature and fusion heat/crystallization heat of the phase change materials were obtained from a DSC (differential scanning calorimetry) during the heating/cooling process. Physical properties, such as viscosity, diameter and its size distribution of MPCS were investigated by a rheometer and a particle characterization system. Meanwhile, the chemical structure of the sample was analyzed using Fourier Transformed Infrared spectroscopy (FTIR). The results showed that the thermal conductivity and the specific heat of MPCS decreased with particle concentration for the temperatures below the melting point. Overall, the MPCS can be considered as Newtonian fluid within the test region (shear rate >200 s?1 and mass fraction <0.35). The viscosity is higher for bigger particle slurries. The findings of the work lead to the conclusion that the present work suggested that MPCMs can be used in “passive” applications or in combination with active cooling systems; and it also provided a new understanding for fabricating microencapsulated phase change slurry, it is for sure that to have a better potential for energy storage. Accordingly, it has demonstrated that the MPCS fabricated in the current research are suitable for potential application as heat transfer media in the thermal energy storage.
G.H. Zhang, C.Y. Zhao, Renewable Energy 36 (2011) 2959-2966

B3122 – Cycle stability of sorption materials and composites for the use in heat pumps and cooling machines

Thermally driven adsorption chillers and heat pumps are a very promising approach toward an efficient use of energy as well as an effective climate protection through reduced CO2 emission of conventional heating and cooling devices. With regard to current market entrance of this technology, this paper presents results on the stability of current available materials like silica gels and zeolites, recently developed materials like aluminophosphates (AlPO) and silica-aluminophosphates (SAPO) and novel materials like metal organic frameworks (MOF) under hydrothermal treatment.Seven materials as powders or granules as well as three composite have been analyzed under continuous thermal cycling in a water vapour atmosphere in order to evaluate their suitability for the use in a periodically working heat pump with water as working fluid.The stability of powders has been analyzed in-situ by thermogravimetry in a first stage short-cycle test. In case of the composite, made up of an active sorption material and a support structure, a cycling-test rig has been developed in order to realize a life-cycle stress. The need for a first stage short-cycle test is demonstrated impressively by the dramatic loss of 40% in sorption capacity of a Cu-BTC sample within the first 15 cycles.
S.K. Henninger, G. Munz, K.-F. Ratzsch, P. Schossig, Renewable Energy 36 (2011) 3043-3049

B3112 – Thermodynamic investigation of the (LiF + NaF + CaF2 + LaF3) system

In this work a thermodynamic assessment of the (LiF + NaF + CaF2 + LaF3) system is reported. For the thermodynamic modeling of the liquid phase, the classical polynomial model, and the modified quasi-chemical model were used in parallel and compared. The extrapolation to higher order systems was done according to the Toop mathematical formalism. Furthermore, differential-scanning calorimetry data of the ternary (LiF + CaF2 + LaF3), (NaF + CaF2 + LaF3), and the quaternary (LiF + NaF + CaF2 + LaF3) mixtures are presented. Good agreement between the experimental data and the thermodynamic assessment was obtained.
M. Beilmann, O. Beneš, R.J.M. Konings, Th. Fanghänel, J. Chem. Thermodynamics 43 (2011) 1515–1524

B3085 – High performance storage composite for the enhancement of solar domestic hot water systems. Part 1: Storage material investigation

This work aims to evaluate the performance of a solar domestic hot water (SDHW) system including a latent storage material. The originality of our approach consists to place a composite made of compressed expanded natural graphite (CENG) and phase change material (PCM) directly inside a flat plate solar collector in order to replace the traditional copper-based solar absorber. According to this target, the study is composed of two steps: the composites preparation and characterization; and the analysis of the system to achieve optimal integration of the material in the process. The present paper is focused on the selection of the most promising composite to implement in the solar collector. In order to reach this objective, several composites based on CENG and various storage materials (paraffin, stearic acid, sodium acetate trihydrate and pentaglycerin) have been elaborated and characterized. The synthesis of all these measurements allowed us to select three composites whose characteristics match their integration into a solar thermal collector.
D. Haillot, V. Goetz, X. Py, M. Benabdelkarim, Solar Energy 85 (2011) 1021–1027

B3064 – Corrosion effects between molten salts and thermal storage material for concentrated solar power plants

Today, thermal energy storage (TES) is a key issue for concentrated solar power plants (CSPs). The available and mature technologies of TES do not mach all the actualised criteria for those properties. Alternative approaches have to be identified and developed to guaranty the expected extension of CSP implementations with respect to the IEA 2050 scenario. In this context, promising hybrid TES systems based upon the combination of sensible heat and liquid/solid phase change material (PCM) sub-systems are considered. For the sensible heat stage, a recycled refractory ceramic made of inertised asbestos-containing waste (IACW) is proposed. For the PCM stage, high temperature inorganic salts are considered. One major aspect of the hybrid TES is the integration of the two stages together. Therefore, the present study is focussed on the needed assessment concerning the compatibility between the IACW and the molten salts in terms of corrosion. Sulphates, phosphates, carbonates and nitrates salts have been experimented and the corrosion effects characterised by in situ NMR, ex situ X-ray diffraction and Scanning Electron Microscopy. Among those available salts, only the nitrates have shown good compatibility with IACW materials. For higher temperature levels, other salts or eutectics will have to be considered to allow hybrid TES with direct contact.
Stéphanie Guillot, Abdessamad Faik, Aydar Rakhmatullin, Julien Lambert, Emmanuel Veron, Patrick Echegut, Catherine Bessada, Nicolas Calvet, Xavier Py, Applied Energy 94 (2012) 174–181

