以LiCoO2为阴极的全固态薄膜锂电池的研究

Amorphous and oriented polycrystalline LiCoO2 thin films, used as cathode material for an all-solid-state thin film battery, were fabricated by using RF magnetron sputtering and annealed at different temperatures. The morphology and structure of LiCoO2 thin films were characterized by scanning electron microscopy and X-ray diffraction. All-solid-state thin film batteries, comprised of LiCoO2 cathode films with different structures, lithium phosphorous oxynitride electrolyte film and metallic lithium anode film, was successfully prepared and their properties were examined by chronopotentiometry. Results showed that the structure and crystallinity of the LiCoO2 films strongly influenced the electrochemical performance of all-solid-state thin film lithium batteries. Worth nothing was the battery with an oriented polycrystalline LiCoO2 film it exhibited the best electrochemical performance, and delivered a discharge capacity of ～55.4 μAh/cm2μm. Furthermore, when subjected to over 450 charge/discharge cycles, that battery suffered no obvious fode in capacity.     

Mn~(2 )对聚N鄄异丙基丙烯酰胺的性能影响

合成了聚N鄄异丙基丙烯酰胺(PNIPAM)与Mn2 的配合物,并用荧光光谱、UV鄄Vis、FTIR、XPS进行了初步表征。说明Mn2 与PNIPAM侧链羰基氧或亚氨基氮原子发生了配位作用。由于Mn2 的发射光谱与PNIPAM激发光谱部分重叠以及Mn2 位于561nm的发射峰在Mn2 鄄PNIPAM体系发射光谱中消失,说明发生了较好的F觟rster能量传递。因此,在307nm紫外区荧光强度比PNIPAM增强了314%,使该配合物表现出较好的抑菌效果,而此时少量Mn2 对其低临界溶解温度(LCST)影响不大。     

钛掺杂对不同形貌LiCoO2电化学性能的影响

采用SEM、XRD、恒电流充放电、电化学交流阻抗谱等方法研究了钛掺杂对不同形貌LiCoO2电化学性能的影响. 结果表明, 钛掺杂在不改变材料晶体结构的情况下, 能显著地改善LiCoO2的电化学性能, 且在较高倍率放电制度下(1 C), 掺杂对不同形貌LiCoO2的放电电压平台的影响效果不同. 掺杂后的二次粒子团聚体以1 C放电, 20次循环后3.8 V平台(电压大于3.8 V时的放电容量占总放电容量的百分比) 的保持率为60％, 优于掺杂后的大粒径一次粒子分散体的平台保持率(40％). 电化学交流阻抗谱研究表明, 钛掺杂对于抑制LiCoO2二次粒子在高倍率放电制度下循环过程中电化学阻抗的增加更为有效.     

Molecular Weight Effects on the Reorganization of Poly(Vinylidene Fluoride), Polyamide 12, and Poly(p-Phenylene Sulfide)

Although reorganization in metastable polymeric crystals has been recognized for over 30 years, the effect of molecular weight on the reorganization process has not been widely investigated. In this work three polymeric systems were studied: poly(vinylidene fluoride), polyamide 12, and poly(p-phenylene sulfide). For the polymers investigated, the lowest molecular weight sample was found to reorganize the most and, conversely, the highest molecular weight sample was found to reorganize the least. Comparisons of each system show that independent of molecular weight the reorganization rates among the three systems could be differentiated with the polyamide showing the greatest reorganization and the poly(phenylene sulfide) the least. Both conventional differential scanning calorimetry (DSC) and temperature-modulated DSC (TMDSC) were used in this study to investigate the reorganization process. This revised version was published online in July 2006 with corrections to the Cover Date.     

