聚乙烯吡咯烷酮分子量对LiFePO4/C形貌及电化学性能的影响

以价廉、低毒的无机盐为原料、去离子水为溶剂,通过简易可行的络合溶胶-凝胶法合成了LiFePO4/C复合正极材料.利用XRD、SEM、EIS及恒流充放电测试考察了聚乙烯吡咯烷酮(PVP)分子量对试样的形貌及电化学性能的影响.结果表明,以PVP-k30为表面活性剂所合成的试样颗粒均匀细小、形貌较规则且单分散性良好;该试样具有优良的电化学性能,0.1C的放电比容量为155.7 mAh/g,3C倍率下放电比容量依然能保持112.4 mAh/g,明显优于其它分子量PVP所制备的试样.     

两步烧结法制备碳包覆的LiFePO4/C复合正极材料的研究

采用两步烧结法处理原位合成的碳包覆的LiFePO4/C复合正极材料,采用XRD、SEM对材料的结构及表面形貌进行了表征;通过CV、EIS及充放电测试仪进行电化学性能测试.结果表明,两步烧结法制备的材料具有良好的倍率性能及循环性能.0.2C时的首次放电比容量为142.5 mAh/g,循环30次后,放电比容量仍达到126.9 mAh/g;0.5 C时的首次放电比容量为122.9 mAh/g;1 C时的首次放电比容量为106.4 mAh/g;2 C时的首次充放电为81.3 mAh/g.     

Ti4+掺杂对磷酸钒锂材料结构和电化学性能的影响

分别采用溶胶-凝胶法和高温固相法制备锂离子电池正极材料Li3V1.93 Ti0 05(PO4) 3/C,研究Ti4+掺杂对Li3 V2(PO4)3材料结构、形貌和电化学性能的影响.结果表明:利用溶胶-凝胶法和高温固相法均得到单斜晶系结构,且无杂相存在,少量Ti4掺杂并未影响材料的结构形貌,但显著改善了电化学性能.溶胶-凝胶法掺杂Ti4+试样在0.2C和12 C放电比容量分别为129 mAh·g-1和102 mAh·g-1,明显高于高温固相法掺杂Ti4+试样,且循环性能良好.研究表明利用溶胶-凝胶法掺杂是一种改善离子掺杂效果的有效路径.     

基于聚合反应制备的钛离子掺杂LiFePO4/C复合材料

首先基于聚合反应合成FePO4/PANI前驱体,再以为LiOH·H2O,FePO4/PANI 和 PVA原料制备了LiFePO4正极材料,此外再对其进行碳包覆以及Ti4+掺杂,三种试样分别标记为LiFePO4,LiFePO4/C及LiFe0.96Ti0.02PO4/C.通过XRD、EDS及充放电测试等手段表征了材料的微观结构与电化学性能.实验结果证明:试样的XRD图谱均与标准LiFePO4图谱一致,不存在无定形碳衍射峰.与未掺杂试样LiFePO4/C相比,LiFe0.96Ti0.02PO4/C的电子电导率与其相近,但离子扩散系数有所改善,Ti4+在晶格中均匀分布,因此与其他两试样相比,其电化学性能更好.试样在C/10、C/2、1C、3C及5C倍率下的放电比容量为158.7 mAh·g-1、153.3 mAh·g-1、147.6 mAh·g-1、136.4 mAh·g-1及123.5 mAh·g-1,具有良好的倍率性能与电位稳定性.     

以酚醛树脂为碳源合成锂离子电池正极材料Li3V2 (PO4)3/C

以酚醛树脂为碳源,分别采用了固相法和溶胶凝胶法合成了锂离子电池正极材料Li3V2(PO4)3/C.结果表明,高分子材料酚醛树脂是一种优良的碳源材料,其热解后得到的导电网络能够有效的提高Li3V2(PO4)3的电化学性能;两种试样的充放电曲线和交流阻抗图谱体现出了试样良好的可逆性,其极化程度很低,电荷转移电阻小;而相对于固相法来讲,溶胶凝胶法和表面活性剂CTAB(十六烷基三甲基溴化铵)的共同作用能够有效的将颗粒粒径控制在纳米级别.用这种方法合成的试样在15 C下充放电比容量也能高于90 mAh/g,5C倍率下循环50次比容量无衰减,证明了以酚醛树脂为碳源并采用溶胶凝胶法合成的试样具有很好的倍率性能与循环性能.     

