20th Cycle Research Articles

Synthesis, impedance and electrochemical studies of lithium iron fluorophosphate, LiFePO4F cathode

Tavorite-structured LiFePO4F is synthesized by solid-state reaction and characterized by Rietveld refined X-ray diffraction, scanning electron microscopy, BET surface area, IR and Raman spectroscopy techniques. The ionic conductivity (σ ionic) of LiFePO4F estimated using impedance analysis at 27°C and at 50°C are 0.6(±0.1)×10−7 and 5.4(±0.1)×10−7Scm−1, respectively, with an energy of activation (Ea)=0.75eV. Its electrochemical behavior were examined by galvanostatic charge–discharge cycling up to 100 cycles, cyclic voltammetry (CV) and electrochemical impedance spectroscopy using Li-metal as the counter and reference electrode, at 0.1C rate in the voltage range, 1.5–4V. LiFePO4F delivers an initial discharge capacity of 115(±3)mAhg−1 which increases to 119(±3)mAhg−1 at the 20th cycle. The capacity degrades slowly thereafter over 100 cycles, with a capacity loss of 19%. CV data show a clear indication of the Fe3+/2+ redox couple at 3.3–2.6V that involves a two-phase reaction. Electrochemical impedance spectra measured at various voltages at selected cycles were fitted to an equivalent circuit and the variation of impedance parameters interpreted.

Molten salt synthesis and characterization of Li4Ti5−xMnxO12 (x = 0.0, 0.05 and 0.1) as anodes for Li-ion batteries

Sub-micrometer sized Li4Ti5−xMnxO12 (x=0.0, 0.05 and 0.1) particles were synthesized by a single step molten salt method using LiCl–KCl as a flux. The synthesized material was structurally characterized by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectra. The XRD analysis revealed the particles to be highly crystalline and have a face-centered cubic spinel structure. The presence of possible functional group was confirmed through FTIR analysis. The FE-SEM images showed the particles to be polyhedral in shape with uniform size distribution. It was also revealed that there was a particle size reduction with the effect of Mn4+ dopant ions. The electrochemical studies performed using cyclic voltammogram (CV), charge–discharge, and electrochemical impedance analysis (EIS) indicate that Li4Ti4.9Mn0.1O4 possesses a better discharge capacity (305mAh/g), cycling stability, and charge carrier conductivity than both Li4Ti4.95Mn0.05O12 (265mAh/g) and Li4Ti5O12 (240mAh/g). The cycling stability reveals that the acceptable capacity fading was observed even after 20th cycle. The results of electrochemical studies infer that Li4Ti4.9Mn0.1O4 could be utilized as a suitable anode material for Li-ion batteries.

Preparation and electrochemical properties of surface-charge-modified Zn2SnO4 nanoparticles as anodes for lithium-ion batteries

Highly crystalline, size-controlled Zn2SnO4 nanoparticles are synthesized by hydrothermal synthesis using two different mineralizers, viz., inorganic Na2CO3 and organic tert-butyl amine. The shape and surface properties of the two types of nanoparticles are totally different owing to the structure-directing abilities and the radicals in the mineralizers, even though both types of nanoparticles show a defect-free and highly crystalline structure. Na2CO3 induces faceted planar morphologies with negative surface charges, whereas tert-butyl amine induces roughly spherical shapes with positive surface charges; these changes have been analyzed by SEM, TEM, and zeta potential measurements. Electrochemical tests performed on these two types of nanoparticles indicate a capacity that gradually fades up to the 20th cycle due to the inevitable structural irreversibility. However, the specific discharge/charge capacities of both Zn2SnO4 anodes become almost constant after 20 cycles, and at 40th cycle, the specific discharge capacities of both nanoparticles are 521.4mAhg−1 for nanoparticles synthesized using tert-butyl amine and 448.0mAhg−1 for nanoparticles synthesized using Na2CO3 with Coulombic efficiencies higher than 96%. Such an excellent cycling stability and reversibility against lithium insertion/extraction can be attributed to the improved pulverization/agglomeration resistances of these materials, resulting from the surface residual charges, i.e., the repulsive forces between like-charged nanoparticles.

