High-temperature X-ray diffraction study of crystallization and phase segregation on spinel-type lithium manganese oxides

To study crystallization process of spinel-type Li_1+xMn_2−xO₄, in-situ high-temperature X-ray diffraction technique (HT-XRD) was utilized for the mixture consisting of Li₂CO₃ and Mn₂O₃ as starting material in the temperature range of 25-700 °C. In-situ HT-XRD analysis directly revealed that crystallization process of Li_1+xMn_2−xO₄ was significantly affected by the difference in the Li/Mn molar ratio in the precursor. Single phase of stoichiometric LiMn₂O₄ formed at 700 °C. The formation of single phase of spinel was achieved at the lower temperature than the stoichiometric sample as Li/Mn molar ratio in the precursor increased. Lattice parameter of the stoichiometric LiMn₂O₄ at 25 °C was 8.24 Å and expanded to 8.31 Å at 700 °C, which corresponds to the approximately 3% expansion in the unit cell volume. From the slope of the lattice parameter change as a function of temperatures, linear thermal expansion coefficient of the stoichiometric LiMn₂O₄ was calculated to be 1.2×10⁻⁵ °C⁻¹ in this temperature range. When the Li/Mn molar ratio in Li_1+xMn_2−xO₄ increased (x > 0.1), the spinel phase segregated into the Li_1+yMn_2−yO₄ (x > y) and Li₂MnO₃ during heating, which involved the oxygen loss from the materials. During the cooling process from 700 °C, and the segregated phase merged into Li_1+xMn_2−xO₄ with oxygen incorporation. Such trend directly observed by in-situ HT-XRD was supported by thermal gravimetric analysis as reversible weight (oxygen) loss/gain at higher temperature (500-700 °C).     

Synthesis of non-stoichiometric lithium nickel cobalt oxides and their structural and electrochemical characterization

Non-stoichiometric phases of lithium nickel cobalt oxides were synthesized by a sol–gel method using oxalic acid as a chelating agent. The structural properties have been examined using X-ray diffraction techniques. Electrochemical coin cell studies showed materials with excess lithium stoichiometry had interesting properties of improved capacity and cyclability. Of all the compositions with excess lithium stoichiometry, Li_1.1Ni_0.8Co_0.2O₂, showed better electrochemical characteristics with a first cycle discharge capacity of 182 mAh/g and a 10th cycle of 172 mAh/g than the ideal stoichiometry LiNi_0.8Co_0.2O₂. The structural and electrochemical properties of Li_xNi_0.8Co_0.2O₂ with x=1.00, 1.05, 1.10 and 1.15 are discussed in detail.     

锂离子电池正极材料锂镍氧化物研究新进展

锂镍氧化物是目前高容量大功率锂离子电池正极材料的主要候选材料之一 .本文详细介绍了锂镍氧化物作为锂离子电池正极材料的实用化困难与其结构的内在联系 ,以及解决这些困难所进行的合成方法和掺杂改性研究的概况 .探索新的合成方法以及多组分掺杂改性应是今后锂镍氧化物的研究方向     

Synthesis of Li[Li0.2Ni0.2Mn0.6]O2 by radiated polymer gel method and impact of deficient Li on its structure and electrochemical properties

Layered Li[Li_0.16Ni_0.21Mn_0.63]O₂ and Li[Li_0.2Ni_0.2Mn_0.6]O₂ compounds were successfully synthesized by radiated polymer gel (RPG) method. The effect of deficient Li on the structure and electrochemical performance was investigated by means of X-ray diffraction, X-ray absorption near-edge spectroscopy and electrochemical cell cycling. The reduced Ni valence in Li[Li_0.16Ni_0.21Mn_0.63]O₂ leads to a higher capacity owing to faster Li⁺ chemical diffusivity relative to the baseline composition Li[Li_0.2Ni_0.2Mn_0.6]O₂. Cyclic voltammograms (CV) and a simultaneous direct current (DC) resistance measurement were also performed on Li/Li[Li_0.16Ni_0.21Mn_0.63]O₂ and Li/Li[Li_0.2Ni_0.2Mn_0.6]O₂ cells. Li[Li_0.16Ni_0.21Mn_0.63]O₂ shows better electrochemical performance with a reversible capacity of 158 mA hg⁻¹ at 1C rate at 20 °C.     

