Preparation,characterization and electrolytic behavior of β-nickel hydroxide

Nickel hydroxide is prepared by neutralizing NiSO₄ solution with 4.8 M NaOH, followed by washing the precipitate and treating the slurry hydrothermally at different temperatures. The parameters varied are: initial nickel concentration; effect of presence of sodium ions during hydrothermal treatment; aging time after hydrothermal treatment. The samples so prepared are chemically analyzed and the physical and electrolytic properties such as tap density, percentage weight loss and discharge capacity are determined. On increasing the temperature from 60 to 160 °C, the discharge capacity increases from 52 to 112 mAh g⁻¹. At 200 °C, the discharge capacity decreases to 94 mAh g⁻¹. Allowing the hydroxide precipitate to age after hydrothermal treatment also causes a decrease in discharge capacity. The presence of excess sodium ions during hydrothermal treatment yields nickel hydroxide with a very low discharge capacity. The maximum discharge capacity of 160 mAh g⁻¹ is obtained for nickel hydroxide prepared under the following conditions: nickel concentration 43 g l⁻¹, neutralizing agent sodium hydroxide, time of hydrothermal treatment 2 h, temperature during hydrothermal treatment 160 °C. XRD patterns and FTIR spectra confirm the precipitate to be β-nickel hydroxide. The sample contains 62.89 wt.% Ni with a tap density of 0.96 g cm⁻³. TG–DTA measurements show a weight loss of 19% with an endothermic peak at 325 °C which corresponds to the decomposition of nickel hydroxide to nickel oxide. The present method of preparing nickel hydroxide through hydrothermal treatment reduces the aging time to 2 h and gives a product with good filtration characteristics.     

Synthesis and electrochemical properties of Mo-doped Li[Ni1/3Mn1/3Co1/3]O2 cathode materials for Li-ion battery

The layered Li[Ni_(1−x)/3Mn_(1−x)/3Co_(1−x)/3Mo_x]O₂ cathode materials (x = 0, 0.005, 0.01, and 0.02) were prepared by a solid-state pyrolysis method (700, 800, 850, and 900 °C). Its structure and electrochemical properties were characterized by XRD, SEM, XPS, cyclic voltammetry, and charge/discharge tests. It can be learned that the doped sample of x = 0.01 calcined at 800 °C shows the highest first discharge capacity of 221.6 mAh g⁻¹ at a current density of 20 mA g⁻¹ in the voltage range of 2.3–4.6 V, and the Mo-doped samples exhibit higher discharge capacity and better cycle-ability than the undoped one at room temperature.     

Improvement in high temperature proton exchange membrane fuel cells cathode performance with ammonium carbonate

Proton exchange membrane (PEM) fuel cells with optimized cathode structures can provide high performance at higher temperature (120 °C). A “pore-forming” material, ammonium carbonate, applied in the unsupported Pt cathode catalyst layer of a high temperature membrane electrode assembly enhanced the catalyst activity and minimized the mass-transport limitations. The ammonium carbonate amount and Nafion^® loading in the cathode were optimized for performance at two conditions: 80 °C cell temperature with 100% anode/75% cathode R.H. and 120 °C cell temperature with 35% anode/35% cathode R.H., both under ambient pressure. A cell with 20 wt.% ammonium carbonate and 20 wt.% Nafion^® operating at 80 °C and 120 °C presented the maximum cell performance. Hydrogen/air cell voltages at a current density of 400 mA cm⁻² using the Ionomem/UConn membrane as the electrolyte with a cathode platinum loading of 0.5 mg cm⁻² were 0.70 V and 0.57 V at the two conditions, respectively. This was a 19% cell voltage increase over a cathode without the “pore-forming” ammonium carbonate at the 120 °C operating condition.     