Applicability of natural colourless topaz as a high-energy beam dosimeter

Thermoluminescence characteristics of colourless topaz collected from Pakistan were studied. The objective of this study was to design and develop a TL dosimeter for high-energy beams. Samples were irradiated with 60Co, 137Cs and linear accelerator (6MV, 15MV). Glow curves of the chips revealed four trapping levels at temperature ranges 71–82°C (Peak 1), 173–185°C (Peak 2), 197–210°C (Peak 3) and 225–260°C (Peak 4). Peak 4 is stable and rose linearly with increase of exposure levels. The TL response vs. exposure showed linear behaviour between 1 and 102Gy. Initial fading is rapid in first 24h and becomes 8% in next 19 days. The variation in response of the last 20th cycle with respect to the 1st cycle was found to be 4% with a maximum variation of 15% within all data points. The thermoluminescence response was observed to be higher at low energy. The chips remained mechanically intact during handling in all experiments. Topaz chips can effectively and efficiently be used as a TLD for high-energy beams.

Variations in the electrochemical properties of metallic elements-substituted LiNiO2 cathodes with preparation and cathode fabrication conditions

Variations in the electrochemical properties of LiNiO2 with preparation and cathode fabrication conditions were studied. The LiNiO2 cathode fabricated with a weight ratio of LiNiO2: acetylene black: binder = 85:10:5, after wet Spex milling for 60 min and drying in a shaking incubator showed the best cycling performance, with a discharge capacity degradation rate of 1.06 mAh/g/cycle between the first cycle and the 20th cycle and a discharge capacity at n = 20 of 143.5 mAh/g at 0.1 C rate. LiNi1−yMyO2 cathodes with active material compositions of LiNiO2, LiNi0.975Ga0.025O2, LiNi0.975Al0.025O2, LiNi0.995Ti0.005O2, and LiNi0.990Al0.005Ti0.005O2 were fabricated under these conditions. Among all the samples, LiNi0.990Al0.005Ti0.005O2 had the highest first discharge capacities at 0.1 C rate (196.3 mAh/g) and 0.5 C rate (147.3 mAh/g). This sample had the smallest R-factor value, indicating that it had the lowest degree of cation mixing. At 0.1 C rate LiNiO2 had the best cycling performance. At 0.5 C rate LiNi0.975Al0.025O2 had the best cycling performance and its discharge capacity degradation rate was 1.28 mAh/g/cycle between the first cycle and the 20th cycle.

Synthesis of Li2MnSiO4 Cathode Material Using Molten Carbonate Flux Method with High Capacity and Initial Efficiency

A Li2MnSiO4 cathode material for lithium-ion batteries was prepared by a molten carbonate flux method. The preparation conditions such as gas atmospheres, heating temperatures and manganese sources were examined. Single phase Li2MnSiO4 was obtained at 500°C with two kinds of manganese sources (manganese oxalate dihydrate and manganese hydroxide), which was confirmed using high-resolution synchrotron X-ray diffraction (XRD). The Li2MnSiO4 prepared using manganese hydroxide has smaller particle size (100–300 nm) and higher specific surface areas (19.4 m2 g−1) than those prepared using manganese oxalate dihydrate (200–600 nm, 12.5 m2 g−1). Former sample showed higher discharge capacity (156 mAh g−1), initial efficiency (89%) and capacity retention (55% on 20th cycle) than latter one (92 mAh g−1, 69% and 37% on 20th cycle).

Highly Ordered Nanoporous Si for Negative Electrode of Rechargeable Lithium-Ion Battery

Highly ordered nanoporous Si was investigated as a rechargeable Li-ion battery anode. Hexagonally arranged nanoporous Si with a 200 nm hole interval was fabricated by direct nanoimprint and the subsequent galvanostatic etching in an aqueous HF solution. Hole size was controlled by changing current density, and larger holes (150 nm) showed higher anodic and cathodic charges during cyclic voltammetry. The use of nanoporous Si with large holes enabled galvanostatic cycling without the disintegration of nanoholes when charge capacity was set to 1400 mAhg−1. In the cycling, coulombic efficiency gradually improved and reached 96% at the last 20th cycle.

