Covalency Measurements via NMR in Lithium Metal Phosphates

³¹P nuclear magnetic resonance (NMR) shifts on the order of thousands of parts per million are observed for olivine LiMPO₄ (M = Mn, Fe, Co, Ni) samples, a promising class of Li ion rechargeable battery electrode materials. Variable-temperature ³¹P NMR measurements of shift are used to determine that the supertransferred hyperfine interaction is the dominant mechanism giving rise to these unusually large observed ³¹P shifts. Various models for predicting ³¹P and ⁷Li shifts in LiMPO₄ (M = Mn, Fe, Co, Ni) were investigated. Alloys of LiFe_1−x Mn _x PO₄, where x varies from 0 to 1, were also investigated by ⁷Li NMR. Covalency constants, calculated from variable-temperature NMR shifts and magnetic susceptibility data, are determined for the P–O–M bonds in LiMPO₄ (M = Mn, Fe, Co, Ni) and compared to the covalency constants of the Li–O–M bond. The sign and relative magnitude of the covalency constants are discussed in terms of positive and negative spin densities at the nuclei of interest. The covalency constants for the Li–O–M and P–O–M bonds were measured for Li_1.8Na_0.2FeMn₂(PO₄)₃ and compared to the covalency constants measured in the olivine LiMPO₄ (M = Mn, Fe, Co, Ni) samples. The Li_1.8Na_0.2FeMn₂(PO₄)₃ structure has a volume per transition metal atom and Li–O–M bond distances that are similar to those of the olivine LiMPO₄ (M = Mn, Fe, Co, Ni) samples. Authors' address: Jeffrey A. Reimer, Department of Chemical Engineering, University of California Berkeley, Berkeley, CA 94720, USA     

Atomic O and H exposure of C-covered and oxidized d-metal surfaces

Carbon coverage, oxidation and reduction of Au, Pt, Pd, Rh, Cu, Ru, Ni and Co layers of 1.5 nm thickness on Mo have been characterized with ARPES and desorption spectroscopy upon exposure to thermal H and O radicals. We observe that only part of the carbon species is chemically eroded by atomic H exposure, yielding hydrocarbon desorption. Exposure to atomic O yields complete carbon erosion and CO₂ and H₂O desorption. A dramatic increase in metallic and non-metallic oxide is observed for especially Ni and Co surfaces, while for Au and Cu, the sub-surface Mo layer is much more oxidized. Although volatile oxides exist for some of the d-metals, there is no indication of d-metal erosion. Subsequent atomic H exposure reduces the clean oxides to a metallic state under desorption of H₂O. Due to its adequacy, we propose the atomic oxygen and subsequent atomic hydrogen sequence as a candidate for contamination removal in practical applications like photolithography at 13.5 nm radiation.     

锂电池正极材料Li(Co,Ni)O2化合物的第一性原理研究

锂离子电池以其高能量存储密度和优良的循环性能而受到广泛关注, 尤其是其正极材料成为储能材料领域的研究热点.本文采用基于密度泛函理论的第一性原理方法对LiCoO2,LiNiO2和Li(Co0.5Ni0.5)O2化合物的晶体结构、电子结构、化学键合特性进行了研究. 结果表明：Li(Co0.5Ni0.5)O2化合物中主要是氧和过渡金属之间成键, 锂原子对晶体总态密度贡献很少. Ni/Co混合后将导致Li(Co0.5Ni0.5)O2中Co的3d轨道和O的2p轨道之间成键得以加强.     

锂电池正极材料Li(Co,Ni)O2化合物的第一性原理研究

锂离子电池以其高能量存储密度和优良的循环性能而受到广泛关注, 尤其是其正极材料成为储能材料领域的研究热点.本文采用基于密度泛函理论的第一性原理方法对LiCoO2,LiNiO2和Li(Co0.5Ni0.5)O2化合物的晶体结构、电子结构、化学键合特性进行了研究. 结果表明：Li(Co0.5Ni0.5)O2化合物中主要是氧和过渡金属之间成键, 锂原子对晶体总态密度贡献很少. Ni/Co混合后将导致Li(Co0.5Ni0.5)O2中Co的3d轨道和O的2p轨道之间成键得以加强.     