LiCoO(2) Concaved Cuboctahedrons from Symmetry-Controlled Topological Reactions

Morphology control of functional materials is generally performed by controlling the growth rates on selected orientations or faces. Here, we control particle morphology by "crystal templating": by choosing appropriate precursor crystals and reaction conditions, we demonstrate that a material with rhombohedral symmetry-namely the layered, positive electrode material, LiCoO(2)-can grow to form a quadruple-twinned crystal with overall cubic symmetry. The twinned crystals show an unusual, concaved-cuboctahedron morphology, with uniform particle sizes of 0.5-2 μm. On the basis of a range of synthetic and analytical experiments, including solid-state NMR, X-ray powder diffraction analysis and HRTEM, we propose that these twinned crystals form via selective dissolution and an ion-exchange reaction accompanied by oxidation of a parent crystal of CoO, a material with cubic symmetry. This template crystal serves to nucleate the growth of four LiCoO(2) twin crystals and to convert a highly anisotropic, layered material into a pseudo-3-dimensional, isotropic material.     

聚4-乙烯基吡啶原位修饰PVDF膜及其负载磷钨杂多酸催化剂的研究

以聚偏氟乙烯(polyvinylidene fluoride,PVDF)微滤膜为基膜,4-乙烯基吡啶(4-vinylpyridine,4VP)为功能单体,采用表面引发电子活化再生原子转移自由基聚合(SI-AGET ATRP)法在基膜表面原位改性,并通过接枝聚合物侧链上的吡啶基团与Keggin型磷钨杂多酸(H3PW12O40·n H2O,HPW)之间的静电作用,制备了新型混合催化膜.实验结果表明,接枝聚合过程表现出"活性"/可控表面引发接枝聚合性质,基膜表面接枝聚合物量随聚合反应时间呈现线性增加,当反应时间为16 h,聚合物接枝量达到2.25 mg/cm2,聚合物接枝量的增多致使其相互堆积并坍塌,造成膜表面出现块状聚集体.然后,利用溴代十六烷对接枝聚合物进行季铵化改性,制得表面含有吡啶鎓盐的阳离子复合膜,通过接枝聚合物侧基中的吡啶和吡啶鎓盐基团与磷钨杂多酸之间的静电作用促使其在改性膜表面上有效负载.负载后的磷钨杂多酸均匀的分布在膜表面及孔道中,并保持其化学结构.负载催化剂前后膜的接触角从80.4°减小到57.8°,体现了亲水性催化剂的负载对膜表面润湿性的显著影响.     

Effect of TiO_2 on the Photodegradation Mechanism of Poly(butylene succinate)

The photodegradation behaviors of poly(butylene succinate)(PBS) and TiO_2/PBS nanocomposite were monitored over a period of six months. Material properties and aging mechanisms were studied and explored by various characterizations including ~1HNMR, FTIR, XRD, mass spectrum, and TGA. The TiO_2/PBS nanocomposite was found to be more thermally stable and mechanically robust than the PBS. During aging, crystal formation and the final crystal structure changed notably. Based on the characterization results, it is proposed that the polymer chains have cleaved at the ester linkage by the dissociation of O–H groups and the conversion of C=O to C–O bonds. It was also believed that polymer chain transfer took place, which resulted in the formation of C=C bonds and O–H groups, and the polyester changed to enol or polyether.     

聚丙撑碳酸酯的辐射效应

研究了室温条件下聚丙撑碳酸酯(PPC)在钴-60和电子加速器辐照过程中的响应行为。结果表明,聚丙撑碳酸酯是一种辐射裂解型聚合物,其分子量随着辐射剂量的增加而减小。1mm厚PPC片材在室温和N2气保护条件下,其裂解G值为Gs,γ-ray=10.81;Gs,EB=4.9。不同的裂解G值表明,O2气在聚丙撑碳酸酯的辐射裂解过程中有重要影响。红外光谱研究表明,辐射后聚丙撑碳酸酯在3474cm-1处的峰宽峰高增加,表明其裂解后端—OH基增加。由于裂解作用,辐射后聚丙撑碳酸酯的抗张强度和断裂伸长率均下降。在通常的辐射消毒剂量范围内(25~50kGy),PPC的保留抗张强度大于23MPa,断裂伸长率大于4%,裂解后试样的力学性能依然能够满足实际应用需要,因此PPC可以经受辐射消毒。     