Influences of melt spinning on electrochemical hydrogen storage performance of nanocrystalline and amorphous Mg2Ni-type alloys

In order to improve the electrochemical hydrogen storage performance of the Mg2Ni-type electrode alloys, Mg in the alloy was partially substituted by La, and the nanocrystalline and amorphous Mg2Ni-type Mg20−xLaxNi10 (x=0, 2) alloys were synthesized by melt-spinning technique. The microstructures of the as-spun alloys were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The electrochemical hydrogen storage properties of the experimental alloys were tested. The results show that no amorphous phase is detected in the as-spun Mg20Ni10 alloy, but the as-spun Mg18La2Ni10 alloy holds a major amorphous phase. As La content increases from 0 to 2, the maximum discharge capacity of the as-spun (20 m/s) alloys rises from 96.5 to 387.1 mA·h/g, and the capacity retaining rate (S20) at the 20th cycle grows from 31.3% to 71.7%. Melt-spinning engenders an impactful effect on the electrochemical hydrogen storage performances of the alloys. With the increase in the spinning rate from 0 to 30 m/s, the maximum discharge capacity increases from 30.3 to 135.5 mA·h/g for the Mg20Ni10 alloy, and from 197.2 to 406.5 mA·h/g for the Mg18La2Ni10 alloy. The capacity retaining rate (S20) of the Mg20Ni10 alloy at the 20th cycle slightly falls from 36.7% to 27.1%, but it markedly mounts up from 37.3% to 78.3% for the Mg18La2Ni10 alloy.

Synthesis and performance of carbon-coated Li3V2(PO4)3 cathode materials for lithium-ion batteries

The carbon-coated monoclinic Li3V2(PO4)3 (LVP/C) cathode materials can be synthesized by one-step heat treatment from a sucrose-containing precursor. Properties of the prepared composite material were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), pore size distribution and specific surface area analyzer, optical particle size analyzer and electrochemical methods. X-ray diffraction results show that LVP sample is monoclinic structure. The sample presents initial discharge capacity of 127.2 mA h/g (at 0.2 C rate), and exhibits better cycling stability (115.1 mA h/g at 30th cycle at 0.2 C rate) and better rate capability (83.1 mA h/g at 50th cycle under 6 C rate) in the voltage range of 3.0–4.3 V. In the voltage range of 3.0–4.8 V, it exhibits a initial discharge capacity of 169.1 mA h/g and good cycling stability (104.9 mA h/g at 20th cycle at 0.5 C rate).

Polymer-mounted N3[dbnd]P(MeNCH2CH2)3N: a green, efficient and recyclable catalyst for room-temperature transesterifications and amidations of unactivated esters

Merrifield resin-supported N3P(MeNCH2CH2)3N shows excellent activity in the transesterification of higher esters such as glyceryl tribenzoate to methyl esters. The catalyst was successfully cycled 20 times (albeit with an increase in reaction time) without compromising yield up to the 20th cycle. The catalyst also showed good performance in amidation reactions of unactivated esters with amino alcohols.

Electrochemical characterization of electrospun SnO x-embedded carbon nanofibers anode for lithium ion battery with EXAFS analysis

