锂离子电池镍掺杂尖晶石LiMn2O4正极材料的电子结构

采用密度泛甬平面波赝势方法对LiMn2O4和LiNi0.5Mn1.5O4的几何结构进行了优化,并计算了相应的电子结构.计算的结果表明:在Li 脱嵌前后,LiMn2O4和LiNi0.5Mn1.5O4均为导体,且锂元素主要以离子形式存在于两种材料中,O2p轨道与Mn(Ni)的3d轨道形成了较强的共价键.Li 嵌入导致Mn(Ni)3d轨道的态密度峰发生移动.Ni的掺杂导致Mn(Ni)和O2p轨道的成键作用得以加强,电子在Mn(Ni)3d轨道的填充发生变化,从而提高了电池的充放电电压.     

Li(Ni0.5Co0.2Mn0.3)1-2xTixNbxO2的合成及电化学性能

采用共沉淀-高温固相烧结法在900oC空气中煅烧,合成了层状复合掺杂型正极材料Li(Ni0.5Co0.2Mn0.3)1-2xTixNbxO2(x=0,0.002,0.005,0.01,0.02).通过扫描电镜(SEM)、X-射线衍射(XRD)和电化学测试等观察与研究掺杂元素对Li(Ni0.5Co0.2Mn0.3)O2的形貌结构和电化学性能的影响.结果表明,适量Ti、Nb掺入Li(Ni0.5Co0.2Mn0.3)O2,降低了材料的阳离子混排程度,且晶胞参数随着掺杂量的增加而增加.与未掺杂材料相比,Ti-Nb复合掺杂的样品具有更好的电性能和高温性能.当x=0.005时,材料的综合性能最好,方型铝壳电池3.0~4.2 V电位区间首次1C放电比容165.9 mAh.g-1,常温循环100周期容量保持率96.5%,55oC循环300周期容量保持率为92.6%,80oC/6 h高温存储后冷却2 h电池厚度膨胀率9.8%.     

Li4Mn5O12包覆对三元正极材料结构和性能的影响

LiNi(1/3)Mn(1/3)Co(1/3)O2具有很高的理论比容量,但是三元正极材料在高电压下长循环时,其表面结构发生较大的衰退,导致电池的循环性能和倍率性能变差。本文采用耐高电压且结构稳定的富锂尖晶石Li4Mn5O(12)包覆LiNi(1/3)Mn(1/3)Co(1/3)O2可以有效改善材料的电化学性能。通过XRD、SEM、XPS和TEM等手段对包覆后的材料进行分析,证实了在LiNi(1/3)Mn(1/3)Co(1/3)O2的表面形成了10nm厚的均匀Li4Mn5O(12)的包覆层;在循环100圈后,包覆后的LiNi(1/3)Mn(1/3)Co(1/3)O2仍具有179.5m Ah/g的放电比容量和88.6%容量保持率,明显高于未包覆的LiNi(1/3)Mn(1/3)Co(1/3)O2的78.3%容量保持率。因此,利用富锂尖晶石Li4Mn5O(12)包覆LiNi(1/3)Mn(1/3)Co(1/3)O2为实现更高能量密度的锂离子电池提供了新的途径。     

LiNi0.5-xAl2xMn1.5-xO4的制备、结构及电化学特征

采用喷雾干燥法合成了LiNi0.5-xAl2xMn1.5-xO4(0≤2x≤0.15)正极材料,研究Al掺杂对LiNi0.5Mn1.5O4材料结构与电化学性能的影响.通过X射线衍射(XRD)、扫描电子显微镜(SEM)、电感耦合等离子体-原子发射光谱(ICP-AES)、傅里叶红外光谱(FTIR)、循环伏安(CV)和充放电测试等手段对其结构及电化学性能进行表征.结果表明,Al取代Ni和Mn使材料的晶体结构发生了转变,空间群由P4332转变为Fd3m,同时增大了锂离子的扩散速率,提高了材料的倍率性能.在室温下,LiNi0.4 5Al0.1Mn1.45O4表现了最好的倍率性能,当放电电流为0.5 C时,放电容量为126 mA.h/g,当放电电流增加到5 C时,放电容量为109 mA.h/g,保持率达到了87%.此外,Al取代Ni和Mn有效降低了材料在高温下的Mn溶解量,从而有效改善了材料在高温大倍率下的循环性能.LiNi0.45Al0.1Mn1.45O4材料在50℃,倍率为3 C时,放电容量为121.7mA.h/g,循环50次后,仍可保留初始容量的94%.     

