锂在共轭双键高分子中的电化学嵌入反应III. 锂嵌入聚噻吩的量子化学计算†

采用Gaussian软件和HF方法, 通过从头计算(ab initio)法选取4-31G基组计算锂离子嵌入聚噻吩过程中结构与结合能的变化关系. 发现噻吩聚合时主要生成三或四聚合物. 聚合物在Li原子(或Li^＋离子)嵌入后, 聚噻吩间距离明显变小, 同时发生电荷转移, 形成稳定嵌合物; 并使噻吩环的C-α—C-β键级变小. 同时, 研究了锂离子(或原子)嵌入后体系的HOMO, LUMO能级. 聚噻吩在嵌入锂离子时LUMO轨道能级变为负值, 成为电池反应得电子的正极. 而金属Li₂ 释放Li^＋后的Li^－的HOMO能级为＋0.7427 eV, 则成为给电子的负极. 由此, 可以完成由锂/聚噻吩在高氯酸锂电解质中组成的放电过程, 并提出嵌合键级概念用来表征锂在聚噻吩间的结合程度.     

锂在共轭双键高分子中的电化学嵌入反应Ⅱ:锂在聚吡咯中嵌入反应的量子化学研究

本文用量子化学CNDO/2方案计算,取文献中吡咯骨架原子的结构参数,再优化锂嵌入聚吡咯的几何参数。结果表明不管是Li~+离子还是中性Li原子,嵌入单个吡咯上还是嵌入两个吡咯之间,它与吡咯环四个碳原子平面的距离都为0.210到0.216nm。且锂与碳原子键合,形成多中心键,锂嵌入聚吡咯后,固有的C_α—C_β双键的键级和键能明显减弱。这与前一报中发现IR谱的15600m~(-1)吸收峰消失相一致。锂正离子嵌入聚吡咯后,使吡咯的前沿π~*矿空轨道的能量由正变为负值,而成为电子接受体(正极),遍及全部聚吡咯的π~*LUMO和HOMO使得聚吡咯呈现导电性能。     

锂在共轭双键高分子中的电化学嵌入反应Ⅱ:锂在聚吡咯中嵌入反应的量子化学研究

本文用量子化学CNDO/2方案计算,取文献中吡咯骨架原子的结构参数,再优化锂嵌入聚吡咯的几何参数.结果表明不管是Li+离子还是中性Li原子,嵌入单个吡咯上还是嵌入两个吡咯之间,它与吡咯环四个碳原子平面的距离都为0.210到0.216nm.且锂与碳原子键合,形成多中心键,锂嵌入聚吡咯后,固有的Ca=Cs双键的键级和键能明显减弱.这与前一报中发现IR谱的1560cm-1吸收峰消失相一致.锂正离子嵌入聚吡咯后,使吡咯的前沿π*空轨道的能量由正变为负值,而成为电子接受体(正极).遍及全部聚吡咯的π*LUMO和HOMO使得聚吡咯呈现导电性能.     

Li＋在PC＋DMF混合溶剂中优先溶剂化的13C NMR研究

利用¹³C NMR光谱技术研究了Li^＋在碳酸丙烯酯(PC)＋N,N-二甲基甲酰胺(DMF)混合溶剂中的优先溶剂化现象. 根据溶剂分子中碳原子的化学位移随锂盐浓度的变化关系, 确定了与Li^＋发生配位的原子. 碳原子的配位位移值随混合溶剂组成的变化关系表明, 在LiClO₄＋PC＋DMF混合物中, DMF分子对Li^＋的溶剂化作用较PC分子强. 定量计算得到, 在n(PC)∶n(DMF)＝1∶1(摩尔比)的混合溶剂中, PC与DMF分子数在Li^＋第一溶剂化层中的比率为0.12, 说明Li^＋优先被DMF分子溶剂化.     

盐湖卤水协同萃取提锂及基础热力学性质

为了充分利用盐湖卤水中丰富的锂资源,提出了以磷酸三丁酯（TBP）-乙酸丁酯（BA）-FeCl₃-260^#磺化煤油体系协同萃取提锂的方法。针对该体系,考察了卤水酸度、n_Fe/n_Li比以及温度对协同萃取过程的影响。根据锂离子及其它主要离子萃取率的变化,确定了最优萃取条件为：pH=2,n_Fe/n_Li=3.0,T=20℃。在最优条件下,单级萃取率达到90%左右。同时,研究了萃取过程的热焓、吉布斯自由能及熵变等基础热力学性质。结果表明,在选定的萃取体系和条件下,锂的萃取反应为放热反应,萃取过程为熵减过程。     

