具有核壳结构的锂离子电池用Sn/C复合负极材料研究

采用碳热还原法以及沥青裂解包覆技术,制备具有核壳结构的Sn/C复合负极材料,对采用改性天然石墨与人造石墨作为内核的效果作了比较,并分析研究壳层的厚度对材料综合性能的影响.结果表明,采用改性天然石墨作为内核能更有效分散Sn金属颗粒,另外沥青裂解碳包覆层的厚度对材料的循环稳定性具有较大的影响.以改性天然石墨为内核,具有(10％+20％)双层包覆结构的负极样品具有最佳的综合性能,首次库伦效率为76.3％,54周的容量保持率为99％.材料结构的设计以及结构的合成工艺是解决锡基合金负极材料体积效应的重要途径.     

锂离子电池炭负极材料的研究——包覆对天然石墨容量衰减的影响

研究了酚醛树脂包覆对天然石墨电化学性能的改善。酚醛树脂热解后形成的包覆石墨首次放电容量达到了460mAh·g-1以上,高于未处理石墨(384mAh·g-1);考察了热处理温度对包覆石墨性能的影响,结果表明在600℃～1000℃的范围内,随着热处理温度的升高,材料的不可逆容量降低,首次充电容量和循环效率提高;循环20周以后包覆石墨的容量仍保持在330mAh·g-1以上,而未处理石墨的容量则降低到300mAh·g-1以下,说明酚醛树脂包覆对抑制石墨的容量衰减有明显的作用。     

沥青包覆天然石墨性能的研究

采用液相及动态熔融法使沥青炭均匀包覆于天然石墨的表面,观察天然石墨的表面结构,测量其物理参数,考核复合材料的充放电性能.结果表明:天然石墨表面存在沥青热解碳,粒径、振实密度增大,复合炭材料的充放电容量、循环性能都得到提高.添加5%沥青经400℃炭化3h、850℃热处理2h的样品,电化学性能最好,可逆容量为362mAh/g,不可逆容量为31.7mAh/g,首次充放电效率为92.0%,30个循环周期后,容量保持率为96.6%     

石墨烯包覆炭硫复合物正极材料的制备及其电化学性能(英文)

利用石墨烯作为新型的阻挡层,设计并制备出具有核壳结构的石墨烯包覆多孔炭/硫复合材料,抑制锂硫电池中的"穿梭效应",以提高正极材料的循环性能。该结构利用多孔炭材料作为储存硫的载体,而石墨烯作为阻挡层可以限制充放电过程中形成的多硫化物向体相电解液中的扩散,从而实现对正极材料的容量和循环性能的提高。此外,提出一种简便的组装方法来实现石墨烯在多孔炭/硫复合材料表面的包覆。利用氧化石墨烯在液相还原过程中官能团的去除来降低亲水性,从而使其自发地包覆在不亲水的多孔炭/硫复合材料表面,形成石墨烯包覆的核壳结构。     

酚醛树脂炭包覆对天然微晶石墨电化学性能的影响

以酚醛树脂包覆天然微晶石墨,经炭化处理制备得到锂离子电池用酚醛树脂炭包覆石墨负极材料。系统考察了酚醛树脂炭包覆量对微晶石墨晶体结构和电化学性能的影响。结果表明,酚醛树脂炭改善了天然微晶石墨的表面形貌,但未改变其晶体结构;包覆适量酚醛树脂炭可以提高负极材料的首次充放电效率,并且可以明显改善其大电流充放电下的循环性能。酚醛树脂包覆量为4%的酚醛树脂炭包覆石墨的首次充放电效率为81.4%,在0.5C的电流密度下经过50次循环后仍有257.9mAh/g的脱锂容量。     

大尺寸各向同性热解炭材料的制备与表征

采用一种新的旋转基体稳态流化床沉积装置制备大尺寸的各向同性热解炭材料。利用金相显微镜、扫描电镜、透射电镜和XRD对各向同性热解炭材料的微观结构进行了表征，并对其力学性能进行了测试。结果表明，改进后的旋转基体稳态流化床沉积工艺能够制备出大尺寸的各向同性热解炭材料。材料的结构均匀，气孔较少，主要由球形颗粒状碳结构组成，构成这种球形颗粒状碳结构的是乱层结构的石墨片层堆积体。各向同性热解炭与传统炭材料相比具有较高的杨氏模量、硬度和强度。     

