炭材料在锂离子二次电池领域的应用

近年来,锂离子二次电池一直是研究与产业的热点。负极材料技术是锂离子电池的关键技术之一,炭材料占据了负极材料95%以上的市场份额。本文论述了炭材料在锂离子电池中的应用,重点介绍了改性石墨材料、中间相炭微球(MCMB)、硬炭材料的应用与进展。其中,改性石墨材料是应用最广的负极材料;中间相炭微球是高端动力电池的首选材料;而硬炭材料是各大厂商研究的热点,有望实现大规模应用。为了满足市场对锂离子电池高能量密度、高倍率、长寿命以及高安全性的需求,对负极材料的研发是一项长期而艰巨的任务。而炭材料在未来相当长的一段时间内将仍在负极材料领域扮演主角。     

中间相沥青基炭负极材料的制备及性能

石油系中间相沥青(MP)经3种方法处理后,对其进行X射线衍射、扫描电镜和电化学性能分析.结果表明:中间相沥青经溶剂萃取-氧化-炭化-石墨化后,作为锂离子蓄电池负极材料,首次充电比容量为422 mAh/g,首次效率为91%,20次循环后比容量保持为375 mAh/g,比石墨的理论比容量要高;经氧化-炭化-石墨化后的MP,电化学性能要差一些,首次充电比容量为401 mAh/g,首次效率为76.5%,稳定后比容量为294 mAh/g;未经石墨化的MP没有明显的充放电平台,充放电曲线呈V字型,比容量仅为194 mAh/g.与已商业化的中间相炭微球相比,中间相沥青基负极材料制备工艺简单,成本低,比容量高,若可以进一步提高其充放电效率,将具有很好的应用前景.     

中间相炭材料包覆天然石墨球

以煤焦油为原料在天然石墨球表面包覆一层中间相炭材料制备出一种复合炭材料.研究了天然石墨球加入量对复合炭材料电化学性能的影响.结果表明:随着天然石墨球添加量的减小,复合炭材料的充放电容量增加,首次充放电效率减小.在200 mL煤焦油中加入70 g天然石墨时所制备的复合炭材料经700℃热处理2 h后性能最佳,可逆比容量达378 mAh/g,充放电效率为91.3%.复合炭材料的循环性能得到了充分改善,30个周期容量保持率97.04%.     

炭黑与石墨混合炭材料对铅酸电池负极性能的影响

本文考察了加入不同含量混合炭材料(如炭黑与石墨)的铅酸电池负极的电化学性能。通过循环伏安测试,研究了炭材料对负极氧化还原性能与析氢电位的影响。通过扫描电镜测试,观察了负极微观形貌的变化。充放电测试结果表明,铅酸电池负极活性物质中炭材料的含量对其倍率放电性能具有重要影响。适量添加炭黑与石墨的混合材料,可以提高负极高倍率条件下的放电容量。当添加3%炭黑和2%石墨混合炭材料时,对负极充电时的析氢电位影响较小,10 C放电条件下得到较高容量。     

活性炭孔结构对铅酸电池负极性能的影响

将具有分级孔结构的活性炭材料添加于铅酸电池负极表层制备得到铅炭电极,并通过不同倍率放电以及部分荷电态、高倍率(HRPSo C)循环测试,考察了铅炭电极高倍率放电性能。结果表明铅酸电池负极表层添加活性炭材料对其倍率放电性能具有重要影响。活性炭中的微米级孔隙可以增加HSO4-离子的流通孔道,提高其迁移速率,抑制负极表面硫酸盐化,提高负极高倍率条件下的放电性能。     

碳化钼/纳米硅/碳复合微球的制备及其储锂性能

石墨负极材料是现在商业化应用最广泛的负极材料。但是商业化石墨负极比容量较低,难以满足现在所需求的高能量密度电池。因此,需要开发新一代高能量密度负极材料。以盐酸多巴胺、钼酸铵、纳米二氧化硅为原料,通过溶液自组装法制备微米球前驱体,后经碳化、镁热还原获得碳化钼复合碳包覆纳米硅(Si@α-MoC_1-x/C)微米球结构,其中α-MoC_1-x原位生成于碳壳层中,二氧化硅还原的硅颗粒稳固结合在壳层之内。纳米硅的引入大大提高了α-MoC_1-x/C复合负极的比容量,同时α-MoC_1-x碳壳层作为保护层,避免电解液与纳米硅直接接触、缓解纳米硅嵌锂后的体积膨胀。产物Si@α-MoC_1-x/C表现良好的循环性能和倍率性能,在200 mA/g电流密度下循环150圈后容量保持率为63.1%(498 mAh/g)。     

不同形貌炭微球的制备及其电化学性能

以2,4-二羟基苯甲酸与甲醛为反应物,F108为表面活性剂,L-赖氨酸为催化剂进行反应,再经碳化、水洗等过程制备了一系列炭微球。透射电子显微镜法(TEM)表明碳化后形成实心炭微球,通过控制水洗温度和水洗时间分别得到中心网格状炭微球和中空炭微球。恒电流充放电测试表明实心微球、中心网格状微球与反应时间分别为36、72 h时所合成的空心微球可逆比容量分别是450、865、559、和576 mAh/g,经过50次循环后可逆比容量分别为299、492、384和339mAh/g。首次和50次循环后可逆容量的大小按微球的形貌排列均是中心网格状炭微球空心炭微球实心炭微球,说明炭微球形貌对材料电化学性能有重要影响,且中心网格状微球性能最佳,比容量均超过石墨理论比容量372 mAh/g。     