SnO x -embedded carbon nanofibers (SnO x /CNF) were synthesized by electrospinning a composite solution of Sn(II) acetate, polyacrylonitrile (PAN), and polyvinylpyrrolidone (PVP) in N,N-dimethylformamide (DMF), followed by stabilization and carbonization. The SnO x for SnO x /CNF-700 was distributed about below 2 nm in diameter, whereas that for SnO x /CNF-800 represented around below 4 nm. The fine structure of SnO x for SnO x /CNF was confirmed by analysis of extended X-ray absorption fine structure (EXAFS). The diameter of the fibers decreased with increasing temperature, whereas both SnO x particles and electrical conductivity of SnO x /CNF increased. Both SnO x /CNF-700 and SnO x /CNF-800 were prepared as disordered structures, whereas SnO x /CNF-900 was synthesized as an SnO 2-like structure. The disordered transformation inducing excellent electrochemical performance originated form CNF prepared by electrospinning and proper heat treatment. Pure SnO 2 displayed low electrochemical performance, indicating a typical large volume change and high mechanical stress. On the contrary, SnO x /CNF-800 represented outstanding specific discharge capacity and exceptional cycle retention at the same time, representing a coulomb efficiency of 71% even in the initial cycle. The specific discharge capacity for SnO x /CNF-800 slightly decreased by the 20th cycle, and then gradually increased by the 100th cycle. The CNF plays an important role as a buffering agent to prevent SnO x particles from agglomerating. The CNF having 1D pathway with high electrical conductivity leads to the promotion of charge transfer as well as mass transfer.

Preparation and electrochemical properties of polysulfide polypyrrole

A novel cathode material, polysulfide polypyrrole was successfully designed and synthesized for high-energy lithium–sulfur secondary batteries. The product was characterized by FT-IR, element analysis and DSC. Character results show that the polymer was obtained with polypyrrole as backbone and S–S side groups attached to it. Polypyrrole backbone in this polymer was used not only as container but also as conductivity passage. Cycle performances of the polymer was examined as active cathode material in lithium batteries, charge–discharge experimental results indicate that the polymer has a specific capacity of 515 mAh g −1 at the first cycle and 452 mAh g −1 at the 20th cycle. The improved cycle properties compared to other polymer disulfides and polysulfide polymers supply a good foundation for practical application of this material in rechargeable lithium batteries.

Synthesis and electrochemical properties of Ti4+ doped Li3−xFe2−xTix(PO4)3/C cathode materials

Abstract Li 3 − x Fe 2 − x Ti x (PO 4 ) 3 /C ( x = 0–0.4) cathodes designed with Fe doped by Ti was studied. Both Li 3 Fe 2 (PO 4 ) 3 /C ( x = 0) and Li 2.8 Fe 1.8 Ti 0.2 (PO 4 ) 3 /C ( x = 0.2) possess two plateau potentials of Fe 3+ /Fe 2+ couple (around 2.8 V and 2.7 V vs. Li + /Li) upon discharge observed from galvanostatic charge/discharge and cyclic voltammetry. Li 2.8 Fe 1.8 Ti 0.2 (PO 4 ) 3 /C has higher reversibility and better capacity retention than that of the undoped Li 3 Fe 2 (PO 4 ) 3 /C. A much higher specific capacity of 122.3 mAh/g was obtained at C/20 in the first cycle, approaching the theoretical capacity of 128 mAh/g, and a capacity of 100.1 mAh/g was held at C/2 after the 20th cycle.

The electrochemical properties of melt-spun Al–Si–Cu alloys

Melt spinning was used to prepare Al 75− X Si 25Cu X ( X = 1, 4, 7, 10 mol%) alloy anode materials for lithium-ion batteries. A metastable supersaturated solid solution of Si and Cu in fcc-Al, α-Si and Al 2Cu co-existed in the alloys. Nano-scaled α-Al grains, as the matrix, formed in the as-quenched ribbons. The Al 74Si 25Cu 1 and Al 71Si 25Cu 4 anodes exhibited initial discharge specific capacities of 1539 mAh g −1, 1324 mAh g −1 and reversible capacities above 472 mAh g −1, 508 mAh g −1 at the 20th cycle, respectively. The specific capacities reduced as the increase of the Cu content. AlLi intermetallic compound was detected in the lithiated alloys. It is concluded that the lithiation mechanism of the Al–Si-based alloys can be affected by the third component. The structural evolution and volume variation can be mitigated due to the formation of non-equilibrium state and the co-existence of nano-scaled α-Al, α-Si, and Al 2Cu for the present alloys.