锂离子电池正极材料LiNi0.5Co0.2Mn0.3O2的合成及其高温容量衰减研究

采用共沉淀-高温固相烧结法合成了富镍型三元复合正极材料LiNi0.5Co0.2Mn0.3O2.恒流充放电测试表明,材料在3.0～4.4 V下0.2C放电容量达到179.2 mAh.g-1,但在55℃下经历100次充放电循环后发生急剧的容量衰减.电化学交流阻抗谱、X射线光电子能谱和原子发射光谱等实验表明,在高温高电压下,电解液与LiNi0.5Co0.2Mn0.3O2电极材料之间的副反应加剧,导致过渡金属原子溶出,该材料局域结构被破坏.同时,电极材料表面还沉积了高阻抗的LiF/MFx层,使得在电极的充放电过程中电荷转移阻抗和Li+扩散阻抗不断增加,以致电池容量急剧衰减.     

层状LiNi0.5Mn0.5O2正极材料的优化合成及电化学性能

采用沉淀法首先得到了Ni0.5Mn0.5(OH)2沉淀物,以其为原料与LiOH反应制备了LiNi0.5Mn0.5O2正极材料。采用XRD、SEM、充放电测试等研究了其结构与电化学性能,同时研究了Li过量时对材料电化学性能和结构的影响。SEM分析表明,Ni0.5Mn0.5(OH)2与LiNi0.5Mn0.5O2产物均为微小晶粒团聚成的颗粒。LiNi0.5Mn0.5O2材料在2.5~4.4V电位区间内,首次放电容量为130mAh/g,0.2C倍率下,50次循环后的容量保持率为87.8%。锂过量有助于形成良好的层状结构材料,并能显著提高材料的比容量和循环性能,Li1.1Ni0.5Mn0.5O2的首次放电容量为149mAh/g,0.2C倍率下,50次循环后的容量保持率为92.6%。     

Ni-Mn共掺杂高电压钴酸锂锂离子电池正极材料

以金属硫酸盐为原料,Na OH和NH3·H2O为沉淀剂,用共沉淀法合成了Co0.9Ni0.05Mn0.05(OH)前驱体,再进行配锂并通过高温固相法合成了Ni-Mn共掺杂高电压钴酸锂锂离子电池正极材料Li(Co0.9Ni0.05Mn0.05)O2。用X射线衍射(XRD)、扫描电镜(SEM)、循环伏安(C-V)、交流阻抗(EIS)和充放电测试研究样品的晶体结构、形貌和电化学性能。结果表明Ni-Mn共掺杂正极材料Li(Co0.9Ni0.05Mn0.05)O2有优秀的电化学性能:在3.0~4.4 V和3.0~4.5 V区间,0.5C倍率下首次放电比容量分别为162.5 m Ah·g-1和185 m Ah·g-1,循环100次后容量保持率分别为94.4%和93.7%。     

锂离子电池正极材料LixNi1／3Mn1／3及电化学性能研究CO1／3O2的合成及电化学性能研究

应用以氢氧化物共沉淀为前驱体的高温固相烧结法合成LiNi1/3Mn1/3Co1/3O2正极材料，研究了沉淀温度及烧结过程锂盐投入量对该材料的结构和电化学性能的影响．结果表明，以室温（-20℃）下合成的氢氧化物为前驱体制备的LiNi1/3Mn1/3Co1/3O2具有较好的电化学性能．高温固相烧结会导致部分LiOH损失，因而在合成过程中需加入过量的氢氧化锂，实验表明Li1.08Ni1/3Mn1/3Co1/3O2材料的电化学性能最优．     

锌掺杂提高LiNi1/3Co1/3Mn1/3O2正极材料的电化学稳定性

通过共沉淀法与固相法相结合制备了掺锌的高稳定性Li(Ni1/3Co1/3Mn1/3)1-xZnxO2(x=0,0.02,0.05)正极材料.循环伏安(CV)曲线表明Zn掺杂使氧化峰与还原峰的电势差减小到0.09 V,电化学阻抗谱(EIS)曲线表明Zn掺杂使电极的阻抗从266Ω减小到102Ω. Li+嵌入扩散系数从1.20×10-11 cm2·s-1增大到2.54×10-11 cm2· s-1. Li(Ni1/3Co1/3Mn1/3)0.98Zn0.02O2正极材料以0.3C充放电在较高的截止电压(4.6 V)下比其他两种材料的电化学循环性能更稳定,其第二周的放电比容量为176.2 mAh·g-1,室温下循环100周后容量几乎没衰减;高温(55°C)下充放电循环100周,其放电比容量平均每周仅衰减0.20%,远小于其他两种正极材料(LiNi1/3Co1/3Mn1/3O2平均每周衰减0.54%;Li(Ni1/3Co1/3Mn1/3)0.95Zn0.05O2平均每周衰减0.38%). Li(Ni1/3Co1/3Mn1/3)0.98Zn0.02O2正极材料以3C充放电时其放电比容量可达142 mAh·g-1,高于其他两种正极材料.电化学稳定性的提高归因于Zn掺杂后减小了电极的极化和阻抗,增大了锂离子扩散系数     

