一种应用前景可观的新能源材料——尖晶石型Li4Ti5O12 *

各种锂离子电池电极材料作为十分重要的新能源材料近些年来受到前所未有的广泛关注。负极材料尖晶石型Li₄Ti₅O₁₂由于其特殊的“零应变”性等优良性质越来越多地受到研究者的青睐,成为一种应用前景可观的锂离子电池用负极材料。同时,其很多性能也很符合电动汽车用储能器件对电极材料的要求,也被研究用于新近提出的非对称超级电容器中。本文介绍了Li₄Ti₅O₁₂的结构和性能;从制备方法（溶胶-凝胶法、固相合成法等）、掺杂改性和与其他材料复合等几个方面介绍了国内外关于Li₄Ti₅O₁₂的制备和改性方面的研究进展;并对Li₄Ti₅O₁₂在各种器件中的应用研究进展做了介绍。     

不同取代位掺杂对Li4Ti5O12结构及性能的影响

锂离子负极材料Li₄Ti₅O₁₂具有资源与性能等方面的优势,正在成为新一代储能和动力领域的研究重点.本文综述了掺杂离子在晶格中所处的不同取代位置及本身性质对Li₄Ti₅O₁₂结构和性能的影响.取代Li的位于四面体(8a)位置的掺杂元素阻碍锂离子的扩散;取代Li的位于八面体(16d)位置的掺杂元素会影响Li离子在晶格中的分布;取代Ti的位于八面体(16d)位置的掺杂元素会影响Li₄Ti₅O₁₂的结构稳定性;取代O的位于八面体(32e)位置的掺杂元素会影响Li₄Ti₅O₁₂的导电性.一定条件下在Li₄Ti₅O₁₂中掺入高价态的元素取代Li⁺、Ti⁴⁺、O^2-,均能提高Li₄Ti₅O₁₂电子导电能力.掺杂元素各异的能带结构和氧化还原行为会影响Li₄Ti₅O₁₂的电化学反应过程.掺杂元素的离子半径和最终能够进入晶格的数量会改变Li₄Ti₅O₁₂的晶格常数和微观组织形貌.     

锂离子电池负极材料Li4Ti5O12的合成及性能研究

本文通过乙酸锂与二氧化钛反应,采用一步高温固相法在不同反应温度（750 °C/800 °C/850 °C）和反应气氛（氮气/空气）下合成Li₄Ti₅O₁₂材料. 通过热重分析、X射线衍射、扫描电子显微镜、循环伏安曲线和充放电曲线分析了Li₄Ti₅O₁₂的晶体结构,观察其微观形貌,并测试其电化学性能. 结果表明,800 °C氮气烧结得到的Li₄Ti₅O₁₂（L-800N）材料粒径较小,该材料在1.0C倍率下的首周期放电比容量达到170.7 mAh·g^-1,100周期循环后的容量保持率高达94.6%,即使是10C高倍率其首周期放电容量依然有143.0 mAh·g^-1,表现出了良好的倍率和循环寿命性能.     

锂离子电池负极材料碳氮包覆钛酸锂的制备及表征

以钛酸正四丁酯为钛源、甲酸锂为锂源、柠檬酸为碳源、脲作为氮源,采用溶胶-凝胶法制备出了氮修饰碳包覆钛酸锂(Li₄Ti₅O₁₂/NC)的复合电极材料。 借助X射线衍射仪(XRD)、X射线光电子能谱分析仪(XPS)、傅里叶变换红外光谱仪(FTIR)、热重分析仪(TGA)、扫描电子显微镜(SEM)和透射电子显微镜(TEM)对Li₄Ti₅O₁₂/NC的晶体结构、组成和形貌进行了表征分析,结果表明,所得产物是由尖晶石结构Li₄Ti₅O₁₂外围包覆NC组成。 恒电流充放电实验结果显示,碳氮包覆量为9.48% 的Li₄Ti₅O₁₂/NC材料在1C下首次放电比容量为212.9 mA·h/g,充放电循环100周后仍能保持160.1 mA·h/g的较高比容量。 碳氮包覆不会改变材料的晶型,但能有效抑制复合材料粒径增大,同时增加复合材料锂脱嵌活性位点,提高其比容量和导电性。     

