介孔钛硅新催化材料

本文综述了介孔钛硅新催化材料的制备方法,归纳评述了各类介孔钛硅材料的制备技术和相应的产物的结构特点,介绍了现有的表征介孔钛硅材料孔结构和钛活性位的重要技术手段和特征,概括了含钛介孔材料在有机物液相催化选择氧化方面的应用,讨论了提高钛位的催化活性、结构稳定性、疏水性、钛硅比等的技术方法;提出了介孔钛硅材料研究存在的问题并展望了将来的研究方向。     

微/纳复合结构硅基负极材料

硅材料因其高的理论比容量(4200 mAh/g)而成为极具发展潜力的锂离子电池负极材料之一。纳米硅负极材料可有效避免材料在循环过程中的粉化现象,同时具有较短的Li~+和电子传输路径,相应电极的电化学性能与微米硅电极相比显著提升,但是纳米结构硅材料比表面积过大、振实密度低等特点限制了其在实际生产中的应用。近年来,使用纳米结构硅材料作为一次结构单元构建微/纳复合结构硅基负极材料的策略被广泛研究。本文综述了微/纳复合结构硅基负极材料的研究进展,总结了微/纳复合结构硅基负极材料中一次颗粒和二次颗粒的选择与结构设计要素,并对具有代表性的微/纳复合结构硅基负极材料物理和电化学性能进行了介绍,提出优化的材料结构和电极设计方案。最后,对微/纳复合结构硅基负极材料存在问题进行简单分析并展望了其研究前景。     

硅材料在锂离子电池负极中的应用研究进展

硅材料作为锂离子电池负极材料具有比容量大的优点，是高容量锂离子负极材料的研究热点之一。论文综述了近年来锂离子电池硅负极材料的研究进展。分别对硅和含硅材料作为锂离子电池负极材料的发展过程、充放电特性、储锂机理及影响其储锂的各因素进行了分析和总结，并对其存在的问题进行了分析。探讨了采用不同复合物、不同制备方法和合成硅化物等改性方法来提高其循环性能的可行性。指出纳米硅基复合物将是硅负极材料最有希望的发展方向。     

锂离子电池硅负极循环稳定性研究进展

硅是已知质量比容量最高的锂离子电池负极材料,研究人员希望通过制造可靠的高容量硅负极,生产高能量密度的锂离子电池. 但由于充放电过程中锂在硅材料中嵌入与释放,硅材料发生巨大的体积变化,以致破碎,并从负极上脱落下来. 硅负极容量随着充放循环次数的增加而迅速下降,是其应用进程中受到的最大制约. 本文结合锂离子电池硅负极研究现状,从硅材料本体结构、整体负极结构两方面介绍几种不同的提高硅负极循环稳定性的方法,并对各种方法的稳定性、成本、制备方法等进行比较,提出对未来硅负极材料研究的展望.     

碳在锂离子电池硅碳复合材料中的作用

随着低比容量硅碳复合材料(<500 mAh/g)在锂离子电池中的商业化应用,硅基负极材料也从实验室研究走向了产业化发展。近年来的研究工作中,许多方法被用来解决硅在循环过程中体积变化(>300%)所带来的一系列问题。在材料结构方面,从最初的硅材料纳米化、硅与其他材料复合等技术手段转变到了硅碳复合材料二次颗粒的结构设计、表面包覆层设计等方法;在应用性能方面,除了早期文献报道的材料比容量、循环性能等参数外,还增加了材料比表面积、振实密度、首次及循环库仑效率等更符合电池实际应用要求的性能参数研究,从而极大地推动了硅基负极材料的商业化应用进程。本文首先综述了近年来硅碳复合材料组成、结构设计的发展脉络,进一步分析了由石墨、软碳、硬碳、碳纤维和石墨烯等碳源合成的硅碳复合材料的结构特点,并对其电化学性能进行分析对比,总结了碳在硅碳复合材料结构及其性能上发挥的作用。最后,对硅碳复合材料制备过程中的结构设计要求和碳材料的选择进行了分析和展望。     

