NMR and FT-IR Investigation of Spinel LiMn2O4 Cathode Prepared by the Tartaric Acid Gel Process

The structure of the lithium manganese tartrate precursor and the synthesis mechanism of LiMn₂O₄ were investigated by FT-IR, NMR, TG/DSC, and XRD in this study. The results of FT-IR and ⁷Li and ¹³C NMR measurements revealed that lithium ions bond with carboxylic acid ligands and the O–H stretching modes of tartaric acid. Manganese ion bonds only with carboxylic acid. Lithium and manganese ions were trapped homogeneously on an atomic scale throughout the precursor. Such a structure eliminates the need for long-range diffusion during the formation of lithium manganese oxides. Therefore, spinel LiMn₂O₄ was synthesized at temperatures as low as 300°C. In this work, the electrochemical properties of Li/Li_xMn₂O₄ were studied. It is clear that the discharge curves exhibit two pseudo plateaus as the LiMn₂O₄ is fired to higher temperatures. The discharge capacity of LiMn₂O₄ increases from 84 to 117 mAh/g as the calcination temperature increases from 300 to 500°C. The LiMn₂O₄ powders calcined at low temperatures with a high specific surface area and an average valence of manganese exhibit a better cycle life.     

Formation Enthalpy Calculation of Oxygen Vacancy Defect in Doped Lithium Niobate Crystals

The relationship between temperature and oxygen vacancy concentration is deduced in this paper. Based on the data of thermal weight-loss experiment, the formation enthalpies of congruent and several doped LN crystals have been calculated. It was found that the formation enthalpy of oxygen vacancies can be decreased evidently by doping valence-changeable ions. The experimental results were discussed and a new reduction process of the photorefractive LN crystal at a relatively low temperature was proposed, and the reduced crystals showed a good effect in practical use.     

DABCOnium: An Efficient and High‐Voltage Stable Singlet Oxygen Quencher for Metal–O2 Cells

Singlet oxygen (¹O₂) causes a major fraction of the parasitic chemistry during the cycling of non‐aqueous alkali metal‐O₂ batteries and also contributes to interfacial reactivity of transition‐metal oxide intercalation compounds. We introduce DABCOnium, the mono alkylated form of 1,4‐diazabicyclo[2.2.2]octane (DABCO), as an efficient ¹O₂ quencher with an unusually high oxidative stability of ca. 4.2 V vs. Li/Li⁺. Previous quenchers are strongly Lewis basic amines with too low oxidative stability. DABCOnium is an ionic liquid, non‐volatile, highly soluble in the electrolyte, stable against superoxide and peroxide, and compatible with lithium metal. The electrochemical stability covers the required range for metal–O₂ batteries and greatly reduces ¹O₂ related parasitic chemistry as demonstrated for the Li–O₂ cell.     

Storage Stability of LiFePO4/C in Humid‐hot Air

Storage stabilities of LiFePO₄/C composite at different conditions are investigated in terms of structural and electrochemical evolutions. The results from different aging tests indicate that moisture and temperature are the key factors that have the most profound effects on the structure homogeneity which in turn influences the electrochemical performance of LiFePO₄/C. Although the storage in a humid‐hot environment, such as saturated humidity air at 50°C, does not greatly influence the discharging capacity of LiFePO₄/C, it does reduce the initial charging capacity, thus the amount of reversible Li⁺ ions in a practical LiFePO₄/graphite cell decreases. This impact is explained by the lithium extraction during the storage, forming olivine FePO₄ and associated Li₃PO₄. Elevated storage temperature also favors the delithiation process. The degree of delithiation increases from about 6% at 50°C to 18% at 80°C. It is also found that re‐calcination at 650°C effectively resolves the problem of the structural heterogeneity of the stored LiFePO₄/C. Therefore both the initial charging capacity and coulombic efficiency of the stored sample in the first cycle revert to the original value of the fresh one.     