B3047 – Adsorption properties of porous materials for solar thermal energy storage and heat pump applications

The water adsorption properties of modified porous sorbents for solar thermal energy storage and heat transformation have been investigated by thermogravimetry (TG) differential thermogravimetry (DTG), microcalorimetry, measurements of water adsorption isotherms, and storage tests. A chabazite type SAPO, a dealuminated faujasite type zeolite, and a mesostructured aluminosilicate, have been synthesized and compared with common zeolites X, Y and silica gel. It has been found that optimized lattice composition and pore architecture contribute to well adapt hydrophilic properties and a beneficial steep isotherm
Jochen Jänchen, Helmut Stach, Energy Procedia 30 ( 2012 ) 289 – 293

B3035 – Thermal storage material from inertized wastes: Evolution of structural and radiative properties with temperature

Hazardous wastes, such as asbestos-containing wastes (ACW) or fly ashes (FA) resulting from municipal solid waste incineration, can be converted into inert materials using plasma torch technology. Depending on the origin of the wastes and on the cooling conditions, the materials obtained at room temperature can be glassy or partially crystallized. The aim of this work is to investigate the potential valorisation of such inertized products as sensible heat material for high temperature thermal storage in thermodynamic solar power plants. Thermal stability and optical properties have been studied from room temperature up to 1000 C by infrared spectroscopy, differential scanning calorimetry and X-ray diffraction. All the studied materials are stable and present high total emissivity within the experimented temperature range. Their physical and chemical characteristics make of them to be good candidates for sensible heat storage materials.
A. Faik, S. Guillot, J. Lambert, E. Véron, S. Ory, C. Bessada, P. Echegut, X. Py, Solar Energy 86 (2012) 139–146

B2876 – Characterisation and improvement of sorption materials with molecular modeling for the use in heat transformation applications

In this paper, several materials for sorption heat transformation applications are evaluated on basis of experimental characterisation and molecular simulation methods. With regard to the application, classical zeolites, ion exchanged zeolites, aluminophosphates as well as silicaaluminophosphates have been analysed. Furthermore samples of metal organic frameworks (MOF) have been evaluated for the use in sorption heat transformation applications with very promising results. In order to understand the fundamental relationship between adsorbent microstructure and water adsorption equilibrium, molecular simulation of water adsorption in various adsorbents are employed. As a result of these simulations within the grand canonical ensemble, the number of water molecules adsorbed in thermodynamic equilibrium under given conditions of temperature and chemical potential (resp. pressure) are obtained. These data are compared with adsorption data from thermogravimetric measurements.
S.K. Henninger, F.P. Schmidt, H.-M. Henning, Adsorption (2011) 17, 833–843

B2871 – Influence of Cycle Temperatures on the Thermochemical Heat Storage Densities in the Systems Water/Microporous and Water/Mesoporous Adsorbents

The adsorption equilibrium of water on microporous adsorbents (zeolites of NaA-, NaY- and NaX-type as well as their ion exchanged forms) and on mesoporous adsorbents (different silica gels and composite material i.e. silica gel + salt hydrate) has been studied experimentally and theoretically. Using the Dubinin theory of pore filling the characteristic curves of the adsorption systems and other relevant dependences such as isotherms, isobars, isosteres and the curve of the differential heat of adsorption were calculated. For all systems investigated the adsorption were calculated. A ads and the desorption potential A des of the closed heat storage system were estimated. These values define the working range of the adsorption/desorption cycle and allow to calculate the specific heat storage density ? h sp. On the basis of ? h sp the different adsorbents were compared in order to select the optimal porous storage material for a given application. The presented experimental and theoretical investigations show that the adsorption systems water-zeolite and water-composites are promising working pairs for thermochemical heat storage processes for hot tap water supply and space heating of single family dwellings. The advantage of the water-composite system is the low desorption temperature (solar energy) the main shortcoming the low temperature lift. The advantage of the water zeolite system is the high temperature lift, the shortcoming are the relative high desorption temperatures.
H. Stach, J. Mugele, J. Jänchen, E. Weiler, Adsorption, July 2005, Volume 11, Issue 3-4, pp 393-404

B2870 – Simultaneous calorimetric and quick-EXAFS measurements to study the crystallization process in phase-change materials

A Calvet-type differential scanning calorimeter has been implemented on a synchrotron beamline devoted to X-ray absorption spectroscopy. As a case study, the complex crystallization process in amorphous Ge15Sb85 phase-change material is followed by simultaneous calorimetric and quick-EXAFS measurements. A first crystallization at 514(1)?K is related to the crystallization of an Sb-rich phase accompanied by segregation of Ge atoms. Upon further heating, the as-formed amorphous Ge regions crystallize at 604(1)?K. A quantitative analysis of the latent heat allows a Ge11Sb89 stoichiometry to be proposed for the first crystallized phase.
Peter Zalden, Giuliana Aquilanti, Carmello Prestipino, Olivier Mathon, Bérangère André, Matthias Wuttig, Marie-Vanessa Coulet, Journal of Synchrotron Radiation, Volume 19, Issue 5, pages 806–813, September 2012

B2821 – Preparation, Thermal Properties and Thermal Reliability of Form-Stable Paraffin/Polypropylene Composite for Thermal Energy Storage