过渡金属氧化物催化剂上NH3 分解Claus反应机理研究

运用浸渍法制备了七种过渡金属氧化物催化剂 .对于NH3 分解反应均可获得很高的NH3 转化率 ;对于NH3 分解Claus反应则可以获得较高的SO2 转化率和单质硫选择性 .通过比较发现Co3 O4 TiO2 和Fe2 O3 TiO2 催化剂的低温活性比较高 .经过XRD表征发现 ,在NH3 分解Claus反应中 ,催化剂的活性相可能是过渡金属硫化物 .结合活性评价和XRD表征结果提出了NH3 分解Claus反应的机理 .     

Metal oxide anodes for Li-ion batteries

Recently metal oxides, especially tin oxides, have been investigated as negative electrodes in Li-ion batteries. Different compounds such as amorphous SnO₂, SnO and SnSiO₃ have been electrochemically cycled versus a metallic lithium electrode. In this study, the reversible capacities as well as the cycling behavior of crystalline SnO₂ thin films and powders have been investigated. SnO₂ powder exhibits a reversible capacity as high as 600 mAh/g over more than 50 cycles versus a metallic lithium electrode. Based on these results, we give clues for the future investigations of metal oxides as anodes in lithium ion batteries and discuss what can be the expected capacities of such negative electrodes. Paper presented at the 4th Euroconference on Solid State Ionics, Renvyle, Galway, Ireland, Sept. 13–19, 1997     

Doped lithium nickel cobalt mixed oxides for the positive electrode in lithium ion batteries

Phase pure aluminium and magnesium doped lithium nickel cobalt mixed oxides Li(Ni,Co_0.1–0.2M_≤0.05)O₂ (M=Al, Mg) were synthesised in laboratory by a synthesis procedure adopted from H.C. Stark. Structural parameters were determined by Rietveld analysis of x-ray diffraction spectra. Electrochemical characterisation took place in three-electrode teflon cells and coin-type cells versus lithium metal. Thermal stability of cathodes without electrolyte was measured by DSC. For aluminium and magnesium doped lithium nickel cobalt mixed oxides Li(Ni,Co_0.1–0.2M_≤0.05)O₂ (M=Al, Mg) the layered structure is stabilised by both aluminium and magnesium. The lithium nickel disorder is decreased by cobalt and is nearly unaffected by aluminium. According to the Rietveld refinements, magnesium seems to reduce the lithium nickel disorder strongly, even though refinements are not totally reliable in this case. Initial capacity and reversibility in the first cycle are nearly unaffected by aluminium, but strongly inferred by magnesium. Both, aluminium and magnesium doping increase the cycling stability of lithium nickel cobalt mixed oxides. Increased thermal stability of charged electrodes without electrolyte by aluminium and magnesium doping seems to be due to limited delithiation. Paper presented at the 8th EuroConference on Ionics, Carvoeiro, Algarve, Portugal, Sept. 16 – 22, 2001.     

Fabrication of Cu@MxOy (M = Cu,Mn, Co,Fe) Nanocable Arrays for Lithium‐Ion Batteries with Long Cycle Lives and High Rate Capabilities

A new strategy is reported to fabricate Cu@M_xO_y (M = Cu, Mn, Co, Fe) nanocable arrays using five‐fold twinned copper (Cu) nanowire (NW) arrays as starting materials, to promote both the cycling stability and high rate capability of M_xO_y as anodes for LIBs. Conductive Cu NW arrays were synthesized on Cu foil via chemical vapor deposition (CVD), followed by the oxidation of their surface so as to form Cu@Cu₂O nanocable arrays. The thickness of the active material (Cu₂O) on the Cu NW arrays can be tuned from 20 nm to 160 nm by simply controlling the oxidation time. Based on this accurate control, the optimal coating thickness of Cu₂O was determined to be around 35 nm. Additionally, the Cu₂O active material shell can be easily transformed to other metal oxides with even higher specific capacities via a “coordinating etching” strategy based on Pearson's principle, resulting in Cu@M_xO_y nanocable arrays (M = Mn, Co, Fe). When applied as electrodes for LIBs, these 3D electrodes show long cycle lives (over 300 cycles) and high rate capabilities.     

