Key Engineering Materials Vols. 336-338

Abstract: The all processes for manufacturing materials parts of solid oxide fuel cell (SOFC) are discussed in the paper. The films are made in one step by the ways of APS, VPS, EVD, which are usually used to produce the electrolyte and interconnect. The films are thin and good gas-resistance, but with relatively high cost. All parts of SOFC are made by the following ways, such as sol-gel, tape casting, tape calendaring and screen printing, which are suitable for manufacturing samples in industry with the cheapest process by co-sintered together ways.

Abstract: AA size Li-ion batteries using LiCoO2, MCMB and lithium metal as cathode, anode and reference electrode respectively were assembled, in order to study the individual effect of anode and cathode on the cyclic and overcharge performances. The experimental results showed that the LiCoO2 cathode was the main electrode related to the capacity decay and discharge voltage drop. Increasing polarization of the LiCoO2 cathode, especially at overcharge situation, and the irreversible change of cathode structure led to reduction of discharge capacity and voltage plateau of batteries.

Abstract: LiNiO2 thin films for the application of cathode of the rechargeable battery were fabricated by Li ion diffusion on the surface oxidized NiO layer. Bi-axially textured Ni-tapes with 50 ~ 80 μm thickness were fabricated using cold rolling and annealing of Ni-rod prepared by cold isostatic pressing of Ni powder. Surface oxidation of Ni-tapes were conducted using tube furnace or line-focused infrared heater at 700 °C for 150 sec in flowing oxygen atmosphere, resulted in NiO layer with thickness of 400 and 800 μm, respectively. After Li was deposited on the NiO layer by thermal evaporation, LiNiO2 was formed by Li diffusion through the NiO layer during subsequent heat treatment using IR heater with various heat treatment conditions. IR-heating resulted in the smoother surface and finer grain size of NiO and LiNiO2 layer compared to the tube-furnace heating. The average grain size of LiNiO2 layer was 0.5~1 μm, which is much smaller than that of sol-gel processed LiNiO2. The reacted LiNiO2 region showed homogeneous composition throughout the thickness and did not show any noticeable defects frequently found in the solid state reacted LiNiO2, but crack and delamination between the reacted LiNiO2 and Ni occurred as the reaction time increased above 4hrs.

Abstract: Here the spinel Li4Ti5O12/C composites were prepared by a modified high temperature solid-state reaction. The as prepared Li4Ti5O12/C composites showed enhanced electrochemical lithium insertion performance in reversible capacity and rate capabilities. The improved electrochemical properties are attributed to the reduced grain size and the improved electronic conductivity caused by the pyrolytic carbon incorporated into the spinel Li4Ti5O12 particle. The spinel Li4Ti5O12/C composites with improved electrochemical properties may find versatile applications in various energy storage devices.

Abstract: Spherical LiNi0.8Co0.2O2 powders with particle size of 8~10μm were prepared based on controlled crystallization, and coated with Al2O3 by Al(OH)3 sol, that was prepared from Al(NO3)3 and NaOH, at first time. SEM, XRD and surface element analysis showed that the nano-sized Al2O3 was coated uniformly on the surface of LiNi0.8Co0.2O2 powder. At 25 °C, the initial discharge capacity decreased from 160 to 149 mAh g-1 after coating of Al2O3. The initial discharge capacity decreased from 168 to 163 mAh g-1 after coating of Al2O at 55 °C. After coating of Al2O3, the capacity retentions increased from 83.8% to 92.6% at the 50th cycle at 25°C, and from 36.3% to 90.8% at the 10th cycle at 55°C. This paves effective way to improve the performance of LiNi0.8Co0.2O2 material for rechargeable lithium ion batteries.

Abstract: The electroactive materials LiFePO4, Li0.98Mg0.01FePO4 and carbon-coated LiFePO4 were synthesized by an improved solid-state reaction and by a sol-gel process and characterized by XRD, SEM, and their electrochemical performance. The reaction conditions favor stabilization of the iron as Fe2+ as well as offering some control of the product morphology and particle size. Electrochemical evaluation of the products reveals a lithium insertion plateau around 3.4V vs Li. Excellent electro- chemical properties in terms of capacity, reversibility and cycling stability have been achieved for doped LiFePO4 synthesized by an improved solid-state reaction. The two methods all produced pure, fine and homogeneous particles.

Abstract: In this paper, homogeneous and well-crystallized LiFePO4 was synthesized by a novel modified solid-state reaction method following by heat treatment at relatively low temperature of 500°C in Ar. No impurities are detected in the XRD patterns. The initial charge specific capacity and discharge specific capacity reach 157.2mAhg-1 and 152.6mAhg-1 respectively at 20°C. Voltage plateaus at around 3.45V were observed in all the curves, indicating that the charge and discharge reaction proceeds as a two-phase reaction. The initial charge specific capacity is 157.2mAhg-1 at 0.1C rate, i.e. 92% of the theoretical capacity, and specific capacity decreases slightly after 100 circles at room temperature.

Abstract: Nanocomposite solid polymer electrolytes (NSPEs) based on poly (vinylidene fluoride) (PVDF) were prepared by dispersing organically modified clay (Cloisite®30B, C30B) consisted of silicate layers in the polymer matrix. And ion conductive properties were investigated in relation to dispersed condition of silicate layers and structural changes of nanocomposites. The characterizations of PVDF/C30B nanocomposites with various C30B contents were analyzed by XRD, DSC, DMA and SEM. In order to confirm the ion conductive properties of NSPEs added to lithium trifluoromethansulfonate (LiCF3SO3) at room temperature, ac impedance analyzer and FT-IR spectrometer were used in this study. The degree of C30B dispersion in PVDF and the degree of crystallinity of PVDF/C30B nanocomposites showed the decrease with C30B contents. As a result, high ionic conductivity was observed in the sample added to 3wt% clay in the polymer matrix and the maximum conductivity was 9x10-4S/cm.

Abstract: Electrolyte of LiPF6-ethylene carbonate (EC)-methyl acetate (MA) was prepared. 1 M LiPF6-EC-MA electrolyte presented the conductivity in excess of 1 mS cm-1 at -50 oC. The cyclic voltammetry showed that the electrolyte was better than conventional electrolyte of LiPF6-ethylene carbonate (EC)-diethyl carbonate (DEC) for the formation of SEI film. 1 M LiPF6-EC-MA electrolyte showed much better cycleability than conventional electrolyte of 1 M LiPF6-EC-DE·C for LiCoO2/Li cell. It is a promising alternative electrolyte for Li-ion batteries.