Hua Kun Liu

Characterization of LiMxFe1–xPO4 (M = Mg, Zr, Ti) Cathode Materials Prepared by the Sol-Gel Method

A series of LiM x Fe 1 - x PO 4 (M = Mg,Zr,Ti) phosphates were synthesized via a sol-gel method. Transmission electron microscopy observations show that LiM x Fe 1 - x PO 4 particles consist of nanosize crystals, ranging from40 to 150 nm. High-resolution TEM analysis reveals that a layer of amorphous carbon was coated on the surface of the LiM x Fe 1 - x PO 4 particles, which substantially increases the electronic conductivity of LiM x Fe 1 - x PO 4 electrodes. The doped LiM x Fe 1 - x PO 4 powders are phase pure. Near full capacity (170 mAh/g) was achieved at the C/8 rate at room temperature for LiM x Fe 1 - x PO 4 electrodes. The doped LiM x Fe 1 - x PO 4 electrodes demonstrated better electrochemical performance than that of undoped LiFePO 4 at high rate.

Nanoparticle-dispersed PEO polymer electrolytes for Li batteries

Nanoparticle-dispersed polymer electrolytes have been prepared by stirring or high-energy ball milling of polyethylene oxide (PEO), lithium salt (LiCF 3 SO 3 , LiCl 4 and LiPF 6 ), and nanometer-size ceramic powder (TiO 2 , SiO 2 and Al 2 O 3 ). The smaller the size of ceramic particles, the better they influence the crystallization kinetics of the PEO polymer chains. High-energy ball milling lowers the glass transition temperature of the composite polymers, and thus increases the ionic conductivity greater than the order of the magnitude compared with the un-milled samples. The highest ionic conductivity was reported when using LiPF 6 as added lithium salt and Al 2 O 3 as dispersed particle. Cyclic voltametric measurements showed that the PEO-system is electrochemically stable in the range of 2-5 V.

Nanosize cobalt oxides as anode materials for lithium-ion batteries

Nanosize cobalt oxides (Co3O4) were synthesised by chemical decomposition of cobalt octacarbonyl in toluene at low temperature. Electrochemical properties of as-prepared Co3O4 as anodes in Li-ion cells were tested. The nanosized Co3O4 electrode demonstrate a stable reversible lithium storage capacity of 360 mAh/g within 30 cycles. The reactivity of as-prepared Co3O4 in Li-ion cells could be attributed to nanosize particles of Co3O4 and its lithiation products.

Transport critical current density in Fe-sheathed nano-SiC doped MgB/sub 2/ wires

The nano-SiC doped MgB/sub 2//Fe wires were fabricated using a powder-in-tube method and an in-situ reaction process. The depression of T/sub c/ with increasing SiC doping level remained rather small due to the counterbalanced effect of Si and C co-doping. The high level SiC co-doping allowed creation of the intra-grain defects and nano-inclusions, which act as effective pinning centers, resulting in a substantial enhancement in the J/sub c/(H) performance. The transport J/sub c/ for all the wires is comparable to the magnetic J/sub c/ at higher fields despite the low density of the samples and percolative nature of current. The transport I/sub c/ for the 10wt% SiC doped MgB/sub 2//Fe reached 660A at 5K and 4.5T (J/sub c/=133000A/cm/sup 2/) and 540A at 20K and 2T (J/sub c/=108000A/cm/sup 2/). The transport J/sub c/ for the 10wt% SiC doped MgB/sub 2/ wire is more than an order of magnitude higher than for the state-the-art Fe-sheathed MgB/sub 2/ wire reported to date at 5K and 10T and 20K and 5T respectively. There is a plenty of room for further improvement in J/sub c/ as the density of the current samples is only 50%.

Structural study of Al-substituted nickel hydroxide

Powder X-ray diffraction (XRD) is employed to identify the phase structure of Al-substituted nickel hydroxide, and its structural change after ageing treatment or charge/discharge cycles. The cell constants and the crystalline size of nickel hydroxides have been obtained by analysing the XRD pattern with Si as an internal standard. Results show that Al-substituted α-phase nickel hydroxide is very stable in strong alkaline medium even after 100 charge/discharge cycles.