This study is focused on the preparation, characterization, and determination of thermal properties and thermal reliability of paraffin/polypropylene (PP) composite as a novel form-stable phase change material (PCM) for thermal energy storage applications. In the composite, paraffin acts as a PCM when PP is operated as supporting material. The composites prepared at different mass fractions of paraffin (50, 60, 70, 80, and 90 w/w%) by solution casting method were subjected to leakage test by heating the composites over the melting temperature of the PCM. The paraffin/PP composite (70/30 w/w%) is found as the maximum paraffin containing composite and was characterized using Fourier transform infrared spectroscopy, optic microscopy, differential scanning calorimetry (DSC), and thermal gravimetric analysis (TGA) techniques. DSC analysis indicated that the form-stable paraffin/PP composite melts at 44.77–45.52 C and crystallizes at 53.55–54.80 C. It has latent heats of 136.16 and-136.59 J/g for melting and crystallization, respectively. These thermal properties make it potential PCM for latent heat thermal energy storage (LHTES) purposes such as solar space heating applications. Accelerated thermal cycling tests indicated that the formstable PCM had good thermal reliability. TGA also showed that the form-stable PCM degrades in two distinguishable steps and had good chemical stability.
Cemil Alkan, Kemal Kaya, Ahmet Sar?, J Polym Environ (2009) 17, 254–258

B2816 – Latent heat nano composite building materials

Heat storage for heating and cooling of buildings reduces the conventional energy consumption with a direct impact on CO2 emissions. The goal of this study was to find the physico-chemical fundamentals for tailoring phase change material (PCM)-epoxy composites as building materials depending on phase change temperature and latent heat using the optimal geometry for each application. Thus, some nano-composite materials were prepared by mixing a PCM with large latent heats with epoxy resin and Al powder. Some polyethylene glycols of different molecular weights (1000, 1500, and 2000) were used as PCMs. Subsequently these PCM-epoxy composites were thermo-physically characterized by DSC measurements and found to be suitable for building applications due to their large latent heat, appropriate phase change temperature and good performance stability. Moreover these cross-linked three dimensional structures are able to reduce the space and costs for encapsulation.
M. Constantinescu , L. Dumitrache, D. Constantinescu, E.M. Anghel, V.T. Popa, A. Stoica, M. Olteanu, European Polymer Journal 46 (2010) 2247–2254

B2730 – Performance prediction of absorption refrigeration cycle based on the measurements of vapor pressure and heat capacity of H2O + [DMIM]DMP system

In this paper, the thermophysical properties of the H2O + 1,3-dimethylimidazolium dimethylphosphate ([DMIM]DMP) system were studied. The boiling point method was adopted to measure the vapor pressures of the system at mass fraction of ionic liquids (ILs) in the range from 0.10 to 0.90 as well as pressures range from 2 kPa to 101 kPa. And the general non-random two-liquid (NRTL) activity coefficient model was used to correlate the experimental data. The heat capacities of the system were determined by a BT2.15 Calvet microcalorimeter at mass fraction of ILs in the range from 0.10 to 0.90 and temperatures range from 303.15 K to 353.15 K. A polynomial equation on temperature and concentration was correlated with satisfactory results. And then theoretical analysis of the coefficient of performance (x) of a single-effect absorption refrigeration cycle was simulated using H2O + [DMIM]DMP as working pair on the basis of the models of vapor pressure and heat capacity. The simulation results show that the x of H2O + [DMIM]DMP system is close to that of conventional working pair H2O + LiBr. In addition, the H2O + [DMIM]DMP system improved the limitations of crystallization and corrosion of H2O + LiBr system
Li Dong, Danxing Zheng, Nan Nie, Yun Li, Applied Energy 98 (2012) 326–332

B2604 – Solidification of a PEG 1500-epoxy nanocomposite around a horizontal pipe

A PCM-epoxy phase change material composite (polyethylene glycol 1500-epoxy) was developed as heat storage building element for houses with low energy consumption. The PCM component, polyethylene glycol 1500, was integrated in an epoxy matrix, and presents a phase change interval of 34–42 C and an enthalpy of solidification of 103.411 kJ/kg. Experiments on solidification were conducted using a Plexiglas test cell filled with the PEG 1500-epoxy nanocomposite material (P15-E) for further implementation of this material in buildings. The forwarded solidification model assumes negligible convection in the liquid region and predicts the time for radial formation of two regions: a mushy-zone and a solid, annular one around the pipe during solidification. The heat transfer during solidification can be also characterized by the time evolution of both liquid and solid radial fronts. The model was analytically solved using Megerlin approximation concerning ‘‘solidification with mushy zone’’, with the third order condition at the external frontier. The experimental values are in agreement with the calculated theoretical curves.
Petrica Mircea Pavel, Mariella Constantinescu, Elena Maria Anghel, Mircea Olteanu, Applied Energy 89 (2012) 482–489

B2596 – Densities, Viscosities, Heat Capacities, and Vapor Liquid Equilibria of Ammonia + Sodium Thiocyanate Solutions at Several Temperatures

Several thermophysical properties were experimentally measured for the ammoniaþsodium thiocyanate mixtures at several temperatures: density from (269.4 to 350.9) K, dynamic viscosity from (269.8 to 369.5) K, and isobaric heat capacity from (304.17 to 364.15) K, all them at a constant pressure of 3 MPa, and vapor liquid equilibria from (253.1 to 393.1) K. All properties were measured in a range of composition from 0.35 to 0.90 in ammonia mass fraction. The experimental techniques used were a vibrating-tube densimeter, a piston-style viscometer, a heat flux Calvet-type calorimeter, and a static method, respectively. The measured data were correlated as a function of temperature and composition using empirical equations and were compared with literature values.
Shrirang K. Chaudhari, Daniel Salavera, Alberto Coronas, J. Chem. Eng. Data 2011, 56, 2861–2869