Enhanced cyclability of triple-metal-doped LiMn2O4 spinel as the cathode material for rechargeable lithium batteries

To improve the cycle performance of spinel LiMn₂O₄ as the cathode of 4-V-class lithium secondary batteries, spinel phases LiM _x Mn_2 − x O₄ (M=Li, Fe, Co; x = 0, 0.05, 0.1, 0.15) and LiFe_0.05M _y Mn_{1.95 − y} O₄ (M=Li, Al, Ni, Co; y = 0.05, 0.1) were successfully prepared using the sol–gel method. The spinel materials were characterized by powder X-ray diffraction (XRD), elemental analysis, and scanning electron microscopy. All the samples exhibited a pure cubic spinel structure without any impurities in the XRD patterns. Electrochemical studies were carried out using the Li|LiM _x Mn_2 − x O₄ (M=Li, Fe, Co; x = 0, 0.05, 0.1, 0.15) and LiFe_0.05M _y Mn_{1.95 − y} O₄ (M=Li, Al, Ni, Co; y = 0.05, 0.1) cells. These cathodes were more tolerant to repeated lithium extraction and insertion than a standard LiMn₂O₄ spinel electrode in spite of a small reduction in the initial capacity. The improvement in cycling performance is attributed to the stabilization in the spinel structure by the doped metal cations.     

高纯氟化锂的分析

本文叙述了适于作超低损耗金属氟化物光纤材料的高纯氟化锂的方法研究。其分析方法为：氟化锂样品经硝酸溶解，重复蒸发除去大部分Ｆ＾－，以石墨炉原子吸收标准加入法直接测定过渡金属，Ｆｅ，Ｃｏ，Ｃｕ，Ｎｉ含量，制得了四种对光纤质量影响最大的过渡金属杂质的含量均低于０．０００１％的氟化。方法的相对标准偏差为Ｆｅ，４２％，Ｃｏ，１６．８％，Ｎｉ８．８％，Ｃｕ６．９％。     

Phosphate materials for cathodes in lithium ion secondary batteries

Olivine phosphates of general formula LiMPO₄ (M=Fe, Co, Ni) were prepared and characterised in order to evaluate new potential cathode materials for secondary lithium ion batteries. The synthesis was performed by soft chemistry methods to avoid problematical and energetic expensive solid state reactions. In all the compounds no secondary phase was detected and the powder morphology was found to be suitable for cathode layers preparation. Only LiFePO₄ and LiCoPO₄ showed reversible lithium deintercalation-intercalation at 3.5 and 4.8 V vs. Li⁺/Li, respectively. The LiCoPO₄ high potential makes this compound very attractive for high energy batteries, but unfortunately its lifetime appears to be too poor. Paper presented at the Patras Conference on Solid State Ionics — Transport Properties, Patras, Greece, Sept. 14 – 18, 2004.     

高分辨率光谱学揭示东太平洋CC区结核金属赋存状态及富集机制

赤道东太平洋克拉里昂-克利珀顿带(CCZ)是全球最有经济潜力的结核成矿带,存在巨量的Mn, Co, Ni, Cu, Zn和Li金属资源。前人对CCZ结核的研究偏重化学、矿物学分析,对结核显微纹层、金属赋存状态缺少高分辨率光谱学分析,制约了对金属富集机制的理解。采用扫描电镜(SEM)、 X射线衍射仪(XRD)、微区X射线荧光面扫(XRF)、激光剥蚀电感耦合多接受质谱仪(LA-ICP-MS)对克拉里昂-克利珀顿带结核的显微纹层展开高分辨率分析,结果表明结核是由水成层韵律和成岩层韵律交替形成的。水成层由水羟锰矿组成,具有低的Mn/Fe, Li, Ni, Cu, Zn和高的Co, Fe, Ti, V含量,推测受铁的羟基氧化物库仑力吸附作用和高价锰氧化物八面体的表面氧化作用,水成层吸纳高含量Co, Ti和V元素。成岩层矿物组分主要是水钠锰矿,吸纳高含量的Li, Ni, Cu和Zn,其吸纳能力随Mn/Fe升高而提高,当Mn/Fe>8达到峰值。笔者认为结核生长环境中的Mn和Fe相对通量控制了结核的矿物类型和化学组分,而金属通量也可能影响了结核的金属成分。     

A preliminary investigation upon the electrochemical behavior of CoO and NiO anodes — comparative study

