晶体的择优取向与LiCoO2正极材料X射线衍射峰的强度比

采用高温固相反应法合成了锂离子电池正极材料LiCoO2, 用粉末X射线衍射(XRD)和扫描电子显微镜(SEM)等技术对材料的形貌与结构进行分析. 平面反射和透射X射线粉末衍射数据表明, 目前商品LiCoO2样品XRD图谱的(104)和(003)衍射峰强度比(I(104)/I(003))主要反映了LiCoO2晶体c轴方向的择优取向, 而不是Li、Co原子的占位有序程度. I(104)/I(003)比值越小, 晶体择优取向度越高. 晶体无择优取向LiCoO2粉末材料的衍射峰强度比I(104)/I(003) 应为95%左右. 因此, 不能用I(104)/I(003) 的比值大小作为实际LiCoO2材料晶体内Li、Co 原子排列是否有序的主要证据. 澄清了长期有争议的关于锂离子二次电池正极材料LiCoO2的X射线衍射峰强度比问题.     

Spontaneous formation and characterization of silica mesoporous crystal spheres with reverse multiply twinned polyhedral hollows

A crystal is an object with translational symmetry. Basic research into and production of new materials necessitates the preparation of crystals of a particular morphology and with well-defined crystal defects. In this work, we found novel silica mesoporous crystal spheres with polyhedral hollows (icosahedral, such as those observed for proteins of virus capsids, decahedral, Wulff polyhedral, etc.) formed by the reverse multiply twinned bicontinuous double diamond mesostructure. Vesicles with a low-curvature lamellar structure were first formed by the self-assembly of amphiphilic carboxylic acid molecules in the presence of a nonionic surfactant and then underwent a structural transformation process that gave a reverse multiply twinned mesoporous shell while maintaining the hollow shape. These polyhedral hollow crystals showed an enhanced contrast of backscattering signatures relative to the incident acoustic signals and thus could be used as a potential contrast agent in medical ultrasonography with drug loadings in the mesopores.     

柠檬酸溶胶凝胶法制备LiCoO_2电极材料及其表征

目前研究较多的锂离子电池正极材料主要有LiCoO2、LiNiO2和LiMn2O4犤1犦,虽然LiCoO2的成本相对较高,但LiCoO2具有最为优良的电化学性能,如高且平稳的充放电平台、高比容量以及良好的循环性能犤2犦,是目前应用最广泛的商品化电极材料。LiCoO2材料主要采用高温固相法犤3～5犦制备,该方法工艺简单,容易实现大规模生产,但缺点是需要较高的焙烧温度和较长的焙烧时间,且反应原料混合均匀程度有限,易导致非化学计量、非均相以及不规则的颗粒形貌等,因此材料的比容量、循环寿命等电化学性能以及反应的可控性还不甚理想。研究表明犤6犦电极材…     

Markov-type evolution of materials into a polar state

Assembling polar building blocks into a solid material by a Markov-chain process of unidirectional growth principally results in a metastable state that shows effects of macroscopic polarity. Stochastic polarity formation can be described by probabilities for the attachment of building blocks to a surface. Because of the polar symmetry of the building blocks, there is a fundamental difference in the probabilities for attaching them "tip-first" or "back-first" to growth sites at a surface. A difference in the corresponding probabilities drives the evolution of a vectorial property through a gain in configurational entropy. Examples from the mechanical, the crystalline and the biological world demonstrate growth-induced macroscopic polarity. In crystals, growth upon centrosymmetric seeds can produce twinned crystals with a "sectorwise" pyroelectric effect. Polarity formation in connective tissues is explained by a Markov-chain mechanism, which drives the self-assembly of collagen fibril segments. An unified stochastic growth model brings up a general concept for the formation of materials with polar properties.     

Single-crystal mesostructured semiconductors with cubic Ia3d symmetry and ion-exchange properties

If the full scientific and technological potential of mesostructured materials is to be achieved, systems with continuous domains in the form of single crystals or films must be prepared. Here we report a reliable and facile system for making large single-crystal particles of chalcogenido mesostructured materials with a highly organized cubic structure, accessible pore structure, and semiconducting properties. Building blocks with square planar bonding topology, Pt(2+) and [Sn(2)Se(6)](4)(-), in combination with long-chain pyridinium surfactants (C(n)PyBr, n = 18, 20) favor faceted single-crystal particles with the highest possible space group symmetry Ia3d. This is an important step toward developing large single-domain crystalline mesostructured semiconductors and usable natural self-assembled antidot array systems. The tendency toward cubic symmetry is so strong that the materials assemble readily under experimental conditions that can tolerate considerable variation and form micrometer-sized rhombic dodecahedral cubosome particles. The c-C(n)PyPtSnSe materials are the first to exhibit reversible ion-exchange properties. The surfactant molecules can be ion-exchanged reversibly and without loss of the cubic structure and particle morphology. The cubosomes possess a three-dimensional open Pt-Sn-Se framework with a low-energy band gap of approximately 1.7 eV.     

