添加Li+对MgO催化性能的影响

本文以IR、TPD、丁烯异构化及直接脱氢反应为手段,对不同Li⁺添加量的MgO催化剂进行了研究。结果表明,表面低配位氧集团是催化剂的主要活性物种,起碱中心作用;表面金属离子起L酸中心作用。酸、碱中心的数目、强度随Li⁺添加量不同而呈规律性变化。这种变化影响了酸、碱中心的协同作用,从而影响其催化活性。     

Spectroscopic, mass spectrometry, and semiempirical investigations of a new 2-(2-methoxyethoxy)ethyl ester of Monensin A and its complexes with monovalent cations

A new 2-(2-methoxyethoxy)ethyl ester of Monensin A (MON7) has been synthesized and its capability of complex formation with Li⁺, Na⁺, and K⁺ cations has been studied by ESI MS, ¹H and ¹³C NMR, FT-IR, and PM5 semiempirical methods. ESI mass spectrometry indicates that MON7 forms complexes with Li⁺, Na⁺, and K⁺ of exclusively 1:1 stoichiometry which are stable up to cv = 70 V. The formation of complexes between MON7 and Na⁺ cations is strongly favored. Starting from about cv = 90 V fragmentation of the respective complexes is observed, primarily characterized by several dehydration steps. The structures of the MON7 complexes with Li⁺, Na⁺, and K⁺ cations are stabilized by intramolecular hydrogen bonds in which the OH groups are always involved. The structures are visualized and discussed in detail. It has been proved that the formation of a pseudo crown ring structure formed by MON7 is preferred in complexes with Na⁺ cations.     

Preparation,Structure and Magnetic Properties of Lithium Substituted NiO by Molten Salt Method

A typical Li⁺ substituted NiO compound, Li_0.29Ni_0.71O, was synthesized by molten nitrate method. The effects of Li⁺ substitution on the structure and magnetic properties of NiO were investigated. X-Ray diffraction(XRD), scanning electron microscope(SEM) and high-resolution transmission electron microscope(HRTEM) analyses confirm the cubic structure of Li_0.29Ni_0.71O, with a primary particle size of 150 nm. Analysis of the Ni X-ray photoelectron spectroscopy(XPS) shows the transformation from Ni²⁺ to Ni³⁺ induced by Li⁺ substitution. Two magnetic transitions were observed at 225 and 55 K which were assigned to the ferrimagnetic ordering and spin glass transition, respectively. The different magnetic behavior with respect to that of NiO was attributed to the break of superexchange interaction Ni²⁺-O-Ni²⁺ and the formation of different spin clusters after non-magnetic Li⁺ doping.     

PEO基聚合物电解质及其锂硫电池性能研究

锂硫电池由于具有高的理论比能量引起了广泛关注,然而传统液态锂硫电池由于多硫化物的“穿梭效应”以及安全问题而限制了其应用,全固态锂硫电池可显著提高电池安全性能并有望解决多硫化物的穿梭问题. 本文采用传统的溶液浇铸法制备了具有不同的[EO]/[Li⁺]的PEO-LiTFSI聚合物电解质,并将其应用于锂硫电池. 研究发现,虽然[EO]/[Li⁺] = 8的聚合物电解质具有更高的离子电导率,但是[EO]/[Li⁺] = 20的电解质与金属锂负极间的界面阻抗更低,界面稳定性更好. Li|PEO-LiTFSI([EO]/[Li⁺]=20)|Li对称电池在60 °C,电流密度为0.1 mA·cm^-2时可稳定循环超过300 h,而Li|PEO-LiTFSI ([EO]/[Li⁺]=8)|Li对称电池循环75 h就出现了短路现象. 基于PEO-LiTFSI([EO]/[Li⁺]=20)电解质的锂硫电池首圈放电比容量为934 mAh·g^-1,循环16圈后放电比容量为917 mAh·g^-1以上. 而基于PEO-LiTFSI ([EO]/[Li⁺]=8)电解质的锂硫电池,由于与锂负极较低的界面稳定性不能够正常循环,首圈就出现了严重过充现象.     

ESI MS, spectroscopic and PM5 semiempirical studies of Colchicine complexes with lithium, sodium and potassium salts

The colchicine complexes with Li⁺, Na⁺ and K⁺ cations have been synthesized and studied by ESI MS, ¹H and ¹³C NMR, FT-IR and PM5 semiempirical methods. It has been shown that colchicine forms stable complexes of 1:1 stoichiometry with monovalent metal cations. For Li⁺ cations also formation of the 2:1 stoichiometry complexes has been detected. The most stable structures of the complexes are those in which the acetamide groups are involved in the coordination process. The structures of the colchicine complexes with Li⁺, Na⁺ and K⁺ cations are visualized and discussed in details.     

