Effect of binder content on the cycle performance of nano-sized Fe2O3-loaded carbon for use as a lithium battery negative electrode

Nano-sized Fe₂O₃-loaded carbon material was prepared by loading Fe₂O₃ on carbon using various carbonaceous materials. Carbonaceous materials strongly affected the electrochemical behavior of nano-sized Fe₂O₃-loaded carbon. In addition, the binder content also significantly affected the cycle performance of nano-sized Fe₂O₃-loaded carbon. The content of binder depended on the type of carbon used. In the optimal condition for binder content, nano-carbons such as acetylene black (AB), tubular carbon nanofibers (CNF), and platelet CNF provided larger capacities than graphite, and tubular CNF showed the greatest capacity after long-term cycling.     

Effect of carbonaceous materials on electrochemical properties of nano-sized Fe2O3-loaded carbon as a lithium battery negative electrode

Nano-sized Fe₂O₃-loaded carbon material was prepared by loading Fe₂O₃ on carbon using various carbonaceous materials. Carbonaceous materials strongly affected the electrochemical behavior of nano-sized Fe₂O₃-loaded carbon. Among the carbons used, nano-carbons such as acetylene black (AB), tubular carbon nanofibers (CNF), and platelet CNF provided larger capacities than other carbons. This may be due to the greater surface area of nano-carbon, which gives a greater distribution of nano-sized Fe₂O₃ particles than other carbons and delivers a greater capacity than other carbons. Investigation of the first-cycle materials by X-ray photoelectron spectroscopy (XPS) revealed that Fe₂O₃ was reduced to Fe metal in the charge process (reduction of Fe₂O₃), and, conversely, Fe metal was not completely oxidized to Fe₂O₃ during discharge (oxidation of Fe). This result may be due to the covering of non-conductive Li₂O formed during charging.     

Performance of Ni/ScSZ cermet anode modified by coating with Gd0.2Ce0.8O2 for an SOFC running on methane fuel

A Ni/scandia-stabilized zirconia (ScSZ) cermet anode was modified by coating with nano-sized gadolinium-doped ceria (GDC, Gd_0.2Ce_0.8O₂) prepared using a simple combustion process within the pores of the anode for a solid oxide fuel cell (SOFC) running on methane fuel. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were employed in the anode characterizations. Then, the short-term stability for the cells with the Ni/ScSZ and 2.0 wt.%GDC-coated Ni/ScSZ anodes in 97%CH₄/3%H₂O at 700 °C was checked over a relative long period of operation. Open circuit voltages (OCVs) increased from 1.098 to 1.179 V, and power densities increased from 224 to 848 mW cm⁻², as the operating temperature of an SOFC with 2.0 wt.%GDC-coated Ni/ScSZ anode was increased from 700 to 850 °C in humidified methane. The coating of nano-sized Gd_0.2Ce_0.8O₂ particle within the pores of the porous Ni/ScSZ anode significantly improved the performance of anode supported cells. Electrochemical impedance spectra (EIS) illustrated that the cell with Ni/ScSZ anode exhibited far greater impedances than the cell with 2.0 wt.%GDC-coated Ni/ScSZ anode. Introduction of nano-sized GDC particles into the pores of porous Ni/ScSZ anode will result in a substantial increase in the ionic conductivity of the anode and increase the triple phase boundary region expanding the number of sites available for electrochemical activity. No significant degradation in performance has been observed after 84 h of cell testing when 2.0 wt.%GDC-coated Ni/ScSZ anode was exposed to 97%CH₄/3%H₂O at 700 °C. Very little carbon was detected on the anodes, suggesting that carbon deposition was limited during cell operation. Consequently, the GDC coating on the pores of anode made it possible to have good stability for long-term operation due to low carbon deposition.     

Synthesis and characterization of high tap-density layered Li[Ni1/3Co1/3Mn1/3]O2 cathode material via hydroxide co-precipitation

Li[Ni_1/3Co_1/3Mn_1/3]O₂ was prepared by mixing uniform co-precipitated spherical metal hydroxide (Ni_1/3Co_1/3Mn_1/3)(OH)₂ with 7% excess LiOH followed by heat-treatment. The tap-density of the powder obtained was 2.38 g cm⁻³, and it was characterized using X-ray diffraction (XRD), particle size distribution measurement, scanning electron microscope-energy dispersive spectrometry (SEM-EDS) and galvanostatic charge–discharge tests. The XRD studies showed that the material had a well-ordered layered structure with small amount of cation mixing. It can be seen from the EDS results that the transition metals (Ni, Co and Mn) in Li[Ni_1/3Co_1/3Mn_1/3]O₂ are uniformly distributed. Initial charge and discharge capacity of 185.08 and 166.99 mAh g⁻¹ was obtained between 3 and 4.3 V at a current density of 16 mA g⁻¹, and the capacity of 154.14 mAh g⁻¹ was retained at the end of 30 charge–discharge cycles with the capacity retention of 93%.     