锂离子电池Sn-Co-C复合负极材料的合成与研究

以纳米金属氧化物和酚醛树脂为原料,采用喷雾干燥法得到前驱体,经高温碳热还原后制备了核壳结构的Sn-Co-C复合负极材料。通过XRD、SEM和TEM分析表明,生成的纳米尺度的Sn-Co合金颗粒均匀分布于碳微球内部。恒流充放电测试表明Sn-Co-C复合负极材料,首次可逆比容量为391 mAh/g,经过100次循环后比容量为307.1 mAh/g,容量保持率为78.5%。由于碳微球对纳米合金颗粒的分散包覆,缓解了充放电时的体积膨胀,抑制了纳米合金颗粒的团聚,从而使其具有较高的可逆比容量和较好的循环性能。     

黄腐酸基催化石墨化炭材料的制备及储钾特性

通过以黄腐酸为碳质前驱体,硝酸铁为催化剂,以催化石墨化法制备出具有两种碳结构(膨胀石墨和微孔炭)的硬炭材料。材料中类石墨微晶的层间距为0.352 nm,XRD结果表明材料d₀₀₂约为0.360 nm,表现出材料的结构特异性。在应用于钾离子电池负极中时,样品FA-9在25 mA/g电流密度下具有402 mAh/g的首次可逆比容量,在1 A/g电流密度下循环500周后比容量可达95 mAh/g,容量保持率达到67.5%。     

石油沥青包覆对石墨负极电化学性能的影响

将沥青煤油溶液过滤后,与天然球化石墨充分混合,蒸发溶剂后真空炭化,获得锂离子电池用沥青包覆天然石墨负极材料,实验研究发现当沥青包覆量在一定范围内时,可明显降低天然石墨的比表面积,提高石墨负极材料的循环性能,同时石墨负极材料的可逆容量及首次充放电效率明显提高.当包覆量为8%时,炭化温度为1 100℃,首次充电比容量为367 mAh/g,首次库仑效率为94.5%,循环20次后可逆容量保持率为92%.可见沥青包覆改性后,天然石墨材料的电化学性能得到明显改善.     

Water-vapor permeability control of PDMS by the dispersion of collagen powder

Polydimethylsiloxane (PDMS) has been widely used as a material for micro-total analysis system (µTAS) devices due to the superior nature of its manufacturability and chemical resistance, etc. PDMS is known to allow the permeation of gas and water vapor. This characteristic was applied to ensure an efficient oxygen supply to cells cultivated in micro-chambers and power-free sample injection into micro-fluidic devices. Some applications, such as long-term experiments with aqueous samples, however, prefer to avert the permeation of water vapor through PDMS. This paper reports on a new method to control the water-vapor permeability of PDMS by dispersing collagen powder (collagen/PDMS polymer). First, we evaluated the manufacturability and material strength of the collagen/PDMS polymer to see whether the polymer could be employed as a material for µTAS devices. Subsequently, we designed and fabricated micro-fluidic devices to directly measure the amount of water vapor permeating through a PDMS or collagen/PDMS membrane, and evaluated the effect of the dispersed collagen. The use of the dispersed collagen powder successfully reduced the water-vapor permeability of PDMS by 54%. Copyright © 2009 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Electrical and dielectric properties of barium titanate – polydimethylsiloxane nanocomposite with 0-3 connectivity modified with carbon nanotube (CNT)

Abstract

This study explored the preparation and electrical properties of 0–3 barium titanate/polydimethylsiloxane nanocomposites by dispersing barium titanate nanoparticles (BaTiO₃; BT) into the polydimethylsiloxane (PDMS) matrix phase. The effect of barium titanate nanoparticles on electrical properties has been investigated systematically, and the relative permittivity of nanocomposites was found to increase significantly with increasing barium titanate content. Different theoretical models were used to predict the dielectric constant of these composites and compare their experimental value with the theoretical value in order to find an appropriate equation. The result indicated that the dielectric properties of composites are influenced not only by relative permittivity of the components but also dependence on interactions between ceramics and polymers. Furthermore, the preparation and dielectric properties of BT/PDMS nanocomposites modified with carbon nanotube (CNT) were also studied. The dielectric results demonstrate that adding CNT can enhance the relative permittivity of the BT/PDMS composite via improvement of dispersion and distribution of the BT nanoparticles in the PDMS matrix phase. Moreover, the electrical outputs from the BT/PDMS/CNT nanocomposites generator were measured under periodic knocking. The nanocomposites innovatively expand the feasibility of self-powered energy systems for smart sensor and energy harvesting applications.     