尖晶石型LiMn2O4薄膜电极的制备及电化学性质研究──电化学石英晶体微天平(EQCM)技术研究

石英晶体微天平(QCM)作为纳克级的质量传感器,可通过测定石英晶体振动频率的变化来测定石英晶体表面微小的质量变化.近年来,电化学石英晶体微天平(EQCM)技术已广泛应用于电化学研究领域[1].在锂嵌入型电极充放电过程中,锂离子在嵌基材料中嵌入脱出会引起电极质量的微小变化,因而利用EQCM技术研究Li+的嵌入脱出过程有其独到之处.     

Vibrational frequencies and infrared intensities of acetonitrile coordinated with metal cations: an ab initio study

Vibrational frequencies and infrared intensities have been calculated at the 6-31G and 6-31G^** levels for acetonitrile and for the complexes of acetonitrile with Li⁺ and Na⁺ cations. The changes in the infrared characteristics from an isolated acetonitrile to acetonitrile coordinated with metal cations (Li⁺ and Na⁺) have been evaluated. The ab initio calculations predict an essential increase of the intensities of the stretching CN, C-C and deformation CH₃, CCN vibrations in the complexes of acetonitrile with Li⁺ and Na⁺ cations.     

Gas-phase chemistry of nitrogen trifluoride NF3: structure and stability of its M–NF3 (M=H, Li, Na, K) complexes

The stationary points characterizing the potential energy profiles of the complex processes of the M⁺(M=H, Li, Na, K) and NF₃ were investigated by QCISD and B3LYP in conjunction with the 6-311+G(2d,2p) basis set. The optimized geometries and NBO analysis indicate that the complexes of M⁺(M=Li, Na, K) and NF₃ exist as ion-dipole molecules. But for H⁺ complexes, there are two stable isomers NF₃H⁺ and NF₂⁺–HF. The interaction distances of isomers follow the sequence H⁺< Li⁺< Na⁺< K⁺. The calculated affinity energies of the most stable isomers of H⁺, Li⁺, Na⁺, and K⁺ complexes exceed 20.1 kJ/mol, and these values suggest that the M⁺–NF₃ (M=H, Li, Na, K) complexes could be observed as stable species in gas phase, which supports Fujii's proposal that Li⁺ ion attachment mass spectrometry can serve as a conceivable technique to quantify the emissions of the NF₃.     

The solvation of Li and Na in acetonitrile from ab initio-derived many-body ion–solvent potentials

Several Li⁺- and Na⁺-acetonitrile models were derived from ab initio calculations at the counterpoise-corrected MP2/TZV++(d,p) level for distorted ion-(MeCN)_n clusters with n=1, 4 and 6. Two different many-body ion-acetonitrile models were constructed: an effective three-body potential for use with the six-site effective pair model of Böhm et al., and an effective polarizable many-body model. The polarizable acetonitrile model used in the latter model is a new empirical model which was also derived in the present paper. Mainly for comparative purposes, two ion-acetonitrile pair potentials were also constructed from the ab initio cluster calculations: one pure pair potential and one effective pair potential. Using all these potential models, MD simulations in the NPT ensemble were performed for the pure acetonitrile liquid and for Li⁺(MeCN) and Na⁺(MeCN) solutions with 1 ion in 512 solvent molecules and with a simulation time of at least 120 ps per system. Thermodynamic properties, solvation-shell structure and the self-diffusion coefficient of the ions and of the solvent molecules were calculated and compared between the different models and with experimental data, where available. The Li⁺ ion is found to be four-coordinated when the new many-body potentials are used, in contrast to the six-coordinated structure obtained for the pure pair and effective pair potentials. The coordination number of Na⁺ is close to six for all the models derived here, although the coordination number becomes slightly smaller with the many-body potentials. For both ions, the solvent molecules in the first shell point their nitrogen ends towards the cation, while in the second shell the opposite orientation is the most common.     

