锂离子电池碳包覆锡负极性能研究

应用水热法分解葡萄糖制作锂离子电池碳包覆锡负极. 充放电测试表明,添加5%（by mass）乙炔黑导电剂的该电极初始放电比容量达967 mAh.g^-1,经50周循环其放电比容量仍保持362 mAh.g^-1,远高于锡电极的比容量（50周循环166 mAh.g^-1）. 碳包覆可防止锡粉团聚,降低锡的不可逆容量损失. 而添加乙炔黑可降低碳包覆电极与电解液间的交流阻抗,改善电极内部锂离子及电子的传导通道,从而也提高了该电极的初始放电比容量.     

锂离子电池硅纳米粒子/碳复合材料

硅由于其超高的理论比容量有望取代石墨成为下一代锂离子电池负极材料,但是硅在充放电过程中巨大的体积膨胀(~300%)会导致材料粉化从集流体上脱落,同时不断形成固相电解质层,造成不可逆容量损失,而材料纳米化和碳复合是解决这些问题的有效手段。本文介绍了硅在循环过程中容量衰减机理,并综述了硅纳米粒子与碳材料复合的最新进展,主要包括包覆型、核壳型以及嵌入型硅碳负极材料,并对核壳型与嵌入型做了重点探究,最后对硅纳米粒子/碳复合材料存在的问题进行分析并展望其研究前景。     

Bi基化合物膜包覆ZnO的制备和电化学性能

为提高锌镍电池ZnO的循环充放电性能,采用Bi(NO3)3水解沉积法对ZnO包覆Bi基化合物膜,系统研究了包覆ZnO的微结构和电化学性能。TEM,XRD和EDS表明由Bi6(NO3)4(OH)2O6·2H2O,BiO和Bi2O3组成的Bi基化合物膜包覆在ZnO表面。表面包覆能提高ZnO的循环性能和放电容量,含5.1wt%Bi的包覆ZnO循环性能稳定,平均放电容量为509mAh·g-1,利用率为78%,性能有较大改善。充放电曲线和循环伏安结果均表明包覆Bi基化合物膜能降低锌镍电池的充电平台,加宽放电平台,提高ZnO的电化学活性。包覆Bi基化合物膜能有效减小活性材料与碱性电解液的接触,抑制ZnO的溶解,提高循环稳定性;而包覆膜的微孔结构又可使活性材料接触到电化学反应必须的H2O和OH-,保证了高的放电容量。     

一种四氧螺环过氧化物的合成

本文报道了一种新型的含双过氧键的螺环化合物的合成。该合成以双氧水为过氧键来源，经酮羰基的缩酮交换反应在底物中引入两个过氧氢基。然后通过汞离子诱发的对双键的加成反应分别将两个过氧氢基的羟基端固定在碳骨架上，形成双过氧螺环结构。螺环两端都含酯基，可供进一步结构修饰、合成衍生物用。     

碳包覆Li3V2(PO4)3正极材料在LiPF6电解液中的表面/界面行为

利用碳热还原法成功制备了碳包覆Li3V2(PO4)3正极材料。X射线衍射研究表明材料具有纯相单斜结构。高分辨透射电子显微镜观察到材料表面存在5～10 nm的包覆碳层。碳包覆Li3V2(PO4)3材料在3.0～4.3 V电压区间内可提供120 mA.h/g(C/4倍率)、115 mA.h/g(1C倍率)和110 mA.h/g(2C倍率)的可逆容量,并且在循环300次后容量保持率超过97%,显示出良好的应用前景。该材料在充放电循环初期经历了不可逆容量损失。高分辨透射电子显微镜研究表明,该不可逆容量损失来源于材料表面生成的固体电解质中间相(SEI膜),红外光谱分析表明,SEI膜的成份主要包括ROCO2Li和RCO2Li等有机物,以及Li2CO3、LixPFy和LixPOyFz等无机物。表面SEI膜经历初期电化学循环后趋于稳定,从而保证碳包覆Li3V2(PO4)3正极材料优良的电化学性能。     

溅射功率对氧化锡薄膜结构和电化学性能的影响

应用射频磁控溅射技术在硅基底上制备氧化锡薄膜,着重研究溅射功率对薄膜结构和电化学性能的影响.XRD,SEM分析及恒电流充放电测试表明,随着溅射功率的增大,薄膜的结晶程度提高;生长速率和晶粒尺寸增大;电池的贮锂容量减少,且首圈不可逆容量损失增大.溅射功率对薄膜的电化学性能有较大的影响.     