Nano-sized lithium manganese oxide dispersed on carbon nanotubes for energy storage applications

Nano-sized lithium manganese oxide (LMO) dispersed on carbon nanotubes (CNT) has been synthesized successfully via a microwave-assisted hydrothermal reaction at 200 °C for 30 min using MnO₂-coated CNT and an aqueous LiOH solution. The initial specific capacity is 99.4 mAh/g at a 1.6 C-rate, and is maintained at 99.1 mAh/g even at a 16 C-rate. The initial specific capacity is also maintained up to the 50th cycle to give 97% capacity retention. The LMO/CNT nanocomposite shows excellent power performance and good structural reversibility as an electrode material in energy storage systems, such as lithium-ion batteries and electrochemical capacitors. This synthetic strategy opens a new avenue for the effective and facile synthesis of lithium transition metal oxide/CNT nanocomposite.     

The effect of chromium substitution on the phase transition of lithium manganese spinel oxides

The phase transition of chromium substituted lithium manganese spinel oxide, LiCr_yMn_2−yO₄ was investigated by low-temperature powder X-ray diffractometry (XRD), differential scanning calorimetry (DSC), and electrical resistivity measurements. The sample prepared at 820 °C resulted in lowering the transition temperature T_t with Cr composition y, whereas T_t of the sample prepared at 750 °C remained constant for 0≤y≤0.17 in LiCr_yMn_2−yO₄. This would be caused by a difference in distribution of the substituted Cr³⁺ ion in octahedral site depending on the preparation temperature. The phase transition was suppressed with increasing the amount of Cr content.     

Rapid evaluation of charge/discharge properties for lithium manganese oxide particles at elevated temperatures

A microelectrode technique was applied to investigate the electrochemical properties of LiMn₂O₄ particles at elevated temperatures. Cyclic voltammograms of LiMn₂O₄ were measured after the particles were exposed to the electrolytes. This technique results in rapid and precise evaluation of the redox behavior of the materials. A significant capacity fading was observed in 1 M LiPF₆/EC+PC electrolytic solution, which indicates that both LiMn₂O₄ and LiPF₆ participate in the reaction to produce an inert material on the particle surface. Next, the capacity fading for two different BET surface area particles were compared using 1 M LiPF₆/EC+PC at 50 °C. The reaction was found not to be controlled by the surface area. Finally, a Li_1.1Mn_1.9O₄ particle was employed. The fading in discharge was ca. 10% for 50 cycles even at 50 °C, which means that the partial substitution of Mn in LiMn₂O₄ by Li substantially enhanced the capacity stability. Electronic Publication     

Synthesis of orthorhombic LiMnO2 by solid-phase reaction under steam atmosphere and a study of its heat and acid-treated phases

Low crystalline orthorhombic LiMnO₂ (o-LiMnO₂) samples were synthesized by reacting either γ-MnOOH or Mn₂O₃ with LiOH·H₂O in the solid phase under steam atmosphere at 120°C. In the closed system, the vapor arising from LiOH·H₂O may strengthen the reactivity of LiOH at the surface of MnOOH or Mn₂O₃ particles, which may enable slow diffusion of Li⁺ ions forming LiMnO₂. These samples were compared with crystalline o-LiMnO₂ prepared by a solid-state reaction method at 700°C in nitrogen gas. The powder X-ray diffraction patterns of low crystalline samples after heating at 400°C in air revealed the formation of a single phase of cubic Li_1.6Mn_1.6O₄, but the crystalline sample revealed a mixed phase of o-LiMnO₂ and LiMn₂O₄ after heating at 400°C in air. The Li⁺/H⁺ exchange in the Li_1.6Mn_1.6O₄ sample progressed topotactically, while maintaining the crystal structure and morphology of the precursor. But heat-treated crystalline o-LiMnO₂ showed a disproportionation reaction with dissolution of Mn²⁺ ions.     

Battery performance of nanostructured lithium manganese oxide synthesized by ultrasonic spray pyrolysis at elevated temperature

Nanostructured lithium manganese oxide with spherical particles was synthesized via ultrasonic spray pyrolysis technique. The material shows a pronounced stability upon prolonged cycling at room temperature at high charge–discharge rates up to 10C. The electrochemical performance of the cell at elevated temperature was remarkably improved by addition of AlPO₄ to the electrolyte. The AC impedance spectroscopy study showed the interface stabilization by the AlPO₄ additives and the suppression of the interface impedance development upon prolonged cycling.     