锂离子电池Si/C/石墨复合负极材料的电化学性能

采用热裂解方法, 热解分散于聚偏二氟乙烯溶液中的硅和石墨, 得到了具有稳定电化学循环性能的Si/C/石墨复合负极材料。透射电子显微镜观察发现, 复合材料形貌为无定型碳包裹硅颗粒的核壳结构。通过系统研究不同Si粒径和石墨含量对电极电化学性能的影响, 发现Si颗粒粒径越小复合材料电化学循环稳定性能越优越, 适当的降低石墨含量有利于电极材料剩余比容量的提高。当Si粒径为50 nm, Si与石墨质量比1:1时, 电极材料具有1741.6 mAh/g的首次放电比容量和72.5%的首次库仑效率, 60次循环后, 可逆比容量保持在820 mAh/g。热解有机物形成碳包覆的结构能有效地改善硅基类负极材料的电化学循环性能。     

硅低温热解活化包覆超细金刚石及其抗氧化和分散稳定性

超细金刚石(UFD)粉体高温易氧化、分散稳定性差使其在高温、溶液等环境中的应用受到极大限制。采用硅低温热解-活化-包覆复合工艺实现了超细金刚石表面包覆改性，成功制备了具有纳米尺度核-壳结构的UFD/Si复合粉体。用拉曼和透谢电镜分别表征了包覆粉末石墨化程度，探究包覆前后粉体的相成分，复合粉体形貌及包覆层厚度；用热重分析仪和傅里叶红外光谱结合粉体在10%硫酸悬浮液中的稳定静置时间分别测定UFD包覆前后的抗氧化性和分散稳定性。结果表明，850℃时的原位热解反应使Si活化量充足，无定型硅层均匀包裹着金刚石颗粒呈椭球形，包覆层厚度为10～30 nm,物相主要为金刚石和无定型硅。核-壳结构的UFD/Si复合粉体具有抗高温氧化性，硅层阻隔了金刚石与氧气直接接触，其初始氧化温度较纯UFD从500℃提高到780℃,945℃时才被彻底氧化。包覆减少了金刚石表面的官能团，减弱了颗粒之间的吸附，包覆Si后的UFD粉体在10%稀硫酸悬浮液中的沉降时间较纯UFD提升了12 h以上。     

酚醛树脂炭/石墨复合炭材料用作锂离子电池负极材料的考察

用不同的方法在石墨的表面包覆上一层酚醛树脂,然后在Ｎ２保护下１０００℃炭化１ｈ制得复合炭材料,并用扫描电子显微镜（ＳＥＭ）对其表面物理形态进行观察分析,研究了复合炭材料的恒电流充放电性能。包覆在石墨表面的具有无定形结构的酚醛树脂炭能够有效阻止石墨在充放电过程中发生层状剥落,从而提高复合炭材料的循环稳定性,其中通过常常法制香的复合炭材料（ＣＰＧ－３０）在十次循环后可逆容量为３２６ｍＡｈ．ｇ＾－１,比     

有机物热解碳包覆人造石墨负极材料的改性研究

采用溶胶-凝胶法在人造石墨表面包覆不同有机物碳源后进行热处理,制备了具有"核-壳"结构的热解无定形碳包覆人造石墨改性负极材料。通过X射线衍射(XRD)、扫描电子显微镜(SEM)、恒电流充放电以及循环伏安(CV)测试等方法研究了碳源种类和包覆量对材料晶格结构、颗粒形貌及电化学性能的影响。结果表明,以聚偏氟乙烯(PVDF)作为碳源、5%(质量分数)的包覆量制备的材料具有较高的可逆比容量(约360mAh/g)和首次库仑效率(88.5%),表现出优异的倍率性能和循环稳定性。这主要是由于5%(质量分数)的PVDF包覆量在石墨表面形成的无定形碳包覆层比较完整且厚度适宜,无定形碳的各向同性结构特征增加了锂离子扩散的通道,促进了电极反应过程的进行。     

