Equilibrium of NH4SCNNH3 system for thermal energy storage

A solid-gas reaction of ammonium thiocyanate (NH₄SCN) and ammonia produces liquid ammoniate (NH₄SCN·nNH₃). The region of the liquid phase and the equilibrium properties of the ammoniate have been determined. Crystalization of the ammoniate was not observed, though the liquid was cooled to − 10°C. The enthalpy changes in the liquid phase were also estimated. Accordingly, this system has a wide range of liquid phase and offers a medium for thermal energy storage or a chemical heat pump system.     

Characterization and electrochemical properties of Cx(VOF3)F as positive material for primary lithium batteries

Vanadium oxide fluoride-graphite intercalation compounds, i.e. C_x(VOF₃)F with 17.2 ≤ × ≤ 38.8, have been prepared from V₂O₅ and graphite in a fluorine atmosphere at 130°C. The structural characteristics of these compounds have been deduced from X-ray diffraction and X-ray photoelectron spectroscopy measurements. Intercalation of VOF₃ and fluorine was pointed out. The electrochemical insertion of lithium into C_17.7(VOF₃)F was investigated by chronopotentiometry and a.c. impedence spectroscopy in propylene carbonate-1 M LiClO₄. The chemical diffusion coefficient, D_Li, was estimated to be close to 4.0 × 10⁻¹⁰cm²s⁻¹ for all the values of the intercalation ratio of lithium under study (0 < y < 1.5).     

Preparation and electrochemical characteristics of quaternary Li-Mn-V-O spinel as the positive materials for rechargeable lithium batteries

Quaternary Li-Mn-V-O spinels were prepared by heating mixtures of MnCO₃, V₂O₅ and LiNO₃ at 700 °C for 36 h in air. The spinel oxides were characterized by X-ray diffraction, FT-IR spectroscopic, density and electrochemical measurements. The unit cell volume in a cubic cell increased with an increase in V content in LiV_xMn_{2 − x}O₄ (x = 0–0.2), while the amounts of lithium intercalated into the spinels in a high potential region around 4 V versus Li/Li⁺ decreased considerably with an increase in V content. Furthermore, the thermodynamics and kinetics of the lithium intercalation process into the spinel Li_nV_xMn_{2 − x}O₄ were studied. The standard free energies of lithium intercalation into the spinels were −291 kJ/mol for x = 0 and −264 kJ/mol for x = 0.05 at n = 0–1 and 25 °C. The chemical and self-diffusion coefficients for lithium in Li_nV_xMn_{2 − x}O₄ spinels were measured as functions of the n and x values by a current-pulse relaxation method. The diffusion coefficients in the spinel with x = 0.05 in the n-value range from 0.3 to 1 were about one order of magnitude lower than that in Li_nMn₂O₄.     

Polymer batteries fabricated from lithium complexed acetylated chitosan

It is found that 0.8 g lithium nitrate added to a solution of 1 g chitosan dissolved in 100 ml 1% acetic acid produces a film, via the solution cast technique, with a maximum electrical conductivity of the order of 10⁻⁴ S cm⁻¹. This film is amorphous. For battery fabrication, metal powder and hydrogen storage material are used for the anode, and a metallic oxide (MnO₂) for the cathode material. The anode contains a mixture of zinc and zinc sulfate in the ratio of 3:1. Batteries with configurations Zn + ZnSO₄·7H₂O/LiCAC/I₂ + C and Zn + ZnSO₄·7H₂O/ LiCAC/MnO₂+C (LiCAC = lithium complexed acetylated chitosan) provide open-circuit voltages of 1.113 and 0.765 V, respectively. The discharge characteristics of the batteries are presented. Unfortunately, only short lifetimes and small discharge currents can be obtained. This is possibly due to incompatibility between the electrode materials and the electrolytes.     

Vapor–liquid equilibrium of ammonia–water–lithium nitrate solutions

Experimental results on the pressure–temperature data for the NH₃‐H₂O binary and NH₃‐H₂O‐LiNO₃ ternary solutions are reported. The pressure was varied between 100 and 800 kPa, while the mass fraction of ammonia was varied in the range 0–0.30. The lithium nitrate concentration of the solution was chosen in the range of 10–50% of mass ratio of lithium nitrate in pure water. An analytical equation for the equilibrium pressure as a function of temperature and concentration was obtained with a good fit to experimental data. © 2011 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.20351     

Ionic conductivity enhancement in LiTi2(PO4)3-based composite electrolyte by the addition of lithium nitrate

