Electrospinning fabrication and electrochemical properties of LiFePO4/C composite nanofibers

LiFePO₄/C composite nanofibers were synthesized by calcination of the [LiOH + Fe(NO₃)₃ + H₃PO₄]/PVP electrospun nanofibers. Polyvinyl pyrrolidone (PVP) was used as the electrospinning template and carbon source. During the calcination [LiOH + Fe(NO₃)₃ + H₃PO₄] were transformed to LiFePO₄ and PVP was decomposed into carbon. The morphology and properties of the as-prepared samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Brunauer–Emmett–Teller (BET) specific surface area analysis, electrochemical impedance spectroscopy and galvanostatic charge–discharge measurements. The results indicate that the mean diameter of as-prepared LiFePO₄/C composite nanofibers is 179.08 ± 29.66 nm and the BET specific surface area is 66.59 m² g^?1. The addition of carbon does not affect the structure of LiFePO₄, but improves its electrochemical performances. At the current density of 0.2 C, the initial discharge capacity of LiFePO₄/C electrode is 133.6 mAh g^?1 and there is no obvious capacity fading after 100 cycles. The formation mechanism of the LiFePO₄/C composite nanofibers was also proposed.     

Preparation and electrochemical performances of LiFePO4/C composite nanobelts via facile electrospinning

LiFePO₄/C composite nanobelts were synthesized by calcination of the [LiOH + Fe(NO₃)₃ + H₃PO₄]/polyvinyl pyrrolidone (PVP) electrospun nanobelts. PVP was used as the electrospinning template and carbon source. During the calcination, [LiOH + Fe(NO₃)₃ + H₃PO₄] were transformed to lithium iron phosphate (LiFePO₄) and PVP was decomposed into carbon. The morphology and properties of the as-prepared samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Brunauer–Emmett–Teller (BET) specific surface area analysis, electrochemical impedance spectroscopy and galvanostatic charge–discharge measurements. The results indicate that the mean width of LiFePO₄/C composite nanobelts is 2.50 ± 0.33 μm, the average thickness is about 162 nm and the BET specific surface area is 19.4 m² g^?1. The addition of carbon does not affect the structure of LiFePO₄, but improves its electrochemical performances. At the current density of 0.2 C, the initial discharge capacity of LiFePO₄/C electrode is 123.38 mAh g^?1 and there is no obvious capacity fading after 50 cycles. The formation mechanism of LiFePO₄/C composite nanobelts was also proposed.     

The fabrication of PPV/C60 composite nanofibers with highly optoelectric response by optimization solvents and electrospinning technology

We have successfully loaded C60 into a PPV precursor using CS2 and ethanol as mixed solvents and fabricated uniform PPV/C60 composite nanofibers by electrospinning for the first time. C60 was homogeneously distributed in nanofibers. The PL spectra analysis confirmed the formation of a composite and revealed the obvious fluorescent quenching comparing with pure PPV nanofibers. Countable electrospun composite nanofibers on a Au interdigitated electrode showed a fast and highly optoelectric response under 100 mW/cm² light irradiation by a Xe lamp. The results showed that photo induced charge transfer took place at the interface of PPV and C60 and suggested the great potential in the field of micro/nano organic optoelectric devices, especially in micro/nano organic photoswitches.     

聚苯胺纳米纤维/石墨烯复合物的制备及其电化学性能

以氧化石墨烯(GO)为基体,采用界面聚合法制备了聚苯胺纳米纤维/氧化石墨烯的复合物(PA-NI/GO),经水合肼还原和APS再氧化得到聚苯胺纳米纤维/石墨烯复合物(PANI/GR)。用FT-IR、UV-Vis、XRD、SEM和TEM对复合物的结构和形貌进行表征,结果表明氧化石墨烯不仅为苯胺提供了聚合的基体,同时对聚苯胺有掺杂作用,聚苯胺纤维夹在片状石墨烯之间呈现"三明治"结构。通过循环伏安和恒流充放电测试发现,PANI/GR复合材料表现出双电层电容和法拉第赝电容双重特点,受协同效应的作用,在电流密度为400mA/g时,比容量高达460F/g,呈现出优异的电化学活性。     