Characterization of Zn- and Fe-substituted LiMnO2 as cathode materials in Li-ion cells

Layered LiMn_1−xM_xO₂ (M = Zn or Fe) (0 ≤ x ≤ 0.3) samples are synthesized from the corresponding sodium analogues by an ion-exchange method using LiBr in n-hexanol at 160 °C. The samples are subjected to physicochemical and electrochemical characterization. X-ray diffraction data indicate the formation of layered structures for the LiMn_1−xZn_xO₂ samples up to x = 0.3 and for LiMn_1−xFe_xO₂ samples up to x = 0.2. Among these, LiMn_0.95Zn_0.05O₂ and LiMn_0.95Fe_0.05O₂ provide the highest capacity values of 180 and 193 mAh g⁻¹, respectively. Both Zn- and Fe-substituted samples display good capacity retention up to 30 charge–discharge cycles. Electrochemical impedance spectroscopy and galvanostatic intermittent titration data corroborate the results obtained from cyclic volatmmetry and charge–discharge cycling.     

Effect of nanofluids on reflood heat transfer in a long vertical tube

Experiments were conducted to investigate the effect of nanofluids on reflood heat transfer in a hot vertical tube. The nanofluids, which are produced by dispersing nano-sized particles in traditional base fluids such as water, ethylene glycol, and engine oil, are expected to have a reasonable potential to enhance a heat transfer. 0.1 volume fraction (%) Al₂O₃/water nanofluid was prepared by two-step method and 0.1 volume fraction (%) carbon nano colloid (CNC) was prepared by the process self-dispersing by carboxyl formed particle surface. Transmission electron microscopy (TEM) images are acquired to characterize the shape and size of Al₂O₃ and graphite nanoparticles. The dispersion behavior of nanofluids was investigated with zeta potential values. And then, the reflood tests have been performed using water and nanofluids. We have observed a more enhanced cooling performance in the case of the nanofluid reflood. Consequently, the cooling performance is enhanced more than 13 s and 20 s for Al₂O₃/water nanofluid and CNC.     

Comparative studies of nickel oxide films on different substrates for electrochemical supercapacitors

Thin nickel oxide (NiO) films were obtained by post-heating of the corresponding precursor films of nickel hydroxide (Ni(OH)₂) cathodically deposited onto different substrates, i.e., nickel foils, and graphite at 25 °C from a bath containing 1.5 mol L⁻¹ Ni(NO₃)₂ and 0.1 mol L⁻¹ NaNO₃ in a solvent of 50% (v/v) ethanol. The surface morphology of the obtained films was observed by scanning electron microscope (SEM). Electrochemical characterization was performed using cyclic voltammetrty (CV), chronopotentiometry (CP) and electrochemical impedance analysis (EIS). When heated at 300 °C for 2 h in air, the specific capacitance of the prepared NiO films on nickel foils and graphite, with a deposition charge of 250 mC cm⁻², were 135, 195 F g⁻¹, respectively. When the deposition charge is less than 280 mC cm⁻², the capacitance of both appears to keep the linear relationship with the deposition charge. The specific capacitance, cyclic stability of the NiO/graphite hybrid electrodes in 1 mol L⁻¹ KOH solution were superior to those on nickel foils mainly due to the favorable adhesion, the good interface behavior between graphite and the NiO films, and the extra pseudo-capacitance of the heated graphite substrates.     

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.     