The electrical and thermal properties of LiTi₂(PO₄)₃ (LTP) and LTP composite electrolytes were investigated. LTP-LiNO₃ composite electrolyte sintered at 900 °C revealed high conductivity (approximately 10⁻⁵ S cm⁻¹ at 25 °C), compared with pure LTP sintered at the same temperature. The thermal behavior in the sintering process of pure LTP and LTP composite electrolytes was examined. Consequently, we found that the conductivity of the composite electrolyte was enhanced by partial melting and subsequent solidification of the pellet at around 800 °C. This phenomenon was attributed to the coexistence of Li₄P₂O₇ which was a byproduct of the decomposition of LiNO₃ and LTP.     

New inverse spinel cathode materials for rechargeable lithium batteries

The synthesis, characterization, and electrochemical properties of LiNi_yCo_{1 − y}VO₄ (0 ≤ y ≤ 1) as the new cathode materials for rechargeable lithium batteries were investigated. A series of LiNi_yCo_{1 − y}VO₄ (y = 0.1 − 0.9) compounds were synthesized by either a solid-state reaction of LiNi_yCo_{1 − y}O₂ and V₂O₅ at 800 °C for 12 h or a solution coprecipitation of LiOH · H₂O, Ni(NO₃)₂ · 6H₂O, Co(NO₃)₂ · 6H₂O and NH₄VO₃, followed by heating the precipitate at 500 °C for 48 h. The products from both preparation methods were analyzed by scanning electron microcopy and inductively-coupled plasma-atomic emission spectroscopy. These compounds are inverse spinels based on the results from Rietveld analysis and the fact that the cubic lattice constant a is a linear function of stoichiometry y in LiNi_yCo_{1 −y}VO₄. Either a 1 M LiC1O₄-EC + PC (1:1) or 1 M LiBF₄-EC + PC + DMC (1:1:4) electrolyte can be used as the electrolyte for Li/LiNi_yCo_{1 − y}VO₄ cells up to y = 0.7. The charge and discharge capacity of a Li/1 M LiBF₄-EC + PC + DMC (1:1:4) /LiNi_0.5Co_0.5VO₄ cell were 43.8 and 34.8 mAh/g, respectively, when the cathode material was prepared by the low temperature coprecipitation method.     

Comparative analysis of a solar‐driven novel salt‐based absorption chiller with the implementation of nanoparticles

The present study exemplifies the comprehensive thermal analysis to compare and contrast ammonia‐lithium nitrate (NH₃‐LiNO₃) and ammonia‐sodiumthiocynate (NH₃‐NaSCN) absorption systems with and without incorporation of nanoparticles. A well‐mixed solution of copper oxide/water (CuO/H₂O) nanofluid is considered inside a flat‐plate collector linked to an absorption chiller to produce 15‐kW refrigeration at ?5°C evaporator temperature. Enhancements in heat transfer coefficient, thermal efficiency, and useful heat gain of the collector are evaluated, and the effect of these achievements on the performance of both absorption chillers have been determined for different source temperatures. A maximum 121.7% enhancement is found in the heat transfer coefficient with the application of the nanofluid at 2% nanoparticle concentration. The maximum coefficient of performance observed for the NH₃‐NaSCN chiller is 0.12% higher than that for the NH₃‐LiNO₃ chiller at 0°C evaporator temperature. Contradictory to this, the average system coefficient of performance of the NH₃‐LiNO₃ absorption system has been found 5.51% higher than that of the NH₃‐NaSCN system at the same evaporator temperature. Moreover, the application of the nanofluid enhanced the performance of the NH₃‐NaSCN and NH₃‐LiNO₃ systems by 2.70% and 1.50%, respectively, for lower generator temperature and becomes almost the same at higher temperatures, which altogether recommends the flat‐plate collector–coupled NH₃‐LiNO₃ absorption system be integrated with a nanofluid.     

Preparation and characterization of LiNiO2 synthesized from Ni(OH)2 and LiOH·H2O

Synthesis of LiNiO₂ by heat-treatment of Li(OH)·H₂O and Ni(OH)₂ is reported. The influence of synthesis conditions on the electrochemical performance of the resulting LiNiO₂ is investigated. Thermal analysis of the synthesis process shows that LiNiO₂ formation proceeds through the transformation of Ni(OH)₂ to a layered compound Ni_1−x(OH)_2−x, followed by solid reaction with LiOH. The most favorable condition is heating a mixture of Li(OH)·H₂O and Ni(OH)₂ at 650°C, and then at 720°C in oxygen. The resulting LiNiO₂ exhibits a considerably high discharge capacity of 145 mA h g⁻¹ and a sufficiently long cycle-life when cycled over a lithium composition range of 0.2≤x≤0.65.     