铝掺杂及钨酸锂表面包覆双效提升富锂锰基正极材料的循环稳定性

采用溶胶-凝胶法合成Al掺杂富锂锰基Li_1.2Mn_0.54-xAl_xNi_0.13Co_0.13O₂（x=0、0.03）锂离子电池正极材料,之后采用一步液相法制备Li₂WO₄包覆层,系统地研究了Al掺杂和Li₂WO₄包覆双效改性对富锂锰基正极材料电化学性能的影响.结果表明,Al掺杂后明显提升富锂锰基正极材料的循环稳定性,包覆层Li₂WO₄明显改善其倍率性能和放电平台电压衰减问题.Li₂WO₄包覆量为5% Li_1.2Mn_0.51Al_0.03Ni_0.13Co_0.13O₂正极材料在2.0~4.8 V充放电电压区间及1000 mA·g^-1电流密度下比容量仍高达110 mAh·g^-1左右,同时在100 mA·g^-1的电流密度下循环300次容量保持率为78%,而且循环过程中放电平台电压衰减也明显减缓.该工作为解决锂离子电池富锂锰基正极材料循环稳定性和平台电压衰减提供了新的思路.     

反应物分散条件对Li1+xV3O8电化学性能的影响

以Li₂CO₃和NH₄VO₃为原料,在不同条件下合成了锂离子电池正极材料用Li_1+xV₃O₈。研究了反应物的分散条件和煅烧温度对产物晶型结构、形貌及电化学性能的影响。 XRD、IR和SEM结果表明,用超声波在无水乙醇中分散反应物得到的前驱体于550 ℃下煅烧,所得产物Li_1+xV₃O₈结晶度低、粒径小、形貌均匀。 充放电、循环伏安等结果表明,该材料在充放电过程中极化低、嵌脱锂位置多、循环稳定性好。 在0.5 C放电条件下,第2次循环放电容量达到268 mA·h/g,100次循环后容量仍保持210 mA·h/g以上。     

LiV3O8在Li2SO4水溶液中的电化学性能

采用低温固相法合成了具有纳米结构的LiV₃O₈材料.扫描电子显微镜（SEM）及透射电子显微镜（TEM）测试显示该材料具有纳米结构.X射线衍射（XRD）表明该材料属于单斜晶系,P2₁Im空间群.并采用循环伏安法（CV）及电化学阻抗谱图测试对该材料在1、2 mol·L^-1Li₂SO₄水溶液及饱和Li₂SO₄水溶液中的电化学行为进行了研究.结果表明,LiV₃O₈在饱和Li₂SO₄水溶液中具有最好的电化学性能.以LiV₃O₈作为负极材料,LiNi_1/3Co_1/3Mn_1/3O₂作为正极材料,饱和Li₂SO₄水溶液作为电解液组成了水性锂离子电池,进行恒流充放电测试,结果表明,在0.5C(1C=300 mA·g^-1)的充放电倍率下,该水性锂离子电池的首次放电比容量为95.2 mAh·g^-1,循环100次后仍具有37.0 mAh·g^-1的放电比容量.     

锂离子电池正极材料Li[Li0.2Mn0.54Ni0.13Co0.13]O2的合成及电化学性能研究

以LiOH•H₂O, Ni₂O₃, Co₃O₄和MnO₂为原料, 经过机械活化后在空气气氛下经高温烧结, 合成了锂离子电池正极材料Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂. 通过X射线衍射(XRD)、扫描电子显微镜(SEM)和电化学性能测试对所得样品的结构、形貌及电化学性能进行了表征. 结果表明, 900 ℃下烧结10 h后可获得晶粒细小均匀的层状Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂材料, 并具有良好的电化学性能, 在室温下以60 mA/g的电流充放电, 首次放电比容量可达到248.2 mAh/g, 循环50次后放电比容量为239.4 mAh/g, 容量保持率为96.45％. 测试了该材料的高低温循环性能.     

