基于稻谷壳的多孔生物质碳锂离子电池负极材料的制备及性能研究

以废弃的稻谷壳为原料,基于酸解-水热碳化-刻蚀法制备了无定形多孔碳材料,采用X射线衍射仪(XRD)、拉曼光谱(Raman)和扫描电子显微镜(SEM)表征了材料结构及形貌,并结合恒流充放电技术测试了材料的电化学性能。结果表明,获得的无定形碳材料呈现出多孔结构,碳电极的首次可逆容量为171.6mAh/g,经历30次循环后依然能保持146.7mAh/g的可逆容量,比未刻蚀碳电极容量(96.3mAh/g)高52%。刻蚀碳电极表现出优异的循环稳定性能,缘于碳材料的多孔结构,可加快锂离子在本体材料和电极/电解液界面间的传输。     

活化剂对大豆壳制备的多孔碳材料储锂性能的影响

生物质多孔碳材料因来源广泛、性价比高,被广泛应用在锂离子电池中,而制备过程中使用的活化剂对材料储锂性能影响较大。因此,以大豆壳为碳源,在不同工艺条件下制备多孔碳材料,通过结构表征和电化学性能测试,考察活化剂对多孔碳材料储锂性能的影响。研究表明：(1)当电流密度为185 mA·g^-1,电压范围为0～3.0 V时,经CaCl₂活化的多孔碳材料(DK-CaCl₂)的首次放充电比容量为639.0/269.5 mA·h·g^-1,而KOH活化的多孔碳(DK-KOH)的首次放充电比容量为986.7/307.5 mA·h·g^-1;(2)大豆壳∶KOH的质量比分别为1∶2、1∶4和1∶8时,得到的多孔碳的首次放充电比容量为544.9/136.8、986.7/307.5和375.1/93.4 mA·h·g^(-1),200次循环后放电比容量分别为88.8、318.9和94.7 mA·h·g^-1。这说明不同活化剂及不同活化比例制备的多孔...     

活化剂对焦煤基多孔碳制备的影响及其在锂硫电池中的应用

煤炭作为一种来源广泛的非金属矿物,是制备大量多孔碳的理想原料。本文以1/3焦煤为原料,NaOH和KOH为活化剂,制备了多孔碳,并研究了硫/多孔碳复合正极材料的电化学性能。结果表明:采用NaOH和KOH单独活化时制备的多孔碳比表面积很大,分别为1 649 m2/g和1 867 m2/g,而采用NaOH和KOH混合活化制备的多孔碳比表面积大幅度下降,当NaOH与KOH质量比为1:1活化时多孔碳的比表面积最小,为290 m2/g。电化学测试表明,NaOH与KOH质量比为1:1混合活化的硫/多孔碳正极材料的电性能优于NaOH和KOH单独活化的硫/多孔碳正极材料,0.2 C下首次放电比容量为790 mA·h/g,库仑效率为93.16%,100次循环后放电比容量为740 mA·h/g。还分析讨论了煤基多孔碳孔径分布对电化学性能的影响。      

高比表面积生物质多孔碳的制备及其电化学性能

以玉米秸秆为碳源(CS),经Na₂CO₃溶液浸泡预处理后，采用KOH活化，制备了多孔生物质碳材料(CS-ACs)。通过形貌、结构表征及电化学性能测试，发现生物质碳材料CS-AC-3具备多级孔道结构，比表面积可达3299m²/g。三电极体系下，该材料在6mol/L NaOH和0.5mol/L Na₂SO₄电解液中，1A/g电流密度下，比电容分别为272F/g、220F/g,循环5000圈后(5A/g),其容量保持率为89%和80%;二电极体系中，以该材料组装的CS-AC-3//CS-AC-3对称电容器具有1.4V的宽电压窗口和较好的电容特性。作为一种可再生廉价碳材料，CS-ACs在实际应用中有好的应用前景。     