溶胶-凝胶法合成3LiMnPO4·Li3V2(PO4)3及其电化学性能研究

以柠檬酸为络合剂,聚乙二醇(PEG)为表面活性剂,偏钒酸铵、乙酸锰、磷酸二氢铵、氢氧化锂为原料,采用溶胶-凝胶法合成了xLiMnPO4·yLi3V2(PO4)3锂离子电池复合正极材料.采用X射线衍射(XRD)、扫描电镜(SEM)对其晶体结构和微观形貌进行表征,结果表明在700℃下烧结15 h合成的3LiMnPO4·Li3V2(PO4)3为结晶良好的两相结构,颗粒粒径相对较小且分布均匀.电化学性能研究表明,3LiMnPO4·Li3V2(PO4)3在室温0.2C倍率下首次充放电容量分别为148.2 mAh/g和141.5 mAh/g,循环50次后放电容量为136.7 mAh/g.     

LiFePO_(3.92)F_(0.08)/C的合成、表征和电化学性能研究（英文）

通过两步固相法反应制备LiFePO4/C和LiFePO3.92F0.08/C。采用XRD、红外(FTIR)、扫描电镜(SEM)、X射线能谱(EDS)对样品的结构和形貌进行分析。结果表明LiFePO3.92F0.08/C中有F的分布并且仍然保持橄榄石结构,但是具有了更好的倍率性能和循环稳定性能。LiFePO3.92F0.08/C在不同倍率下的首次放电比容量分别为154.9(0.2 C)、124.3(1 C)、83.2 mAh/g(10 C)。特别是在1 C倍率下循环30次后,放电比容量仍达122.1 mAh/g,容量损失仅为2.16%。F-掺杂能够提高材料电子电导率和锂离子扩散系数进而显著改善其电化学性能。     

柠檬酸含量对LiFePO4/C复合正极材料形貌及电化学性能的影响

采用水热-高温煅烧法制备了具有不同形貌的LiFePO4/C复合材料,探讨了柠檬酸含量对其形貌和电化学性能的影响.结果表明,柠檬酸的添加对LiFePO4/C复合材料的形貌具有显著的影响.通过添加柠檬酸调控LiFePO4/C复合材料的形貌,可以极大地改善LiFePO4/C复合材料的电化学性能.当柠檬酸与LiFePO4的摩尔比为1∶2时,LiFePO4/C复合材料呈纳米片状,颗粒粒径最小,比表面积最大,在0.1C和5C时放电比容量为160.3mA·h·g1和130.9 mA·h·g-1.     

镁、溴共掺杂对锂离子电池正极材料LiMn2O4电化学性能的影响

通过溶胶凝胶法制备出LiMn2O4和LiMn1.92 Mg0.08O3.84Br0.16锤离子电池正极材料,并用XRD、SEM、XPS、充放电测试和CV对其结构、形貌、化学成份以及电化学性能进行了研究.结果表明,Mg、Br的掺杂未改变LiMn2O4的结构.在0.5C倍率下,LiMn1.92Mg0.08O3.84Br0.16的放电比容量为119 mAh/g,与LiMn2O4相比,其首次放电比容量提高了3.6;,循环100次后,LiMn1.92Mg0.08O3.84Br0.16的容量保持率高达86.9;.在5C倍率下,LiMn192Mg0.08O384Br0.16的放电比容量为91.1 mAh/g,比LiMn2O4提高了24.1;.实验表明,Mg、Br共同掺杂提高了LiMn2O4的放电比容量,并明显改善其循环稳定性和倍率性能,从而获得了较好的综合电化学性能.     

Co掺杂对富锂锰基正极材料Li1.2Ni0.2Mn0.6O2电化学性能的影响

本文以醋酸盐为原料,采用溶胶凝胶法制备富锂锰基固溶体正极材料Li1.2Ni0.2Mn0.6O2.研究Co掺杂后对Li1.2 Ni0.2-x/2Mn0.6-x/2 CoxO2(x=0,0.01,0.02,0.05)材料结构以及电化学性能的影响.XRD和SEM测试表明:Co掺杂后样品结构未发生改变,均属于富锂锰基正极材料.电化学测试表明:Co掺杂能改善材料的倍率性能,提高材料的放电比容量.其中,x=0.02的材料Li1.2Ni0.19Mn0.59Co0.02O2具有最优异的电化学性能,0.05 C下的首次放电比容量由未掺杂的的217 mAh·g-1提升至332.6 mAh·g-1;0.1 C下经40次循环后放电比容量为171.6 mAh·g-1,保持率为85.5;.     

Modelling of mechanism of agglomeration of KCl crystallization

The article presents an analysis into agglomeration during KCl vacuum crystallization. The theoretical and experimental investigations into the mechanism of agglomeration during mass crystallization result in an extension of the growth phenomena within the known model equations. The basis for this is essentially constituted by the collision model concepts of the theory of floculation in disperse systems. The parameters derived from the microprocess analysis (energy dissipation, content of solids, growth rate of individual grains) lead to model equations which are confirmed by laboratory and test trials.     