锡基复合氧化物的高能球磨法制备及其电化学性能

随着锂离子电池的发展,人们越来越多地要求可充锂离子电池电极材料具有更高的容量.许多研究小组正致力于寻找和开发能够取代现有碳材料(理论最大比容量为372 mAh·g-1)的新型负极材料[1].锡氧化物基材料由于其高的储锂容量和低的锂离子脱嵌平台电压倍受人们关注,有望作为新一代锂离子电池负极材料[2～5].通过在线X-射线研究,Courtney等[4,5]提出了这类材料作为锂离子电池负极材料的两步反应机理:在首次放电过程中,锡氧化物被不可逆地还原成金属锡,同时生成氧化锂;随后,金属锡与锂发生可逆的合金化与去合金化反应,用反应式表示如下:     

锂离子电池预锂化补锂策略研究进展

锂离子电池(LIBs)因高能量密度和长循环寿命而被广泛用于储能电子产品、电动汽车等众多领域。然而,在锂离子电池首次充放电过程中,固体电解质界面(SEI)膜的形成会造成电解液发生不可逆分解、初始活性Li⁺损失(ALL)和不可逆容量损失,会影响电池体系容量和能量密度的发挥,对于硅基负极电池体系而言尤为显著。基于这一问题,亟需开发各种补锂策略来降低活性锂损失,有效提高电池体系的首次库仑效率(ICE),从而实现更高的能量密度和循环稳定性。结合现阶段所做工作,从正负极角度出发,将预锂化补锂策略分为正极预锂化和负极预锂化,主要包括富锂正极材料、富锂预锂化试剂、惰性锂金属粉、含锂有机溶液等一系列预锂化补锂措施。通过系统的分类、比较与总结后,对预锂化以实现电池的高能量密度和长循环寿命提出建议,有助于为预锂化策略走向商业化提供启示。     

碳硅烷树枝状化合物的功能化研究

本文根据碳硅烷树枝状化合物功能基的种类及反应特性,介绍了有关含硅树枝状化合物的功能化的方法,并对功能化含硅树枝状化合物的用途做了相应评述.     

不同取代基的噻碳菁和吲哚碳菁染料对其在溴化银微晶上吸附能力及形成J-聚集体尺寸分布的影响

本文研究了5-位不同取代基的噻碳菁和吲哚碳菁染料对其在立方型颗粒和T-颗粒溴化银微晶上吸附能力的影响,并采用ACFEM(Analytical Color Fluore scence Electron Microscopy)研究了上述结构染料对其吸附在溴化银微晶所形成的J-聚集体尺寸分布的影响。实验结果表明,对吲哚碳菁染料来说,立方体溴化银微晶表面的吸附能力较T-颗粒溴化银微晶表面的吸附能力强;但对噻碳菁染料来说则相反,它们在T-颗粒溴化银微晶表面的吸附能力较立方体溴化银微晶表面的吸附能力强。另外,对5-位不同取代基的噻碳菁染料而言,无论是在立方型颗粒或T-颗粒溴化银微晶上的吸附能力来说,含取代基(无论4-取代基是吸电子型还是推电子型)的噻碳菁染料较未取代的噻碳菁染料强;而5-位取代基是吸电子型的噻碳菁染料更有利于其吸附在T-颗粒溴化银微晶表面。此外,本文还进一步证明了溴化银微晶表面上染料J-聚集体的生长过程是符合奥斯瓦尔特成熟过程的。吲哚碳菁染料在T-颗粒溴化银微晶上形成的J-聚集体的平均尺寸明显大于在立方体溴化银微晶上形成的J-聚集体的平均尺寸。吸附在立方体溴化银微晶上的5-不同取代基的噻碳菁染料对其形成J-聚集体尺寸分布的影响的研究结果表明,含取代基(-CH₃,-Ph,-Cl)的噻碳菁染料形成的J-聚集体的尺寸分布几乎相同,但与未取代的噻碳菁染料形成的J-聚集体的尺寸分布明显不同;5-位含取代基的噻碳菁染料形成的J-聚集体平均尺寸大于未取代的噻碳菁染料的。     