锂离子电池硅基负极及其相关材料

锂离子电池是目前电脑、通讯、消费电子品以及未来电动车动力系统的主要能源。硅基负极材料因其具有较高理论比容量(4200 mAh·g^-1,为石墨10倍以上),被视为最理想的下一代锂离子电池负极材料。然而硅负极在充放电过程中巨大的体积膨胀造成极片材料的粉化脱落、SEI膜的持续增长、正极锂离子的不断消耗,以及现有商业化粘结剂与硅表面较弱的相互作用等诸多缺陷,造成电池容量快速的衰减,阻碍了硅基材料在锂离子电池中的商业化应用。本文对硅基负极材料及其相关电池材料,如硅材料结构、粘结剂、电解液及添加剂等,进行了系统全面的总结。最后对硅基材料目前研究进展和未来发展方向做出总结与评述,以期为下一代硅基电池体系发展提供参考。     

硅材料在锂离子电池负极中的应用研究进展

硅材料作为锂离子电池负极材料具有比容量大的优点,是高容量锂离子负极材料的研究热点之一.论文综述了近年来锂离子电池硅负极材料的研究进展.分别对硅和含硅材料作为锂离子电池负极材料的发展过程、充放电特性、储锂机理及影响其储锂的各因素进行了分析和总结,并对其存在的问题进行了分析.     

锂离子电池硅基负极粘结剂发展现状

在锂离子电池负极材料的研究中，硅材料以其高达4200 mAh·g^-1的理论比容量，成为近年来新能源电池领域的研究热点.但是在锂化/去锂化过程中，硅负极体积变化高达300%，导致快速的容量衰减和较短的循环寿命.目前硅负极改性最有效的方法之一，是通过粘结剂来保持活性物质、导电添加剂和集流体间的接触完整性，减少硅材料在充放电循环过程中体积变化引起的裂化和粉碎，保持硅负极的高容量，提升电池循环性能.基于硅材料作为锂离子电池负极的优异特性，以及目前锂离子电池粘结剂的发展，将针对锂离子电池硅基负极粘结剂做出系统讨论，描述不同粘结剂对电池性能的主要影响，为锂离子电池硅基负极粘结剂的开发和应用提供研究方向.     

硅纳米晶的制备及其在太阳电池中的应用研究

硅纳米晶由于量子限域效应的作用而产生了多种不同于体硅材料的新特性,如荧光效应显著、光学带隙可调等,因而在微电子、光伏、生物医学等领域受到极大的重视。本文介绍了分立的硅纳米晶颗粒和硅纳米晶薄膜的制备方法,并对比了不同方法制备硅纳米晶体的优缺点。着重介绍了硅纳米晶体在太阳电池中应用的几种方式,包括利用纯硅纳米晶薄膜制备太阳电池、硅纳米晶体与有机薄膜基质结合形成复合结构太阳电池、含有硅纳米晶颗粒的硅墨水在太阳电池中的应用等。     

硅负极黏结剂的研究进展

硅材料在锂离子电池负极中具有极高的应用前景, 当前的挑战是其脱锂嵌锂过程中大幅度的体积变化对负极性能的影响. 本文综合评述了黏结剂策略在解决硅材料体积效应问题方面的独特优势, 探讨了硅用黏结剂的发展历程和多功能趋势, 系统总结了硅用黏结剂在提升硅负极电化学性能上的研究进展, 并对未来硅用黏结剂发展的新思路和新方向进行了展望.     

Atmosphere effects in the processing of silicon carbide and silicon oxycarbide thin films and coatings

Silicon carbide and silicon oxycarbide films were prepared from solutions of polycarbosilane and methyldimethoxysilane + tetraethoxysilane, respectively, and deposited on different substrates (Si wafers, stainless steel plates, sapphire and SiC fibers). The coatings were heated at different temperatures and in different atmospheres, such as regular grade argon, ultra high purity and argon vacuum. The films were characterized using different techniques (FT-IR, XRD, SIMS, Ellipsometry).The influence of the processing parameters (heat treatment temperature and atmosphere) on the final microstructure of the coatings is discussed in this article.     

Band distortions and inversions in FTIR spectra of silicon dioxide on silicon

We report the FTIR spectra as a function of incident angle and polarization of a 307 Å layer of silicon dioxide on silicon substrate. Bands normally obscured in transmission spectra are revealed and can dominate the reflection spectra at incident angles away from normal. Strong band distortions were observed as the incident angle and polarization were varied. Our experimental results are in excellent agreement with calculations based on published optical constants. Thus, quantitative interpretations of IR spectra of silicon dioxide on silicon should be made with caution.     

