Enhancement of capacity and cycle-life of Sn4 + δP3 (0 ≤ δ ≤ 1) anode for lithium secondary batteries

Various compositions of tin-rich, non-stoichiometric, solid solutions of Sn_4 + δP₃ are synthesized by a mechanochemical method. The materials are tested as anodes for lithium secondary batteries to enhance reversible capacity and cycleability. Investigative analyses show that the region for the solid-solution formation of Sn_4 + δP₃ is 0 ≤ δ ≤ 1. The reaction mechanism of the tin-rich solid solutions is similar to that of stoichiometric Sn₄P₃, except for the absence of a topotactic lithium insertion reaction during the first cycle. As the tin content is increased, tin-rich phosphide exhibits better cycleability and retains a higher reversible capacity, namely, about 20% more than that of stoichiometric Sn₄P₃.     

Formation and consumption of NO in H2 + O2 + N2 flames doped with NO or NH3 at atmospheric pressure

Flat premixed burner-stabilized H₂ + O₂ + N₂ flames, neat or doped with 300–1000 ppm of NO or NH₃, were studied experimentally using molecular-beam mass-spectrometry and simulated numerically. Spatial profiles of temperature and concentrations of stable species, H₂, O₂, H₂O, NO, NH₃, and of H and OH radicals obtained at atmospheric pressure in lean (? = 0.47), near-stoichiometric (? = 1.1) and rich (? = 2.0) flames are reported. Good agreement between measured and calculated structure of lean and near-stoichiometric flames was found. Significant discrepancy between simulated and measured profiles of NO concentration was observed in the rich flames. Sensitivity and reaction path analyses revealed reactions responsible for the discrepancy. Modification to the model was proposed to improve an overall agreement with the experiment.     

Crystallographic and electrochemical characteristics of La0.7Mg0.3Ni3.5 − x(Al0.5Mo0.5)x (x = 0–0.8) hydrogen storage alloys

The crystal structure, hydrogen storage property and electrochemical characteristics of the La_0.7Mg_0.3Ni_3.5 − x(Al_0.5Mo_0.5)_x (x = 0–0.8) alloys have been investigated systematically. It can be found that with X-ray powder diffraction and Rietveld analysis the alloys are of multiphase alloy and consisted of impurity LaNi phase and two main crystallographic phases, namely the La(La, Mg)₂Ni₉ phase and the LaNi₅ phase, and the lattice parameter and the cell volume of both the La(La, Mg)₂Ni₉ phase and the LaNi₅ phase increases with increasing Al and Mo content in the alloys. The P–C isotherms curves indicate that the hydrogen storage capacity of the alloy first increases and then decreases with increasing x, and the equilibrium pressure decreases with increasing x. The electrochemical measurements show that the maximum discharge capacity first increases from 354.2 (x = 0) to 397.6 mAh g⁻¹ (x = 0.6) and then decreases to 370.4 mAh g⁻¹ (x = 0.8). The high-rate dischargeability of the alloy electrode increases lineally from 55.7% (x = 0) to 73.8% (x = 0.8) at the discharge current density of 1200 mA g⁻¹. Moreover, the exchange current density of the alloy electrodes also increases monotonously with increasing x. The hydrogen diffusion coefficient in the alloy bulk increases with increasing Al and Mo content and thus enhances the low-temperature dischargeability of the alloy electrode.     

Solid-state Li/LiFePO4 polymer electrolyte batteries incorporating an ionic liquid cycled at 40 °C

The cycle behaviour and rate performance of solid-state Li/LiFePO₄ polymer electrolyte batteries incorporating the N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR₁₃TFSI) room temperature ionic liquid (IL) into the P(EO)₂₀LiTFSI electrolyte and the cathode have been investigated at 40 °C. The ionic conductivity of the P(EO)₂₀LiTFSI + PYR₁₃TFSI polymer electrolyte was about 6 × 10⁻⁴ S cm⁻¹ at 40 °C for a PYR₁₃⁺/Li⁺ mole ratio of 1.73. Li/LiFePO₄ batteries retained about 86% of their initial discharge capacity (127 mAh g⁻¹) after 240 continuous cycles and showed excellent reversible cyclability with a capacity fade lower than 0.06% per cycle over about 500 cycles at various current densities. In addition, the Li/LiFePO₄ batteries exhibited some discharge capability at high currents up to 1.52 mA cm⁻² (2 C) at 40 °C which is very significant for a lithium metal-polymer electrolyte (solvent-free) battery systems. The addition of the IL to lithium metal-polymer electrolyte batteries has resulted in a very promising improvement in performance at moderate temperatures.     