Tin–graphite materials prepared by reduction of SnCl4 in organic medium: Synthesis,characterization and electrochemical lithiation

Tin–graphite materials were prepared by chemical reduction of SnCl₄ by t-BuONa-activated NaH. TEM imaging showed that the crude material is composed of an amorphous organic matrix containing tin present either as nanosized particles deposited on the graphite surface or as free aggregates. Subsequent washings with ethanol and water allow removal of side products as well as most part of the organic matrix. Electrochemical insertion of lithium occurred in graphite and in tin. The initial reversible massic capacity of 630 mAh g⁻¹ decayed to a stable value of 415 mAh g⁻¹ after 12 cycles. This capacity value was lower than the expected maximum one of 650 mAh g⁻¹ corresponding to a Sn/12C molar composition and assuming the formation of LiC₆ and Li₂₂Sn₅. Even if this massic capacity is not much improved by comparison with that of graphite, it must be pointed out that the volume capacity of this graphite/Sn material is much larger (2137 mAh cm⁻³) than that corresponding to graphite (837 mAh cm⁻³). It was hypothesized that the part of tin bound to graphite could be responsible for the stable reversible capacity. To the contrary, graphite unsupported tin aggregates would contribute to the observed gradual decline in the storage capacity. Therefore, the improvement in cycleability, compared to that of massive metals, could be attributed both to the nanoscale dimension of the metal particles and to interactions between graphite and metal the nature of which remaining to be precised.     

In situ polyol-assisted synthesis of nano-SnO2/carbon composite materials as anodes for lithium-ion batteries

Nano-SnO₂/carbon composite materials were synthesized in situ using the polyol method by oxidizing SnCl₂·2H₂O in the presence of a carbon matrix. All the as-synthesized composites consisted of SnO₂ nanoparticles (5–10 nm) uniformly embedded into the carbon matrix as evidenced by TEM. XRD confirmed the presence of nano-sized SnO₂ particles that are crystallized in a rutile structure and XPS revealed a tin oxidation state of +4. Cyclic voltammetry of the composites showed an irreversible peak at 1.4 V in the first cycle and a typical alloying/de-alloying process at 0.1–0.5 V. The best composite (“composite I”, 15 wt% SnO₂) showed an improved lithium storage capacity of 370 mAh g^?1 at 200 mA g^?1 (～C/2) which correspond to 32% improvement and lower capacity fade compared to commercial SnO₂ (50 nm). We have also investigated the effect of the heating method and we found that the use of a microwave was beneficial in not only shortening reaction time but also in producing smaller SnO₂ particles that are also better dispersed within the carbon matrix which also resulted in higher lithium storage capacity.     

Synthesis and characterization of spherical morphology [Ni0.4Co0.2Mn0.4]3O4 materials for lithium secondary batteries

Spherical morphology [Ni_0.4Co_0.2Mn_0.4]₃O₄ materials have been synthesized by ultrasonic spray pyrolysis. The Li[Ni_0.4Co_0.2Mn_0.4]O₂ powders were prepared at various pyrolysis temperatures between 500 and 900 °C. The Li[Ni_0.4Co_0.2Mn_0.4]O₂ material prepared at a pyrolysis temperature of 600 °C samples are exhibited excellent electrochemical cycling performance and delivered the highest discharge capacity at over 180 mAh g⁻¹ between 2.8 and 4.4 V. The structural, electrochemical, morphological property and thermal stability of the powders were characterized by X-ray diffraction (XRD), galvanostatic charge/discharge testing, scanning electron microscopy (SEM), and differential scanning calorimeter (DSC), respectively.     

Electrochemical behavior of plasma-fluorinated graphite for lithium ion batteries

Electrochemical properties of plasma-fluorinated graphite samples have been investigated in 1 mol dm⁻³ LiClO₄ ethylene carbonate (EC)/diethyl carbonate (DEC) solution at 25 °C. Fluorine contents in plasma-fluorinated graphite samples were in the range of 0–0.3 at.% by elemental analysis and surface fluorine concentrations obtained by X-ray photoelectron spectroscopy (XPS) were in the range of 3–12 at.%. Raman spectroscopy revealed that surface disordering of graphite was induced by plasma fluorination. Plasma treatment increased the surface areas of graphite samples by 26–55% and the pore volumes for the mesopores with diameters of 1.5–2 and 2–3 nm. Plasma-fluorinated graphites showed capacities higher than those of original graphites and even higher than the theoretical capacity of graphite, 372 mAh g⁻¹, without any change of the profile of charge–discharge potential curves. The increments in the capacities were approximately 5, 10 and 15% for graphites with average particle diameters, 7, 25 and 40 μm, respectively. Furthermore, the coulombic efficiencies in first cycle were nearly the same as those for original graphites or higher by several percents.     