Cycle-life testing of 100-Ah class lithium-ion battery in a simulated geosynchronous-Earth-orbit satellite operation

In this paper, we review our work on cycle-life testing of a 100-Ah class lithium-ion battery in a simulated geosynchronous-Earth-orbit (GEO) satellite operation. The battery consists of ten 100-Ah lithium-ion (10) cells in a series, with a high energy density exceeding 100 Wh kg⁻¹ at the battery level. We simulate the eclipse period in real-time testing with five depth-of-discharge (DOD) patterns at an ambient temperature of 15 °C. We also simulate a sun-shine period in 8-day thermally accelerated full-charge storage at an ambient temperature of 25 °C, which in our experience corresponds to full-charge storage of a half-year operation at 0 °C. Eighteen eclipse seasons have presently been completed, corresponding to 9 years of GEO operation. The battery maintained a high voltage near 3.4 V at the end of the discharge, even when the DOD was set at 70%. The voltage dispersion of 10 cells was also sufficiently small in the range of 48 mV. The cell temperature reached a maximum of 29 °C and maintained minimal dispersion smaller than 4 °C even when the battery was discharged at a high DOD of 70%.     

High thermal conductivity negative electrode material for lithium-ion batteries

Experimental thermophysical property data for composites of electrode and electrolyte materials are needed in order to provide better bases to model and/or design high thermal conductivity Li-ion cells. In this study, we have determined thermal conductivity (k) values for negative electrode (NE) materials made of synthetic graphite of various particle sizes, with varying polyvinylidene difluoride (PVDF) binder and carbon-black (C-Black) contents, using various levels of compression pressure. Experiments were conducted at room temperature (RT), 150 and 200°C. Requirements for designing a high thermal conductivity NE-material are suggested. Detailed statistical data analysis shows that the thermal conductivity of the NE-material most strongly depends on compression pressure, followed by graphite particle size, C-Black content and finally PVDF content. The maximum k-value was achieved for the samples made of the largest graphite particles (75 μm), the smallest C-Black content (5 wt.%) and the highest compression pressure (566 kg cm⁻²). Increasing the PVDF content from 10 to 15 wt.% increased the k-values by 11–13% only. The k-values of all samples decreased with increasing temperature; at 200°C, the k-values were close to each other irrespective of preparation procedure and/or raw material contents. This most likely is due to the relaxation of contact pressure among the graphite particles because of PVDF melting at 155–160°C.     

Sulfonic-functionalized heteropolyacid–silica nanoparticles for high temperature operation of a direct methanol fuel cell

Sulfonic-functionalized heteropolyacid–SiO₂ nanoparticles were synthesized by grafting and oxidizing of a thiol-silane compound onto the heteropolyacid–SiO₂ nanoparticle surface. The surface functionalization was confirmed by solid-state NMR spectroscopy. The composite membrane containing the sulfonic-functionalized heteropolyacid–SiO₂ nanoparticles was prepared by blending with Nafion^® ionomer. TG–DTA analysis showed that the composite membrane was thermally stable up to 290 °C. The DMFC performance of the composite membrane increased the operating temperature from 80 to 200 °C. The function of the sulfonic-functionalized heteropolyacid–SiO₂ nanoparticles was to provide a proton carrier and act as a water reservoir in the composite membrane at elevated temperature. The power density was 33 mW cm⁻² at 80 °C, 39 mW cm⁻² at 160 °C and 44 mW cm⁻² at 200 °C, respectively.     

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.     

Organic–inorganic composites based on room temperature ionic liquid and 12-phosphotungstic acid salt with high assistant catalysis and proton conductivity

Proton-conducting composite material was synthesized from 1-butyl-3-methyl-imidazolium chloride (BMImCl) and 12-phosphotungstic acid (PWA). The structure, assistant catalytic effect and ionic conductivity of the composites for the as-synthesized, 200 and 400 °C annealed samples were studied, respectively. The as-synthesized salt was crystal and kept Keggin structure even being annealed at 400 °C, but the organic part was partly decomposed with increasing of the annealing temperature. The partly decomposed BMIm/PWA salt formed by annealing at 400 °C associated with Pt catalyst had excellent assistant catalytic effect on methanol electro-oxidation and displayed a high proton conductivity of 2 mS cm⁻¹ at 30 °C under 96% relative humidity condition.     