Temperature dependence of effective thermal conductivity and diffusivity of ZnxTe100−x (x = 5, 10, 30 and 50) chalcogenide material

Measurements of thermophysical properties of Zn_xTe_100−x (x = 5, 10, 30 and 50) chalcogenide material in pellet form have been made in the temperature range from room temperature (15 °C) to 200 °C and in cooling cycle from 200 °C to 15 °C using transient plane source (TPS) technique. In heating mode the values of effective thermal conductivity (λ_e) and effective thermal diffusivity (χ_e) increase from 15 °C to 200 °C. During the cooling mode λ_e and χ_e decrease slightly in the temperature range from 200 °C to 160 °C below which λ_e and χ_e remain almost constant at all temperatures. Such type of behaviour shows thermal hysteresis in this sample, which can be explained on the basis of the change in structure of the material. XRD studies suggest that the material is polycrystalline in nature.     

Effect of the Sm content on the structure and electrochemical properties of La1.3 − xSmxCaMg0.7Ni9 (x = 0–0.3) hydrogen storage alloys

La_1.3 − xSm_xCaMg_0.7Ni₉ (x = 0–0.3) hydrogen storage alloys were prepared by inductive melting and the effect of the Sm content on the structure and electrochemical properties was investigated in the paper. The Sm substitution for La in La_1.3 − xSm_xCaMg_0.7Ni₉ (x = 0–0.3) alloys does not change the main phase structure (the rhombohedral PuNi₃-type structure), but leads to a shrinkage of unit cell and a decrease of hydrogen storage capacity. With the increase of the Sm content in the alloys, the maximum discharge capacity of electrode decreases from 400.2 (x = 0) to 346.6 mAh g⁻¹ (x = 0.3), but the high-rate dischargeability and cycling stability is improved. After 100 cycles, the capacity retention rate increases from 75 (x = 0) to 85% (x = 0.3).     

Physical characteristics and rate performance of (CFx)n (0.33 < x < 0.66) in lithium batteries

Sub-fluorinated graphite fluorides (CF_x)_n compounds, 0.33 < x < 0.63 were prepared from natural graphite and characterized by TGA, SEM-EDX and XRD. Their cathode behavior in lithium batteries was investigated under different discharge rates and compared to commercial petroleum coke based (CF)_n. At low discharge rate, the energy density increases with the fluorine content x. However, at higher rates, sub-fluorinated compounds performed better than commercial (CF)_n. The result is discussed with relation to higher electrical conductivity of sub-fluorinated compounds.     

The effects of partial substitution of Cr for Ni on the electrochemical properties of Mg1.75Al0.25Ni1−xCrx (0 ≤ x ≤ 0.3) electrode alloys

In this paper, the substitution of different amounts of Cr for Ni in the hydrogen storage electrode alloy of Mg_1.75Al_0.25Ni has been carried out to form quaternary Mg_1.75Al_0.25Ni_1−xCr_x (0 ≤ x ≤ 0.3) alloys by means of solid diffusion method (DM). The XRD profiles exhibited that the quaternary alloys still kept the same main phase of Mg₃AlNi₂ (S.G. Fd3m) as that of ternary Mg_1.75Al_0.25Ni alloy. The electrochemical studies found that Cr substituted quaternary alloy reached its maximum discharge capacity (165 mAh g⁻¹) after 2 cycles, which was larger than that of the Mg_1.75Al_0.25Ni alloy (154 mAh g⁻¹). Among these quaternary alloys, the Mg_1.75Al_0.25Ni_0.9Cr_0.1 electrode alloy was found possessing the highest cycling capacity retention rate. Cyclic voltammetry (CV) results and anodic polarization curves demonstrated that appropriate content (x lower than 0.1) of Cr effectively improved the reaction activity of electrode and inhibited the cycling capacity degradation to some degree. Electrochemical impedance spectroscopy (EIS) analyses indicated that the increase of Cr content would raise the polarization resistance R_p on the particle surface of these quaternary alloys.     

Synthesis and characterizations of Li[CrxLi(1−x)/3Mn2(1−x)/3]O2 (0.15 ≤ x ≤ 0.3) cathode materials in rechargeable lithium batteries

A series of Li[Cr_xLi_(1−x)/3Mn_2(1−x)/3]O₂ (0.15 ≤ x ≤ 0.3) cathode materials was prepared by citric acid-assisted, sol–gel process. Sub-micron sized particles were obtained and the X-ray diffraction (XRD) results showed that the crystal structure was similar to layered lithium transition metal oxides (R-3m space group). The electrochemical performance of the cathodes was evaluated over the voltage range 2.0–4.9 V at a current density of 7.947 mA g⁻¹. The Li_1.27Cr_0.2Mn_0.53O₂ electrode delivered a high reversible capacity of up to 280 mAh g⁻¹ during cycling. Li[Cr_xLi_(1−x)/3Mn_2(1−x)/3]O₂ yielded a promising cathode material.     