苯并唑类聚合物近期的研究概况(下)

较全成地综述了最近几年国内外关于苯并唑类聚合物的化学改性，结构物性和分子模拟的工作，及其在分子复合材料中的近期应用情况，其中下篇主要讲述苯并唑类聚合物的结构物理性质和分子模拟的工作，以及在分子复合材料中的应用。     

线性聚酯酰胺对聚碳酸亚丙酯的改性

通过己内酯和氨基己酸开环、缩合反应制备了酯段含量为81%的线性聚酯酰胺（PEA）,并用熔融共混的方法制备了PEA/聚碳酸亚丙酯（PPC）共混物,考察了PEA的引入对共混体系相容性、热力学稳定性和机械性能的影响。 结果表明,PEA与PPC之间有较好的相容性,共混物的热力学稳定性比PPC有显著提高,当PEA质量分数为3%时,共混体系的起始分解温度（T-5%）和最大分解速率时的温度（Tmax）比PPC分别提高了52.7%和46.4%。 通过调节PEA的含量可以使共混体系同时达到增强和增韧的效果。     

Deuterium Isotope Effect on Solution Behavior of Thermoresponsive Star-Shaped Poly(2-isopropyl-2-oxazoline)

Thermosensitive star-shaped poly(2-isopropyl-2-oxazoline) (molar mass M≈21000 g mol^?1) in D₂O solution was studied by the static and dynamic light scattering methods. The behavior of the polymer investigated in deuterated water is similar qualitatively to that observed previously in undeuterated water. At the same time, the considerable quantitative changes of polymer behavior in D₂O were seen. Deuterium substitution of solvent affects the phase transition temperature by decreasing its value by 1°C. The temperature interval of phase transition in D₂O solution expands (by about 1°C) in comparison with that in H₂O solution.     

Evaluation and Improvement of the Stability of Poly(ethylene oxide)-based Solid-state Batteries with High-Voltage Cathodes

Solid-state batteries (SSBs) with high-voltage cathode active materials (CAMs) such as LiNi_1−x−yCo_xMn_yO₂ (NCM) and poly(ethylene oxide) (PEO) suffer from “noisy voltage” related cell failure. Moreover, reports on their long-term cycling performance with high-voltage CAMs are not consistent. In this work, we verified that the penetration of lithium dendrites through the solid polymer electrolyte (SPE) indeed causes such “noisy voltage cell failure”. This problem can be overcome by a simple modification of the SPE using higher molecular weight PEO, resulting in an improved cycling stability compared to lower molecular weight PEO. Furthermore, X-ray photoelectron spectroscopy analysis confirms the formation of oxidative degradation products after cycling with NCM, for what Fourier transform infrared spectroscopy is not suitable as an analytical technique due to its limited surface sensitivity. Overall, our results help to critically evaluate and improve the stability of PEO-based SSBs.     

Hofmeister Effect on Thermo-responsive Poly(N-isopropylacrylamide)Hydrogels Grafted on Macroporous Poly(vinyl alcohol) Formaldehyde Sponges

In this work,the Hofmeister effects of nine kinds of anions at different concentrations on the lower critical solution temperature(LCST)of the macroporous thermo-responsive poly(N-isopropylacrylamide)grafted poly(vinyl alcohol)formaldehyde(PVF-g-PNIPAM)hydrogels are investigated with differential scanning calorimetry(DSC).Four kinds of anions with strong hydration,including CO3^2–,SO4^2–,S2 O3^2–,and F^–,and four kinds of anions with weak hydration,including Br^–,NO3^–,I^–,and ClO4^–,and Cl^–as a medium anion are systematically studied and found to demonstrate the effects of the residual hydroxyl groups and network structure of PVF on the LCST values of PVF-g-PNIPAM hydrogels in comparison with that of neat PNIPAM.On the one hand,the existence of hydroxyl groups on PVF backbone promotes the solubility of grafted PNIPAM due to their hydrophilicity and hydrogen-bond interactions with water.On the other hand,the network structure of as-prepared samples restricts free movements of grafted PNIPAM chains,which results in the increase of LCST values.In addition,the difference of grafting percentage also influences the variation of LCST values of PVF-g-PNIPAM hydrogels under salt concentration.     