Reactivity of pulverized coals during combustion catalyzed by CeO2 and Fe2O3

Effects of CeO₂ and Fe₂O₃ on combustion reactivity of several fuels, including three ranks of coals, graphite and anthracite chars, were investigated using thermo-gravimetric analyzer. The results indicated that the combustion reactivity of all the samples except lignite was improved with CeO₂ or Fe₂O₃ addition. It was interesting to note that the ignition temperatures of anthracite were decreased by 50 °C and 53 °C, respectively, with CeO₂ and Fe₂O₃ addition and that its combustion rates were increased to 15.4%/min and 12.2%/min. Ignition temperatures of lignite with CeO₂ and Fe₂O₃ addition were 250 °C and 226 °C, and the combustion rates were 12.8% and 19.3%/min, respectively. When compared with those of lignite without catalysts, no obvious catalytic effects of the two catalysts on its combustion reactivity were revealed. The results from the combustion of the three rank pulverized coals catalyzed by CeO₂ and Fe₂O₃ indicated significant effects of the two catalysts on fixed carbon combustion. And it was found that the higher the fuel rank, the better the catalytic effect. The results of combustion from two kinds of anthracite chars showed obvious effects of anthracite pyrolysis catalyzed by CeO₂ and Fe₂O₃ on its combustion reactivity.     

The nanometer magnetic solid base catalyst for production of biodiesel

Nanometer magnetic solid base catalysts were prepared by loading CaO on Fe₃O₄ with Na₂CO₃ and NaOH as precipitator, respectively. The optimum conditions for preparation of this catalyst were investigated. The influence of the proportion of Ca²⁺ to Fe₃O₄ on the catalytic performance has been studied. The catalyst with highest catalytic activity has been obtained when the proportion of Ca²⁺ to Fe₃O₄ is 7:1; the catalytic activity of the catalyst calcined from Ca(OH)₂ to Fe₃O₄ is better than that calcined from CaCO₃ to Fe₃O₄; under the conditions of methanol/oil molar ratio of 15:1, catalyst dosage of 2 wt% and temperature of 70 °C, the biodiesel yield reaches to 95% in 80 min, even to 99% finally. The catalytic activity and recovery rate of the nanometer magnetic solid base catalysts are much better than those of CaO. Calcination temperature was determined by differential thermogravimetric analysis. Ca₂Fe₂O₅, a kind of new metal multiple oxide, was found in the catalyst through X-ray diffraction. At the end, these catalysts were characterized by scanning electronic microscope (SEM), transmission electron microscopy (TEM), and vibrating sample magnetometer (VSM).     

Effect of Fe2P on the electron conductivity and electrochemical performance of LiFePO4 synthesized by mechanical alloying using Fe3+ raw material

LiFePO₄ and LiFePO₄/Fe₂P composites have been produced using raw Fe₂O₃ materials by mechanical alloying (MA) and subsequent firing at 900 °C. The LiFePO₄ prepared by firing at 900 °C for 30 min showed a maximum discharge capacity of 160 mAh g⁻¹ at C/20, which is at a higher capacity and improved cell performance compared with the LiFePO₄ prepared using for a longer firing times. LiFePO₄/Fe₂P composites have been synthesized by the reduction reaction of phosphate in excess of carbon. By transmission electron microscopy (TEM) and scanning electron microscopy (SEM) it was determined that the LiFePO₄ phase was agglomerated with a primary particle size of 40–50 nm around the surface of Fe₂P with particle size of 200 nm. The electronic conductivity of the LiFePO₄/Fe₂P composite increased in proportion with the amount that the Fe₂P phase and discharge capacity increased during the cycling. The sample containing 8% of Fe₂P in LiFePO₄/Fe₂P composite showed a high discharge capacity and rate capability at high current.     

Graphite–FeSi alloy composites as anode materials for rechargeable lithium batteries

Iron–silicon are prepared by annealing elemental mixtures at 1000 °C followed by mechanical milling. Graphite–Fe₂₀Si₈₀ alloy composites have been prepared by ball-milling a mixture of Fe₂₀Si₈₀ alloy and graphite powder. The microstructure and electrochemical performance of the composites are characterized by X-ray diffraction and an electrochemical method. The FeSi₂ matrix is stable for extended cycles and acts as a buffer for the active centre, Si. The Fe₂₀Si₈₀ alloy electrode delivers large initial capacity, but the capacity degrades rapidly with cycling. Fe₂₀Si₈₀ alloy–graphite composite electrodes, however, show good cycleability and a high reversible capacity of about 600 mAh g⁻¹. These composites appear to be promising candidates for negative electrodes in lithium rechargeable batteries.     