α–h Diagram and principle of exergy coupling of GAX cycle

Ammonia absorption chiller systems of a single-stage cycle and a Generator Absorber heat exchanger cycle (GAX) were simulated and studied. At heat source temperatures of T_H = 120 °C, T_M = 25 °C and T_L = 5 °C, the coefficient of performances of the two cycles are 0.589 and 0.776, the GAX cycle is higher 31.8% than the single-stage cycle. And the exergy efficiencies of the two cycles are 15.4% and 27.4%, the GAX cycle is higher up to 77.9%. This paper proposes a new method that adopts the energy quality factor α as a evaluation criterion and also uses the α–h diagram as a thermodynamic analysis tool graphically, and a concept that divides absorption cycle to a heat pump subcycle and a heat engine subcycle. By means of the α–h diagram, the thermodynamic frameworks of the two cycles were illustrated. The comparison analysis indicates that the improvement of cycle performance depends on its thermodynamic perfectibility. In fact, the exergy demand of heat pump subcycle in the GAX cycle is as the same as that of the single-stage cycle, however, the energy cascading use and the exergy coupling framework of the heat engine subcycle in GAX cycle is retrofitted, so that the exergy consumption is reduced and the increased benefit is obtained from the overall cycle.     

Heating load vs. COP characteristic of an endoreversible Carnot heat-pump subjected to the heat-transfer law q ∝ (ΔTn)m

The relation between heating load and coefficient of performance (COP) of an endoreversible Carnot heat-pump is derived based on a new generalized convective heat-transfer law and generalized radiative heat-transfer law, q ∝ (ΔTⁿ)^m. Our results include those obtained in many literature studies and can provide some theoretical guidance for the designs of real heat pumps.     

Transport and electrochemical properties of the LiyCrxMn2−xO4 (0 < x < 0.5) cathode material

In this paper structural, electrical, electrochemical and thermal (DSC) characterization of series of manganese spinel samples with manganese substituted to different degree (x = 0–0.5) with chromium are presented. The conductivity and thermoelectric power measurements were performed in wide temperature range also versus oxygen partial pressure and for deintercalated samples. Electrochemical studies of these cathode materials were conducted in Li/Li⁺/Li_yCr_xMn_2−xO₄ type cells. Substitution of manganese with chromium causes disappearance of the phase transition characteristic of LiMn₂O₄ spinel. Studies of electrical properties reveal that Cr ions do not participate in charge transport at low temperatures. In the charge curves of Li/Li⁺/Li_yCr_xMn_2−xO₄ cells there are two visible plateaux, separated with distinct potential jump (∼0.5 V), which position on Li content perfectly matches the Mn³⁺ content in the doped cathode material. The lower plateau is related to the Mn³⁺ → Mn⁴⁺ oxidation, while the next of higher voltage, of the dopant Cr³⁺ → Cr⁴⁺ oxidation. The schematic diagrams of relative Mn–Cr electronic levels alignment are proposed.     

Life cycle assessment (LCA) of an integrated biomass gasification combined cycle (IBGCC) with CO2 removal

Based on the results of previous studies, the efficiency of a Brayton/Hirn combined cycle fuelled with a clean syngas produced by means of biomass gasification and equipped with CO₂ removal by chemical absorption reached 33.94%, considering also the separate CO₂ compression process. The specific CO₂ emission of the power plant was 178 kg/MW h. In comparison with values previously found for an integrated coal gasification combined cycle (ICGCC) with upstream CO₂ chemical absorption (38–39% efficiency, 130 kg/MW h specific CO₂ emissions), this configuration seems to be attractive because of the possibility of operating with a simplified scheme and because of the possibility of using biomass in a more efficient way with respect to conventional systems. In this paper, a life cycle assessment (LCA) was conducted with presenting the results on the basis of the Eco-Indicator 95 impact assessment methodology. Further, a comparison with the results previously obtained for the LCA of the ICGCC was performed in order to highlight the environmental impact of biomass production with fossil fuels utilisation. The LCA shows the important environmental advantages of biomass utilisation in terms of reduction of both greenhouse gas emissions and natural resource depletion, although an improved impact assessment methodology may better highlight the advantages due to the biomass utilisation.     