Electrochemical characterization of blend polymer electrolytes based on poly(oligo[oxyethylene]oxyterephthaloyl) for rechargeable lithium metal polymer batteries

Solid polymer electrolytes composed of poly(ethylene oxide)(PEO), poly(oligo[oxyethylene]oxyterephthaloyl) and lithium perchlorate have been prepared and characterized. Addition of poly(oligo[oxyethylene]oxyterephthaloyl) to PEO/LiClO₄ reduced the degree of crystallinity and improved the ambient temperature ionic conductivity. The blend polymer electrolyte containing 40 wt.% of poly(oligo[oxyethylene]oxyterephthaloyl) showed an ionic conductivity of 2.0 × 10⁻⁵ S cm⁻¹ at room temperature and a sufficient electrochemical stability to allow application in the lithium batteries. By using the blend polymer electrolytes, the lithium metal polymer cells composed of lithium anode and LiCoO₂ cathode were assembled and their cycling performances were evaluated at 40 °C.     

LiMn2O4 cathode materials synthesized by the cellulose–citric acid method for lithium ion batteries

A new technique was employed to synthesize spinel LiMn₂O₄ cathode materials by adding cellulose and citric acid to an aqueous solution of lithium and manganese salts. Various synthesis conditions such as the calcination temperature and the citric acid-to-metal ion molar ratio (R) were investigated to determine the ideal conditions for preparing LiMn₂O₄ with the best electrochemical characteristics. The optimal synthesis conditions were found to be R = 1/3 and a calcination temperature of 800 °C. The initial discharge capacity of the material synthesized using the optimal conditions was 134 mAh g⁻¹, and the discharge capacity after 40 cycles was 125 mAh g⁻¹, at a current density of 0.15 mA cm⁻² between 3.0 and 4.35 V. Details of how the initial synthesis conditions affected the capacity and cycling performance of LiMn₂O₄ are discussed.     

Intermediate temperature fuel cells based on doped ceria–LiCl–SrCl2 composite electrolyte

A new type of oxide-salt composite electrolyte, gadolinium-doped ceria (GDC)–LiCl–SrCl₂, was developed and demonstrated its promising use for intermediate temperature (400–700 °C) fuel cells (ITFCs). The dc electrical conductivity of this composite electrolyte (0.09–0.13 S cm⁻¹ at 500–650 °C) was 3–10 times higher than that of the pure GDC electrolyte, indicating remarkable proton or oxygen ion conduction existing in the LiCl–SrCl₂ chloride salts or at the interface between GDC and the chloride salts. Using this composite electrolyte, peak power densities of 260 and 510 mW cm⁻², with current densities of 650 and 1250 mA cm⁻² were achieved at 550 and 625 °C, respectively. This makes the new material a good candidate electrolyte for future low-cost ITFCs.     

Sonochemical synthesis of amorphous manganese oxide coated on carbon and application to high power battery

The nanocomposite material of amorphous manganese oxide and acetylene black (HSMO/AB), was synthesized by sonochemical method. The acetylene black particles were homogeneously coated with amorphous manganese oxide. In order to demonstrate that these characteristic structures were suitable for rapid discharge–charge, the composite material was tested under large current density. The result exhibited 185 mAh g⁻¹ in specific discharge capacity under 10 A g⁻¹ in current density. Assuming that an operating voltage of 2.5 V, this capacity corresponded 20 kW kg⁻¹ in power density and 90 Wh kg⁻¹ in energy density.     

Preparation of LiMn2O4 at the low temperature of 250 °C using eutectic self-mixing method

Spinel LiMn₂O₄ as a cathode material for lithium rechargeable batteries is prepared at the low temperature of 250 °C without any artificial mixing procedures of reactants. The phase transitions of lithium manganese oxide are found three times on heating at 250 °C. The prepared material exhibits the initial discharge capacity of 85.5 mAh g⁻¹ and the discharge capacity retention of 91.5% after 50 cycles.     