The fixation strength of tibial PCL press-fit reconstructions

A secure tibial press-fit technique in posterior cruciate ligament reconstructions is an interesting technique because no hardware is necessary. For anterior cruciate ligament (ACL) reconstruction, a few press-fit procedures have been published. Up to the present point, no biomechanical data exist for a tibial press-fit posterior cruciate ligament (PCL) reconstruction. The purpose of this study was to characterize a press-fit procedure for PCL reconstruction that is biomechanically equivalent to an interference screw fixation. Quadriceps and hamstring tendons of 20 human cadavers (age: 49.2±18.5years) were used. A press-fit fixation with a knot in the semitendinosus tendon (K) and a quadriceps tendon bone block graft (Q) were compared to an interference screw fixation (I) in 30 porcine femora. In each group, nine constructs were cyclically stretched and then loaded until failure. Maximum load to failure, stiffness, and elongation during failure testing and cyclical loading were investigated. The maximum load to failure was 518±157N (387-650N) for the (K) group, 558±119N (466-650N) for the (I) group, and 620±102N (541-699N) for the (Q) group. The stiffness was 55±27N/mm (18-89N/mm) for the (K) group, 117±62N/mm (69-165N/mm) for the (I) group, and 65±21N/mm (49-82N/mm) for the (Q) group. The stiffness of the (I) group was significantly larger (P=0.01). The elongation during cyclical loading was significantly larger for all groups from the 1st to the 5th cycle compared to the elongation in between the 5th to the 20th cycle (P<0.03). All techniques exhibited larger elongation during initial loading. Load to failure and stiffness was significantly different between the fixations. The Q fixation showed equal biomechanical properties compared to a pure tendon fixation (I) with an interference screw. All three fixation techniques that were investigated exhibit comparable biomechanical properties. Preconditioning of the constructs is critical. Clinical trials have to investigate the biological effectiveness of these fixation techniques.

Gelatin-templated biomimetic calcification for β-galactosidase immobilization

The alginate–gelatin–calcium phosphate hybrid carrier, which was the alginate capsule covered with gelatin film and calcified shell, was successfully prepared through a facile biomimetic mineralization process, and further utilized to immobilize β-galactosidase. Gelatin was firstly used to inspire and template the assembly of calcium phosphate for enzyme immobilization at ambient temperature and neutral pH. The surface morphology, swelling performance and mechanical stability of calcium alginate capsules and alginate–gelatin–calcium phosphate hybrid capsules were investigated. Experimental results indicated that the assembled calcium phosphate shell significantly enhanced the mechanical stability and lowered the swelling degree of the capsule, additionally improved the immobilization efficiency and dramatically inhibited the leakage of β-galactosidase. Thus, the relative activity of β-galactosidase immobilized in alginate–gelatin–calcium phosphate capsules was more than 60% after the 20th cycle and about 90% after 30 d storage. Meanwhile, β-galactosidase immobilized in hybrid capsules, in comparison to free enzyme and enzyme immobilized in calcium alginate capsules, exhibited the broadest temperature and pH ranges.

Synthesis and evaluation of polythiocyanogen (SCN) x as a rechargeable lithium-ion battery electrode material

Polythiocyanogen, (SCN) x , is a promising lithium-ion battery electrode material due to its high theoretical capacity (462 mAh g −1), safe operation, inexpensive raw materials, and a simple and less energy-intensive manufacturing process. The (SCN) x was prepared from the solution of trithiocyanate (SCN) 3 − in methylene dichloride (MDC), which was prepared by electrochemical oxidation of ammonium thiocyanate (NH 4SCN) in a two-phase electrolysis medium of 1.0 M NH 4SCN in 0.50 M H 2SO 4 + MDC. The (SCN) 3 − underwent auto catalytic polymerization to (SCN) x during MDC removal. Battery electrodes with (SCN) x as the active material were prepared, and tested in Swagelok cells using lithium foil as the counter and reference electrode. The cells delivered capacities in the range of 200–275 mAh g −1 at the discharge–charge rate of 0.2 C. The cells were tested up to 20 cycles and showed repeatable performance with a coulombic efficiency of 97% at the 20th cycle. The results presented here indicate that (SCN) x is a promising lithium-ion battery electrode-material candidate for further studies.

