Studies on the effects of coated Li2CO3 on lithium electrode

Although a lithium metal anode has a high energy density compared with a carbon insertion anode, the poor rechargeability prevents the practical use of anode materials. A lithium electrode coated with Li₂CO₃ was prepared as a negative electrode to enhance cycleability through the control of the solid electrolyte interface (SEI) layer formation in Li secondary batteries. The electrochemical characteristics of the SEI layer were examined using chronopotentiometry (CP) and impedance spectroscopy. The Li₂CO₃-SEI layer prevents electrolyte decomposition reaction and has low interface resistance. In addition, the lithium ion diffusion in the SEI layer of the uncoated and the Li₂CO₃-coated electrode was evaluated using chronoamperometry (CA).     

A mild hydrolysis of esters mediated by lithium salts

When treated with amine bases such as triethylamine and various lithium salts in wet solvents, esters are efficiently hydrolyzed to the corresponding acids in good yields. Esters incorporating an α- or β-heteroatom with respect to the ester carbonyl group are hydrolyzed rapidly even at room temperature. To further demonstrate the usefulness of this method, one example is provided where hydrolysis of acetylated camphorsultam is mediated by LiBr.     

Effects of Strong Ion‐Pairing on the Electrochemical Reduction of Cyclooctatetraene in Tetrahydrofuran in the Presence of Lithium Ion. Peak Coalescence Does Not Imply Potential Inversion

The first study of the voltammetric reduction of cyclooctatetraene (COT) in tetrahydrofuran (THF) in the presence of lithium ion is reported. A single wave is observed at ?2.23 V vs. Ag/0.1 M AgNO₃. Density functional calculations have been carried out on a variety of COT/Li/THF species in order to clarify the nature and role of ion pairing in this system. The dominant species in solution are the COT/Li/(THF)₂ anion radical and the COT/Li₂/(THF)₄ dianion. Computer simulations have been carried out to further understand the effects of ion pairing on the reduction. The simulations show that coalescence of two waves into one can occur in the presence of strong ion pairing even when the second reduction potential is negative of the first.     

甲状腺机能亢进症头发锌、硒、钒、锂、锗5种微量元素的动态变化

测定了２４例甲亢治疗前后及３０例健康对照的头发锌、硒、钒、锂及锗的含量，发现未治疗的甲亢头发锌、硒、钒、锂及锗含量较对照组低，Ｚｎ、Ｓｅ、Ｌｉ、Ｇｅ，Ｐ＜０．００１，Ｖ，Ｐ＜０．０１．甲亢经６～１２周抗甲亢药物治疗后．头发中５种元素均较治疗前上升（Ｐ＜０．００１），且头发钒和锂含量治疗后已达到对照组水平，Ｖ，Ｐ＞０．２，Ｌｉ，Ｐ＞０．１，而头发锌、晒及锗含量治疗后仍低于对照组（Ｐ＜０　．００１）．结论：甲亢头发锌、硒、钒、锂及锗含量降低．经６～１２周抗甲亢治疗可使头发钒及锂含量恢复正常水平，而其余３种元素则可能需要更长时间的抗甲亢治疗才能恢复至正常水平。     

Synthesis and phase transition of Li-Mn-O spinels with high Li/Mn ratio by thermo-decomposition of LiMnC2O4(Ac)

LiMnC₂O₄(Ac) precursor in which Li⁺ and Mn²⁺ were amalgamated in one molecule was prepared by solid-state reaction at room-temperature using manganese acetate, lithium hydroxide and oxalic acid as raw materials. By thermo-decomposition of LiMnC₂O₄(Ac) at various temperatures, a series of Li_1+y[Mn_2−xLi_x]_16dO₄ spinels were prepared with Li₂MnO₃ as impurities. The structure and phase transition of these spinels were investigated by XRD, TG/DTA, average oxidation state of Mn and cyclic voltammeric techniques. Results revealed that the Li-Mn-O spinels with high Li/Mn ratio were unstable at high temperature, and the phase transition was associated with the transfer of Li⁺ from octahedral 16c sites to 16d sites. With the sintering temperature increasing from 450 to 850 °C, the phase structure varied from lithiated-spinel Li₂Mn₂O₄ to Li₄Mn₅O₁₂-like to LiMn₂O₄-like and finally to rock-salt LiMnO₂-like. A way of determining x with average oxidation state of Mn and the content of Li₂MnO₃ was also demonstrated.     