锂离子电池负极材料用Co3O4及其复合材料研究进展

锂离子电池的性能主要由正、负极材料决定,负极材料Co₃O₄具备理论容量高、振实密度大、化学性质稳定等特点倍受关注,但存在导电性不好、倍率性能较差等缺点. 解决该问题的手段：一方面可通过材料的纳米化与特殊形貌化如球状、纤维状、片状等,缩短锂离子嵌入和脱出行程;另一方面可通过材料的复合化,促进电子的快速传输和缓冲活性材料在充放电过程中的体积效应. 根据Co₃O₄颗粒的形貌特性对现有研究进行了分类与综述,阐述了改性手段的可能性机理,并对如何提高Co₃O₄的电化学性能提出了一些想法.     

锂离子电池高容量合金基含锂负极材料的研究进展

现有的以石墨为负极的锂离子电池能量密度逐渐接近其理论极限. 基于合金化反应机制的高容量含锂负极材料Li_xM_y(M为能够和锂发生合金化反应的元素)是一类新兴的负极材料, 具有数倍于石墨的储锂比容量, 且可以为电池提供活性锂源. 这些特性使其能够与高容量无锂正极材料(如S, O₂, FeF₃和V₂O₅等)相匹配, 构建下一代高比能锂离子电池新体系. 本文综述了近年来高容量合金基含锂负极材料(如Li_xSi, Li_xSn, Li₃P和Li_xAl基系列材料)的研究进展, 分析了所面临的挑战, 概述了材料的合成与电极的制备方法, 并介绍了它们在常规锂离子电池、 锂离子-硫电池及锂离子-空气电池等多个全电池体系中的应用实例, 提出并举证了其电化学性能优化与调控的策略, 最后展望了未来的研究方向.     

二氧化碳和丙烯直接合成甲基丙烯酸的NiPMo/TiO2催化剂的研究

用溶胶-凝胶法以磷钼酸(MPA)的镍盐溶液水解钛酸四丁酯制备了NiPMo/TiO2催化剂.使用ICP、 XRD、 TG-DTA、 IR、 TPD-MS和微反应技术研究了催化剂的化学组成、热稳定性、化学吸附性质和催化反应性能.杂多钼酸盐与TiO2通过O2-在TiO2表面发生了键合.在623 K下,杂多阴离子仍保持原有的Keggin结构.CO2在Lewis酸位Ni(Ⅱ)和Lewis碱位Ni-O-Mo的桥氧协同作用下生成CO2卧式吸附态Ni(Ⅱ)←O-(CO)←(O--Ni).丙烯有多种吸附态在催化剂上吸附.在563 K、 1 MPa和空速1500 h-1的反应条件下,丙烯的摩尔转化率为3.2%,产物MAA选择性为95%.     

Toward new camptothecins. Part 6: Synthesis of crucial ketones and their use in Friedländer reaction

In the context of the preparation of camptothecin and luotonin A analogs, the synthesis of some key keto-precursors and their use in Friedländer condensation are described. This paper also focuses on the stability of these keto intermediates and emphasizes the major differences between indolizinones and pyrroloquinazolinones series. Noteworthy is also the report of some original structures isolated as by-products of some experiments.     

α-Amino acid derived enaminones and their application in the synthesis of N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates and other heterocycles

A new and simple synthesis of novel N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates, which exist in equilibrium with their 4-oxo tautomers, has been developed in two steps starting from N-protected α-amino acids. The key intermediates are enaminones, which can also be isolated, characterized, and used for the construction of other functionalized heterocycles, before they spontaneously decompose to pyrrole products. 4-Hydroxypyrroles are prone to partial aerial oxidation but can be efficiently alkylated or reduced to stable polysubstituted pyrrolidine derivatives.     

Specific intramolecular aromatic CH insertion of diazosulfonamides

The chemoselectivity in the intramolecular CH insertion of various diazosulfonamides has been experimentally studied. The results reveal that the aliphatic 1,4-, 1,5-, or 1,6-C(sp³)?H insertions of diazosulfonamides are not accessible, while the aromatic 1,5-C(sp²)?H insertion can be realized specifically by adjusting the diazo-adjacent group. In addition, the general chemoselectivities in the intramolecular CH insertions of diazosulfonyl compounds are summarized. Generally, diazosulfones undergo both aromatic 1,5-C(sp²)?H and aliphatic 1,5- and 1,6-C(sp³)?H insertions, while diazosulfonates undergo aliphatic 1,5- and 1,6-C(sp³)?H insertions. However, diazosulfonamides only undergo aromatic 1,5-C(sp²)?H insertion.     