活化剂对氮掺杂多孔碳/硫复合正极材料电化学性能的影响

以葡萄糖为碳源、乙酰胺为氮源、氢氧化钾(KOH)为活化剂,通过水热碳化及烧结处理,制备了氮掺杂多孔碳材料,将其与硫进行复合得到多孔碳/硫复合正极材料,考察了不同质量活化剂对多孔碳材料比表面积、孔容孔径及多孔碳/硫复合正极材料电化学性能的影响。结果表明:多孔碳前驱体与活化剂质量比为1∶4时制备的多孔碳材料具有最大的比表面积和孔隙率,且该材料与硫复合得到的多孔碳/硫复合正极材料具有最优的电化学性能、较高的放电比容量和良好的循环性能。     

生物质衍生碳/MnO2复合材料在超级电容器中的应用进展

超级电容器具有充放电速度快、能量密度高、循环稳定性好等优点，而电极材料决定超级电容器的电化学性能。可再生生物质经过高温炭化可制备不同微观结构的碳材料，然而，这些碳材料存在比容量低的缺点；MnO₂具有高理论比电容，缺点是循环稳定差。生物质衍生碳与MnO₂复合可以实现两者优势互补。首先介绍了生物质衍生碳/MnO₂复合材料的制备方法，包括化学法、水热法和电沉积法。然后，按照不同生物质衍生碳的微观结构进行分类，综述了多孔碳/MnO₂、碳球/MnO₂、碳纤维管/MnO₂、碳纳米片/MnO₂和三维碳/MnO₂复合材料的制备及在超级电容器中的应用性能。最后，总结了综合性能最优的生物质衍生碳/MnO₂复合材料，并针对该领域存在的问题提出了其未来发展方向。     

棉花基多孔碳材料的合成、微结构及超电性能研究

由于制备方法简单并且原料易得, 多孔碳合成广泛采用生物质材料, 并用于能源存储。以天然生物质棉花作为碳源, 通过简单的一步法制备得到氮掺杂多孔碳材料。这种多孔碳材料在碳化温度为750℃时具有480 m²/g的比表面积和6.84%的高含氮量。当用作超级电容器电极材料时, 这种碳材料显示出了良好的电容性能。在1 mol/L硫酸电解液中, 电流密度为1 mol/L时, 比电容可以达到252 F/g, 并且在循环10000圈之后仍能保留94%的原电容。这种低成本的棉花基碳材料为超级电容器应用提供了可能。     

CuxO用于调控全无机碳基CsPbI2Br钙钛矿太阳能电池的界面性能

基于CsPbI₂Br的全无机碳基钙钛矿太阳能电池由于碳电极与钙钛矿层间接触性能较差和能带不匹配等问题,导致其光电转化效率较低。本文采用简单的葡萄糖还原法结合煅烧技术制备了两种不同形貌和结构的规则八面体构型Cu_xO,将之作为无机空穴传输材料,制备了结构为导电玻璃(FTO)/SnO₂/CsPbI₂Br/CuxO/C的碳基钙钛矿太阳能电池,研究了CuO和Cu₂O的形貌、结构对光电性能的影响机制。结果显示：CuO和Cu₂O皆具有良好的化学稳定性和p型载流子传输特性,可有效增强CsPbI₂Br钙钛矿层与碳电极层之间的界面接触,改善载流子传输性能,减少电荷复合,延长光电子寿命。基于Cu₂O和CuO的CsPbI₂Br基碳基钙钛矿太阳能电池(C-PSC)器件的光电转换效率最高分别为11.62%和13.22%,分别比空白对照器件的光电转化效率提高了19.5%和36.0%。此外,通过添加Cu₂     