Among the variety of alternate anode materials being studied, the research on the exploration of 3d-metal oxide anodes gains paramount importance in the recent time, as it is bestowed with an easy preparation method and a less complicated decomposition mechanism. Towards this direction, an attempt to synthesize the compound CoO and to investigate the electrochemical behavior of the same both individually and in comparison with NiO compounds was made with a view to understand the extent to which the chosen candidates, viz., CoO and NiO can be exploited as high capacity anodes. Between the two oxides, CoO exhibited a specific capacity of at least 550 mAh/g, against NiO with an average capacity of ∼330 mAh/g. Also, the magnitude of irreversible capacity loss and the extent of capacity fade upon cycling corresponding to CoO anode were found to be lesser than NiO anodes. The enhanced specific capacity values and the better cycleability properties of CoO anodes are believed to be due to the inherent electrochemical characteristics of the compound. The type and the nature of SEI formed over the electrode surface and the formation of possible progressive agglomeration of the products of decomposition are expected to be the factors responsible for the difference in the electrochemical behavior of CoO and NiO anodes. In short, electrochemical characterization of the individual oxides are studied and probable reasons for the observed difference in the charge-discharge behavior of CoO and NiO anodes are discussed in this communication.     

有机共沉淀-火焰原子吸收光谱法测定高纯稀土氧化物中痕量铅镉钴镍铁铜

本文研究了吡咯啶二硫代氨基甲酸铵(APDC)共沉淀痕量铅镉钴镍铁铜的最佳条件;金属-PDC配合物的稳定性及共存元素的干扰等。沉淀溶解于小体积的甲基异丁酮(MIBK)中,采用微量进样技术,将有机相直接喷入空气-乙炔火焰,原子吸收光谱法测定之。该法已成功地应用于荧光级氧化镧和氧化钇中题示元素的测定。     

Structural and electrochemical study on Li(Li1/3Ti5/3)O4 anode material for lithium ion batteries

Chemical and electrochemical studies have shown that various titanium oxides can incorporate lithium in different ratios. Other compounds with a spinel-type structure and corresponding to the spinel oxides LiTi₂O₄ and Li₄Ti₅O₁₂ have been evaluated in rechargeable lithium cells with promising features. The spinel Li[Li_1/3Ti_5/3]O₄ [1–5] compound is a very appealing electrode material for lithium ion batteries. The lithium insertion-deinsertion process occurs with a minimal variation of the cubic unit cell and this assures high stability which may reflect into long cyclability. In addition, the diffusion coefficient of lithium is of the order of 10⁻⁸ cm²s⁻¹ [5] and this suggests fast kinetics which may reflect in high power capabilities. In this work we report a study on the kinetics and the structural properties of the Li[Li_1/3Ti_5/3]O₄ intercalation electrode carried out by: cyclic voltammetry, galvanostatic cycling and in-situ X-ray diffraction. The electrochemical characterization shows that the Li[Li_1/3Ti_5/3]O₄ electrode cycles around 1.56 V vs. Li with a capacity of the order of 130 mAhg⁻¹ which approaches the maximum value of 175 mAhg⁻¹ corresponding to the insertion of 1 equivalent per formula unit. The delivered capacity remains constant for hundred cycles confirming the stability of the host structure upon the repeated Li insertion-deinsertion process. This high structural stability has been confirmed by in situ Energy Dispersion X-ray analysis. Paper presented at the 7th Euroconference on Ionics, Calcatoggio, Corsica, France, Oct. 1–7, 2000.     

Synthesis and conductivities of the apatite-type systems, La9.33+xSi6−yMyO26+z (M=Co, Fe, Mn) and La8Mn2Si6O26

Apatite-type oxides of formula (La/Sr)_10−xSi₆O_26+y have been attracting significant interest recently, because of their high oxide ion conductivity. In this paper we report the synthesis and conductivities of phases based on doping La_9.33Si₆O₂₆ with Co, Fe, Mn on the Si site, according to the formula La_9.33+x/3Si_6−xM_xO₂₆ (M=Co, Fe, Mn). Substitution limits observed were x≤1.5 (Co), x≤1.25 (Fe), x≤0.5 (Mn). Higher Mn levels could be achieved by substituting onto the La site, with it being possible to prepare the phase La₈Mn₂Si₆O₂₆. The highest conductivities were observed for the Co doped samples, although investigations into the dependence of conductivity on p(O₂) (0.2–10⁻⁵ atm.) indicated that the conductivity was dominated by the electronic component in these cases. In contrast, the conductivities for the Fe and Mn doped samples were mainly ionic in the same p(O₂) range. Experiments into varying the oxygen content of these doped phases indicated that increasing the oxygen content above the nominally stoichiometric O₂₆ appears to increase the oxide ion conductivity. Preliminary studies of the reactivity of the electrolyte La_9.33Si₆O₂₆ with potential SOFC cathode materials (La_1−xSr_xMO₃; M=Co, Fe, Mn) suggests that reaction can occur at high temperatures leading to the incorporation of the transition metal into the apatite electrolyte. However, the fact that these doped phases exhibit high conductivities suggests that this may limit any problems caused by such a reaction at the electrolyte-electrode interface. Paper presented at the 8th EuroConference on Ionics, Carvoeiro, Algarve, Portugal, Sept. 16–22, 2001.     