Synthesis and electrochemical characteristics of oxysulfide spinel material for lithium secondary batteries

Oxysulfide spinel LiMn₂O_3.98S_0.02 powders with monodispersed, and highly homogeneous particles were synthesized by a sol-gel method using an aqueous solution of metal acetates and sulfide containing glycolic acid as a chelating agent. The oxysulfide spinel, LiMn₂O_3.98S_0.02 electrode initially delivers 80 mAh g⁻¹, steadily increases during cycling, and reaches 99 mAh g⁻¹ at the 20th cycle. The substitution of a small amount S for O in LiMn₂O₄ spinel helps to maintain structural integrity during cycling, which then overcomes the Jahn–Teller distortion in the spinel Mn phase in the 3 V region.     

Synthesis of nickel nanoparticles supported on metal oxides using electroless plating: Controlling the dispersion and size of nickel nanoparticles

Nickel nanoparticles supported on metal oxides were prepared by a modified electroless nickel-plating method. The process and mechanism of electroless plating were studied by changing the active metal (Ag) loading, acidity, and surface area of metal oxides and were characterized by UV–vis spectroscopy, transmission electron microscopy, scanning electron microscopy, and H₂ chemisorption. The results showed that the dispersion of nickel nanoparticles was dependent on the interface reaction between the metal oxide and the plating solution or the active metal and the plating solution. The Ag loading and acidity of the metal oxide mainly affected the interface reaction to change the dispersion of nickel nanoparticles. The use of ultrasonic waves and microwaves and the change of solvents from water to ethylene glycol in the electroless plating could affect the dispersion and size of nickel nanoparticles.     

Partially substituted lithium manganese oxides as 3 V cathode materials for secondary lithium batteries

Low temperature synthesis and electrochemical properties of partially substituted lithium manganese oxides are reported. We demonstrate various metallic cations (Cu²⁺, Ni²⁺, Fe³⁺, Co³⁺) can be incorporated in the 3 V layered cathodic material Li_0.45MnO_2.1. New compounds Li_0.45Mn_0.88Fe_0.12O_2.1, Li_0.45Mn_0.84Ni_0.16O_2.05, Li_0.45Mn_0.79Cu_0.21O_2.3, Li_0.45Mn_0.85Co_0.15O_2.3 are prepared. These 3 V cathode materials are characterized by the same shape of discharge-charge profiles but different values of the specific capacity, between 90 mAh g⁻¹ and 180 mAh g⁻¹. The best results in terms of capacity and cycle life are obtained with the selected content of 0.15 Co per mole of oxide, as the optimum composition. The high kinetics of Li⁺ transport in Li_0.45Mn_0.85Co_0.15O_2.3 compared to that in the Co-free material is consistent with a substitution of Mn(III) by Co(III) in MnO₂ sheets.     

Synthesis and electrochemical study of Li-Mn-Ni-O cathodes for lithium battery applications

Cathode powders of the Li–Mn–Ni–O system have been prepared at a Mn/(Mn+Ni) ratio varying from 0 to 1. The solid state reaction method was used to obtain the cathode materials by mixing MnO₂, LiCO₃ and NiO. A 20% excess of lithium was used in the precursors. The materials produced were examined by X-rays to identify their structure. Batteries were assembled by using these materials as cathode with a liquid electrolyte consisting of EC/DC 1:1, 1 LiPF₆ and Li anode. Their capacity, cycle fading and charge-discharge conditions were evaluated.Presented at the 3rd International Meeting "Advanced Batteries and Accumulators", June 16th–June 20th 2002, Brno, Czech Republic     

Influence of sequential lithium insertions on the physical properties of spinel manganese oxide

We present first principles studies based on density functional theory (DFT) to investigate the lithium intercalation process in spinel manganese oxide compound. The lattice volume change, energetics, and insertion voltage were systematically examined upon sequential lithium insertions into the lattice. The charge transfer mechanism upon lithium intercalation was studied by analyzing the calculated spectra of density of states. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