Electrochemical characteristics and impedance spectroscopy studies of nano-cobalt silicate hydroxide for supercapacitor

Cobalt silicate hydroxide (Co₃[Si₂O₅]₂[OH]₂) was prepared by chemical method for use in electrochemical capacitors. X-ray diffraction (XRD) and transmission electron microscopy (TEM) tests indicate that the material was pure hexagonal phase with uniform nanometer size distribution. Cyclic voltammeter (CV) and galvanostatic charge/discharge measurements show that the cobalt silicate hydroxide-based electrode has stable electrochemical capacitor properties between potential range of 0.1–0.55 V with a maximum specific capacitance of 237 F g⁻¹ in alkaline solution and 95% of capacity efficiency was reached after 150 cycles. Electrochemical impedance spectra (EIS) investigation illustrates that the capacitance of the test electrode was mainly consisted of pseudo-capacitance, which was caused by underpotential deposition of H₃O⁺ at the electrode surface.     

A novel sol–gel method to synthesize nanocrystalline LiVPO4F and its electrochemical Li intercalation performances

Lithium vanadium fluorophosphate, LiVPO₄F, a cathode material for lithium ion batteries, was synthesized by a sol–gel method followed by low temperature calcinations. V₂O₅·nH₂O hydro-gel, NH₄H₂PO₄, LiF and carbon were used as starting materials to prepare a precursor, and LiVPO₄F was finally obtained by sintering the precursor at 550 °C for 2 h. X-ray diffraction results show that the LiVPO₄F sample is triclinic structure. TEM image indicates that the LiVPO₄F particles are about 70 nm in diameter embedded in carbon network. The LiVPO₄F system showed the discharge capacity of about 130 mAh g⁻¹ in the range of 3.0–4.6 V at the first cycle, and the discharge capacity remained about 124 mAh g⁻¹ after 30 cycles. The sol–gel method is suitable for the preparation of LiVPO₄F cathode materials with good electrochemical Li intercalation performances.     

In situ X-ray diffraction and X-ray absorption studies of high-rate lithium-ion batteries

A combination of in situ synchrotron X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) was used to study a two-electrode lithium-ion cell made from electrodes from a high-rate lithium-ion battery. The cathode was LiNi_0.85Co_0.15O₂. Both the XRD and the XAS were done in the transmission mode. XAS was done while the cell was charged at the C/2 rate to 4.5 V. The near edge Co and Ni spectra (XANES) indicated that all of the charge compensation occurred on the Ni and the Co did not change its oxidation state during charge. The Co EXAFS indicated that the Co is randomly distributed in the NiO₂ layers. XRD data were collected on a beam line with a position sensitive detector. Complete high quality XRD patterns could be obtained in as little as 3 min. The patterns covered the range between the (0 0 3) and the (1 1 3) reflections of the cathode material and included the (0 0 2) reflection from graphite in the anode. Data were collected while the cell was cycled at rates between the C/4 and 2C rate. In all cases, at the beginning of charge, there is an initial expansion along the c-axis and a concomitant contraction along the a- and b-axes. Towards the end of charge there is a contraction along the c-axis and a slight expansion along the a- and b-axes. After high rate charges there are relaxation processes that last for a few minutes after termination of charge. The results indicate with proper choice of the active materials and electrode design lithium-ion cells can be charged and discharged at high rate with high utilization of the active material.     

Nanoparticled Li(Ni1/3Co1/3Mn1/3)O2 as cathode material for high-rate lithium-ion batteries

Nanoparticle of Li(Ni_1/3Co_1/3Mn_1/3)O₂ with size smaller than 40 nm was obtained by non-aqueous system co-precipitation method. The particle morphology and crystal plane orientation were observed by TEM and HRTEM. Electrochemical properties of this nanostructued material were studied with experiment cells. The results show that the material has high capacity of 160 mAh g⁻¹ and excellent rate capability for charge and discharge. For the 50C and 100C rate, its capacity remains above 100 mAh g⁻¹ after tens of cycles.