Studies of electrochemical properties of lithium cobalt oxide

The electrochemical characteristics of high-temperature (HT) LiCoO₂ (900 °C) and low-temperature (LT) LiCoO₂ (450 °C) were studied. From cyclic voltammetry results, lithium intercalating into LT-LiCoO₂ generates two current peaks at 3.8 and 3.3 V, respectively, which is contrast to the intercalation of lithium into HT-LiCoO₂. The resistance of lithium extraction is smaller than that of lithium insertion. The diffusion coefficients of Li⁺ ions in LiCoO₂ have an order of 10⁹⁻ cm²/s.     

Electrochemical properties of iodine-containing lithium manganese oxide spinel

Iodine-containing, cation-deficient, lithium manganese oxides (ICCD-LMO) are prepared by reaction of MnO₂ with LiI. The MnO₂ is completely transformed into spinel-structured compounds with a nominal composition of Li_1−δMn_2−2δO₄I_x. A sample prepared at 800 °C, viz. Li_0.99Mn_1.98O₄I_0.02, exhibits an initial discharge capacity of 113 mA h g⁻¹ with good cycleability and rate capability in the 4-V region. Iodine-containing, lithium-rich lithium manganese oxides (ICLR-LMO) are also prepared by reaction of LiMn₂O₄ with LiI, which results in a nominal composition of Li_1+xMn_2−xO₄I_x. Li_1.01Mn_1.99O₄I_0.02 shows a discharge capacity of 124 mA h g⁻¹ on the first cycle and 119 mA h g⁻¹ a on the 20th cycle. Both results indicate that a small amount of iodine species helps to maintain cycle performance.     

Preparation,electrical and thermal properties of new anode material based on Ca-doped perovskite CeAlO3

Tetragonal perovskite phase Ce_0.9Ca_0.1AlO_2.95 + x was obtained for the first time. Such phase, containing cerium in the oxidation state of 3+, can be promising anode materials for a solid oxide fuel cells (SOFCs). Ce_0.9Ca_0.1AlO_2.95 + х (space group I4/mcm) was synthesized by the solid-phase method at 1400°С in a nitrogen flow with using ammonium oxalate (NH₄)₂C₂O₄ to create a reducing atmosphere. Thermogravimetry results showed that Ce_0.9Ca_0.1AlO_2.95 + x was stable to oxidation up to 500°С in air and up to 700°С in argon (partial pressure of oxygen рО₂ = 10⁻⁴ bar). The thermal expansion coefficient measured by dilatometry was equal to 11.16·10⁻⁶ К⁻¹. The temperature dependences of the electrical conductivity (for undoped phase CeAlO₃ σ ≈ 1·10⁻³ S/cm and for doped Ce_0.9Ca_0.1AlO_2.95 + x σ ≈ 3·10⁻² S/cm at 500°С in air) were obtained by the electrochemical impedance spectroscopy measurements). The electrical conductivity of these samples at the temperatures range of 350–500°С was almost independent of the partial pressure of oxygen рО₂ from 10⁻¹⁸ to 0.21 bar, however, there was a slight negative slope at T > 500 °C (рО₂). The total ionic transport numbers measured by the EMF method were close to 1·10⁻³, which indicated the dominance of electronic conductivity. The measurement of the sign of the thermal-EMF showed that positive charge carriers (holes) were dominant charge carriers.     

Effect of synthesis conditions on the properties of LiFePO4 for secondary lithium batteries

LiFePO₄ is one of the promising materials for cathode of secondary lithium batteries due to its high energy density, low cost, environmental friendliness and safety. However, LiFePO₄ has very poor electronic conductivity (∼10⁻⁹ S cm⁻¹) and Li-ion diffusion coefficient (∼1.8 × 10⁻¹⁴ cm² s⁻¹) at room temperature. In an attempt to improve electrochemical properties, Li_XFePO₄ with various amounts of Li contents were investigated in this study. Li_XFePO₄ (X = 0.7–1.1) samples were synthesized by solid-state reaction. High resolution X-ray diffraction, Rietveld analysis, BET, scanning electron microscopy, and hall effect measurement system were used to characterize these samples. Electronic conductivities of the samples with Li-deficient and Li-excess in Li_xFePO₄ were 10⁻³ to 10⁻¹ S cm⁻¹. Discharge capacities and rate capabilities of the samples with Li-deficient and Li-excess in Li_XFePO₄ were higher than those of stoichiometric LiFePO₄ sample. Li_0.9FePO₄ samples fired at 700 °C had discharge capacity of 156 and 140 mAh g⁻¹ at 0.1 C- and 2 C-rate, respectively.     