Relationship of Morphological Types of Dynamic Forms of Crystals

Crystallography Reports - The relationship of morphological spectra (sets of data on the morphological types of real polyhedral crystals and their probabilities under current physicochemical...     

Velocities of Disappearance and Lifetime of Faces of Growing Crystals

The formulae for absolute R_disap and relative R velocities of disappearance and lifetime τ of faces of growing crystals have been derived for stationary growth. It was shown that the quantities are determined by the relative growth velocity R_A/R_critA of the vanishing face A with respect to the critical growth velocity R_critA and by the geometry of a crystal expressed by the trigonometric functions of interfacial angles β and γ formed between face A and the adjacent faces. R increases and τ decreases with the increase in R_A/R_critA to certain limiting values. The calculations have been verified and illustrated by the experimental results for triclinic potassium bichromate (KBC) crystals. Results enable ones to predict values of velocities of disappearance and lifetimes of undesirable, supplementary faces of any real crystal.     

Development of Pauling's concepts of geometric characteristics of atoms

The evolution of the geometric characteristics introduced by Pauling and their dependence on the specific features of the structure and chemical bonds have been considered. The values of the covalent and van der Waals radii are given as well as their relationships and mutual transitions.     

Comparative analysis of two methods of calculation of the orientation of domain walls in ferroelastics

Two types of domain-wall equations are analyzed: the equations derived by the Sapriel method and the equations obtained by interface matching of the thermal-expansion tensor. It is shown that, for W-type domain walls, these methods yield the same equations. For W′-type domain walls, the equations obtained by different methods coincide for proper ferroelastics and differ for improper ferroelastics.     

Dependence of the parameters of equations of viscous flow on chemical composition of silicate melts

The temperature dependence of viscosity of silicate melts is discussed in the framework of the Avramov–Milchev (AM) equation. The composition is described by means of two parameters: the molar fraction, x, and the “lubricant fraction”, l. The molar fraction is the sum of the molar parts x_i of all oxides dissolved in SiO₂, the molar fraction of the latter being 1 ? x. It is shown that, with sufficient precision, two of the parameters of the AM equation can be presented as unique functions of the molar fraction. On the other hand, x is not sufficient to determine properly the reference temperature T_r , at which viscosity is η_r = 10¹³ [dPa.s]. Therefore, additional parameter, “lubricant fraction” l, is introduced. For each of the components, l_i is a product of molar part x_i and a specific dimensionless coefficient 0 ≤ k_i ≤ 1 accounting for the specific contribution of this component to the increased mobility of the system. It is demonstrated that, for l > 0, the reference temperature is related to the “lubricant fraction” l through the reference temperature T_r,SiO2 of pure SiO₂.     

A review of measurement of thermophysical properties of silicon melt

Measurements of thermophysical properties of Si melt and supplementary study of X-ray scattering/diffraction by the authors' group were reviewed. The values obtained differed variously from those of literature. Density was 2–3% larger, surface tension 20–30% smaller, viscosity up to 40% larger, electrical conductivity 8% smaller, spectral emissivity more or less in good agreement with literature values, and thermal diffusivity a few percent larger. An anomalous density jump was found near the melting point. Surface tension and viscosity also showed anomaly. A strange time-dependent change of density was observed over 3 h after melting. X-ray analyses suggested a slight change in local atom ordering, but showed no sign of cluster formation. An addition of 0.1 at% gallium caused the density jump to disappear, while that of boron caused no change. An EXAFS study of the former melt indicated a strong interaction between Ga and Si atoms as if molecules of GaSi₃ existed. The implications of the measured properties are a possibility of soft-turbulence in an Si melt in a relatively large crucible, a more complicated manner of intake of oxygen depleted molten Si from the free surface region to underneath the growing crystal, and a relaxation of the melt after melting arising from trapped gas species.     

Generation of crystal structures of heteromolecular compounds by the method of discrete modeling of packings

Within the method of discrete modeling of packings, an algorithm of generation of possible crystal structures of heteromolecular compounds containing two or three molecules in the primitive unit cell, one of which has an arbitrary shape and the other (two others) has a shape close to spherical, is proposed. On the basis of this algorithm, a software package for personal computers is developed. This package has been approved for a number of compounds, investigated previously by X-ray diffraction analysis. The results of generation of structures of five compounds—four organic salts (with one or two spherical anions) and one solvate—are represented.