锂金属电池中的复合负极

锂金属具有理论比容量高、电位低等优点,被认为是电极中的“圣杯”。然而,锂金属负极在循环过程当中存在着不可控的枝晶生长、体积膨胀等问题,严重地阻碍了锂金属电池的商业化进程。本综述首先概述了锂枝晶的形成机理,然后对由小及大,自内而外,总结了近年来三种不同层次的锂金属电池复合负极:锂金属负极内部结构的复合、锂金属电池内部结构的复合以及锂金属电池内部环境与外界操作条件的复合。最后,本综述对未来多层次锂金属电池复合负极的前景做出了展望。     

纳米MgO掺杂改善LiNi1/3Co1/3Mn1/3O2正极材料

将氢氧化物共沉淀法制备的(Ni_1/3Co_1/3Mn_1/3)（OH）₂在500℃热处理5 h得到具有尖晶石结构、纳米尺寸的氧化物M₃O₄(M=Ni_1/3Co_1/3Mn_1/3).将其与LiOH及不同量的纳米MgO混合均匀,并在850℃热处理24 h制备了Li(Ni_1/3Co_1/3Mn_1/3)_1/xMg_xO₂（x=0,0.01,0.02,0.03,0.04,0.05）正极村料.随着Mg掺杂量的增大,正极材料的晶胞参数增大;少量的Mg掺杂增大了锂离子的扩散系数,而过度掺杂却使锂离子扩散系数有所降低,其中Li(Ni_1/3Co_1/3Mn_1/3)_0.98Mg_0.02O₂的锂离子扩散系数最大,其脱出和嵌入扩散系数分别为D_Li-dein=29.20×10^-11cm²·S^-1和D_Li-in=4.760×10^-11cm²·s^-1;其以3C倍率充放电的平均放电比容量为139.3 mAh·g^-1,比未掺杂的原粉约高9.5 mAh·g^-1;另外其循环性能也得到了大幅度改善.     

Molecular orbital theory of the hydrogen bond : XXXII. The effect of H and Li association on the A---T and G---C pairs

Ab initio molecular orbital calculations have been performed to determine the structures and stabilization energies of the A---T and G---C base pairs and their complexes with H⁺ and Li⁺, H⁺ and Li⁺ association stabilizes the A---T pair except for Li⁺ association at O₄ in thymine. Protonation of thymine stabilizes the A---T pair to a greater extent than protonation of adenine. The association of H⁺ and Li⁺ with guanine stabilizes the G---C pair, but protonation of cytosine destabilizes G---C. Changes in the structures of the hydrogen bonds in the A---T and G---C pairs reflect changes in hydrogen bond strengths.     

Effect of small cations on the hydrogen bond between an N-aromatic heterocycle and amine

The influence of an Li⁺ ion on the structure and bonding of the H-bond interaction of an N-aromatic heterocycle and a singly bonded N-amine is studied by ab initio SCF calculations with imidazole (Imh) and NH₃ serving as models of the two families. Full optimization of structures have been carried out for DZ, DZP and TZP basis sets. The computed H-bond energy for Imh/ NH₃ of −6.4 kcal/mol is in close agreement with a recent experiment. An appreciable three-body interaction of −3.8 kcal/mol is found for the complex Imh/NH₃/Li⁺.     

一种有助于稳定锂金属循环的富氟化位点框架结构

锂金属是下一代高能量密度二次电池的理想负极材料,然而它的应用仍然受制于较差的循环稳定性。近期,二维氟化界面被广泛用于改善锂金属负极的成核机制、沉积形貌和循环稳定性。本工作通过将体积缩小化的氟化石墨颗粒与锂离子传导网络结合,获得了一种富氟化位点的三维框架结构。实验结果证明此类三维氟化结构可显著提升锂金属负极在不同电流密度和容量下的循环稳定性,且优于二维氟化界面结构。通过本工作的研究,证明了相较于单纯的二维氟化界面,三维锂离子传导网络和富氟化位点的合理结合可以成为一种改进的界面结构用于锂金属负极保护,为高能量密度锂金属电池的负极保护提供了新的设计思路。     

On the affinities of ammonia and water for Li, Na and K

The affinities of ammonia for Na⁺ and K⁺, recently determined experimentally, have been computed by the ab initio SCF method using ended polarized gaussian basis sets and shown to be satisfactory Furthermore, the corresponding values computed at the same level of accuracy for the three cations Li⁺, Na⁺, K⁺ and the two ligands NH₃ and H₂O are shown to yield the order Li⁺ > Na⁺ > K⁺ for each ligand and NH₃ > H₂O for each ion, in agreement with experiment. An analysis of the factors involved in the binding provides a consistent rationalization of these regularities and of some observed correlations.     