Enthalpies of solution and of crystallization of lithium nitrate and of lithium nitrate trihydrate in water at 25°C

The enthalpies of crystallization of LiNO₃ and LiNO₃–3H₂O from aqueous solutions at 25°C, measured by a calorimetric method and determined from the previously published data on the concentration dependence of the enthalpy of solution, are reported. The results are compared with the values obtained from the concentration dependences of the activity coefficients and from the temperature dependences of the solubilities. The enthalpy of solution at infinite dilution and the enthalpy of hydration are given.     

中间相Si-Cu合金作为锂离子电池负极材料的第一性原理研究

采用第一性原理平面波赝势法,对中间相Si-Cu合金作为锂离子电池负极材料的嵌脱锂机理进行研究.结果表明,4个Si-Cu合金相中Si0.125Cu0.875合金相具有最低的体积膨胀系数及最低的嵌锂电位,导电性在4个合金相中排第二位,具有最佳的电化学综合性能.     

脉冲电沉积抑制锂枝晶生成的研究

采用脉冲充电方法替代传统充电方法,研究了在有机电解液 0.5 mol·L^-1 LiBr/PC (碳酸丙烯酯)中,在铜电极上沉积锂的表面变化. 扫描电镜观测结果显示,在传统直流充电时电极表面明显地出现了枝晶,而使用脉冲充电时能够抑制枝晶的生长. 交流阻抗测试结果显示,在占空比为 0.5 时,沉积锂表面固体电解质界面(solid electrolyte interphase,SEI)膜电阻最大,沉积锂表面枝晶较少;单次脉冲电沉积时间过长,会使沉积锂表面 SEI 膜电阻减小,沉积锂表面枝晶增加;电流密度大于等于 2 mA·cm^-2时,脉冲电沉积可有效抑制枝晶生长.     

Nano-crystalline FeOOH mixed with SWNT matrix as a superior anode material for lithium batteries

Nano-crystalline FeOOH particles(5～10 nm) have been uniformly mixed with electric matrix of single-walled carbon nanotubes(SWNTs)for forming FeOOH/SWNT composite via a facile ultrasonication method. Directly using the FeOOH/SWNT composite(containing 15 wt%SWNTs) as anode material for lithium battery enhances kinetics of the Li+insertion/extraction processes, thereby effectively improving reversible capacity and cycle performance, which delivers a high reversible capacity of 758 mAh g-1under a current density of 400 mA g-1even after 180 cycles, being comparable with previous reports in terms of electrochemical performance for FeOOH anode. The good electrochemical performance should be ascribed to the small particle size and nano-crystalline of FeOOH, as well as the good electronic conductivity of SWNT matrix.     

Synthesis of Single‐Crystalline Spinel LiMn2O4 Nanorods for Lithium‐Ion Batteries with High Rate Capability and Long Cycle Life

The long‐standing challenge associated with capacity fading of spinel LiMn₂O₄ cathode material for lithium‐ion batteries is investigated. Single‐crystalline spinel LiMn₂O₄ nanorods were successfully synthesized by a template‐engaged method. Porous Mn₃O₄ nanorods were used as self‐sacrificial templates, into which LiOH was infiltrated by a vacuum‐assisted impregnation route. When used as cathode materials for lithium‐ion batteries, the spinel LiMn₂O₄ nanorods exhibited superior long cycle life owing to the one‐dimensional nanorod structure, single‐crystallinity, and Li‐rich effect. LiMn₂O₄ nanorods retained 95.6 % of the initial capacity after 1000 cycles at 3C rate. In particular, the nanorod morphology of the spinel LiMn₂O₄ was well‐preserved after a long‐term cycling, suggesting the ultrahigh structural stability of the single crystalline spinel LiMn₂O₄ nanorods. This result shows the promising applications of single‐crystalline spinel LiMn₂O₄ nanorods as cathode materials for lithium‐ion batteries with high rate capability and long cycle life.