B2594 – Calorimetric studies of thermochemical heat storage materials based on mixtures of MgSO4 and MgCl2

Attapulgite granulate impregnated with mixtures of MgSO4 and MgCl2 hydrates was investigated for suitability as a composite thermal energy storage material. These mixtures were chosen because of the very different deliquescence relative humidities of the salts. The thermochemical heat storage of these materials was characterized by measurements of isothermal heat of sorption and thermogravimetry (TG). The salt mixtures showed a different sorption behavior compared to pure MgSO4. The reduction of the deliquescence relative humidity of the mixture by the partial substitution of MgSO4 by MgCl2 increases the capacity of condensation and therefore the released heat. The energy density of the composite heat storage material containing a salt mixture of 20 wt% MgSO4 and 80 wt% MgCl2 was 1590 kJ/kg measured by calorimetry (at 30 °C/85% RH) with a desorption temperature of 130 °C.
K. Posern, Ch. Kaps, Thermochimica Acta, 502 (2010) 73–76

B2588 – Heat capacity of NaNO2

Heat capacity in solid state was for the sodium nitrite (NaNO2) measured by using two types of calorimeters. The measurements were performed in the temperature range 273.15–583.15 K. Three phase changes were observed in this temperature range – one melting and two transitions between different structural modifications. Concerning the transitions between structural modifications, the first was observed at 437.2 ± 0.1 K and the second was found at 438.7 ± 0.1 K. Temperature of melting was then determined to be 553.2 ± 0.2 K with the corresponding heat of fusion being equal to 13.9 ± 0.1 kJ mol?1.
L. Kourkova, R. Svoboda, G. Sadovska, V. Podzemna, A. Kohutova, Thermochimica Acta, 491 (2009) 80–83

B2550 – Polyaniline/1-tetradecanol composites. Form-stable PCMS and electrical conductive materials

Polyaniline (PANI)/1-tetradecanol (TD) composite materials, a kind of novel composite that can conduct electricity and store thermal energy at the same time, thus possess the ability to endure certain heat shock, were prepared for the first time. FTIR and XRD results showed that there were some interactions existed between PANI and TD. The thermal stability of the composites exhibited both the characteristics of PANI and TD. The DSC experiments showed that the highest phase change enthalpy of the composites could be as 73% as that of TD, indicating it was a good form-stable phase change material. The thermal conductivity of the composites was also improved. The AC (Alternating Current) conductivity of the composites was enhanced to close to that of PANI when the mass fraction of PANI in the composite was increased to 46%. Heat shock experiments showed that the heat shock resistibility of the composite was greatly improved comparing to that of pure PANI.
J. L. Zeng, J. Zhang, Y. Y. Liu, Z. X. Cao, Z. H. Zhang, F. Xu, L. X. Sun, Journal of Thermal Analysis and Calorimetry, Vol. 91 (2008) 2, 455–461

B2549 – Thermal conductivity enhancement of MWNTS on the PANI/tetradecanol form-stable PCM

We prepared PANI/tetradecanol/MWNTs composites via in-situ polymerization. DSC results indicated that the composites are good form-stable phase change materials (PCMs) with large phase change enthalpy of 115 J g–1. The MWNTs were randomly dispersed in the composites and significantly enhanced the thermal conductivity of the PCMs from 0.33 to 0.43 W m–1 K–1. The form-stable PCMs won’t liquefy even it is heated at 80°C, so that the MWNTs were fixed in the composite and the phase separation of the MWNTs from PANI/tetradecanol/MWNTs composites won’t occur.
J. L. Zeng, Y. Y. Liu, Z. X. Cao, J. Zhang, Z. H. Zhang, L. X. Sun, F. Xu, Journal of Thermal Analysis and Calorimetry, Vol. 91 (2008) 2, 443–446

B2487 – Effect of LiPF6 on the thermal behaviors of four organic solvents for lithium batteries

The thermal behaviors of four organic solvents with/without LiPF6 were measured by C80 microcalorimeter at a 0.2°C min–1 heating rate. With the addition of 1 M LiPF6, the ethylene carbonate (EC) and propylene carbonate (PC) show the exothermic peaks at elevated temperature, which lessen their stabilities. The exothermic peak temperatures of EC and PC based LiPF6 solutions are at 212 and 223°C, respectively, in argon filled vessel. However, two endothermic peak temperatures were detected in diethyl carbonate (DEC) based LiPF6 solution at 182 and 252.5°C, respectively, in argon filled vessel. Dimethyl carbonate (DMC) based LiPF6 solution shows two endothermic peak temperatures at 68.5 and 187°C in argon filled vessel at elevated temperature. Consequently, it is concluded that LiPF6 play a key role in the thermal behavior of its organic solution.
Q.S. Wang, J.-H. Sun, G.-Q. Chu, X.-L. Yao, C.-H. Chen, Journal of Thermal Analysis and Calorimetry, Vol. 89 (2007) 1, 245–250

B2454 – Phase diagram of palmitic acid-tetradecanol mixtures obtained by DSC experiments

A series of PA–TD mixtures were prepared and their thermal properties were studied by DSC and thermal conductivity measurement. The phase diagram of the binary system was constructed, which showed an eutectic behavior for the solid–liquid equilibrium line. The eutectic composition of the binary system was at the mass fraction of TD near 0.7 with an eutectic temperature of about 29°C. At TD side, PA was partially miscible in the TD solid matrix and the solid phase transition of TD had an effect on the solidus line. The eutectic composition mixture could be viewed as a new phase change material with large thermal energy storage capacity.
J. L. Zeng, Z. Cao, D. W. Yang, F. Xu, L. X. Sun, L. Zhang, X. F. Zhang, Journal of Thermal Analysis and Calorimetry, Vol. 95 (2009) 2, 501–505