Nb 掺杂LiFePO4/C 的一步固相合成及电化学性能

用固相法一步合成了Nb掺杂的LiFePO4/C复合材料, 研究了Nb掺杂量对材料电化学性能的影响. 结果表明, Nb掺杂后LiFePO4/C复合材料的电化学性能明显提高. 在0.5C、1C和2C充放电倍率下, 名义成分为Li0.96Nb0.008FePO4/C正极材料的比容量分别为161、148和132 mAh•g−1, 已达到实用化水平. 阻抗谱和循环伏安特性测试显示, Nb掺杂有效地降低了复合材料电极的阻抗和极化, 说明Nb掺杂的主要作用是提高了LiFePO4的电子电导率.     

Apparent Molar Volume, Heat Capacity, and Conductance of Lithium Bis(trifluoromethylsulfone)imide in Glymes and Other Aprotic Solvents

Lithium bis(trifluoromethylsulfone)imide (LiTFSI) is a promising electrolyte for high-energy lithium batteries due to its high solubility in most solvents and electrochemical stability. To characterize this electrolyte in solution, its conductance and apparent molar volume and heat capacity were measured over a wide range of concentration in glymes, tetraethylsulfamide (TESA), acetonitrile, -butyrolactone, and propylene carbonate at 25°C and were compared with those of LiClO₄ in the same solvents. The glymes or n(ethylene glycol) dimethyl ethers (nEGDME), which have the chemical structure CH₃–O–(CH₂–CH₂–O) _n –CH₃ for n = 1 to 4, are particularly interesting since they are electrochemically stable, have a good redox window, and are analogs of the polyethylene oxides used in polymer-electrolyte batteries. TESA is a good plasticizer for polymer-electrolyte batteries. Whenever required, the following properties of the pure solvents were measured: compressibilities, expansibilities, temperature and pressure dependences of the dielectric constant, acceptor number, and donor number. These data were used in particular to calculate the limiting Debye-Hückel parameters for volumes and heat capacities. The infinite dilution properties of LiTFSI are quite similar to those of other lithium salts. At low concentrations, LiTFSI is strongly associated in the glymes and moderately associated in TESA. At intermediate concentrations, the thermodynamic data suggests that a stable solvate of LiTFSI in EGDME exists in the solution state. At high concentrations, the thermodynamic properties of the two lithium salts approach those of the molten salts. These salts have a reasonably high specific conductivity in most of the solvents. This suggests that the conductance of ions at high concentration in solvents of low dielectric constant is due to a charge transfer process rather than to the migration of free ions.     

Synthesis and electrochemical properties of yttrium-doped LiMn<Subscript>0.98</Subscript>Y<Subscript>0.02</Subscript>O<Subscript>2</Subscript> for lithium secondary batteries

Yttrium-doped lithium manganese oxide (LiMn_0.98Y_0.02O₂) was prepared by ion exchange of lithium for sodium in NaMn_0.98Y_0.02O₂ precursors obtained by using rheological phase reaction method. This material had small particle size, which was composed of grain size of about 100 nm. Especially, LiMn_0.98Y_0.02O₂ delivered the initial discharge capacity of about 191 mA h g⁻¹ at room temperature when cycled between 2.0 and 4.4 V vs Li/Li⁺. Moreover, it showed an excellent cycling behavior, its specific capacity remained above 173 mA h g⁻¹ after 20 cycles, and the material did not transform into spinel structure during the electrochemical cycling according to the cyclic voltammograms and X-ray powder diffraction. The electrochemical results revealed that the doping of Y³⁺ improved the performance of LiMnO₂ considerably.     

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.     

A novel method for asymmetric synthesis of both enantiomers of α-substituted carboxylic acid derivatives from optically active 1-chlorovinyl p-tolyl sulfoxides and lithium ester enolates with 1,4-chiral induction from the sulfur chiral center

Treatment of optically active 1-chlorovinyl p-tolyl sulfoxides, which were synthesized from symmetrical ketones and (R)-(−)-chloromethyl p-tolyl sulfoxide in three steps, with lithium enolate of carboxylic acid tert-butyl esters gave optically active adducts having a substituent at the α-position with high 1,4-chiral induction from the sulfur chiral center in high yields. The adducts were converted to optically active esters and carboxylic acids having a chiral center at the α-position. When this addition reaction was carried out with the ester enolate generated from excess carboxylic acid tert-butyl ester with LDA in the presence of HMPA, the diastereomer of the adduct was obtained. By using the two reaction conditions for the generation of the ester enolates, a new method for asymmetric synthesis of both enantiomers of carboxylic acid derivatives having a substituent at the α-position from the one chiral source, (R)-(−)-chloromethyl p-tolyl sulfoxide, was realized.