电感耦合等离子体发射光谱法测定二次电池废料中锂、镍、钴、锰的含量

采用HCl-HNO 3溶解样品,使用电感耦合等离子体发射光谱(ICP-OES)法直接测定二次电池废料中含量低于20%的锂、镍、钴和锰的含量。选用元素最佳分析谱线和仪器合适的工作条件测定实际样品,实验结果表明共存元素对测定结果基本没有影响。相对标准偏差(n=11,RSD<2%)。通过不同方法的测试结果对比,同一样品的不同测定结果基本吻合,结果表明,方法操作快速简便,分析结果准确,能够满足二次电池废料中20%以下的锂、镍、钴和锰的测定。     

咪唑类Schiff碱配体及其含Mn配合物的合成及表征

锰在某些生物的氧化还原部位起着重要的作用[1] 。目前 ,已知的含锰金属酶有含锰超氧化物歧化酶 (ＭｎＳＯＤ)、含锰过氧化氢酶 (ＭｎＣａｔａｌａｓｅ)、含锰核糖核苷酸还原酶 (ＭｎＲＲ)、绿色植物光系统Ⅱ (ＰＳⅡ )中的氧释放配合物 (ＯＣＥ)等[2 ] 。生物体中锰的价态有 +2、+3、和 +4(最近发现有 +5 ) ,而且锰离子通常具有高自旋特征。正是这些特点使锰在生物体的氧化还原过程中发挥着重要的作用。我们合成了 1 甲基咪唑、1 甲基 2 羟甲基咪唑、1 甲基 2 咪唑醛等 3种咪唑类化合物以及1 甲基 2 咪唑醛与邻苯二胺的ｓｃｈｉｆｆ…     

三元锂离子电池容量衰减机理研究进展

三元锂离子电池主要是指使用镍钴锰酸锂(NCM)或镍钴铝酸锂(NCA)作为正极材料的锂离子电池,三元锂离子电池广泛应用于电动汽车、3C电子产品、储能等领域。然而,三元锂离子电池的循环寿命已成为其进一步发展的最大障碍,因此了解三元锂离子电池的容量衰退机理具有重要意义。三元锂离子电池的衰退机理主要包括五个方面:晶体结构的改变和相变、活性材料的损失、电解质的分解和消耗、可脱嵌锂离子的损耗以及固体电解质界面的形成。本文总结了近年来相关方面的研究进展,以期更全面地总结三元锂离子电池的容量衰减机理,并对三元锂离子电池的应用前景进行了展望。     

The effect of Al substitution on the reactivity of delithiated LiNi1/3Mn1/3Co(1/3−z)AlzO2 with non-aqueous electrolyte

The high temperature reactions between 1 M LiPF₆ EC:DEC and Al-doped LiNi_1/3Mn_1/3Co_(1/3−z)Al_zO₂ charged to 4.3 V were studied by accelerating rate calorimetry (ARC) and compared with those of charged LiNi_1/3Mn_1/3Co_1/3O₂ and LiMn₂O₄. Al substitution for Co in LiNi_1/3Mn_1/3Co_1/3O₂ improves the thermal stability. Materials with z > 0.06 are less reactive with electrolyte than spinel LiMn₂O₄ at all temperatures studied. The maximum self-heating rate (SHR) attained and the specific capacity decrease as the Al content increases. There is a range of compositions near z = 0.1 that show excellent promise as materials which are both safer than and more energy dense than spinel LiMn₂O₄.     

Synthesis, characterization, and electrochemical properties of ordered mesoporous carbons containing nickel oxide nanoparticles using sucrose and nickel acetate in a silica template

New ordered mesoporous carbons containing nickel oxide nanoparticles have been successfully synthesized by carbonization of sucrose in the presence of nickel acetate inside SBA-15 mesoporous silica template. The obtained samples were characterized by X-ray diffraction (XRD), nitrogen adsorption-desorption, and transmission electron microscopy (TEM). The NiO nanoparticles were embedded inside the mesoporous carbon framework due to the simultaneous pyrolysis of nickel acetate during carbonization. The electrochemical testing of the as-made nanocomposites showed a large specific capacitance of 230 F g⁻¹ using 2 M KOH as the electrolyte at room temperature. This is attributed to the nanometer-sized NiO formed inside mesoporous carbons and the high surface area of the mesopores in which the NiO nanoparticles are formed. Furthermore, the synthetic process is proposed as a simple and general method for the preparation of new functionalized mesoporous carbon materials, for various applications in catalysis, sensor or advanced electrode material.