Preparation of submicrometer-sized titania hollow spheres by templating sulfonated polystyrene latex particles

Submicrometer-sized titania hollow spheres with tunable shell thickness and smooth surfaces have been successfully synthesized by employing sulfonated polystyrene (PS) latex particles as a template in sol-gel method. The structure of the particles was characterized by scanning electron microscopy and transmission electron microscopy. The shell thickness was readily tuned by altering the concentration of titanium tetrabutoxide (TBOT) in ethanol solutions. The surface roughness as well as the shell thickness has the tendency to increase with the increase in the concentration of TBOT. The diameter of the hollow spheres was on the average of 20-26% smaller than the diameter of template PS latex particles. Some titania fragments were also observed for the sample with the highest TBOT concentration.     

A tool for studying contact electrification in systems comprising metals and insulating polymers

We describe an analytical system for in situ measurement of the charge that develops by contact electrification when a ferromagnetic sphere rolls on the surface of a polymer. This system makes it possible to survey the ability of polymeric surfaces to charge by contact electrification. Because the measurement of charge using this tool does not require physical contact of the charged sphere with the measuring electrode, it also enables the kinetics of charging to be examined. The research has focused on the contact charging of spheres having a core-and-shell geometry (a common core of ferromagnetic steel, and a variable shell of thin films of metals, or metals with surface oxides) rolling on the surface of polymeric slabs; it has generated an internally consistent set of data that include the polarity and magnitude of charging for a homologous series of polymers that differ chemically in the pendant group on a polyethylene backbone.     

Wave propagation in elasto-plastic granular systems

Due to the nonlinear nature of the inter-particle contact, granular chains made of elastic spheres are known to transmit solitary waves under impulse loading. However, the localized contact between spherical granules leads to stress concentration, resulting in plastic behavior even for small forces. In this work, we investigate the effects of plasticity in wave propagation in elasto-plastic granular systems. In the first part of this work, a force–displacement law between contacting elastic-perfectly plastic spheres is developed using a nonlinear finite element analysis. In the second part, this force–displacement law is used to simulate wave propagation in one-dimensional granular chains. In elasto-plastic chains, energy dissipation leads to the formation and merging of wave trains, which have characteristics very different from those of elastic chains. Scaling laws for peak force at each contact point along the chain, velocity of the leading wave, local contact and total dissipation are developed.     

Controlled synthesis of Pt-loaded yolk–shell TiO2@SiO2 nanoreactors as effective photocatalysts for hydrogen generation

Yolk–shell and hollow structures are powerful platforms for controlled release, confined nanocatalysis, and optical and electronic applications. This contribution describes a fabrication strategy for a yolk–shell nanoreactor (NR) using a post decoration approach. The widely studied yolk–shell structure of silica-coated TiO₂ (TiO₂@SiO₂) was used as a model. At first, anatase TiO₂ spheres were prepared, and subsequently were given a continuous coating of carbonaceous and silica layers. Finally, the carbonaceous layer was removed to produce a yolk–shell structure TiO₂@SiO₂. By using an in-situ photodeposition method, Pt-encased spheres (Pt-TiO₂@SiO₂) were synthesized with Pt nanoparticles grown on the surface of the TiO₂ core, which contained void spaces suitable for use as NRs. The NR showed enhanced hydrogen production with a rate of 24.56 mmol·g⁻¹·h⁻¹ in the presence of a sacrificial agent under simulated sunlight. This strategy holds the potential to be extended for the synthesis of other yolk–shell photocatalytic NRs with different metal oxides.     