Metastable Self‐Assembly of Theta‐Shaped Colloids and Twinning of Their Crystal Phases

Anisotropic colloids self‐assemble into different crystal structures compared to spherical colloids. Exploring and understanding their self‐assembly behavior could lead to creation of new materials with hierarchical structures through a bottom‐up process. Herein, we report metastable self‐assembly of theta‐shaped SiO₂ colloids interacting with a depletion force in a quasi‐two‐dimensional space and we demonstrate that both a metastable “prone” crystal phase and a stable “standing” crystal phase can be formed, depending on the self‐assembly path. Path selection stems from an interplay between particle–particle interactions and particle–wall interactions. In particular, a twinning of the metastable crystals was observed and two twinning mirror axes were found. A variety of complex twinned crystals were formed by each individual mirror axis or their combinations.     

Achiral Calcium‐Oxalate Crystals with Chiral Morphology from the Leaves of Some Solanacea Plants

The leaves of some plants, particularly among the Solanacea, contain crystals of calcium oxalate with a peculiar chiral pseudo‐tetrahedral morphology, even though the calcium oxalate crystal structure is centrosymmetric, hence achiral. We studied the morphology of these crystals extracted from the leaves of three Solanacea plants: the potato, the hot pepper, and a species of wild Solanum. The crystal morphology was the same in all three species. Based on the examination of more than 100 crystals from each plant, we showed that the crystal morphology is chiral with invariant chirality. We suggest that morphological chirality is induced by macromolecules during nucleation from a specific, genetically encoded crystal plane, and is further established during subsequent controlled crystal growth. This is one of few examples where it is possible to deduce a molecular mechanism for biologically induced breaking of morphological symmetry in organisms. A very high level of recognition is required by the macromolecules to allow them to distinguish between symmetry‐related crystal planes. It is also surprising that this finely controlled mechanism of crystal formation, including the chiral morphology, has been conserved during evolution.     

Effect of Additional Poly Vinyledene Fluoride (PVDF) on LiCoO2 Cathodes

LiCoO2 as one of cathodes in lithium ion battery was prepared using ball mill on 800 Hz for 10 h, followed by ultra–sonic process in order to form LiCoO2 nanoparticle. Poly(vinyledene fluoride) PVDF was added into LiCoO2 nanoparticle using dimethylsulfoxide (DMSO) to form LiCoO2/PVDF composite. The addition of PVDF was able to fill the voids on LiCoO2 matrix, therefore the space gap between particles in the matrix could be eliminated. The morphology, crystal structure and composite conductivity of LiCoO2/PVDF were analysed using scanning electron microscope (SEM), X-ray diffraction (XRD) and conductivity meter. The results showed that LiCoO2 with PVDF had bigger conductivity value than LiCoO2 without PVDF.     

Unidirectional crystallization of charged colloidal silica due to the diffusion of a base

Dilute aqueous dispersions of charged colloidal silica (particle volume fraction = approximately 0.03-0.04, particle diameter = 110 nm) exhibit unidirectional crystal growth due to the diffusion of a weak base, pyridine (Py). Similar diffusion-crystallization is enabled by a salt of a weak acid and a strong base, sodium hydrogen carbonate (NaHCO3). The resulting crystals consist of columnar (or cubic) crystal grains with a maximum height of a few centimeters and a maximum width of 1 cm. The crystal growth process is attributed to a combination of (i) the diffusion of Py or NaHCO3 accompanied by a charging reaction of the silica particles and (ii) the charge-induced crystallization of the silica colloids. Theoretical growth curves based on the reaction-diffusion model for the case of Py were in good agreement with the observed curves. We also report the immobilization of the resulting large crystals by using a polymer hydrogel matrix.     