LiNi0.49Mn1.49Y0.02O4的合成及其电化学性能研究

应用柠檬酸辅助溶胶-凝胶法.合成了Y3+掺杂的尖晶石LiNi0.49Mn1.49Y0.02O4材料.XRD、循环伏安、恒流充放电和交流阻抗测试结果表明,Y3+的掺杂能提高LiNi0.5Mn1.5O4的倍率和循环性能.在电压区间3.5～4.9V,1C倍率下,其初始放电比容量为114.9 mAh.g-1,100次循环后放电比容量仍可达113.0 mAh.g-1,容量保持率为98.3%.掺杂Y3+能减小材料界面阻抗.     

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.     

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.     

Facile synthesis of bicyclic 1-arylpyrazol-5-ones

In this Letter, we described a facile method for constructing fused bicyclic 1-arylpyrazol-5-one ring system. We employed various methylene-containing carboxylic acids as the substrates and proved that the pyrazolone ring closure requires activated methylene group in intermediate II. Accordingly, a series of structurally diversified, fused bicyclic 1-arylpyrazol-5-ones was prepared in moderate to high yields using the requisite substrates.     

A carbanion induced synthesis of highly congested pyrazole and imidazole containing heterocycles

An efficient approach to the synthesis of highly congested di, penta and hexacyclic pyrazoles as well as imidazole fragment containing novel heterocyclic molecule has been developed through a carbanion induced transformation of suitably functionalized 2H-pyran-2-ones, benzo[h]chromene and thiochromeno[4,3-b]pyrans. Due to the presence of fluorescence, we report their prime application metal sensor as off/on switching in ferric ions.     

Synthesis of pyrrolo[1,2-a]pyrazines and pyrazino[1,2-a]indoles by Curtius reaction in Morita-Baylis-Hillman derivatives

Synthesis of substituted pyrrolo[1,2-a]pyrazines and pyrazino[1,2-a]indoles from the Morita-Baylis-Hillman derivatives of acrylates via saponification followed by Curtius reaction is described.     

正丁胺对激光染料荧光谱影响的研究

用正丁胺作为碳源,采用射频辉光放电制备碳膜,选用激光染料R6G和聚乙二醇混合液作为蒸气源,采用单源热蒸发,在蒸发室与染料同时沉积得到混合膜,用拉曼光谱和红外光谱分析了碳膜的结构和键合方式,分析表明:碳膜中存在胺基团和氢原子.混合膜的荧光谱测量结果表明,认为正丁胺对染料荧光谱的影响是因为胺基和氢原子的存在.     

Selective synthesis of 4,5-dihydroimidazo- and imidazo[1,5-a]quinoxalines via modified Pictet–Spengler reaction

An efficient tandem approach for the selective synthesis of 4,5-dihydroimidazo[1,5-a]quinoxalines 6a–g and imidazo[1,5-a]quinoxalines 7a–h by the reaction of 2-imidazolyl anilines 4a–c with aryl aldehydes 5a–k under mild reaction conditions is described. Introduction of electron releasing alkyl groups in substrates 4a–b was found to be instrumental for the success of the reaction.     

Understanding the Diels-Alder reactivity of 1,2-azaborine analogues

The Diels-Alder reactivity of 1,2-heteroborines (H₄C₄B(H)X, X?=?NH, PH, AsH; O, S, Se) has been computationally explored by means of Density Functional Theory (DFT) calculations. The influence of the HB?=?X fragment on the reactivity of the system has been quantitatively analyzed in detail by means of the so-called Activation Strain Model (ASM) of reactivity. It is found that the interaction between these species and the dienophile is significantly stronger than that computed for their all-carbon isoelectronic counterpart, benzene. In addition, the strain energy plays a key role in the observed reactivity trends. The role of the aromaticity strength of these heteroarenes on the reactivity is also assessed.