Evaluation of different approaches for improving the cycle life of MgNi-based electrodes for Ni-MH batteries

Several methods have been investigated to enhance the cycle life of amorphous MgNi used as the negative electrode for Ni-MH batteries. The first approach involves modifying its surface composition in different ways, including the electroless deposition of a chromate conversion coating, the addition of chromate salt or NaF into the electrolyte and the mechanical coating of the particles with various compounds (e.g. TiO₂). Another approach consists of developing (MgNi + AB₅) composite materials. However, the cycle life of these modified MgNi electrodes remains unsatisfactory. On the other hand, the modification of the bulk composition of the MgNi alloy with elements such as Ti and Al appears to be more effective. For instance, a Mg_0.9Ti_0.1NiAl_0.05 electrode retains 67% of its initial discharge capacity (404 mAh g⁻¹) after 15 cycles compared to 29% for MgNi. The charging conditions also have a great influence on the electrode cycle life as demonstrated by the existence of a charge input threshold below which minor capacity decay occurs. In addition, the particle size has a major influence on the electrode performance. We have developed an optimized electrode constituted of Mg_0.9Ti_0.1NiAl_0.05 particles with the appropriate size (>150 μm) showing a capacity decay rate as low as ∼0.2% per cycle when charged at 300 mAh g⁻¹.     

Performance assessment of a direct expansion air conditioner working with R407C as an R22 alternative

This paper presents an experimental investigation of a direct expansion air conditioner working with R407C as an R22 alternative. Experiments are conducted on a vapor compression refrigeration system using air as a secondary fluid through both the evaporator and the condenser. The influences of the evaporator air inlet temperature (20–32 °C), the evaporator air flow rate (250–700 m³/h) and the evaporator air humidity ratio (9 and 14.5 g_wv/kg_a) at the condenser air temperature and volume flow rate of 35 °C and 850 m³/h, respectively on the system performance are investigated. Experimental results revealed that the evaporator air inlet temperature has pronounced effects on the air exit temperatures, pressures of the evaporator and the condenser, cooling capacity, condenser heat load, compressor pressure ratio and the COP of both refrigerants at humidity ratios of 9 and 14.5 g_wv/kg_a. Significant effects of the evaporator air flow rate are also gathered on the preceding parameters at the same values of mentioned-humidity ratios. The best performance, in terms of operating parameters as well as COP, can be accomplished using R22 compared to R407C. The inlet humidity ratio affects dramatically the performance of vapor compression system using R22 and R407C. The raising up humidity ratio from 9 to 14.5 g_wv/kg_a leads to an augmentation in the average cooling capacity by 29.4% and 38.5% and an enhancement in the average COP by 30% and 24.1% for R22 and R407C, respectively.     

Crystal chemistry and electrochemical characterization of layered LiNi0.5−yCo0.5−yMn2yO2 and LiCo0.5−yMn0.5−yNi2yO2 (0 ≤ 2y ≤ 1) cathodes

The crystal chemistry and electrochemical performance of the layered LiNi_0.5−yCo_0.5−yMn_2yO₂ and LiCo_0.5−yMn_0.5−yNi_2yO₂ oxide cathodes for 0 ≤ 2y ≤ 1 have been investigated. Li₂MnO₃ impurity phase is observed for Mn-rich compositions with 2y > 0.6 in LiNi_0.5−yCo_0.5−yMn_2yO₂ and 2y < 0.2 in LiCo_0.5−yMn_0.5−yNi_2yO₂. Additionally, the Ni-rich compositions encounter a volatilization of lithium at the high synthesis temperature of 900 °C. Compositions around 2y = 0.33 are found to be optimum with respect to maximizing the capacity values and retention. The rate capabilities are found to bear a strong relationship to the cation disorder in the layered lattice. Moreover, the evolution of the X-ray diffraction patterns on chemically extracting lithium has revealed the presence of Li₂MnO₃ phase in addition to the layered phase for the composition LiNi_0.25Co_0.25Mn_0.5O₂ with an oxidation state of manganese close to 4+, which results in a large anodic peak at around 4.5 V due to the extraction of both lithium and oxygen.     