CoFe2O4自形成磁性液体场致结构化对磁化的影响

The Langevin paramagnetic theory can’t describe the relation between magnetization of ferrofluids and applied magnetic field. The structuralization of ferrofluids, which is considered the main influence factor of the magnetization, is regarded. The part of magnetization works is deposited when the structure is forming. This action influences the magnetization of ferrofluids directly or indirectly. On the base of the “compressing” model, the Langevin function that usually describes the magnetization of ferrofluid is modified, and a well-fitted curve is obtained. An equation of the relation between the equivalent volume fraction after being “compressed” and the intensity of magnetic field is discovered, which approximately describes the process of magnetization. The relation between the approximate initial susceptibility and the volume fraction can be obtained from modified formula.     

KMnO4-mediated oxidative CN bond cleavage of tertiary amines: Synthesis of amides and sulfonamides

KMnO₄-mediated oxidative CN bond cleavage of tertiary amines producing secondary amine was introduced, which was trapped by electrophiles (acyl chloride and sulfonyl chloride) to form amides and sulfonamides. The reaction could take place at mild condition, tolerating a wide range of function groups and affording products in moderate to excellent yields.     

Highly regioselective Buchwald–Hartwig amination at C-2 of 2,4-dichloropyridine enabling a novel approach to 2,4-bisanilinopyridine (BAPyd) libraries

The highly regioselective Buchwald–Hartwig amination at C-2 of the cheap and readily accessible reagent, 2,4-dichloropyridine with a range of anilines and heterocyclic amines is described. This new methodology is robust and provides a facile access to 4-chloro-N-phenylpyridin-2-amines on 0.25 mol scale. These intermediates undergo a further Buchwald–Hartwig amination at higher temperature to enable rapid exploration of the chemical space at C-4 and to provide a library of 2,4-bisaminopyridines.     

Chemistry of heterocyclic compounds at the A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences, over 50 years (Review)

The review contains a concise historical account and information on the most significant researches undertaken by the staff at the A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences on the Chemistry of Heterocyclic Compounds. Dedicated to Academician of the Russian Academy of Sciences B. A. Trofimov on his 70th jubilee. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1443–1502, October, 2008.     

N-Heterocyclic carbene-palladacyclic complexes: synthesis,characterization and their applications in the C-N coupling and α-arylation of ketones using aryl chlorides

N-Heterocyclic carbene-palladacyclic complexes 3 were successfully achieved in a one-pot procedure under mild conditions. The structure of 3a was unambiguously confirmed by X-ray single crystal diffraction and it was an active catalyst in the Buchwald-Hartwig amination and α-arylation of ketones even at very low catalyst loadings (0.01?mol%).     

Iodine-mediated oxidative Pictet-Spengler reaction using terminal alkyne as the 2-oxoaldehyde surrogate for the synthesis of 1-aroyl-β-carbolines and fused-nitrogen heterocycles

An efficient iodine-mediated oxidative Pictet-Spengler reaction in dimethyl sulphoxide (DMSO) using terminal alkynes as the 2-oxoaldehyde surrogate for the synthesis of aryl (9H-pyrido[3,4-b]indol-1-yl)methanones is described. The scope of the protocol includes the total synthesis of Fascaplysin, Eudistomins Y₁ and Y₂. The methodology is extended for preparing pyrrolo[1,2-a]-quinoxaline and indolo[1,5-a]quinoxaline derivatives. The utility of 1-aroyl-β-carbolines was demonstrated by performing palladium-catalyzed β-carboline directed ortho-C(sp2)-H functionalization of the phenyl ring with thiomethyl (SMe) group using DMSO as source and for accessing 4-aryl-canthin-6-ones.