The microstructure and electrochemical characteristics of LiFePO4/carbon-network composite

LiFePO4/carbon-network composite was synthesized by a high temperature solid-state method using the natural sawdust as carbon precursor. The microstructure of the as-synthesized sample was characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), respectively. The results revealed that the LiFePO4 particles with diameters ranging from 30 to 150 nm were well connected by carbon networks. The electrochemical performance of the composite was characterized using galvanostatic charge-discharge technique. The initial discharge capacity of LiFePO4/carbon-network cathode reached 126 mAh x g(-1) with 0.2 C rate.     

Enhancement of electrochemical properties on TiO2/carbon nanofibers by electrospinning process

In the present work, we report the preparation of TiO₂–carbon/carbon dual nanofibers using an electrospinning technique. The dual nanofibers were synthesized using a modified side-by-side spinneret, which allowed the fabrication of the desired dual nanofiber architecture in a one-step process. A subsequent heat treatment permitted the control on the crystal structure of the synthesized dual nanofibers. Scanning electron microscopy and transmission electron microscopy results confirmed the continuity and duality of the obtained nanofibers. The difference in composition between the fibers composing the dual fibers was clearly observed by energy dispersive X-ray spectroscopy. The effect of heat treatment on crystallinity was evident on the results obtained from the X-ray diffraction and selected area electron diffraction studies; where, depending on the heat treatment conditions, clear signals for anatase and rutile phases of TiO₂ were observed. Electrochemical studies suggest an improvement on the conduction properties of TiO₂–carbon/carbon dual nanofibers compared to single TiO₂–carbon nanofibers, attributed to the carbon nanofiber contribution attached to the TiO₂ nanofibers. Based on the morphological and structural features of this novel nanostructured material, and to the electrochemical performance observed, it has a wide range of potential applications.     

Comparison of electrochemical performances of LiFePO4/C composite materials by two preparation routes

This study reports on the preparation of LiFePO₄/C composite materials prepared by the hydrothermal and sol–gel processes for comparison. The synthesis condition on the hydrothermal process was performed at 170 °C for 19 h. The polystyrene (PS) polymer was used as a carbon source; the PS was added at a range of 0–5 wt.%. The temperature of the post-thermal process was set at 750–850 °C. The citric acid (denoted as CA) was used as the reducing agent and the carbon source in the sol–gel process. The temperatures of the sintering process were set at a range of 650–850 °C. The optimal sintering temperature was at 850 °C for 12 h in the hydrothermal process; the optimal carbon residue content was approximately 3.20 wt.%. It was revealed that the highest discharge capacity of LiFePO₄/C composites by the hydrothermal process at 0.1 C is 163 mAh g^?1. The optimal sintering temperature was found to be at 750 °C for the sol–gel process. The highest carbon content was approximately 11.94 wt.% as the molar ratio of CA is 1.0. The highest discharge capacity of LiFePO₄/C composites by the sol–gel process at 0.1 C was approximately 130.35 mAh g^?1.     

葡萄糖酸亚铁原位碳化LiFePO4/C的制备及电化学性能研究

以葡萄糖酸亚铁为碳源和部分铁源,采用固相法制备了LiFePO4/C复合正极材料。利用XRD和SEM对所得样品进行了结构与形貌表征。以LiFePO4/C作锂二次电池正极组装电池,用电化学工作站和充放电测试系统对样品进行电化学性能测试。当碳包覆量为4.75%,650℃烧结10h时所制备的LiFePO4/C复合材料在0.1、0.2和1C倍率下最高放电比容量分别为161.6、147.2和123.3mAh/g。1C倍率下经50次循环材料的放电比容量无衰减。实验结果表明,由于葡萄糖酸根和铁离子之间较强的化学键,阻止了葡萄糖酸根热解过程中在材料内部的不均匀扩散,其热解后在材料颗粒表面形成均匀导电碳层,并在颗粒之间形成丝状无定形碳,有效抑制了晶粒的生长,提高了活性物质利用率,形成了完整的导电网络,增强了材料的综合电化学性能。     