First-principles study of LiMPO4 compounds (M=Mn,Fe, Co,Ni) as electrode material for lithium batteries

The intercalation voltages of cathode materials for rechargeable lithium-ion batteries are calculated for lithium-orthophosphate oxides LiMPO₄ (M=Mn, Fe, Co and Ni) using density-functional theory within the local-density (LDA) and LDA?+?U approximations. We show that the LDA?+?U approximation is able to reproduce the experimental volumes as well as the experimentally observed magnetic structures of the lithiated and non-lithiated compounds for which LDA qualitatively fail. Moreover, we find that, using the LDA?+?U approach, the experimental evolution of the lithium intercalation voltage along the series can be reproduced accurately.     

Enhancement of antiferromagnetic interaction and transition temperature in M<Subscript>3</Subscript>TeO<Subscript>6</Subscript> systems (M = Mn,Co, Ni,Cu)

Several M₃TeO₆ (M = Mn, Co, Ni, Cu) oxides order antiferromagnetically at low temperatures (?60 K), while displaying interesting dielectric properties at high temperatures (ferroelectricity below 1000 K in M = Ni case). We have investigated and analyzed the structural and magnetic properties of Mn-doped Co₃TeO₆ and Ni₃TeO₆, which order antiferromagnetically at temperatures higher than their undoped counterparts.     

Fourier Transform Infrared and Raman Spectra of 4-Vinylpyridine and its Transition Metal(II) Tetracyanonickelate Complexes

Abstract

Infrared and Raman spectra (4000-200 cm^?1) were recorded for 4-vinylpyridine and vibrational assignments made for fundamental modes on the basis of frequency shifts of the coordinated ligand, of the group vibrational concept and comparison with the assignments for related molecules. the infrared spectra of M(4-vinylpyridine)₂Ni(CN)₄ (M=Mn, Cd, Fe, Co, Ni or Cu) are reported.     

Eco-friendly combustion-based synthesis of metal aluminates MAl<Subscript>2</Subscript>O<Subscript>4</Subscript> (M = Ni,Co)

Nanosized metal aluminates, MAl₂O₄ (M = Ni, Co), have been prepared following a nonpolluting, low temperature, and self-sustaining starch single-fuel combustion synthesis. The mixed fuel-coordinating actions of starch have given rise to an intermediary precursor which afforded monodisperse metal aluminate nanoparticles. The thermal analysis of the [M(II), Al(III)]-starch precursors indicates a similar thermochemical reactivity for the two compounds, displaying a sequence of well-defined decomposition stages associated with three endothermic effects and three/four (nickel/cobalt) exothermic ones. The XRD data confirm the formation of spinelic phase and a continuous growth of particle sizes with the increase of calcination temperatures. The mechanisms proposed for the formation of metal aluminates essentially consist in a combination of solid-state reactions of amorphous NiO/Co₃O₄ and Al₂O₃ simple oxides. The evaluation criterion of Ni(II) cations into the spinelic lattice is original and is based on the distinct occupancy degree of tetrahedral and octahedral sites in NiAl₂O₄ and γ-Al₂O₃. TEM/HRTEM investigations performed on the cobalt(II) and nickel(II) aluminate oxide powders resulted after calcination at 800 and 900 °C, respectively, for 1 h show the formation of irregular and isolated plate-like particles for Co(II)-based spinelic oxides (the average particle size is 16.6 nm) and submicron aggregates of small, bimodal, and almost uniform (as shape and size) of NiAl₂O₄ mixed oxide (the mean particle size is 33.6 nm). The NIR–UV–Vis spectra for the resulted MAl₂O₄ (M = Co, Ni) mixed oxides reveal a massive presence of tetrahedral divalent cations both for short- and long-time calcined samples. NiO impurities are detected using FTIR and electronic spectra for all NiAl₂O₄ samples.