液晶自组装多层级结构及其应用

液晶的分层组装与刺激响应特性使其在先进功能材料的开发与应用领域具有独特的优势.通过特定的技术手段诱导其自组装行为,可带来新奇的光学、机械、电磁等性能,进而实现一系列全新的技术应用.本文主要针对近晶相、胆甾相、蓝相这三种特殊的液晶相态,系统介绍了多形态焦锥畴结构,分层油纹,螺旋结构,双螺旋扭曲柱立方晶格等多层级结构,重点论述了材料组分优化,几何结构限制以及外场激励等条件下液晶多层级结构的大面积精细操控,回顾了其在粒子操控、表面改性、光子技术等领域的相关技术应用,并总结展望了液晶组装技术与应用的发展前景.     

LiCoO2掺杂对锰酸锂结构和性能的影响

用固相反应合成了LiCoO2掺杂改性的LiMn2O4锂离子电池正极材料,优化了LiMn2O4的改性路径及制备条件.利用SEM、XRD对产物的结构进行了表征,并测试了产物的电化学性能.结果表明:所得产物均具有尖晶石型LiMn2O4结构.LiCoO2的掺入增加了尖晶石结构的稳定性,改善了尖晶石型LiMn2O4的充放电循环性能.     

基片温度对LiCoO2薄膜结构与电化学性能的影响

采用射频(RF)磁控溅射技术制备了用于全固态薄膜锂电池的非晶态和多晶LiCoO2阴极薄膜,利用XRD和SEM研究了沉积温度对LiCoO2薄膜结构和形貌的影响,并研究了高温退火后薄膜的电化学性能.研究结果表明,随著基片温度的不同,薄膜成分、表面形貌以及电化学行为有明显差异.室温沉积的薄膜很难消除薄膜中Li2CO3的影响,经过高温退火处理后也无法形成有效的多晶LiCoO2薄膜,而150℃沉积的薄膜经过高温退火后形成了有利于锂离子嵌入的多晶LiCoO2结构,薄膜显示出了较好的电化学性能.     

Influences of different cobalt sources on the properties of synthesized LiCoO2

Since 1991, LiCoO2 used as cathode material of lithium-ion rechargeable batteries has attracted much attention in the industry of portable power apparatus such as mobiles, laptops and camcorders, etc. However, the production technologies of LiCoO2 have always been possessed by the foreign corporations. Although a plenty of research work has been performed in domestics, it is almost impossible to surpass the technological rampart, which renders our state to subject to much foreign exchange consumption.Many preparation methods such as solid state reaction, sol-gel process and hydrothermal synthesis et al have been reported in the literature. Via our studies, it is found that in the process of LiCoO2 synthesis not only lithium sources but also cobalt sources can play an important part in the physical and electrochemical properties, and also have a remarkable influence on the properties of LiCoO2.But as for the different synthesis methods, the necessary cobalt source is different, and as for the same synthesis method, the LiCoO2 prepared with different cobalt sources has different electrochemical performance.So far, the detailed findings on the LiCoO2 cathode material synthesized with various cobalt sources have not been reported yet in the literature. In this paper, the following work has been carried out.The LiCoO2 cathode material was synthesized by liquid-phase soft-chemistry process and solid state reaction at higher temperature with different cobalt sources respectively, and characterized by XRD, BET, SEM, TEM, laser particle size distribution and electrochemical testing. Its properties were compared. The effects of different cobalt sources, aqueous ammonia and ethanol additives on the physical and electrochemical properties of LiCoO2 cathode materials were investigated. The results have demonstrated that the different cobalt sources, aqueous ammonia and ethanol additives have remarkable influences on the physical and electrochemical properties of LiCoO2 cathode material. When liquid-phase soft-chemistry process is used to synthesize LiCoO2 cathode material,most excellent cobalt source when high-temperature solid state reaction method is used to prepare LiCoO2 cathode materials. The optimal sintering temperature range is 800℃～820 ℃ when liquid-phase soft-chemistry process is used to synthesize LiCoO2 cathode materials. Liquid-phase soft-chemistry process is superior to high-temperature solid state reaction method when LiCoO2 cathode materials is prepared.     

Novel application of LiCoO_2 as a high-performance candidate material for supercapacitor

Electrochemical performances of LiCoO2 as a candidate material for supercapacitor are systematically investigated. LiCoO2 nanomaterials are synthesized via hydrothermal reaction with consequent calcination process. And the particle size increases as the calcination temperature rises.LCO-650 sample with the largest particle size displays the maximum capacitances of 817.5 Fg-1with the most outstanding capacity retention rate of 96.8% after 2000 cycles. It is shown that large particle size is beneficial to the electrochemical and structural stability of Li CoO2 materials. We speculate that the micron-sized waste LiCoO2 materials have great potential for supercapacitor application. It may provide a novel recovered approach for spent LIBs and effectively relieve the burdens on the resource waste and environment pollution.     