B2452 – Gelled Na2HPO4 12H2O with amylose-g-sodium acrylate: heat storage performance, heat capacity and heat of fusion

A novel gelling method was studied to stabilize phase change material Na2HPO4,12H2O with amylose grafted sodium acrylate. Gelled Na2HPO4,12H2O shows stable heat storage performance prepared at optimized conditions: 2.7mass/mass% sodium acrylate, 0.4 mass/mass% amylose, 0.05–0.09 mass/mass% N, N0-methylene-bisacrylamide, 0.05–0.09 mass/mass% K2S2O8 and Na2SO3 (mass ratio 1:1), at 50 °C. Na2HPO4,12H2O was dispersed in gel network as tiny crystals less than 0.1 mm. Melting points were in the range 35.4 ± 2 °C. Short-term thermal cycling proves the effectiveness of the novel method for eliminating phase separation in the gelled salt. Adiabatic calorimetric measurement of heat capacities shows two phase transitions, which correspond to melting of Na2HPO4 12H2O and freezable bond water in gel, respectively. Heat of fusion of pure Na2HPO4,12H2O was determined as 260.9 J g-1. Distribution of extra water is: free water:freezable water:nonfreezing water = 0:0.85:0.15.
X.-Z. Lan, Z.-C. Tan, Q. Shi, Z.-H. Gao, J Therm Anal Calorim (2009) 96:1035–1040

B2395 – Effect of ZnO modification on the performance of LiNi0.5Co0.25Mn0.25O2 cathode material

ZnO was coated on LiNi0.5Co0.25Mn0.25O2 cathode (positive electrode)material for lithiumion battery via sol–gel method to improve the performance of LiNi0.5Co0.25Mn0.25O2. The Xray diffraction (XRD) results indicatedthat the lattice structure of LiNi0.5Co0.25Mn0.25O2wasnot changeddistinctly after surface coating and part of Zn2+ might dope into the lattice of the material. Energy dispersive spectroscopy (EDS) andXray photoelectron spectroscopy (XPS) proved that ZnO existed on the surface of LiNi0.5Co0.25Mn0.25O2. Charge and discharge tests showed that the cycle performance and rate capabilitywere improved by ZnO coating, however, the initial capacity decreased dramatically with increasing the amount of ZnO. Differential scanning calorimetry (DSC) results showed that thermal stability of the materials was improved. The XPS spectra after charge–discharge cycles showed that ZnO coated on LiNi0.5Co0.25Mn0.25O2 promoted the decomposition of the electrolyte at the early stage of charge–discharge cycle to form more stable SEI layer, and it also can scavenge the free acidic HF species from the electrolyte. The electrochemical impedance spectroscopy (EIS) results showed ZnO coating could suppress the augment of charge transfer resistance upon cycling.
Rui Guo, Pengfei Shi, Xinqun Cheng, Ling Sun, Electrochimica Acta 54 (2009) 5796–5803

B2123 – Study of a PCM based energy storage system containing Ag nanoparticles

In this paper, organic phase change material (PCM)/Ag nanoparticles composite materials were prepared and characterized for the first time. The effect of Ag nanoparticles on the thermal conductivity of PCM was investigated. 1-tetradecanol (TD) was selected as a PCM. A series of nano-Ag-TD composite materials in aqueous solution were in-situ synthesized and characterized by means of thermal conductivity evaluation method, TG-DSC, IR, XRD and TEM. The results showed that the thermal conductivity of the composite material was enhanced as the loading of Ag nanoparticles increased. The composite materials still had relatively large phase change enthalpy. Their phase change enthalpy could be correlated linearly with the loading of TD, but their phase change temperature was a little bite lower than that of pure TD. The thermal stability of the composite materials was close to that of pure TD. It appeared that there was no strong interaction between the Ag nanoparticles and the TD. Furthermore, the experiment results indicated that the Ag nanoparticles dispersed uniformly in the materials, occurred in the forms of pure metal.
J.L. Zeng, L.X. Sun, F. Xu, Z.C. Tan, Z.H. Zhang, J. Zhang and T. Zhang, Journal of Thermal Analysis and Calorimetry 87 (2007) 369-373

B2056 – Some temperature-sensitive properties of pure linear alkanes and n-ary mixtures

In this paper, the results of thermomechanical analyses (TMA), dynamic mechanical analyses (DMA) on pure linear alkanes and a commercial wax are discussed with the help of structural analyses and differential thermal analyses (DTA) performed at various temperature. Examination of the results show that thermal expansion of pure alkanes is around 10^(-4) K-1 at room temperature. It decreases continuously until 0.3 x 10^(-4) K-1 in the structural state corresponding to the rotator phase (alpha-RII). As concerns DMA, the storage modulus is ranged between 750 MPa (for the commercial wax) at room temperature and 1 MPa near the melting point. It decreases by stages when temperature is increasing. This general evolution is observed with pure linear alkanes as well as with the studied commercial product. Each stage corresponds to the stabilization of a solid phase, whereas a solid-solid transition is highlighted by an increase of the curve's slope. Density measurements performed at various temperature confirm such an evolution. In fact, the density (included between 0.92 and 0.94 g cm-3 at room temperature) decreases by stages versus temperature.
D. Petitjean, J.F. Schmitt, J.M. Fiorani, V. Laine, M. Bouroukba, M. Dirand, C. Cunat, Fuel 85 (2006) 1323-1328