Evaluation of exchange‐correlation functionals in comparison to B3LYP for the description of silicon and Cu‐doped silicon clusters

Several developed exchange‐correlation functionals in density functional theory have been systematically applied to describe the geometries and electronic properties of small silicon (Si_n+1, n < 5) and doped silicon (CuSi_n) clusters. The performance of the various approaches is done with their critical comparison with B3LYP and available high level wave function methods. Our calculations indicate that all functional give reasonable results. Further, OLYP/6‐311+G* approach generally agrees with B3LYP results. The good performance of OLYP is of significant interest knowing that the hybrid functionals are computationally more demanding than nonhybrid schemes. So, we recommend OLYP/6‐311+G* approach for studying the doped silicon clusters and understanding the electronic properties of silicon by the presence of doped metal impurities. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008     

介孔硅与大孔硅的结构、电学和气敏特性

采用双槽电化学腐蚀法在P型单晶硅表面制备两种多孔硅.根据它们的孔径将它们分为介孔硅和大孔硅.使用扫描电子显微镜(SEM)观察两种多孔硅表面和断面形貌,介孔硅和大孔硅的表面化学键用傅里叶变换红外(FTIR)光谱仪来研究,通过I-V特性测试表征两种多孔硅电学特性,随后在室温下测试其气敏特性.结果表明:介孔硅具有较高的气体灵敏度,大孔硅具有较好的气体响应恢复特性.介孔硅对NO2气体具有较好的选择性,大孔硅对NH3气体具有较好的选择性.     

Solvolytic and Thermolytic Reactions of Heterocyclic Pentacoordinate Silicon Compounds

When cyclic pentacoordinate SiCl compounds of the type A are reacted with methanol or water substitution of the SiCl bond and ring opening with cleavage of the SiN bond takes place with formation of tetracoordinate Si compounds. These compounds undergo an interesting thermal reaction resulting in a partial reformation of the cyclic pentacoordinate starting compounds A .     

电化学法制备硅纳米线

Silicon nanowires were synthesized from nanometer silicon dioxide powder under potentiostatic electrolysis at -1.20 V (vs Pt reference) for 4 h in molten CaCl₂ at 900 ℃. The morphology, structure and chemical composition of the samples prepared by electroreduction method were characterized by field-emission scanning electron microscopy(FE-SEM), High-resolution transmission electron microscopy(HRTEM) coupled with electron energy dispersive spectroscopy(EDS), laser Raman and X-ray diffraction(XRD). The results revealed that silicon nanowires were crystalline with a diamond cubic structure, the diameter was distributed from 50 nm to 80 nm and the length was generally several micrometers. The formed nanowires basically consisted of silicon monocrystalline and amorphous oxide sheath.     

Reversible CO2 Addition to a Si=O Bond and Synthesis of a Persistent SiO2–CO2 Cycloadduct Stabilized by a Lewis Donor–Acceptor Ligand

The donor‐stabilized sila‐β‐lactone 1 reacts with CO₂ via a remarkable reversible [2+2]‐cycloaddition reaction to form the spiro‐cyclic silicon carbonate derivative 2 . Furthermore, photolysis of 2 under pressure of CO₂ affords the first persistent SiO₂–CO₂ cycloadduct 3 , presenting a Si₂O₄‐like structure, which is stabilized by a Lewis donor–acceptor type ligand. As predicted by theoretical calculations, in marked contrast to the thermodynamically stable SiO₂ dimer, the SiO₂–CO₂ mixed cycloadduct 3 is labile and readily releases CO₂.     

Intramolecular Halo Stabilization of Silyl Cations—Silylated Halonium- and Bis-Halo-Substituted Siliconium Borates

The stabilizing neighboring effect of halo substituents on silyl cations was tested for a series of peri-halo substituted acenaphthyl-based silyl cations 3 . The chloro- ( 3 b ), bromo- ( 3 c ), and iodo- ( 3 d ) stabilized cations were synthesized by the Corey protocol. Structural and NMR spectroscopic investigations for cations 3 b – d supported by the results of density functional calculations, which indicate their halonium ion nature. According to the fluorobenzonitrile (FBN) method, the silyl Lewis acidity decreases along the series of halonium ions 3 , the fluoronium ion 3 a being a very strong and the iodonium ion 3 d a moderate Lewis acid. Halonium ions 3 b and 3 c react with starting silanes in a substituent redistribution reaction and form siliconium ions 4 b and 4 c . The structure of siliconium borate 4 c ₂[B₁₂Br₁₂] reveals the trigonal bipyramidal coordination environment of the silicon atom with the two bromo substituents in the apical positions.