超级电容器用PVDC基碳电极的研究现状

碳电极是超级电容器的关键材料,在很大程度上决定了超级电容器的性能,其发展趋势是高比表面积、高堆积密度、高中孔率、高电导率、高纯度和高性价比以及良好的电解液浸润性(即"六高一良好")。目前,活性碳纤维、碳凝胶、碳纳米管、模板碳等各种碳材料作为超级电容器电极材料的研究均有报道,但较低的比电容和相对较低的体积密度限制了它们在高能量需求的超级电容器电极方面的实际应用。为解决上述问题,关于具有高比表面积的多孔碳材料的研究逐渐活跃起来,特别是一些免活化的制备方法如共混聚合物裂解法、微乳液模板溶胶-凝胶聚合法及模板法等。然而,共聚混合物的制备、超临界干燥、模板的去除等使以上免活化制备方法较传统方法更为复杂。用聚偏二氯乙烯(PVDC)作为前驱体制备多孔碳可实现脱氯-活化一步完成。PVDC基碳作为超级电容器电极材料的优势在于:(1)来源广、成本低;(2)PVDC高碳密度的长链构型可促进芳香环化,与小分子相比,其所需碳化能量低,制备多孔碳材料无需额外活化过程;(3)以PVDC为碳前驱体比以其他材料为前驱体制备的多孔碳材料具有较高的比电容,目前PVDC基碳电极的比电容可达400F·g~(-1)。然而,高性能超级电容器的碳电极材料既要有高比表面积,又要有与电解液离子尺寸相适应的孔径,二者彼此制约。因此,目前研究的重点是在更微观层面上实现碳材料微观结构的调控与优化。目前,超级电容器用PVDC基碳电极的制备方法可分为脱氯-活化多步法与脱氯-活法一步法。脱氯-活化多步法是将PVDC直接机械研磨或高温热解,接着在不同活化作用后得到多孔碳材料的方法。此法得到的多孔碳具有较高的比表面积,但制备过程复杂。模板法不需要额外活化作用,但仍需两步才可得到多孔结构,获得的多孔碳材料虽然具有比表面积大、孔体积大及分级孔径分布的优点,但比电容相对较低。PVDC结构特殊,在高温热解或机械研磨过程中加入强碱,可实现脱氯-活化一步完成,得到PVDC基多孔碳材料,该法工序简单,脱氯率较高,且不会破坏PVDC的固有结构。此外,PVDC连接在亚乙烯基上的氯元素活性高,与含N-/O-聚合物中的N-/O-相比更易离开基团,可在较低温度实现脱氯碳化,且脱氯后的空位对杂质原子较敏感,易实现掺杂。本文分别从PVDC脱氯-活化多步碳化、脱氯-活化一步碳化及氮掺杂三方面综述了超级电容器用PVDC基碳电极的孔结构、比表面积及电化学性能方面的研究进展,并对超级电容器用PVDC基碳电极的研究进行了展望。     

多孔生物质碳材料的制备及应用研究进展

多孔生物质碳材料是一种由糖类或含碳有机废弃物制备的新型功能材料,具有比表面积大,孔隙率高,性能稳定,绿色环保的优点。其常见的制备工艺有直接碳化法,水热法以及活化法等。近年来,多孔生物质碳材料在土壤改良剂、吸附剂和电极材料等领域的应用受到了研究人员的广泛关注。介绍了多孔生物质碳材料的原料来源、制备工艺和应用情况,并对该材料今后的研究方向提出了建议。     

Hierarchical carbon nanostructure design: ultra-long carbon nanofibers decorated with carbon nanotubes

Hierarchical carbon nanostructures based on ultra-long carbon nanofibers (CNF) decorated with carbon nanotubes (CNT) have been prepared using plasma processes. The nickel/carbon composite nanofibers, used as a support for the growth of CNT, were deposited on nanopatterned silicon substrate by a hybrid plasma process, combining magnetron sputtering and plasma-enhanced chemical vapor deposition (PECVD). Transmission electron microscopy revealed the presence of spherical nanoparticles randomly dispersed within the carbon nanofibers. The nickel nanoparticles have been used as a catalyst to initiate the growth of CNT by PECVD at 600°C. After the growth of CNT onto the ultra-long CNF, SEM imaging revealed the formation of hierarchical carbon nanostructures which consist of CNF sheathed with CNTs. Furthermore, we demonstrate that reducing the growth temperature of CNT to less than 500°C leads to the formation of carbon nanowalls on the CNF instead of CNT. This simple fabrication method allows an easy preparation of hierarchical carbon nanostructures over a large surface area, as well as a simple manipulation of such material in order to integrate it into nanodevices.     