LixNi0.5Co0.5O2的态密度计算及电化学性能研究

>为获得综合性能更好的锂离子二次电池正极材料, 分析了Co掺杂对Li_xNiO₂电化学性能的影响. 采用密度泛函DFT理论对Li_xNiO₂和Li_xNi_0.5Co_0.5O₂的平均放电电压和态密度进行了计算. 同时, 用共沉淀法制备了Li_xNiO₂和Li_xNi_0.5Co_0.5O₂锂离子二次电池正极材料, 并对其进行了XRD结构分析和恒流充放电测试. 实验和计算结果表明: 随锂离子嵌入正极(电池放电), 电池的电压逐渐降低, 材料的态密度峰向低能量方向移动; 与Li_xNiO₂相比, Li_xNi_0.5Co_0.5O₂的电压平台相对较高(当0.25≤x≤0.5), 而且在Li^＋嵌/脱时, Li_xNi_0.5Co_0.5O₂的结构变化相对较小; Co离子的掺入, 减小了NiO₆八面体的畸变度, 使材料的电化学稳定性得以提高. 在钴掺杂镍酸锂体系中, NiO₆和CoO₆具有相互的稳定作用.     

电场对金属串配合物M3(dpa)4Cl2 (M=Co,Rh, Ir; dpa=dipyridylamide)结构的影响

应用密度泛函理论PBE0 方法研究具有分子导线潜在应用的金属串配合物M₃(dpa)₄Cl₂ (1: M=Co, 2: M=Rh, 3: M=Ir; dpa=dipyridylamide)在电场作用下的几何和电子结构. 结果表明: 配合物基态均是二重态. 1和2的M₃⁶⁺金属链形成三中心三电子σ键, 3 中M₃⁶⁺形成三中心四电子σ键且存在弱的δ键. 随金属原子周期数增大其M―M键增强、LUMO与HOMO能隙减小、金属原子的反铁磁耦合减弱以至消失且自旋密度向配体的离域增强. 在Cl4→Cl5 电场作用下, 低电势端的M3－Cl5 键缩短, 高电势端的M2―Cl4 键增长, M―M平均键长略为缩短, M―M键增强, 有利于分子线的电子传递; 分子能量降低, 偶极矩线性增大. 低电势端Cl5的负电荷向高电势端Cl4 转移, 且3 中金属原子的正电荷由高电势端向低电势端的转移较明显, 自旋电子由低电势端向高电势端金属原子移动, 但桥联配体dpa^-与M和Cl 所在的分子轴间没有电荷转移. 电场使LUMO与HOMO能隙减小, 有利于分子的电子输运. 随金属原子周期数增大, 电场作用下M―M平均键长变化减小, LUMO、HOMO的能级交错现象减少.     

SO2钳合反应机理的密度泛函研究

采用密度泛函理论(DFT)在B3LYP/6-311+G**水平上计算了SO₂与2,4-己二烯之间的钳合反应, IRC计算结果表明该反应是协同反应. 反应中, 这两个反应物同时把自己的HOMO电子填入对方的LUMO轨道, 这与传统的4＋2环加成机理不同. 反应前SO₂的HOMO轨道与2,4-己二烯的LUMO轨道之间能级相差很大(8.4 eV), 但随着反应进行, 2,4-己二烯的反键LUMO轨道逐渐演变成一个成键轨道, 能级下降, 使得SO₂的HOMO上电子可以向该轨道流动. 反应的净结果是有0.23e的负电荷由SO₂向2, 4-己二烯转移.     

Li＋在PC＋DMF混合溶剂中优先溶剂化的13C NMR研究

利用¹³C NMR光谱技术研究了Li^＋在碳酸丙烯酯(PC)＋N,N-二甲基甲酰胺(DMF)混合溶剂中的优先溶剂化现象. 根据溶剂分子中碳原子的化学位移随锂盐浓度的变化关系, 确定了与Li^＋发生配位的原子. 碳原子的配位位移值随混合溶剂组成的变化关系表明, 在LiClO₄＋PC＋DMF混合物中, DMF分子对Li^＋的溶剂化作用较PC分子强. 定量计算得到, 在n(PC)∶n(DMF)＝1∶1(摩尔比)的混合溶剂中, PC与DMF分子数在Li^＋第一溶剂化层中的比率为0.12, 说明Li^＋优先被DMF分子溶剂化.     

含锂沸石Li-FER提高PEO复合聚合物电解质电导率

通过离子交换方法使锂部分取代了镁碱沸石（FER）孔道壁上羟基中的氢，制得含锂沸石Li-FER. 将这种沸石作为无机填料加入到PEO/LiClO₄聚合物电解质中，可以使其室温电导率提高三个数量级以上. 电化学测量表明， 锂离子与PEO和含锂沸石中氧的相互作用提高了聚合物电解质中锂离子的迁移数. 另一方面， 采用XRD, DSC, PLM等方法研究了电解质的结晶状况.结果表明, Li-FER可以作为PEO链段结晶的成核剂，使PEO电解质的晶粒得到细化， 结晶度降低，为Li⁺的传输提供了更多的非晶区通道. 这是Li-FER的加入促使PEO聚合物电解质电导率提高的两个主要原因.     