Synthesis and electrochemical performance of nano-metastructured LiFePO4/C cathode material

The nano-metastructured LiFePO4/C composites were synthesized by carbothermal reduction method using starch gel as carbon source and dispersing media to obtain high tap density LiFePO4 with excellent electrochemical performance. The raw materials were coated by starch gel as compact precursors, which was sintered at 750 degrees C for 8 h to obtain high-density LiFePO4/C composite aggregated with nano-sized particles. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations showed that the primary particles had an average size of about 50-80 nm and the aggregates had a homogeneous particle size distribution of about 400 nm. The asprepared samples had a shortened lithium-ion diffusion length but with higher tap density, thus leading to the excellent electrochemical performance of the cathode materials. Electrochemical results showed that the samples delivered high discharge capacities of 155.6 and 120.7 mAh/g at 0.2C and 5C rates, respectively, with excellent cycling performance.     

不同碳源对LiFePO4/C复合材料性能的影响

采用机械液相活化法与高温固相法相结合制备了锂离子电池正极材料LiFePO4和LiFePO4/C.考察了蔗糖、柠檬酸、葡萄糖、酒石酸等不同碳源对材料性能的影响,并采用XRD、 SEM和恒电流充放电测试等方法对材料的结构、表面形貌及电化学性能进行了研究,利用Raman光谱和TEM分析材料中碳的存在状态.结果表明,得到的样品结构均为橄榄石型,碳源的加入能有效地减小材料的颗粒尺寸,并且材料的电导率比纯LiFePO4的电导率提高了5个数量级.LiFePO4/C样品的表面包覆层均为非晶碳,以柠檬酸为碳源合成的LiFePO4/C材料,具有较小的颗粒尺寸,均匀多孔的表面碳包覆层和最佳的电化学性能.在0.1C下第3次的放电比容量达141.0mAh/g,循环10次后容量无衰减.     

静电纺丝法制备自支撑硅碳负极及电化学性能研究

硅/聚丙烯腈(Si/PAN)纳米纤维通过简单的电纺丝方法制备出锂离子电池的电极材料,并对其进行干燥、热处理和碳化处理制得Si/C自支撑锂离子电池负极材料.该材料尺寸可调,且具有良好的柔性.通过XRD、SEM、TG-DSC、拉曼光谱和电化学性能测试分别对其结构、形貌和电化学性能等进行分析测试.结果 表明,硅含量较低时,自...     

磷酸铁锂微球制备及其电化学性能研究

采用两步法合成磷酸铁锂,第一步先以氯化铁、磷酸二氢铵和磷酸为原料,用水热法合成球状磷酸铁,并研究了温度、不同铁源对其形貌的影响;第二步将制得的磷酸铁与氢氧化锂、PEG-10000混合,在氮气气氛保护下,750℃高温烧制成磷酸铁锂。用X射线衍射(XRD)、扫描电子显微镜(SEM)等表征了磷酸铁及磷酸铁锂的纯度和形貌。制得的磷酸铁锂微球在0.1C充放电时,比容量达到143.5mAh/g。     

Ag/MnO2复合电极材料的制备及其电化学性能

过渡金属氧化物MnO₂因其制备工艺简单、储量丰富、环保且具有较高的理论比容量,在电池储能方面有较大潜力。本论文借助溶胀法对水热合成的δ-MnO₂进行剥离制得MnO₂纳米片。再利用紫外光照以及NaBH₄的还原作用在MnO₂纳米片表面负载Ag纳米颗粒,从而得到Ag/MnO₂复合材料。对Ag/MnO₂复合材料进行了结构和形貌表征以及电化学性能测试。结果表明,作为锂离子电池负极材料,Ag/MnO₂的电化学性能明显优于纯相δ-MnO₂。Ag/MnO₂在100 mA/g电流密度下的首次可逆比容量达到1 001.1 mA·h/g,库伦效率为79.9%;在0.1、0.2、0.5、1.0、2.0 A/g电流密度下的平均可逆比容量分别为936.3、607.5、429.5、351.1和278 mA·h/g,当电流密度重新回到0.1 A/g时,其平均可逆比容量仍可达到658.7 mA·h/g。...     