Carbon anode materials from polysiloxanes for lithium ion batteries

Three kinds of silicon-containing disordered carbons have been prepared by pyrolysis of polysiloxanes with different amounts of phenyl side groups. X-ray powder diffraction, X-ray photoelectron spectroscopy and electrochemical capacity measurements were performed to study their behaviors. Graphite crystallites, micropores, and silicon species affect their electrochemical performances. All of them present high reversible capacities, >372 mAh/g. Since the graphite crystallites are very small, they contribute very little to reversible capacity. The number of micropores produced by gas emission during the heat-treatment process decides whether they exhibit reversible capacity. Si mainly exists in the form C–Si–O and influences the irreversible capacity. There is no evident capacity fading in the first ten cycles, indicating promising properties for these disordered carbons.     

Synthesis, characterisation and liquid crystal properties of 2,5-bis[5-alkyl(alkoxy)phenyl-1,3,4-oxadiazole]bromobenzenes

A series of new thermal bilateral liquid crystal compounds with the phenylenebis-1,3,4-oxadiazole structure was synthesised. The molecular structures of the oxadiazole compounds were confirmed by FT-IR and ¹H NMR spectroscopy, elemental analysis and mass spectrometry. Thermogravimetric analysis indicates that the compounds in an atmosphere of nitrogen have good thermal stability. Measurements using differential scanning calorimetry, polarising optical microscopy and temperature-dependent wide-angle X-ray diffraction indicated that the liquid crystalline properties are related to the length of the end groups. When the end group was tert-butyl or alkoxy with four and six carbons, the compounds exhibit no liquid crystal phase. However, compounds with end groups containing more than eight carbons show significant bidirectional thermally-induced liquid crystal properties and the structure of the liquid crystal phase is the lamellar smectic A phase. All the compounds exhibit blue fluorescence.     

Surface functionalization of ordered mesoporous carbons--a comparative study

Hexagonally structured mesoporous carbons C15 and CMK-5 and cubically structured carbon C48 were synthesized using ordered silica SBA-15 and MCM-48 as templates and carbon precursors of different structures. The surfaces of these ordered carbons were chemically functionalized by employing an approach, in which the selected diazonium compounds were in situ generated and reacted with the carbon frameworks of the mesoporous carbons. The aromatic organic molecules containing chlorine, ester, and alkyl groups were covalently attached to the surface of these ordered mesoporous carbons. The presence of functional groups on the modified carbons was confirmed with Fourier transform infrared spectroscopy, thermogravimetric analysis, and nitrogen adsorption. The BET-specific surface area and the pore width of ordered carbons were significantly reduced, whereas the primary structure of these ordered carbons and their unit cells were intact. Basically, the density of grafted functional groups is related to the specific surface area of the sample, particularly the surface area of mesopores. The surface functionalization reaction takes place only on the external surface of carbon C15, while it occurs on both of the internal and external surface of CMK-5 carbon with the nanopipe structure. The presence of the micropores in CMK-5 carbon should be responsible for its lower grafting density because the small micropores are inaccessible in the reaction. It was also proposed that the preferred adsorption/reaction in C48 may be related to the observed unsymmetrical degradation of the XRD patterns for the functionalized C48 samples. The chemical modification process considerably reduced the primary mesopores in these ordered carbons by approximately 1-1.5 nm, affording carbons with micropores in the cases of C15 and C48, and mixed micropores and small mesopores in the case of CMK-5. A grafting density of approximately 0.9-1.5 micromol/m(2) was achieved under current research.     