Lithium versus Mono/Polyvalent Ion Intercalation: Hybrid Metal Ion Systems for Energy Storage

The energy storage by redox intercalation reactions is, nowadays, the most effective rechargeable ion battery. When lithium is used as intercalating agents, the high energy density is achieved at an expense of non‐sustainability. The replacement of Li⁺ with cheaper monovalent ions enables to make greener battery alternatives. The utilization of polyvalent ions instead of Li⁺ permits to multiplying the battery capacity. Contrary to Li⁺, the realization of quick and reversible intercalation of bigger monovalent and of polyvalent ions is a scientific challenge due to kinetic constraints, polarizing ion effects and Coulomb interactions. Herein we provide a vision how to make the intercalation of these ions feasible. The idea is to perform dual intercalation of ions having different charges, radii, preferred coordination and diffusion pathway topology. All these features are demonstrated by the recent knowledge on selective and non‐selective intercalation properties of oxides and polyanion compounds with layered and tunnel structures. Based on dual intercalation properties, the fabrication of hybrid metal ion batteries is presented and discussed.     

Electrochemical Intercalation of Lithium into Graphite in Acetonitrile Solutions: The Effect of the Anion Nature

Effect of the anion nature on the cathodic intercalation of lithium into graphite is studied. The duration of a discharge process and the capacity of Li _x C₆ electrodes increase in the row Cl^– HSO₄ ^– < ClO₄ ^– < SCN^–. The highest negative potential of an Li _x C₆ electrode is reached when lithiating in an LiSCN non-aqueous solution. X-ray diffraction and microstructure analyses confirm the presence in the electrode's upper layers of predominantly layered compounds Li _x C₆A _y , where A is anion. In deep layers, the principal intercalation product is Li _x C₆.     

Electrochemical intercalation reaction of lithium into sulfides of nonlayer structure: I. Lithium intercalation in lead sulfide

The reaction mechanism of cell Li/PbS has been studied with coulombic titration, cyclic voltammetry and X-ray diffraction methods. It was found that in the first stage of discharge (0< y ≤1.5), the intercalation of lithium into lead sulfide took place. The X-ray diffraction patterns showed that the main crystalline structure of PbS remained unchanged after lithiation, and the lithium intercalated probably locates in the center of the cubic-interspace of the crystal. The intercalation free energy of Li into PbS forming LiPbS was found to be ?300.48 KJ·mol^?1 (at 25°C). The chemical diffusion coefficient of lithium in Li_yPbS (0<y≤1) was determined by electrochemical method to be about 10^?11 cm²S-1.     

Phase Formation and Kinetics of Electrochemical Intercalation of Lithium into Intermetallic Compounds MgCd and MgCd3

Electrochemical intercalation of lithium into intermetallic compounds (IMC) MgCd and MgCd₃ out of propylene carbonate solutions of LiBF₄ is studied. According to chronopotentiometry data, during the intercalation, lithium forms compounds with cadmium: Li₃Cd on MgCd or LiCd and Li₃Cd on MgCd₃. Reactions of solid-phase substitution, which occur on the electrodes, are accompanied by the destruction of initial IMC and generation of magnesium atoms. Chronoamperometry of MgCd–(Li) and MgCd₃–(Li) shows the lithium intercalation to be limited by nonstationary diffusion of lithium in the solid phase. The lithium diffusion in MgCd is slower and that in MgCd₃is faster than in Cd. The calculated potential dependences of the diffusion coefficient for lithium in MgCd and MgCd₃ are linear in semilogarithmic coordinates.     

An n-Type Polythiophene Derivative with Excellent Thermoelectric Performance

Typical n-type conjugated polymers are based on fused-ring electron-accepting building blocks. Herein, we report a non-fused-ring strategy to design n-type conjugated polymers, i.e. introducing electron-withdrawing imide or cyano groups to each thiophene unit of a non-fused-ring polythiophene backbone. The resulting polymer, n-PT1 , shows low LUMO/HOMO energy levels of −3.91 eV/−6.22 eV, high electron mobility of 0.39 cm² V⁻¹ s⁻¹ and high crystallinity in thin film. After n-doping, n-PT1 exhibits excellent thermoelectric performance with an electrical conductivity of 61.2 S cm⁻¹ and a power factor (PF) of 141.7 μW m⁻¹ K⁻². This PF is the highest value reported so far for n-type conjugated polymers and this is the first time for polythiophene derivatives to be used in n-type organic thermoelectrics. The excellent thermoelectric performance of n-PT1 is due to its superior tolerance to doping. This work indicates that polythiophene derivatives without fused rings are low-cost and high-performance n-type conjugated polymers.     