Sol-gel synthesis, microstructure and adsorption properties of hollow silica spheres

Spherical colloidal particles with a hollow interior and a mesoporous shell are particularly useful for drug delivery and release because such spheres combine the unique properties of hollow interior (for storing the drug) with mesoporous shell (for controlled release). Hollow silica spheres (HSS) with a mesoporous shell were prepared via a sol-gel process in the presence of dual templates polystyrene spheres and cetyltrimethylammonium bromide for creating the hollow core and mesopore shell. The effect of the ratio of silica precursor over polystyrene spheres on particle morphology and pore structure of the HSS was investigated. The adsorption kinetics of methyl blue on the HSS was evaluated and correlated with the mesoporous shell structure.     

Synthesis of submicrometer-sized hollow titania spheres with controllable shells

Submicrometer-sized hollow titania spheres with controllable shells have been prepared using polystyrene particles as a template in conjunction with the sol–gel method. The hollow spherical structures could be confirmed by transmission electron microscope (TEM) and scanning electron microscope (SEM). The void sizes of the hollow spheres were 15–20% smaller than the diameters of the polystyrene template. The shell thickness and surface roughness of the hollow titania spheres increased with increasing the concentrations of titanium tetrabutoxide ethanol solutions. Furthermore, when the volume ratio of titanium tetrabutoxide to ethanol was 1:5, a porous titania structure was yielded, rather than dispersive hollow titania spheres. As expected, the shell thickness of the hollow titania spheres could be readily controlled by altering the number of the titanium tetrabutoxide layers coated on the polystyrene template.     

Electronic shell structure of cluster quantum mechanical effects in the semiclassical approximation

The electronic shell structure of spherical and circular potential wells of finite depth is examined as an extension of the semiclassical analysis of Balian and Bloch. The resulting analytical expressions for the electronic density of states are in good agreement with results of numerical calculations. For circular discs the oscillating structure in the density of states shows a different supershell pattern than for spheres. This is a consequence of the difference in the effective multiplicity of the closed paths, which is determined by the quantization momentum. The positions of the maxima and minima in the density of states depend strongly on the phase shifts in the particle waves arising for each reflection at the cluster surface. These phase shifts have to be determined from a quantum mechanical calculation. Thus the electronic shell structure of spherical clusters has a close similarity with electromagnetic resonances of dielectric spheres (whispering gallery modes).     

Synthesis of hollow spheres with mesoporous silica nanoparticles shell

Hollow spheres with mesoporous silica nanoparticles shell were synthesized with the use of cetyltrimethylammonium bromide (CTAB) and polystyrene (PS) hollow spheres as dual templates. The key to this study is that the uneven surface of the template provides nucleation sites for mesoporous nanoparticles, resulting in the formation of hollow spheres with mesoporous silica nanoparticles shell. The final products with hierarchical mesopores can be obtained through a simple one-step approach.     

Synthesis and characterization of ZrO2 hollow spheres

ZrO₂ hollow microspheres with the average diameter of about 500 nm and the shell thickness of about 50 nm were synthesized by a facile technique using carbon spheres as templates. The corresponding ZrO₂ hollow microspheres were obtained by calcining the precursors of C-Zr(OH)₄ core-shell heterostructures, which were synthesized with the precipitation of ZrCl₄ solution with aqueous ammonia on the surface of colloid carbons. SEM, XRD, TGA and BET were used to characterize the composition, morphology, size and crystal structure of synthesized products. The effects of ultrasonic dispersion and separation process on the hollow spheres were studied, and the surfactant PEG-1000 was added to tune the shell structure of synthesized ZrO₂ hollow spheres.     

Graphene-wrapped hybrid spheres of electrical conductivity

We present a simple approach for the fabrication of monodisperse electroconductive hybrid spheres using graphene sheet-wrapping via ionic interaction-based self-assembly. The graphene sheets partially charged with anion, which were prepared by controlled chemical reduction of graphite oxide, were mixed with monodisperse polymer nanospheres containing cationic surface charge to form ionic self-assembled hybrid spheres of core-shell structure. The resulting graphene-wrapped hybrid spheres were found to have graphene layer thickness of ca. 10 nm and to exhibit electrical conductivity of 1.33-4.21 S/m as well as monodisperse distributions in shape and diameter.