B1878 – Enthalpy of melting and solidification of sulfonated paraffins as phase change materials for thermal energy storage

Paraffins are used as phase change material (PCM) for latent heat thermal energy storage (LHTES). The efficiency of a PCM is dependent on the encapsulated quantity and energy storage capacity per unit mass during its melting and solidifying. Two different kinds of paraffin (docosane and hexacosane with melting points of 317.15 and 329.45 K, respectively) were sulfonated at three different mole percentages to increase the LHTES efficiency for this purpose. The sulfonation of paraffin samples was proven by Fourier transform infrared (FT-IR) spectroscopy. Adiabatic Bomb Calorimetry was used to determine sulfonation percentages of paraffin samples. Enthalpies of melting and solidifying of docosane, hexacosane, and their sulfonated derivatives were measured by differential scanning calorimetry (DSC) method. Thermal properties obtained by the DSC analysis indicated that the enthalpy of melting and solidifying of docosane and hexacosane could be extended by sulfonation.
Cemil Alkan, Thermochimica Acta 451 (2006) 126-130

B1462 – Studies of the water adsorption on Zeolites and modified mesoporous materials for seasonal storage of solar heat

Zeolites and mesoporous materials were systematically modified by ion exchange and impregnation with hygroscopic salts to improve their storage capacity in thermochemical storage of heat. The sorption properties of those potential storage materials against water were investigated with physico-chemical methods such as thermogravimetry, differential scanning calorimetry, microcalorimetry and isotherm measurements confirming the improvement of the storage properties. Selected materials were pelleted and investigated in a lab-scaled storage to prove the performance of the modified storage materials. Two zeolite based materials with a charging temperature of approximately 450 K but a high temperature lift and an improved storage density of up to 576 kJ/L were found. Impregnated mesoporous materials show a much lower temperature lift, however, they offer a potential storage density of about 864 kJ/L at a charging temperature of about 390 K.
J. Jänchen, D. Ackermann, H. Stach, W. Brösicke, Solar Energy 76 (2004) 339-344

B0873 – Development of latent heat storage type ONDOL systeme

Kim, You Ho & Song, Hyun-Kap, Research Reports 8 (1992) 17-48

B0393 – Etude par microcalorimétrie différentielle d’hydrates salins (stockage d’énergie)

J.D. Sauzade et al., AFCAT, La Gaillarde (1983) 22

B0392 – Calorimétrie et analyse enthalpique différentielle pour la caractérisation de mélanges stockeurs d’énergie thermique

J.P. Bros, M. Gaune-Escard, AFCAT, La Gaillarde (1983) 8

A2115 – The thermal stability of molten nitrite/nitrates salt for solar thermal energy storage in different atmospheres

The study of the thermal decomposition of molten nitrite/nitrates salt used for thermal energy storage (TES) in concentrating solar power (CSP) was carried-out with a HITEC (Reg. U.S. Patent – Coastal Chemical Company) type salt. This salt is the commercial mixture of NaNO3–KNO3–NaNO2 in the proportions 7–53–40 wt.% (NO2/NO3 weight ratio of 0.7). The study was done by simultaneous DSC/TG-MS analysis between room temperature and 1000 °C in gas atmospheres of argon, nitrogen, air and oxygen. It was found that: •The thermal stability of the salt can be significantly enhanced by controlling the atmosphere. •By two assessment criteria, TG and DSC, the salt operated in an inert atmosphere could be used at temperature of at least 610 °C and when operated in an oxidising atmosphere up to between 650 °C and 700 °C. Oxidising atmosphere was found to change the chemistry of the salt by converting some nitrite to nitrate, and although this may have a bearing on increasing the melting point, it has the benefit of rising the thermal decomposition temperature.
Rene I. Olivares, Solar Energy 86 (2012) 2576–2583

A1344 – Synthesis and characterisation of LiNi(1-x-y)CoxAlyO2 cathodes for lithium-ion batteries by the PVA precursor method

Polycrystalline powders of LiNi(1-x)CoxO2 and LiNi(1-x-y)CoxAlyO2 were synthesized at 720°C from the nitrate-PVA precursor method. The water was removed by two different processes: (i) evaporation-drying at 110°C, (ii) spray-drying at 150°C. In both cases a gel is obtained wherein LiNO3 crystallizes in evaporated-dried samples but not in spray-dried samples which are more amorphous. All precursors give single phase powders with micronic well-shaped grains. The best electrochemical performances are obtained from evaporated samples with a capacity remaining higher than 160 mAh/g for LiNi0.82Co0.18O2 and 140 mAh/g for LiNi0.82Co0.13Al0.05O2 after 20 cycles. The lower performances of the spray-dried samples seem to be related to Li2CO3 formation with subsequent non-stoichiometry as a consequence of the improved homogeneous distribution of the constituent cations in the polymer.
P.H. Duvigneaud, T. Segato, Journal of the European Ceramic Society 24 (2004) 1375-1380

A1304 – Effects of metal oxide coatings on the thermal stability and electrical performance of LiCoCO2 in a Li-ion cell

A study is made of the effects of MgO and Al2O3 coatings on the electrical properties of LiCoO2 cathode material on the thermal stability (differential scanning calorimetry (DSC)) of the charged cathode, and on the safety characteristics of 18650 Li-ion cells. Powdery active material is coated with Mg or Al alkoxide solutions followed by heat treatment in air at temperatures between 300 and 800°C. The presence of the coating is confirmed by an elemental depth-profile analysis of the powder surface using secondary ion mass spectroscopy (SIMS) and X-ray photoelectron spectroscopy (XPS). Both oxide coatings, especially the Al2O3 coating, substantially improve the charge-discharge voltage characteristics, rate capability, capacity and rate-capability retention on cycling and thermal stability of the LiCoO2 cathode. These beneficial effects are demonstrated in 18650 Li-ion cells.
H-J. Kweon, J.J. Park, J.W. Seo, G.B. Kim, B.H. Jung, H.S. Lim, Journal of Power Sources 126 (2004) 156-162