Positive thin electrodes obtained from hydrothermally synthesized 4BS for lead-acid batteries

Tetrabasic lead sulfate, 4 PbO·PbSO₄ (4BS), was prepared from an aqueous suspension of leady oxide by using a simple hydrothermal method. Digesting the paste at a moderate temperature (125 °C) and heating for a short time (30 min) ensured the obtainment of particles of small, uniform size. The material was deposited on a lead alloy substrate 0.2 mm thick by spraying from aqueous suspensions. The deposits were highly uniform and homogeneous, with a coating thickness of 100 μm. A multi-step charge algorithm involving no preliminary soaking provided the best 4BS → PbO₂ conversion. The resulting electrodes delivered a capacity of 115 Ah kg⁻¹ with excellent capacity retention over more than 500 cycles at 100% depth of discharge (DOD).     

Synthesis and electrochemical properties of lithium cobalt oxides prepared by molten-salt synthesis using the eutectic mixture of LiCl–Li2CO3

Lithium cobalt oxide powders have been successfully prepared by a molten-salt synthesis (MSS) method using a eutectic mixture of LiCl and Li₂CO₃ salts. The physico-chemical properties of the lithium cobalt oxide powders are investigated by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), particle-size analysis and charge–discharge cycling. A lower temperature and a shorter time (∼700°C and 1 h) in the Li:Co=7 system are sufficient to prepare single-phase HT-LiCoO₂ powders by the MSS method, compared with the solid-state reaction method. Charge–discharge tests show that the lithium cobalt oxide prepared at 800°C has an initial discharge capacity as high as 140 mA h g⁻¹, and 100 mA h g⁻¹ after 40 cycles. The dependence of the synthetic conditions of HT-LiCoO₂ on the reaction temperature, time and amount of flux with respect to starting oxides is extensively investigated.     

The role of ambient conditions on the performance of a planar,air-breathing hydrogen PEM fuel cell

This paper presents experimental data on the effects of varying ambient temperature (10–40 °C) and relative humidity (20–80%) on the operation of a free-breathing fuel cell operated on dry-hydrogen in dead ended mode. We visualize the natural convection plume around the cathode using shadowgraphy, measure the gas diffusion layer (GDL) surface temperature and accumulation of water at the cathode, as well as obtain polarization curves and impedance spectra. The average free-convection air speed was 9.1 cm s⁻¹ and 11.2 cm s⁻¹ in horizontal and vertical cell orientations, respectively. We identified three regions of operation characterized by increasing current density: partial membrane hydration, full membrane hydration with GDL flooding, and membrane dry-out. The membrane transitions from the fully hydrated state to a dry out regime at a GDL temperature of approximately 60 °C, irrespective of the ambient temperature and humidity conditions. The cell exhibits strong hysteresis and the dry membrane regime cannot be captured by a sweeping polarization scan without complete removal of accumulated water after each measurement point. Maximum power density of 356 mW cm⁻² was measured at an ambient temperature of 20 °C and relative humidity of 40%.     

Cresol–formaldehyde based carbon aerogel as electrode material for electrochemical capacitor

Carbon aerogels have been prepared through a polycondensation of cresol (Cm) with formaldehyde (F) and an ambient pressure drying followed by carbonization at 900 °C. Modification of the porous structures of the carbon aerogel can be achieved by CO₂ activation at various temperatures (800, 850, 900 °C) for 1–3 h. This process could be considered as an alternative economic route to the classic RF gels synthesis. The obtained carbon aerogels have been attempted as electrode materials in electric double-layer capacitors. The relevant electrochemical behaviors were characterized by constant current charge–discharge experiments, cyclic voltammetry and electrochemical impedance spectroscopy in an electrolyte of 30% KOH aqueous solution. The results indicate that a mass specific capacitance of up to 78 F g⁻¹ for the non-activated aerogel can be obtained at current density 1 mA cm⁻². CO₂ activation can effectively improve the specific capacitance of the carbon aerogel. After CO₂ activation performed at 900 °C for 2 h, the specific capacitance increases to 146 F g⁻¹ at the same current. Only a slight decrease in capacitance, from 146 to 131 F g⁻¹, was observed when the current density increases from 1 to 20 mA cm⁻², indicating a stable electrochemical property of carbon aerogel electrodes in 30% KOH aqueous electrolyte with various currents.     