Ag/poly(3,4-ethylenedioxythiophene) nanocomposites as anode materials for lithium ion battery

Ag/poly(3,4-ethylenedioxythiophene) (PEDOT) nanocomposites were synthesized through polymerizing 3,4-ethylenedioxythiophene (EDOT) and reducing Ag(I) acetate into neutral Ag via a simultaneous one-pot method. Ag/PEDOT nanocomposites were formed as a core-shell structure keeping Ag nanoparticles well-dispersed in PEDOT polymer with high surface area and high electrical conductivity. The charge capacity in the initial cycle for Ag/PEDOT nanocomposites showed 291 mAh/g, and also that in the 20th cycle was the highest with 209 mAh/g among the other samples. The morphology of Ag/PEDOT nanocomposites makes Li ions transfer easier, and this results in the enhanced electrochemical performance because of sufficient charge transfer in the interface and convenient mass transfer. PEDOT acted as the soft buffering material to restrain volume expansion and SEI film because of its unique structure having large entangled molecules.

Electrochemical hydrogen storage characteristics of nanocrystalline and amorphous Mg 2Ni-type alloys prepared by melt-spinning

The nanocrystalline and amorphous Mg 2Ni-type alloys with nominal compositions of Mg 2Ni 1- x Mn x ( x=0, 0.1, 0.2, 0.3, 0.4) were synthesized by melt-spinning technique. The spun alloy ribbons with a continuous length, a thickness of about 30 μm and a width of about 25 mm are obtained. The structures of the as-spun alloy ribbons were characterized by XRD and HRTEM. The electrochemical hydrogen storage characteristics of the as-spun alloy ribbons were measured by an automatic galvanostatic system. The electrochemical impedance spectrums (EIS) were plotted by an electrochemical workstation. The hydrogen diffusion coefficients ( D) in the alloys were calculated by virtue of potential-step measurement. The results show that all the as-spun ( x=0) alloys hold a typical nanocrystalline structure, whereas the as-spun ( x=0.4) alloy displays a nanocrystalline and amorphous structure, confirming that the substitution of Mn for Ni facilitates the glass formation in the Mg 2Ni-type alloy. The substitution of Mn for Ni significantly improves the electrochemical hydrogen storage performances of the alloys, involving the discharge capacity and the electrochemical cycle stability. With an increase in the amount of Mn substitution from 0 to 0.4, the discharge capacity of the as-spun (20 m/s) alloy increases from 96.5 to 265.3 mA·h/g, and its capacity retaining rate ( S 20) at the 20th cycle increases from 31.3% to 70.2%. Furthermore, the high rate dischargeability (HRD), electrochemical impedance spectrum and potential-step measurements all indicate that the electrochemical kinetics of the alloy electrodes first increases then decreases with raising the amount of Mn substitution.

Inexpensive synthesis of anatase TiO 2 nanowires by a novel method and its electrochemical characterization

We demonstrate a simple, rapid, inexpensive and novel approach for the synthesis of a kind of anatase TiO 2 nanowires. The method is based on a hydrothermal method under normal atmosphere without using the complex Teflon-lined autoclave, high concentrations NaOH solution and long reaction time. The as-prepared materials are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical measurements. The obtained anatase TiO 2 nanowires show excellent performance. The initial Li insertion/extraction capacity is 260 and 224 mA h g − 1 at 20 mA g − 1 , respectively. In the 20th cycle, the reversible capacity still remains about 216 mA h g − 1 , exhibiting excellent cycling stability. The discharging capacity is about 159 mA h g − 1 in the 20th cycle at 200 mA g − 1 , demonstrating a good high-rate performance. Anatase TiO 2 nanowires might be a promising anode material for lithium-ion batteries.