Experimental investigation on two-phase flow boiling heat transfer of five refrigerants in horizontal small tubes of 0.5, 1.5 and 3.0 mm inner diameters

An experimental investigation on two-phase flow boiling heat transfer with refrigerants of R-22, R-134a, R-410A, C₃H₈ and CO₂ in horizontal circular small tubes is presented. The experimental data were obtained over a heat flux range of 5–40 kW m^?2, mass flux range of 50–600 kg m^?2 s^?1, saturation temperature range of 0–15 °C, and quality up to 1.0. The test section was made of stainless steel tubes with inner diameters of 0.5, 1.5 and 3.0 mm, and lengths of 330, 1000, 1500, 2000 and 3000 mm. The experimental data were mapped on Wang et al. (1997) [5] and Wojtan et al. (2005) [6] flow pattern maps. The effects of mass flux, heat flux, saturation temperature and inner tube diameter on the heat transfer coefficient are reported. The experimental heat transfer coefficients were compared with some existing correlations. A new boiling heat transfer coefficient correlation that is based on a superposition model for refrigerants in small tubes is presented with 15.28% mean deviation and ?0.48% average deviation.     

Crystallographic and electrochemical characteristics of icosahedral quasicrysyalline Ti45−xZr35−xNi17+2xCu3 (x = 0–8) powders

Ti_45−xZr_35−xNi_17+2xCu₃ (x = 0, 2, 4, 6 and 8) icosahedral quasicrystalline phase (I-phase) alloy powders are synthesized by mechanical alloying and subsequent annealing techniques, and the crystallographic and electrochemical characteristics are investigated. The alloy powders are I-phase, and the quasi-lattice constant decreases with increasing x value. The maximum discharge capacity of the I-phase alloy electrodes first increases and then decreases with increasing x value, and the Ti₃₉Zr₂₆Ni₂₉Cu₃ I-phase electrode exhibits the highest discharge capacity of 274 mAh g⁻¹. The high-rate dischargeability at the discharge current density of 240 mA g⁻¹ increases from 55.31% (x = 0) to 74.24% (x = 8). Cycling stability also increases with increasing x value. The improvement in electrochemical characteristics may be ascribed to the added nickel, which not only improves the electrochemical activity, but also makes the alloy more resistant to oxidation.     

Electrochemical properties of the Li-ion polymer batteries with P(VdF-co-HFP)-based gel polymer electrolyte

Gel polymer electrolytes consisting of 25 wt.% P(VdF-co-HFP), 65 wt.% ethylene carbonate + propylene carbonate and 10 wt.% LiN(CF₃SO₂)₂ are prepared using by a solvent-casting technique. The electrodes are for use in lithium-ion polymer batteries. The electrochemical characteristics of the gel polymer electrolytes are evaluated by means of ac impedance and cyclic voltammetry. The charge–discharge performance of lithium polymer and lithium-ion polymer batteries is examined. A LiCoO₂ | gel polymer electrolyte (GPE) | mesocarbon microbeads (MCMB) cell delivers a discharge capacity of 146.8 and 144.5 mAh g⁻¹ on the first and the 20th cycle, respectively. The specific discharge capacity is greater than 140 mAh g⁻¹ for up to 20 cycle at all the current densities examined.     

Life cycle assessment of a Brassica carinata bioenergy cropping system in southern Europe

The energetic and environmental performance of production and distribution of the Brassica carinata biomass crop in Soria (Spain) is analysed using life cycle assessment (LCA) methodology in order to demonstrate the major potential that the crop has in southern Europe as a lignocellulosic fuel for use as a renewable energy source.The Life Cycle Impact Assessment (LCIA) including midpoint impact analysis that was performed shows that the use of fertilizers is the action with the highest impact in six of the 10 environmental categories considered, representing between 51% and 68% of the impact in these categories.The second most important impact is produced when the diesel is used in tractors and transport vehicles which represents between 48% and 77%. The contribution of the B. carinata cropping system to the global warming category is 12.7 g CO₂ eq. MJ⁻¹ biomass produced. Assuming a preliminary estimation of the B. carinata capacity of translocated CO₂ (631 kg CO₂ ha⁻¹) from below-ground biomass into the soil, the emissions are reduced by up to 5.2 g CO₂ eq. MJ⁻¹.The production and transport are as far as a thermoelectric plant of the B. carinata biomass used as a solid fuel consumes 0.12 MJ of primary energy per 1 MJ of biomass energy stored. In comparison with other fossil fuels such as natural gas, it reduces primary energy consumption by 33.2% and greenhouse gas emission from 33.1% to 71.2% depending on whether the capacity of translocated CO₂ is considered or not.The results of the analysis support the assertion that B. carinata crops are viable from an energy balance and environmental perspective for producing lignocellulosic solid fuel destined for the production of energy in southern Europe. Furthermore, the performance of the crop could be improved, thus increasing the energy and environmental benefits.