Observation Of Mode Selective Vibrational Excitation Of SF6 By Collisions With 4–10 eV Li And H Ions

Structured time of flight spectra of both Li⁺ and H⁺ ions scattered from ground state SF₆, have been measured at angles (5.0° v_c.m. 16.6°) less than the rainbow angle at E_c.m., = 4.3 eV and 9.7 eV, respectively. The structure can be arttributed to vibrational excitation of the v₃ mode by H⁺ and excitation of the v₄ mode by Li⁺. The relative transition probabilities obey a Poisson distribution and can be explained by a simple forced oscillator model.     

新一代动力锂离子电池磷酸锰锂正极材料的研究现状与展望

磷酸锰锂（LiMnPO₄）正极材料具有能量密度高、成本低、安全性高和热稳定性好等优点,目前已成为锂电产业界研究的热点,有望成为继磷酸铁锂（LiFePO₄）之后的新一代正极材料. 然而,磷酸锰锂的电子电导率和锂离子扩散率均很低,其电化学性能提高较为困难,至今尚无法制备出满足实际应用的高性能LiMnPO₄正极材料,严重制约了LiMnPO₄材料及其电池的发展. 本文从LiMnPO₄的结构特性出发,对近年来国内外在碳包覆、离子掺杂、纳米化和控制晶体形貌等改性研究、全电池研究、专利情况以及商业化尝试等多方面进行了综述,并对LiMnPO₄的发展进行了展望.     

Li含量对Li/MgO丙烷氧化脱氢制烯烃反应催化性能的影响

采用浸渍法制备了不同Li含量的Li/MgO催化剂,并通过TG-DTA、N_2吸附及XRD等手段对其进行了表征;对丙烷在Li/MgO催化剂表面的两种吸附状态所占据的空间体积大小进行了计算,研究了Li含量对其丙烷氧化脱氢制烯烃反应催化性能的影响。结果表明,随着Li/MgO催化剂中Li含量的增加,丙烷转化率与乙烯、甲烷、乙烷和COx的选择性均先增加,在Li物质的量分数为3%时达到最高,然后随Li含量增加而降低,而丙烯选择性则出现相反的变化趋势。丙烷在Li/MgO催化剂上的吸附和反应同时受动力学和热力学两个因素的制约;Li负载量不同,反应活性位Li+O-分散状态也不同,导致产物分布发生变化。活性位分散度高时受热力学因素影响,有利于生成丙烯;活性位分散度低时受吸附动力学影响,更趋向于生成乙烯等其他产物。     

Ab initio study on the structures, energies, and vibrational frequencies of acetone complexes with metal monocations and dications

The structures, interaction energies, and vibrational frequencies of acetone and its complexes with proton and various metal monocations/dications such as H⁺, Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, Be²⁺, Mg²⁺, Ca²⁺, and Zn²⁺ have been investigated from the ab initio calculations. The linear or bent structure for the cation-acetone complexes has been found to be deeply influenced by the amount of charge transfer. The amount of red-shift of CO stretching frequencies of acetone is almost equivalent regardless of the kind of alkali metal monocations. This behavior can be attributed to the electrostatic nature of the interactions rather than orbital interactions. This phenomenon has been supported by the highest occupied molecular orbitals of the acetone complexes investigated, charge transfer based on natural bond orbital (NBO) atomic charges, and the inversely proportional behavior of the interaction energies to the interatomic distances r(M⁺O).     

Li+,Eu3+共掺杂La2MoO6红色荧光粉的Pechini法合成及近紫外/蓝光激发下的发光特征

采用Pechini法合成了白光LED用红色荧光粉La_1.9-xMoO₆:0.10Eu³⁺,xLi⁺(x=0,0.10,0.20,0.25),并对样品分别进行了X射线衍射(XRD)、扫描电子显微镜(SEM)、电子能谱(EDX)以及荧光光谱(PL)等技术手段分析。 PL光谱显示该荧光粉可被近紫外光(395 nm)和蓝光(466 nm)有效激发,产生616和623 nm强的红光发射,归属于Eu³⁺的⁵D₀→⁷F₂电偶极跃迁。该荧光粉与近紫外LED芯片(370~410 nm)和蓝光LED芯片(450~470 nm)均匹配良好,具有潜在的商业应用价值。 共掺Li⁺离子作为敏化剂能显著提高荧光粉的发光强度,且最优掺杂量为x=0.20。