乳液共混法制备PANI/PAN复合纳米纤维

采用乳液共混法,在N,N二甲基甲酰胺( DMF)中进行聚苯胺(PANI)的乳液聚合,并将该乳液与聚丙烯腈(PAN)的DMF溶液共混形成PANI/PAN复合分散体系;通过静电纺丝技术制备PANI/PAN复合纳米纤维.利用傅里叶红外测试仪(FT-IR)、紫外可见分光光度计(UV-vis)对乳液聚合产物进行了鉴定;利用数显电...     

碳热还原法合成Mg掺杂LiFePO4/C正极材料及电化学性能研究

利用碳热还原法合成了Li1-xMgxFePO4/C(x=0.00、0.01、0.02、0.03、0.04、0.05、0.1)正极材料,通过XRD、SEM、BET、CV、EIS和恒流充放电实验研究了不同掺杂量对产物结构和电化学性能的影响。结果表明少量Mg的掺杂未影响到LiFePO4的晶体结构,但显著改善了其电化学性能。其中,Li0.98Mg0.02FePO4/C材料具有更好的电化学性能,0.1C倍率放电时,首次放电容量达到165.2mAh/g,且循环性能良好。另外,对合成材料的红外光谱进行了研究和指认。     

A novel Ag/graphene composite: facile fabrication and enhanced antibacterial properties

In this work, a novel Ag/graphene composite was synthesized as a promising antibacterial agent. The high-quality graphene was prepared from the expandable graphite first and silver nanoparticles (Ag NPs) were then supported on the graphene sheets by a facile chemical reduction. TEM, SEM, and XPS characterizations show the crystalline of Ag NPs with a typical diameter of 45–50 nm are homogeneously decorated onto graphene sheets without aggregation. Furthermore, the antibacterial activity of composite is investigated using the agar well diffusion method. Results reveal the Ag/graphene composites exhibit outstanding and stable antibacterial activity against E. coli due to good dispersibility of Ag NPs and high-quality of graphene substrate.     

利用静电纺丝技术制备纳米黏土/聚乳酸复合纳米纤维与其表征

利用静电纺丝技术制备了纳米黏土/聚乳酸(PLA)复合纳米纤维,并将该复合纳米纤维收集成无纺布薄膜,采用SEM和TEM观察了复合纳米纤维的微观形貌和结构,分别利用XRD和TGA测试了复合纳米纤维的结晶行为及热学行为,并分析了复合纳米纤维薄膜的拉伸力学性能随纳米黏土含量的变化关系。结果表明:当PLA含量为10wt%、纳米黏土含量为1wt%、CHCl3与DMF体积比为3∶1溶剂条件下,所制备的纳米黏土/PLA复合纳米纤维的细度和均匀性均得到改善;XRD测试结果表明,纳米黏土成功附着在PLA中。TGA和力学测试结果表明,纳米黏土/PLA复合纳米纤维的热稳定性和力学性能相对于纯PLA纤维有较大幅度提高,当纳米黏土含量为1wt%时,其初始分解温度提高了60℃,拉伸强度、断裂伸长率和弹性模量分别提高了111.3%、74.9%和20.0%。     

正极材料LiFePO4性能的改进

介绍了LiFePO4作为钴、镍等锂电池代替品的优势及缺点,并针对纯磷酸铁锂极低的电子导电率和锂离子扩散速率这一缺点的改进进行总结。改进的方法主要有3种,一是对高温固相法、微波法、溶胶凝胶等合成工艺改进;二是对LiFePO4包覆导电材料,合成LiFePO4与导电物质的复合物;三是掺杂改性,改善LiFePO4内部的导电性。最后介绍了国内外LiFePO4的发展现状,提出国内LiFePO4发展所要面对的问题。