Polymer-controlled crystallization of zinc oxide hexagonal nanorings and disks

In this study, we have developed a novel route to the synthesis of ZnO nanorings, disks, and diskoidlike crystals on a large scale by a facile solution-based method by using polymers as crystal growth modifiers. The crystals precipitated with polyacrylamide (PAM) as the additive show ringlike morphology. A possible growth mechanism of the ZnO nanostructures based on typical polymer-crystals interactions in a mild aqueous solution is given. The polymer contains in the side chain a large number of amide ligands that are able to coordinate with Zn(2+) ions, that is, the otherwise just weakly exposed (001) face, leading to a lowering of surface energy and inhibition of growth along this direction and the formation of ringlike morphologies. While in the presence of carboxyl-functionalized polyacrylamide (PAM-COOH), nearly monodispersed disklike crystals were observed and finally evolved into diskoidlike microstructures with the reaction time prolonged. Polymer-directed crystal growth and mediated self-assembly of nanocrystals may provide promising routes to rational synthesis of various ordered inorganic and inorganic-organic hybrid materials with complex form and structural specialization.     

Twinned dichlorobis(2,6-dichloropyrazine-N4)zinc(II)

For crystals of the title compound, [ZnCl₂(C₄H₂Cl₂N₂)₂], metric considerations suggest a monoclinic unit cell. However, the symmetry of the diffraction pattern shows the crystals to be triclinic, with very similar lattice constants a and b, and α and β. All crystals ex­amined were twinned. The discrepancy between the reliability indices for merging in the monoclinic lattice metric symmetry and the triclinic crystal symmetry constitutes an indicator for the volume ratio between the components. The asymmetric unit contains three independent mol­ecules. At the molecular level, the compound shows a distorted tetrahedral coordination around one Zn atom.     

Phase diagram of spherical particles interacted with harmonic repulsions

We construct the phase diagram of spherical particles interacted with harmonic repulsions, which are ultrasoft and bounded at fully overlapping. This simple potential form can be used for describing the thermodynamic properties and dynamic behavior of interpenetrable globular micelles, microgels, starlike polymer solutions, and so on. Using dissipative particle dynamics simulations combined with thermodynamic integration, we compute chemical potentials of fluid phase and a number of crystal structures. In addition to the face-centered cubic and body-centered cubic structures, we also find the tetragonal, hexagonal, orthorhombic, and diamond crystal structures stable for this system. In the phase diagram, we identify multiple re-entrant melting regions and polymorphic transitions between the crystals.     

Facile preparation of macroscopic soft colloidal crystals with fiber symmetry

A facile, efficient way to fabricate macroscopic soft colloidal crystals with fiber symmetry by drying a latex dispersion in a tube is presented. A transparent, stable colloidal crystal was obtained from a 25 wt % latex dispersion by complete water evaporation for 4 days. The centimeter-long sample was investigated by means of synchrotron small-angle X-ray diffraction (SAXD). Analysis of a large number of distinct Bragg peaks reveals that uniaxially oriented colloidal crystals with face-centered cubic lattice structure were formed. The measurement of evaporation rates under different conditions indicates that the water evaporates primarily through the optically clear regions (i.e., via the solid material) even when the region is more than 2 mm thick.     

Structure modification in crystallizations according to molecular dynamic simulations of NaCl clusters

A simulation of crystallization and a structural study of an overcooled NaCl melt are reported. A criterion is suggested for classifying the structural states of ions in the transition mode of nucleation. It is shown that in the bulk of overcooled liquid, short-lived crystal phase germs appear and vanish. A distribution of the critical clusters according to form and size was found. It was assumed that crystal growth occurred by collective synchronization of particle motions in crystal and liquid near the interface. The NaCl nanocrystals formed during nucleation are cubic crystals with clear-cut faces and edges. Overcooling the liquid to a greater extent led to the formation of defective polycrystalline structures.     

Mechanism of pore formation and structural characterization for mesoporous Mg-Al composite oxides

Mg-AI layered double hydroxides (LDH) with different particle sizes were prepared using different aging times at high supersaturation by a new method developed in our laboratory. The key features of this method are a very rapid mixing and nucleation process followed by a separate aging process. By calcination of LDH at 500癈, mesoporous Mg-AI composite oxides with an extremely narrow pore size distribution were produced. The crystal structure of the Mg-AI composite oxides was a multiphasic one consisting of MgO-like crystals and a layered material.