短切炭纤维增强沥青基C/C复合材料的组织特征

利用新型、高效的模压半炭化成型工艺，在大气环境下制备出了短切炭纤维增强沥青基C／C复合材料制品，并借助光学显做镜和扫描电镜对其微观组织和断口形貌进行了观察。通过分析，解释了短切炭纤维增强沥青基C／C复合材料中炭纤维损伤的形成机制，提出了作为增强体相的短切炭纤维和焦炭颗粒与基体炭之间独特的界而结构模型。研究还表明：复合材料中明显存在着基体相和颗粒相一基体相的显微结构不仅呈层片状，而且层片状的结构好像数层桔子皮，将颗粒相包裹起来，这种“桔皮包裹”式的结构与炭纤维表面的POG结构基本相似。     

短切炭纤维增强沥青基C/C复合材料的力学性能

利用模压半炭化成型工艺在大气环境下制备出了短切炭纤维增强沥青基C／C复合材料（简称SCFRC）。研究了短切炭纤维的体积分数对SCFRC材料的体积密度和力学性能的影响规律。借助光学显微镜和扫描电镜对其微观组织和断口形貌进行了观察，分析了短切炭纤维对SCFRC材料的增强机制。结果表明，当短切炭纤维的体积分数由0％增大到11．8％时，SCFRC材料的力学性能随之呈线性增加；短切炭纤维增强SCFRC材料的机制主要有裂纹偏转效应、桥联效应以及脱粘和拔出效应。     

Kinetics of chemical vapor infiltration of carbon nanofiber-reinforced carbon/carbon composites

Preforms containing 0, 5, 10, 15 and 20 wt.% carbon nanofibers (CNFs) were fabricated by spreading layers of carbon cloth, and infiltrated by using the technique of isothermal chemical vapor infiltration (ICVI) at the temperature of 1100 °C under the total pressure of 1 kPa and with the flow of the mixture of propane/nitrogen in a ratio of 13:1. The infiltration rates increased with the rising of CNF content, and after 580 h of infiltration, the achievable degree of pore filling was the highest when the CNF content was 5 wt.%, but the composite could not be densified efficiently as the CNF content ranged from 10 to 20 wt.%. An analysis of the results, based on the effective diffusion coefficient and on the in-pore deposition rates, shows that the CNFs, due to their higher aspect ratio, accelerate overgrowth at pore entrances and thus lead to incomplete pore filling.     

软硬混编预制体增强沥青基4D-C/C材料的拉伸破坏行为

以X-Y平面依次铺设炭纤维束、Z向穿插炭棒的4D软硬混编为预制体,采用沥青液相常压、高压浸渍/炭化-石墨化循环致密工艺制备4D-C/C复合材料。通过该材料Z向(炭棒方向)的拉伸实验,测定其拉伸性能和力学行为,并采用SEM分析试样表面及断口形貌。结果表明:宏观上拉伸试样以炭棒整体拔出的形式破坏;细观尺度上,试样表面形成了与载荷方向垂直的贯穿性裂纹,裂纹以2 mm左右的距离呈等间距分布;材料进一步的破坏过程中,基体裂纹在X-Y向纤维束中呈线性扩展,快速分割了基体材料,使4D-C/C复合材料的拉伸破坏演变为1D-C/C复合材料的破坏模式,由于炭棒与基体炭界面结合弱,炭棒以拔出方式失效和破坏。     

Diamond formation on carbon/carbon composite

A carbon/carbon composite was used as substrate for low-pressure diamond deposition. To enhanced diamond nucleation on carbon/carbon composites, a total of ten surface preparation methods have been investigated. These methods involved the use of atomic hydrogen etching, mechanical polishing, sonication, or coating. Diamond nucleation was found to occur on either the defects of the carbon/carbon composite substrates or diamond particulate left on the substrates. The defects were created primarily by atomic hydrogen etching during the coating process. Seeding with diamond powders was performed by dip coating, sonication, or spray-coating processes. It was found that these seeding processes resulted in excellent nucleation of diamond.     