Influence of pore structure on electric double-layer capacitance of template mesoporous carbons

The behavior of two types of mesoporous carbons with different pore structures (i.e. unimodal and bimodal) as electrode material in an electrochemical double-layer capacitor has been analyzed. The carbon samples were prepared using mesostructured silica materials (MSM) as templating agents. The unimodal mesoporous carbon has a BET surface area of 1550 m² g⁻¹, and a pore volume of 1.03 cm³ g⁻¹; the porosity is mainly made up of structural mesopores of ca. 3 nm that exhibit a narrow pore size distribution (PSD). The bimodal carbon shows larger surface area (1730 m² g⁻¹) and larger pore volume (1.50 cm³ g⁻¹); the porosity is composed of two types of mesopores: structural (size around 3 nm) and complementary (size around 16 nm) mesopores. Both carbons show a disordered 3-D pore structure. Heat treatments at high temperatures (1000 °C) for long times (11 h) do not significantly change the pore structure with respect to the two synthesised carbons (800 °C). From the synthesized and heat-treated carbons, electrodes were processed as composites in which the carbons, polivinilidene fluoride (PVDF) and carbon black (CB) were the components. The effect of the heat treatment and relative CB content on specific capacitance, energy density and power density were studied. We found a specific capacitance of 200 F g⁻¹ for low current density (1 mA cm⁻²) and 110 F g⁻¹ for high current density (150 mA cm⁻²). Moreover, the curve of the specific capacitance versus current density shows three regimes, which are related to the three types of pore: micropores, structural mesopores and complementary mesopores. An energy density of 3 Wh kg⁻¹ at a power density of 300 W kg⁻¹ was obtained in some particular cases.     

Thermal transient behavior of an ANG storage during dynamic discharge phase at room temperature

Throughout this work the thermal behavior of an adsorptive natural gas (ANG) storage under dynamic discharge conditions at room temperature of 27 °C was studied. The work was conducted in a gravimetrically built experimental unit where the storage chamber was equipped with axial and radial distributed thermocouples and the storage was discharged at different discharge rates. The results demonstrated that maximum methane discharge rate of 5 L min⁻¹ in activated carbon/methane system resulted in the severest temperature drop corresponding to further drop of about 40% compared to that at 1 L min⁻¹. This extreme thermal condition claimed a reduction of 15.2% in methane dynamic delivery capacity with respect to the isothermal delivery capacity. Ethane and propane have high enthalpies of desorption, and hence high portions of these gases may influence the performance of ANG storages through their thermal impact. A gas mixture with 14.98% and 14.54% volumes of ethane and propane resulted in higher temperature drop than methane claiming a reduction of 19.4% in the dynamic delivery capacity comparing with methane delivery capacity.     

Electrochemical cycling behavior of LiCoO2 cathode prepared by mechanical alloying of hydroxides

Well-ordered high-temperature LiCoO₂ (HT-LiCoO₂) is synthesized by mechanical alloying (MA) of LiOH·H₂O and Co(OH)₂ powders and subsequent firing. Its electrochemical properties are investigated. The maximum discharge capacity of a sample mechanically alloyed and fired at 600 °C for 2 h is 152 mAh g⁻¹ at the C/40 rate, which is comparable to that obtained from a sample made by conventional solid state reactions. The cycleability is inferior, however, due to a relatively low crystallinity. When the firing temperature is increased to 850 °C, the first discharge capacity of 142 mAh g⁻¹ at the C/5 rate is increased by more than 10%, and retains 93% of its maximum value after 30 cycles. These cycling properties are about the same, or slightly higher, than those synthesized by firing a sample mixture of the same starting materials at 600 °C for 8 h and then at 850 °C for 24 h. Consequently, given the lower firing temperature and/or reduced reaction time, MA could prove a promising synthetic process for cathode materials used in rechargeable lithium batteries.