空心Fe_2O_3微球负极材料的制备及电化学性能研究

以FeCl_3·7 H_2O和尿素为原料,采用水热合成法制备了空心Fe_2O_3微球。探讨不同合成温度对样品形貌的影响,利用X射线衍射光谱法(XRD)、扫描电子显微镜法(SEM)等分析技术对样品的结构、形貌进行了系统的研究,采用恒流充放电等方法测试了材料的电化学性能。结果表明:空心Fe_2O_3微球由二维纳米片自组装而成,当合成温度为200℃时,制备的样品具有良好的电化学性能,电流密度为200 m A/g,首次放电比容量为1 415 m Ah/g,可逆比容量为955m Ah/g,具有较好的循环性能和倍率性能。     

Fe3O4/壳聚糖核壳磁性微球的制备及特性

以Fe3O4作为磁性内核,利用液体石蜡作有机分散介质,甲醛、戊二醛作交联剂,通过反相悬液交联法制备了单分散、窄分布的强磁性Fe3O4/壳聚糖核壳微球。对磁粉内核的制备条件及微球性能进行了研究,并对产物进行了初步的性能表征。     

Choice and optimization of ratio of components to develop fast-mounted thermostable heat-insulating constructions

Fast-mounted heat-insulating constructions based on foamed synthetic rubbers, polyethylene, and polyurethane are characterized by a thermostability up to 150°C and emit toxic substances when burnt. However, there is a need for heat insulation of surfaces with higher coolant temperatures, such as pipelines, equipment of nuclear and thermal power plants, and heating systems with remote heat sources. One of the most promising types of heat insulation materials for creation of fast-mounted heat insulation constructions is the syntactic foams or thin-film multilayer heat-insulating coatings (TFMHIC), which are created using hollow microspheres and various types of binders. The formation of TFMHIC on the heat-insulating surface is carried out mostly by means of spraying methods that have well proven themselves at coating on flat and cylindrical surfaces of large area, but they turned out ineffective for cylindrical surfaces with a diameter of 300 mm and less, since they are characterized by a large degree of carryover of composite material. This article analyzed the binders and microspheres promising to create the fast-mounted heat-insulating constructions based on TFMHIC with high thermostability. Based on the analysis, a conclusion is drawn that organicsilicon binding and glass microspheres are promising for use in the heat-insulating constructions with thermostability up to 300°C. The results of experimental research are given that point to the possibility of predicting the optimal composition of heat-insulating material characterized by a high degree of filling with microspheres with maintaining the mechanical strength, by means of performing the analysis of rheological characteristics of nonpolymerized liquid compositions of heat-insulation material. The index of tensile strength in bending was the criterion for evaluating the mechanical strength of heat-insulating material. The critical volume concentrations of filling the heat-insulating material with glass microspheres, whose excess leads to a reduction in its strength characteristics, are determined.     

磁性微球制备方法

在总结近年来国内外有关磁性微球研究成果的基础上,对磁性微球进行了分类,着重对高分子磁性微球的几种主要制备方法和工艺过程进行了概述。     

正极材料LiNi1/3Co1/3Mn1/3O2的研究进展

介绍了LiNi1/3Co1/3Mn1/3O2的晶体结构和作为锂离子电池正极材料的电化学反应特征,总结了合成条件和制备方法对其物理性能和电化学性能的影响,以及不同掺杂元素(B,F,Mg,Fe,Al,Si等)对其的改性作用.     

Gender and race in predicting achievement in computer science

In the study described here, 65 prospective computer or information science majors worked through a tutorial on the basics of Perl. Eighteen students were African American. All actions were recorded and time-stamped, allowing us to investigate the relationship among six factors that we believed would predict performance in an introductory computer science (CS) course (as measured by course grade) and how much students would learn from the tutorial (as measured by the difference between pre-test and post-test performance). These factors are: preparation (SAT score, number of previous CS courses taken, and pretest score), time spent on the tutorial as a whole and on individual chapters, amount and type of experimentation, programming accuracy and/or proficiency, approach to materials that involve mathematical formalisms, and approach to learning highly unfamiliar material (pattern-matching procedures). Gender and race differences with respect to these factors were also investigated.     

锂离子电池正极材料LiMPO4的研究进展

综述了锂离子电池正极材料LiMPO4(M=Co、Ni、Mn和Fe)的研究进展,重点对材料的制备、结构以及性能作了探讨,并分析了LiMPO4材料的发展趋势。LiFePO4以其优良的电化学性能,被认为是最有前途的锂离子电池正极材料。     

溶剂热制备绒球状ZnCo_2O_4/CNT多孔微球

用溶剂热法制备绒球状钴酸锌(ZnCo_2O_4)/碳纳米管(CNT)复合材料。用XRD、SEM技术分析物相和形貌,用恒流充放电及循环伏安法测试电化学性能。添加CNT使ZnCo_2O_4呈多孔结构,可提高作为锂离子电池负极材料的电化学性能。以500 mA/g的电流在0.01~3.00 V循环,ZnCo_2O_4/CNT的首次充、放电比容量分别为1 002.3 mAh/g、1 284.9 mAh/g,首次库仑效率达78.00%;第50次循环的充、放电比容量分别为1 197.2 mAh/g、1 209.8 mAh/g,库仑效率达98.96%。