Graphitization behaviour of carbon fibre-glassy carbon composites

Carbon fibre-carbon composites were fabricated by aligning PAN-based carbon fibre unidirectionally in furfuryl alcohol resin char. The graphitization behaviour was investigated by an X-ray diffraction technique and by the measurement of magnetoresistance. The time-temperature superimposition study for interlayer spacing resulted in an activation energy of 242±35 kcal mol⁻¹. The kinetic study on magnetoresistance agreed with the result of X-ray measurement. The activation energy is that for the graphitization of the layer structure formed in the glassy carbon matrix of the composites. The graphitization mechanism of the layer structure is the same as that of soft carbons.     

Mesoscale evolution of non-graphitizing pyrolytic carbon in aligned carbon nanotube carbon matrix nanocomposites

Polymer-derived pyrolytic carbons (PyCs) are highly desirable building blocks for high-strength low-density ceramic meta-materials, and reinforcement with nanofibers is of interest to address brittleness and tailor multi-functional properties. The properties of carbon nanotubes (CNTs) make them leading candidates for nanocomposite reinforcement, but how CNT confinement influences the structural evolution of the PyC matrix is unknown. Here, the influence of aligned CNT proximity interactions on nano- and mesoscale structural evolution of phenol-formaldehyde-derived PyCs is established as a function of pyrolysis temperature (\(T_{\mathrm {p}}\)) using X-ray diffraction, Raman spectroscopy, and Fourier transform infrared spectroscopy. Aligned CNT PyC matrix nanocomposites are found to evolve faster at the mesoscale by plateauing in crystallite size at \(T_{\mathrm {p}}\) \(\sim\)800 \(^{\circ }\hbox {C}\), which is more than \(200\,\,^{\circ }\hbox {C}\) below that of unconfined PyCs. Since the aligned CNTs used here exhibit \(\sim\)80 nm average separations and \(\sim\)8 nm diameters, confinement effects are surprisingly not found to influence PyC structure on the atomic-scale at \(T_{\mathrm {p}}\) \(\le \)1400 \(^{\circ }\hbox {C}\). Since CNT confinement could lead to anisotropic crystallite growth in PyCs synthesized below \(\sim\)1000 \(^{\circ }\hbox {C}\), and recent modeling indicates that more slender crystallites increase PyC hardness, these results inform fabrication of PyC-based meta-materials with unrivaled specific mechanical properties.     

Development of vapor grown carbon fibers (VGCF) reinforced carbon/carbon composites

C/C composites are developed using vapor grown carbon fibers (VGCF) with two types of pitches as matrix precursor. The composites are carbonized at 1000°C by applying the isostatic pressure throughout the carbonization process and further heat treated at different temperatures up to 2500°C in the inert atmosphere. By applying iso-static pressure one can able to developed VGCF based C/C composites possessing the very high bulk density (1.80 g/cm³) and apparent density (2.01 g/cm³) only by heat treatment up to 2500°C without any densification cycle. This high value of density is due to the extremely strong fiber-matrix interactions and self sintering between the VGCF fibers during carbonization process under iso-static pressure. From the SEM study it reveals that, fiber-matrix interactions are strong and fiber boundaries merges with each other, also there is not a evidence of matrix shrinkage cracks in case 1500°C heat treated composites. On the other hand, in 2500°C heat treated composites, there is evidence of uniform fiber-matrix interfacial cracks and porosity in nanometer dimensions. This is due to the change in fiber morphology above HTT 1500°C. But the formation of nano width cracks does not affect on the mechanical properties of composites. The compressive strength increases from 95MPa of 1500°C to 105 MPa of 2500°C heat treated composites. However, hardness decreases due to the increase in the degree of graphitization of composites on 2500°C. The study reveals that by controlling processing condition and the uniform dispersion of VGCF fibers in the matrix phase, it can be possible to developed nano porosity at fiber-matrix interface.