Fast formation and superconductivity of MgB2 thick films grown on stainless steel substrate

Abstract The fabrication, characterisation, and superconductivity of MgB 2 thick films grown on stainless steel substrate were studied. X-ray diffraction (XRD), scanning electron microscopy, and magnetic measurements were carried out. It was found that the MgB 2 thick films can be fast formed by heating samples to 660°C then immediately cooling down to room temperature. XRD shows above 90% MgB 2 phase and less than 10% MgO. However, the samples sintered at 800°C for 4 h contain both MgB 4 and MgO impurities in addition to MgB 2 . The fast formed MgB 2 films appear to have a good grain connectivity that gives a J c of 8×10 4 A/cm 2 at 5 K and 1 T and maintained this value at 20 K in zero field.

Superconductivity and flux pinning in Y and heavily Pb codoped Bi-2212 single crystals

Studies of superconductivity and flux pinning were carried out on (Bi1.64Pb0.36)Sr2Ca1−xYxCu2O8+y (x=0, 0.05, 0.11, 0.33) single crystals grown by the self-flux method. X-ray diffraction, transport, and magnetic measurements were performed for purposes of characterization. X-ray analysis revealed that the c lattice parameter systemically decreases as the Y doping level increases. The superconducting transition temperature Tc decreases from 80 to 30 K as x increases. A strong annealing effect on Tc and superconducting volume has been observed. Resistance measurements show that x=0.33 samples are semiconductive over a wide temperature range between 4.2 and 300 K for the as-grown state, but become metallic with Tc of 65–70 K after air or oxygen annealing. Flux pinning was studied by measuring the hysteresis loop at different temperatures and different fields. A peak effect was observed in all the codoped samples. Results show that at low temperatures, the peak field is smaller than in solely Pb doped crystal...

Electrochemical performance of nanocrystalline lead oxide in VRLA batteries

Nanocrystalline lead oxide was prepared through two-step chemical reactions and has been tested as the electrode active material for the valve-regulated lead acid (VRLA) battery. By using this nanocrystalline lead oxide, the pasted electrodes can be directly formatted without a curing process. The initial specific capacity of the new electrode was 30% higher than that of the electrode with the conventional ball-milled leady oxide and the cycle behaviour of the new electrode was also improved.

Beneficial effects of red lead on non-cured plates for lead-acid batteries

Abstract In order to find a more convenient processing method and more suitable paste formula for making VRLA batteries, hydrogen peroxide solution and red lead (Pb 3 O 4 ) have been used together during the paste preparation. The use of hydrogen peroxide solution to replace the conventional sulphuric acid solution can accelerate the oxidation of free lead in the paste and therefore reduce the time for the plate curing, while the addition of red lead can enhance the cell formation and improve the cell performance. Based on these two beneficial functions, a new process for making VRLA cells was proposed and investigated. Cells were assembled directly from freshly pasted plates without undergoing the conventional plate curing and drying process, and the battery formation that followed was successful. The new processing resulted in an increase in the production efficiency and a substantial reduction in production time and cost. The battery performance, in terms of both the initial discharge capacity and the cycle life, is also improved by the use of red lead.

Characterization of nanosize molybdenum trisulfide for lithium batteries and MoS3 structure confirmation via electrochemistry

Nanosize molybdenum trisulfide, MoS 3 , was synthesized in a polyoxyethylene(2) nonylphenyl ether/cyclohexane/water microemulsion by acidifying ammonium tetrathiomolybdate solubilized in the water cores of inverse micelles. MoS 3 was also prepared by thermal decomposition for comparison. X-ray diffraction, TEM, and electrochemical testing characterized the molybdenum trisulfide. By comparing the cyclic voltammetry results on MoS 3 and S electrodes in lithium cells, the conclusions about the structure of MoS 3 from previous research work have been confirmed. That is, the molybdenum trisulfide molecules were not a mixture of MoS 2 and elemental S. Molybdenum trisulfide exists as Mo 3 S 9 clusters, which are, in turn, linked by bridging S-S bonds.