Synthesis and mesomorphic properties of new Schiff base esters with different alkyl chains

A new series of Schiff base esters,4-(dimethylamino)benzylidene-4'-alkanoyloxyanilines containing even number of carbons at the end group of the molecules(C_(n-1)H_(2n-1)COO,n = 6,8,10,12,14,16,18) were synthesized.The present compounds were monotropic liquid crystals.It was also found that the end groups of the molecules had effect on the mesomorphic properties.     

Synthesis,characterisation and liquid crystal properties of 2,5‐bis[5‐alkyl(alkoxy)phenyl‐1,3,4‐oxadiazole]bromobenzenes

A series of new thermal bilateral liquid crystal compounds with the phenylenebis‐1,3,4‐oxadiazole structure was synthesised. The molecular structures of the oxadiazole compounds were confirmed by FT‐IR and ¹H NMR spectroscopy, elemental analysis and mass spectrometry. Thermogravimetric analysis indicates that the compounds in an atmosphere of nitrogen have good thermal stability. Measurements using differential scanning calorimetry, polarising optical microscopy and temperature‐dependent wide‐angle X‐ray diffraction indicated that the liquid crystalline properties are related to the length of the end groups. When the end group was tert‐butyl or alkoxy with four and six carbons, the compounds exhibit no liquid crystal phase. However, compounds with end groups containing more than eight carbons show significant bidirectional thermally‐induced liquid crystal properties and the structure of the liquid crystal phase is the lamellar smectic A phase. All the compounds exhibit blue fluorescence.     

Liquid-phase adsorption of multi-ring thiophenic sulfur compounds on carbon materials with different surface properties

This work examines the effects of structural and surface properties of carbon materials on the adsorption of benzothiophene (BT), dibenzothiophene (DBT), 4-methyldibenzothiophene (4-MDBT) and 4,6-dimethyl-dibenzothiophene (4,6-DMDBT) in the presence of 10 wt % of aromatics in liquid alkanes that simulate sulfur compounds in diesel fuels. The equilibrium-adsorption capacity varies significantly, from 1.7 to 7.0 mg-S/g-A. The results show that different carbon materials have significantly different sulfur-adsorption capacities and selectivities that depend not only on textural structure but also on surface functional groups. The adsorption of multi-ring sulfur compounds on carbon materials was found to obey the Langmuir isotherm. On the basis of adsorption tests and the characterization of carbon materials by BET and XPS, the oxygen-containing functional groups on the surface appear to play an important role in increasing sulfur-adsorption capacity. The adsorption-selectivity trend of the carbon materials for various compounds increases in the order of BT < naphthalene < 2-methylnaphthalene < DBT < 4-MDBT < 4,6-DMDBT, regardless of carbon material types. This selectivity trend for sulfur compounds is dramatically different and almost opposite from that previously observed for adsorption over nickel-based adsorbents. The regeneration of spent activated carbons was also conducted by solvent washing. The high-adsorption capacity and selectivity for methyl DBTs indicate that certain activated carbons are promising adsorbents for selective adsorption for removing sulfur (SARS) as a new approach to ultra deep desulfurization of diesel fuels.     