An improved absorption refrigeration cycle driven by unsteady thermal sources below 100°C

This paper deals with an improved absorption refrigeration cycle with staged absorption. Instead of having only one absorber, the improved cycle uses a series of absorbers among which one is cooled by the external medium and the others are cooled by refrigerant at staged pressures between the evaporation pressure and condensation pressure. Ammonia–lithium nitrates (NH₃–LiNO₃) are selected as the working fluids and the calculation results for the two‐staged cycle and the three‐staged cycle are analysed in detail. It is demonstrated that the improved cycle is able to steadily run when driven by low‐grade thermal sources as low as 65°C, and to produce deep refrigeration temperature as low as −40°C. Copyright © 2000 John Wiley & Sons, Ltd.     

Effect of (Al,Mg) substitution in LiNiO2 electrode for lithium batteries

Stabilized lithium nickelate is receiving increased attention as a low-cost alternative to the LiCoO₂ cathode now used in rechargeable lithium batteries. Layered LiNi_1−x−yM_xM_yO₂ samples (M_x = Al³⁺ and M_y = Mg²⁺, where x = 0.05, 0.10 and y = 0.02, 0.05) are prepared by the refluxing method using acetic acid at 750 °C under an oxygen stream, and are subsequently subjected to powder X-ray diffraction analysis and coin-cell tests. The co-doped LiNi_1−x−yAl_xMg_yO₂ samples show good structural stability and electrochemical performance. The LiNiAl_0.05Mg_0.05O₂, cathode material exhibits a reversible capacity of 180 mA h g⁻¹ after extended cycling. These results suggest that the threshold concentration for aluminum and magnesium substitution is of the order of 5%. The co-substitution of magnesium and aluminium into lithium nickelate is considered to yield a promising cathode material.     

Chemical and structural instabilities of lithium ion battery cathodes

The chemical and structural stabilities of various layered Li_1−xNi_1−y−zMn_yCo_zO₂ cathodes are compared by characterizing the samples obtained by chemically extracting lithium from the parent Li_1−xNi_1−y−zMn_yCo_zO₂ with NO₂BF₄ in an acetonitrile medium. The nickel- and manganese-rich compositions such as Li_1−xNi_1/3Mn_1/3Co_1/3O₂ and Li_1−xNi_0.5Mn_0.5O₂ exhibit better chemical stability than the LiCoO₂ cathode. While the chemically delithiated Li_1−xCoO₂ tends to form a P3 type phase for (1 − x) < 0.5, Li_1−xNi_0.5Mn_0.5O₂ maintains the original O3 type phase for the entire 0 ≤ (1 − x) ≤ 1 and Li_1−xNi_1/3Mn_1/3Co_1/3O₂ forms an O1 type phase for (1 − x) < 0.23. The variations in the type of phases formed are explained on the basis of the differences in the chemical lithium extraction rate caused by the differences in the degree of cation disorder and electrostatic repulsions. Additionally, the observed rate capability of the Li_1−xNi_1−y−zMn_yCo_zO₂ cathodes bears a clear relationship to cation disorder and lithium extraction rate.     