A1286 – Conductivity improvements to spray-produced LiFePO4 by addition of a carbon source

We present order-of-magnitude conductivity data for "carbon-included" lithium iron phosphate (LFP) powders lightly pelletised as used as cathodes in Li-ion batteries. The powders were synthesised by a spray pyrolysis method, with a short ameliorating sinter to optimise phase purity. Carbon was introduced into the materials by adding stoichiometric amounts of sucrose into the starting ingredients. We obtained X-ray diffraction patterns and electrical conductivity estimates for carbon contents of between 0 and 31 wt.%. The resultant conductivities spanned almost seven orders of magnitude.
S.L. Bewlay, K. Konstantinov, G.X. Wang, S.X. Dou, H.K. Liu, Materials Letters 58 (2004) 1788-1791

A1266 – Proton conducting composite membrane from Daramic/Nafion for vanadium redox flow battery

A microporous separator (Daramic) was impregnated by soaking in a 5 wt.% Nafion solution to obtain a proton conducting composite membrane with modified properties for the vanadium redox flow battery (VRB). Nafion uptake by Daramic with thickness 0.25mm is 6.5 wt.%. Infrared spectroscopy (IR), thermogravimetric analysis (TGA) and ion exchange capacity (IEC) have also been carried out to confirm incorporation of Nafion into the Daramic membrane. The new Daramic/Nafion composite membranes give acceptable low electrical resistance, although the measured area resistances are higher for the composite membranes with different thickness than that for the untreated membranes. A reduction in water uptake of the membranes is observed after impregnation. Open circuit voltage measurement with time of the proton conducting composite membrane showed promising results compared with that of the untreated Daramic membrane when used in the VRB.
B. Tian, C.W. Yan, F.H. Wang, Journal of Membrane Science 234 (2004) 51-54

A1109 – Study of a PCM based energy storage system containing Ag nanoparticles

In this paper, organic phase change material (PCM)/Ag nanoparticles composite materials were prepared and characterized for the first time. The effect of Ag nanoparticles on the thermal conductivity of PCM was investigated. 1-tetradecanol (TD) was selected as a PCM. A series of nano-Ag-TD composite materials in aqueous solution were in-situ synthesized and characterized by means of thermal conductivity evaluation method, TG-DSC, IR, XRD and TEM. The results showed that the thermal conductivity of the composite material was enhanced as the loading of Ag nanoparticles increased. The composite materials still had relatively large phase change enthalpy. Their phase change enthalpy could be correlated linearly with the loading of TD, but their phase change temperature was a little bite lower than that of pure TD. The thermal stability of the composite materials was close to that of pure TD. It appeared that there was no strong interaction between the Ag nanoparticles and the TD. Furthermore, the experiment results indicated that the Ag nanoparticles dispersed uniformly in the materials, occurred in the forms of pure metal.
J.L. Zeng, L.X. Sun, F. Xu, Z.C. Tan, Z.H. Zhang, J. Zhang and T. Zhang, Journal of Thermal Analysis and Calorimetry 87 (2007) 369-373

A1057 – Chemistry and electrochemistry of nanostructured iron oxyhydroxides as lithium intercalation compounds for energy storage

The structural characterization and electrochemical performance of three nanosized iron oxyhydroxides (beta-FeOOH, gamma-FeOOH and delta-FeOOH) are reported in this work. The interest of having small particle sizes is to be able to circumvent the low intrinsic ionic conductivity of these materials through the increase of the active volume proportion of the operating grain, during the insertion process. Low temperature synthesis routes, in aqueous media, were thus used to obtain such crystallites with nanometer dimensions. The theoretical specific capacity of these materials is as high as 300 mA h g-1 which is actually very interesting for lithium batteries applications. However, the electrochemical behaviour greatly depends on the structure of the compounds. A phase transformation was, for example, evidenced in the case of gamma-FeOOH first lithiation whereas the best performance were obtained with beta-FeOOH, which develops a stable capacity of 180 mA h g-1, after 10 cycles, at C/10.
C. Benoit, C. Bourbon, P. Berthet, S. Franger, Journal of Physics and Chemistry of Solids 67 (2006) 1265-1269

A1026 – Sulphur-polypyrrole composite positive electrode materials for rechargeable lithium batteries

A novel conducting sulphur-polypyrrole composite material was prepared by the chemical polymerization method with sodium ptoluenesulphonate as the dopant, 4-styrenesulphonic sodium salts as the surfactant, and FeCl3 as the oxidant. The new material was characterized by Raman spectroscopy, thermogravimetric analysis, and scanning electron microscopy. Nanosize polypyrrole particles were uniformly coated onto the surface of the sulphur powder, which significantly improved the electrical conductivity, the capacity and the cycle durability in a lithium cell compared with the bare sulphur electrode.
J. Wang, J. Chen, K. Konstantinov, L. Zhao, S.H. Ng, G.X. Wang, Z.P. Guo, H.K. Liu, Electrochimica Acta 51 (2006) 4634-4638

A0974 – Electrochemical properties of LiCrxNi(0.5-x)Mn0.5O2 prepared by co-precipitation method for lithium secondary batteries