Storage stability of ketones on carbon adsorbents

Activated coconut carbon constitutes the more widely used sorbent for preconcentration of volatile organic compounds in sampling workplace air. Water vapour is always present in the air and its adsorption on the activated carbon surface is a serious drawback, mainly when sampling polar organic compounds, such as ketones. In this case, the recovery of the compounds diminishes; moreover, ketones can be decomposed during storage. Synthetic carbons contain less inorganic impurities and have a lower capacity for water adsorption than coconut charcoal. The aim of this work was to evaluate the storage stability of various ketones (acetone, 2-butanone, 4-methyl-2-pentanone and cyclohexanone) on different activated carbons and to study the effect of adsorbed water vapour under different storage conditions. The effect of storage temperature on extraction efficiencies was significant for each ketone in all the studied sorbents. Recovery was higher when samples were stored at 4 degrees C. The results obtained for storage stability of the studied ketones showed that the performance of synthetic carbons was better than for the coconut charcoals. The water adsorption and the ash content of the carbons can be a measure of the reactive sites that may chemisorb ketones or catalize their decomposition. Anasorb 747 showed good ketone stability at least for 7 days, except for cyclohexanone. After 30-days storage, the stability of the studied ketones was excellent on Carboxen 564. This sorbent had a nearly negligible ash content and the adsorbed water was much lower than for the other sorbents tested.     

CnD-m簇离子的结构特性和形成动力学研究

对较小碳原子簇负离子Ｃ－ｎ结构的研究是从直链向单环乃至双环构型发展的．氢原子在碳原子簇中起着电子给予体的作用［１,２］．但以往的研究未发现碳原子数的奇偶性和氢原子数目对簇离子构型的影响．我们以激光溅射氘代蒽样品,产生了丰富的碳／氢团簇负离子ＣｎＤ－ｍ...     

Brominated boron dipyrrins: synthesis, structure, spectral and electrochemical properties

meso-Anisyl boron dipyrrins (BODIPYs) 1-6 containing one to six bromines at the pyrrole carbons have been synthesized by treating meso-anisyl dipyrromethane with 'n' equivalents of N-bromosuccinimide in THF at room temperature followed by oxidation with DDQ, neutralization with triethylamine and further complexation with BF(3)·OEt(2). The brominated compounds were characterized by HR-MS mass, detailed (1)H, (19)F and (11)B NMR and X-ray diffraction studies. The crystal structures solved for compounds 2-6 indicate that the boron dipyrrinato framework comprised two pyrrole rings and one six membered boron containing ring in one plane like other reported BODIPYs. However, the dihedral angle between the BODIPY core and the meso-anisyl group varied from 48° to 88° and the meso-anisyl ring has an almost perpendicular orientation in penta 5 and hexabrominated 6 BODIPYs. The absorption and emission studies showed a bathochromic shift and reached a maximum for tetrabrominated derivative 4, after which there was no change in the peak maxima for penta 5 and hexabrominated 6 derivatives. However, the quantum yields were reduced with the increasing number of bromines. The electrochemical studies revealed that brominated BODIPY compounds 1-6 are easier to reduce compared to unsubstituted meso-anisyl BODIPY 8 and the reduction potential is linearly related to the number of Br groups.     

Cyclodextrins adsorbed onto activated carbons: preparation, characterization, and effect on the dispersibility of the particles in water

We have investigated the adsorption equilibrium of selected cyclodextrins onto activated carbons. A number of parameters were examined including the type of carbon material, the size of macrocyclic cavity, and the chemical nature of the oligosaccharide (e.g., neutral, anionic, or cationic cyclodextrin). Adsorption isotherm studies revealed that the maximum amount of cyclodextrin immobilized on the carbon surface is obtained for the native β-CD, while the adsorption capacity of the ionic cyclodextrins derivatives strongly depends on the net surface charge of the activated carbon. The affinity of cyclodextrins for activated carbons was further utilized to prepare modified activated carbons containing controlled amounts of cyclodextrins through an adsorption process. The resulting materials were characterized by N(2) adsorption-desorption volumetric measurements, FTIR and Raman spectroscopy, while the quantitative determination of the oligosaccharide content on activated carbons was performed by gravimetric measurements. On the basis of the Turbiscan results, it was found that the chemical structure of cyclodextrins, which are incorporated in the carbon framework, had significant influence on the dispersibility and stabilization of the solid particles in water. Agglomeration and precipitation of the carbon particles were markedly suppressed with substituted cyclodextrins whose hydroxyl groups were partially substituted by methyl or alkylammonium groups.