Improved performance of Li hybrid solid polymer electrolyte cells

The seminal research by Wright et al. on polyethylene oxide (PEO) solid polymer electrolyte (SPE) generated intense interest in all solid-state rechargeable lithium batteries. Following this a number of researchers have studied the physical, electrical and transport properties of thin film PEO electrolyte containing Li salt. These studies have clearly identified the limitations of the PEO electrolyte. Chief among the limitations are a low cation transport number (t₊), high crystallinity and segmental motion of the polymer chain, which carries the cation through the bulk electrolyte. While low t₊ leads to cell polarization and increase in cell resistance high T_g reduces conductivity at and around room temperatures. For example, the conductivity of PEO electrolyte containing lithium salt is <10⁻⁷ S cm⁻¹ at room temperature. Although modified PEO electrolytes with lower T_g exhibited higher conductivity (∼10⁻⁵ S cm⁻¹ at RT) the t₊ is still very low ∼0.25 for lithium ion. Numerous other attempts to improving t₊ have met with limited success. The latest approach involves integrating nano domains of inorganic moieties, such as silcate, alumosilicate, etc. within the polymer component. This approach yields an inorganic–organic component (OIC) based polymer electrolyte with higher conductivity and t₊ for Li⁺_. This paper describes the improved electrical and electrochemical properties of OIC-based polymer electrolyte and cells containing Li anode with either a TiS₂ cathode or Mag-10 carbon electrode. Several solid polymer electrolytes derived from silicate OIC and salt-in-polymer constituent based on Li triflate (LiTf) and PEO are studied. A typical composition of the SPE investigated in this work consists of 600 kDa PEO, lithium triflate (LiTf, LiSO₃CF₃) and 55% of silicate based on (3-glycidoxypropyl)trimethoxysilane and tetramethoxysilane at molar ratio 4:1 and 0.65 mol% of aluminum(tri-sec-butoxide) (GTMOS-Al1-900k-55%). Several pouch cells consisting of Li/OIC-based–SPE/cathode containing OIC-based–SPE–LiTf binder were fabricated and tested, these cells are called modified cells. The charge/discharge and impedance characteristics of the new cells (also called modified cells) are compared with that of the pouch cells containing the conventional PEO–LiTf electrolyte as the cathode binder, these cells are called non-modified cells. The new cells can be charged and discharged at 70 °C at higher currents. However, the old cells can be charged and discharged only at 80 °C or above and at lower currents. The cell impedance for the new cells is much lower than that for the old cells.     

LiN1 − xCoxCoxO2 prepared at low temperature using β-Ni1 − xCox OOH and either LiNO3 or LiOH

LiNi_{1 − y}Co_yO₂ has been prepared at 400 °C by using β-Ni_{1 − y}Co_yOOH and either LiNO₃ or LiOH. The mechanism of these reactions was clarified by differential thermal and thermogravimetric analyses. The material prepared with LiNO₃ is well crystallized because LiNO₃ melts and then reacts with the oxyhydroxide in a viscous state. However, when LiOH is used, a solid-solid diffusion reaction takes place and leads to a material with broad X-ray diffraction peaks. The electrochemical characteristics of these materials were evaluated and compared with those prepared by the usual processes at high temperature.     

Highly conductive proton-conducting electrolyte with a low sintering temperature for electrochemical ammonia synthesis

BaCe_0·7Zr_0.1Gd_0.2O_3-δ (BCZG) powder is synthesized by a citrate sol-gel method, and different amounts of Li₂CO₃ are introduced to lower the sintering temperature. The densification temperature of BCZG ceramic is decreased drastically to 1250 °C by using Li₂CO₃ as sintering aid. BCZG with 2.5 wt% of Li₂CO₃ (BCZG-2.5L) can not only remarkably promote the sintering process of BCZG but also enhance its electrical conductivity. The total ionic conductivity of BCZG-2.5L attains to 1.9 × 10⁻² S cm⁻¹ at 600 °C in a wet H₂ atmosphere. Ammonia synthesis at atmospheric pressure is conducted on (2K, 10Fe)/Ni-BCZG | BCZG-2.5L | Ni-BCZG electrolytic cell with an applied voltage of 0.2–1.6 V at a temperature of 450–600 °C. The highest NH₃ formation rate of 1.87 × 10⁻¹⁰ mol s⁻¹ cm⁻² and the highest current efficiency of 0.53% is achieved at 500 °C with an applied voltage of 0.8 V.     

Electrochemical properties of cobalt-exchanged spinel lithium manganese oxide

Cobalt-exchanged LiCo_yMn_2−yO₄ (y=0.0, 0.1, 0.2, 0.3, 0.4, 0.5) is prepared at 800°C in air. The crystal symmetry of the LiCo_yMn_2−yO₄ is determined as cubic spinel with space group Fd3m. The lattice parameter and the discharge capacity decrease with increase in substituted Co content, but the cycle performance is enhanced. The first discharge capacity of LiCo_0.2Mn_1.8O₄ is 96 mAh g⁻¹ in the 3.7–4.3 V range and 109 mAh g⁻¹ in the 3.7–5.1 V range. A Mn(II) peak is observed in the cyclic voltammogram for spinel LiMn₂O₄. It is difficult to remove this Mn(II) with conventional preparation methods. The peak disappears in cobalt-exchanged spinel sample, LiCo_yMn_2−yO₄ (y>0.1), and the cycle performance is enhanced.