The purpose of this research is to study a new synthesis of LiCrxNi(0.5-x)Mn0.5O2 (x = 0, 0.05 and 0.1) using a co-precipitation method for lithium secondary batteries. Investigations are made of the morphology, cyclic voltammetry and charge-discharge cycling of LiCrxNi(0.5-x)Mn0.5O2/Li cells. The particle size of LiNi0.5Mn0.5O2 has a narrow distribution range from 200 to 300 nm. The peak current of LiCr0.05Ni0.45Mn0.5O2 and LiCr0.1Ni0.4Mn0.5O2 in the 2.7 and 2.9V regions increases with increasing addition of Cr in LiCrxNi(0.5-x)Mn0.5O2. The discharge capacity of the LiNi0.5Mn0.5O2 electrode is 185 and 150 mAh g-1 at 1 and 15 cycles, respectively. The fading in capacity of Cr-doped LiNi0.5Mn0.5O2 is less than that of LiNi0.5Mn0.5O2 during cycling. LiCrxNi(0.5-x)Mn0.5O2 cathodes with 1M LiPF6 in an ethyl carbonate-dimethyl carbonate (EC-DMC) electrolyte exhibit good cycling performance.
G-T. Kim, J-U. Kim, Y-J. Sim, K-W. Kim, Journal of Power Sources 158 (2006) 1414-1418

A0952 – Optimizing synthesis of silicon/disordered carbon composites for use as anode materials in lithium-ion batteries

Pyrolysis conditions for the production of silicon/disordered carbon (Si-DC) nanocomposites using PVA as the carbon source were optimized in this work. It was found that the optimum sintering temperature for the Si-DC nanocomposites is 800°C. In order to achieve good cell performance, a high argon gas flow rate and a slow heating rate are preferred in sample preparation. The morphology of the carbon source (PVA) affects the electrochemical performance of the Si-DC nanocomposites as well. The key point to obtain Si-DC nanocomposites with good electrochemical performance is to reduce the chances of pyrolysis gases (especially CO2) to react with carbon, thereby preventing carbon burnoff during the sintering process.
Z.P. Guo, D.Z. Jia, L. Yuan, H.K. Liu, Journal of Power Sources 159 (2006) 332-335

A0940 – Iodide-based electrolytes: A promising alternative for thermal batteries

Molten iodide-based salts due to their low melting points were envisaged to improve the performances of thermal batteries. Iodide-based salt drying and the determination of the basic properties (electrochemical window, conductivity, thermal heat capacity, ... ) of some electrolytes were carried out. The results obtained showed that some of iodide-based electrolytes are suitable for thermal batteries. In addition, the LiF-LiCl-LiI and LiF-LiBr-KBr electrolytes were tested in Li-Si/FeS2 single cells in the temperature of thermal battery operating conditions. The LiF-LiCl-LiI electrolyte could be considered as an interesting alternative for the improvements of thermal battery performances.
P. Masset, Journal of Power Sources 160 (2006) 688-697

A0746 – Retained molten salt electrolytes in thermal batteries

In high temperature electrical generators such as thermal batteries, the molten salt electrolyte needs to be retained by a binder, e.g. MgO.We have pointed out that the magnesia volume fraction was a more accurate parameter than the usually used weight fraction. Moreover, based on our technique measurements, we defined a magnesia volume fraction range (27-30 vol.%) where the electrolyte retention could be considered as efficient whatever its nature. And finally, we proposed a microstructure description of the retained electrolyte.
P. Masset, S. Schoeffert, J-Y. Poinso, J-C. Poignetc, Journal of Power Sources 139 (2005) 356-365

A0592 – Nano-structured SnO2-carbon composites obtained by in situ spray pyrolysis method as anodes in lithium batteries

In this paper, we report on a series of SnO2-carbon nano-composites synthesized by in situ spray pyrolysis of a solution of SnCl2.2H2O and sucrose at 700°C. The process results in super fine nanocrystalline SnO2, which is homogeneously distributed inside the amorphous carbon matrix. The SnO2 was revealed as a structure of broken hollow spheres with porosity on both the inside and outside particle surfaces. This structure promises a highly developed specific surface area. X-ray diffraction (XRD) patterns and transmission electron microscope (TEM) images revealed the SnO2 crystal size is about 5-15 nm. These composites show a reversible lithium storage capacity of about 590 mAh g-1 in the first cycle. The discharge curve of the composite indicates that lithium is stored in crystalline tin, but not in amorphous carbon. However, the conductive carbon matrix with high surface area provides a buffer layer to cushion the large volume change in the tin regions, which contributes to the reduced capacity fade compared to nonacrystalline SnO2 without carbon.
L. Yuan, K. Konstantinov, G.X. Wang, H.K. Liu, S.X. Dou, Journal of Power Sources 146 (2005) 180-184

A0591 – An investigation of polypyrrole-LiFePO4 composite cathode materials for lithium-ion batteries

A series of polypyrrole-LiFePO4 (PPy-LiFePO4) composites were synthesised by polymerising pyrrole monomers on the surface of LiFePO4 particles. AC impedance measurements show that the coating of polypyrrole significantly decreases the charge-transfer resistance of LiFePO4 electrodes. The electrochemical reactivity of polypyrrole and PPy-LiFePO4 composites for lithium insertion and extraction was examined by charge/discharge testing. The PPy-LiFePO4 composite electrodes demonstrated an increased reversible capacity and better cyclability, compared to the bare LiFePO4 electrode.
G.X. Wang, L. Yang, Y. Chen, J.Z. Wang, Steve Bewlay, H.K. Liu, Electrochimica Acta 50 (2005) 4649-4654