Lithium Intercalation into Titanium Dioxide Films from a Propylene Carbonate Solution

Intercalation of lithium from an LiClO₄ propylene carbonate solution into thin-film TiO₂ (rutile) electrodes produced by thermal oxidation of a titanium substrate are studied using cyclic voltammetry and impedance measurements at 0.01 to 10⁵ Hz. An equivalent circuit adequately modeling the impedance spectra of TiO₂- and Li _x TiO₂ electrodes throughout the frequency range studied is proposed. The electrochemical characteristics of film electrodes, the reversibility of intercalation-deintercalation process, the effect of surface passivation on the lithium transfer rate, and the dependence of electric, kinetic, and diffusion parameters on the electrode potential (composition) are discussed. The diffusion coefficient of lithium in Li _x TiO₂ is 10^–12 cm²/s, as estimated by the impedance method.     

高效锂离子筛吸附剂MnO2•0.5H2O的软化学合成及吸附性能研究

以MnCl₂•4H₂O, LiOH•H₂O等试剂为初始原料, 采用溶胶-凝胶、水热处理、固化等软化学合成步骤制备了锂离子筛前驱体Li_1.6Mn_1.6O₄, 并经稀盐酸抽锂后得到了高选择性锂离子筛吸附剂MnO₂•0.5H₂O. 着重对合成过程中锂锰比, 氧化剂用量等因素影响进行了探讨, 并对所制备吸附剂的吸附性能进行了研究. 结果表明, 经软化学合成步骤制备的锂离子筛对Li^＋有良好的吸附量和选择性, 在未来从海水、卤水等液态锂资源富集或提取锂的应用中具有很大的潜力.     

Li＋在基于N,N-二甲基甲酰胺混合溶剂中的溶剂化

利用红外和拉曼光谱技术研究了Li^＋在不同浓度、不同溶剂组成的LiBF₄/N,N-二甲基甲酰胺-乙腈、LiBF₄/N,N-二甲基甲酰胺-四氢呋喃电解质溶液中的优先溶剂化现象. 红外和拉曼光谱的分析表明, Li^＋主要与DMF分子相互作用, 导致该分子的C＝O伸缩振动谱带、N—C＝O形变谱带、CH₃摇摆谱带等发生了分裂. Li^＋与其它溶剂分子的相互作用较弱, 谱带的分裂现象并不明显. Li^＋溶剂化数的计算显示, Li^＋第一溶剂化层内DMF分子的数目一般大于2, 这说明 Li^＋在混合溶剂体系内优先与DMF分子相互作用. 量子化学计算支持了这一结论.     

Reactivity of a Tetra(o‐tolyl)diborane(4) Dianion as a Diarylboryl Anion Equivalent

Lithium and magnesium salts of tetra(o‐tolyl)diborane(4) dianion, having B=B double bond character, were synthesized. It was clarified that the lithium salt of the dianion has a high‐lying HOMO and a narrow HOMO–LUMO gap, which were perturbed by dissociation of Li⁺ cation, as judged by UV/Vis spectroscopy and DFT calculations. The lithium salt of the dianion reacted as two equivalents of a diarylboryl anion with CH₂Cl₂ or S₈ to give boryl‐substituted products.     

Lithium Intercalation into Nanostructured Films Based on Oxides of Tin and Titanium

The lithium intercalation into nanostructured films of mixed tin and titanium oxides is studied. X-ray diffraction and Moessbauer spectroscopy analyses reveal that films consist of a rutile solid solution (Sn, Ti)O₂ and an amorphous tin oxide enriched with Sn²⁺ ions. The films specific capacity during the first cathodic polarization in a 1 M lithium imide solution in dioxolane is 200–700 mA h/g, of which nearly one half is the irreversible capacity. During the second cycle, the latter is 15% of that in the first cycle. As the films are thin (<1 m), their capacity does not depend on the current density at 1–80 mA/g. During the electrode cycling, the capacity decreases by 2 mA h/g each cycle. The effective lithium diffusion coefficient, determined by a pulsed galvanostatic method, is 10^–11 cm²/s; it slightly increases with the film lithiation. During the first cycle, the amorphous phase of oxides is reduced to tin metal, the solid solution (Sn, Ti)O₂ decomposes, SnO₂ disperses to become an x-ray amorphous phase, and TiO₂ precipitates as a rutile phase. Lithium reversibly incorporates into the tin metal, yielding Li _y Sn, and into a disperse SnO₂ phase, yielding Li _x SnO₂.