Biodegradable Poly(butylene adipate-co-terephthalate)/Poly(glycolic acid) Films: Effect of Poly(glycolic acid) Crystal on Mechanical and Barrier Properties

Binary biodegradable polymers films, poly(butylene adipate-co-terephthalate)(PBAT) and poly(glycolic acid)(PGA), were prepared through batch melt mixing to obtain Film Ⅰ and Film Ⅱ under two different processing conditions. PGA crystals played a major role in enhancing the mechanical and barrier properties of the films. For Film Ⅰ, there were initial PGA crystals before the film blowing process, the PGA molecular chain further crystallized, forming the oriented crystallization of PGA. Moreover, ...     

Effect of molecular weight distribution on the rheological behaviour of poly(vinylidene fluoride) (PVDF)

In this study, six samples of commercial poly(vinylidene fluoride) are investigated. Dynamic and steady-state shear flow experiments are carried out in the melt state in order to relate their rheological behaviour to their molecular weight distributions. This rheological investigation is performed through the use of some simple parameters related to the viscosity, elasticity and relaxation times. Plots of flow curves in reduced coordinates are used to confirm the above results.     

Effect of SO2 on Performance of Solid Oxide Fuel Cell Cathodes

Effects of SO₂ in ambient air on the performance and durability of solid oxide fuel cell(SOFC) cathode were evaluated by galvanostatic measurement. Comparison between two cathode materials was made to consider the cathode degradation mechanisms. The degradation performance is associated with a slow decomposition of the La_0.6Sr_0.4Co_0.2Fe_0.8O₃(LSCF) due to the segregation of strontium oxide. Negligible deterioration for (La_0.7Sr_0.3)MnO₃ (LSM) cathode was caused by SO₂ poisoning under a current density of 200 mA/cm². Metal sulphate formation may explain a slight deterioration under increasing high the concentration of SO₂. It was verified that the poisoning mechanism for the two cathode materials resulted from the gradual decomposition of the cathode materials.     

Effect of pH on Poly(acrylic acid) Solution Polymerization

The free-radical redox-initiated aqueous solution polymerization of fully and partially neutralized acrylic acid was carried out at room temperature under full exposure to air. The effect of neutralization degree on the polymerization rate and product properties was studied. Increasing neutralization of the reaction mixture with sodium hydroxide resulted in greater conversion of acrylic acid to sodium acrylate. The rate of polymerization, determined from a gravimetric off-line water removal technique, was shown to decrease significantly with decreasing degree of neutralization. Molecular weight also decreased with decreasing degree of neutralization. The glass transition temperature and hydrophilicity of the polymer product decreased with increasing degree of neutralization. In-line infrared monitoring was also used to monitor the reaction progress and was shown to be an effective tool for this purpose.     

Effect of Tacticity of Poly(Methyl Methacrylate) on Conductivity of Poly(Ethylene Oxide)-Poly(Methyl Methacrylate) Blend-Based Polymeric Electrolytest

Abstract

Polymer electrolytes based on blends of poly(ethylene oxide) (PEO) with various stereoisomers of poly(methyl methacrylate) (PMMA) were studied by means of impedance spectroscopy and DSC. It was found that isotactic poly(methyl methacrylate) (1PMMA)-based electrolytes exhibit ambient temperature conductivities at least one order of magnitude higher than the electrolytes containing other stereoisomers of PMMA. The highest value of room temperature conductivity equal to 9 × 10^?5 S/cm was measured for a sample containing 30 wt% IPMMA. The effect observed results from the presence of a flexible amorphous phase in PEO-IPMMA blends which is favorable for fast ionic transport. A small increase of ionic conductivity with decreasing molecular weight of the added atactic poly(methyl methacrylate) was also observed.