Preparation and electrochemical performance of nitrogen-doped carbon-coated Bi2Mn4O10 anode materials for lithium-ion batteries

To inhibit rapid capacity attenuation of Bi₂Mn₄O₁₀ anode material in high-energy lithium-ion batteries, a novel high-purity anode composite material Bi₂Mn₄O₁₀/ECP-N (ECP-N: N-doped Ketjen black) was prepared via an uncomplicated ball milling method. The as-synthesized Bi₂Mn₄O₁₀/ECP-N composite demonstrated a great reversible specific capacity of 576.2 mA·h/g after 100 cycles at 0.2C with a large capacity retention of 75%. However, the capacity retention of individual Bi₂Mn₄O₁₀ was only 27%. Even at 3C, a superior rate capacity of 236.1 mA·h/g was retained. Those remarkable electrochemical performances could give the credit to the introduction of ECP-N, which not only effectively improves the specific surface area to buffer volume expansion and enhances conductivity and wettability of composites but also accelerates the ion transfer and the reversible conversion reaction.     

In-situ TEM analysis of the reduction of nanometre-sized Mn3O4 precipitates in a metal matrix

The objective of the present work is the in-situ study of the transformation of small oxide precipitates in a metal matrix by conventional and high-resolution transmission electron microscopy (HRTEM). As an example the reduction of Mn₃O₄ into MnO for nano-sized oxide precipitates in a silver matrix was studied in detail. A convenient method for monitoring the reduction process is shown for a large number of precipitates simultaneously. It is based on two-beam dark-field images showing distinct Moiré patterns for the MnO and the various types of Mn₃O₄ precipitates embedded within an Ag matrix. A controlling factor of the transformation kinetics appeared to be the rate in which the system can relax the strains due to the accompanying volume reduction of the precipitates. Other interesting aspects of the Mn₃O₄ to MnO transformation scrutinized and explained were the shape change of the precipitates upon reduction and the fact that mixed Mn₃O₄/MnO precipitates were only detected within a small temperature/time interval. Ostwald ripening of the MnO precipitates was observed as well.     

Thermal, structural and magnetic properties of some zinc phosphate glasses doped with manganese ions

(MnO)_x·(P₂O₅)₄₀·(ZnO)_60−x glasses containing different concentrations of MnO ranging from 0 to 20 mol% were prepared by the melt-quenching technique. The samples had a fixed P₂O₅ content of 40 mol% and the MnO:ZnO ratio was varied. The thermal, structural and magnetic properties of these glasses were investigated by means of differential thermal analysis (DTA), electron paramagnetic resonance (EPR) and magnetic susceptibility measurements. Compositional dependence of the glass transition (T_g), crystallization (T_p) and melting temperatures were determined by DTA investigations. From the dependence of the T_g on the heating rate (a), the activation energy of the glass transition (E_g) was calculated. The fragility index (F) for the studied glasses was determined to see whether these materials are obtained from kinetically strong-glass-forming (KS) or kinetically fragile-glass forming (KF) liquids. The EPR spectra of the studied glasses revealed absorptions centered at g ≈ 2.0, 3.3 and 4.3. The compositional variations of the intensity and line width of these absorption lines was interpreted in terms of the variation in the concentration of the Mn²⁺ and Mn³⁺ ions in the glass and the interaction between the manganese ions. EPR and magnetic susceptibility data reveal that both Mn²⁺ and Mn³⁺ ions are present in the studied glasses, their relative concentration being dependent on the glass composition. Magnetic susceptibility data reveal an antiferromagnetic interaction between the manganese ions for the glasses containing 20 mol% MnO.     

Phase transition of lithiated-spinel Li2Mn2O4 at high temperature

1 Introduction Lithium manganese oxides are the most attractive cathode materials for rechargeable lithium-ion batteries because of their low-cost and less toxicity when compared with either cobaltates or nickelates[1?3]. Among these oxides, the spinel-fr…     

Structural and electrochemical characteristics of Li x Mn2O4 spinel synthesized using a microwave-assisted method

The structural and electrochemical features of Li _x Mn₂O₄ spinel synthesized by the microwave-assisted method are discussed. The thermal gravimetric analysis shows that almost 84% of all the initial reactants undergo chemical transformation associated with the weight loss in the course of the microwave-assisted synthesis. The composition of the initial components influences the heating rate negligibly, and the temperature reaches 400°C within around 15 minutes. The X-ray phase analysis shows that the Li _x Mn₂O₄ samples contain impurities such as MnO₂ and Mn₂O₃, the amount of which decreases with the increase in the lithium content. The electrochemical characteristics of the Li _x Mn₂O₄ are strongly influenced by the composition of the starting components, which is particularly noticeable upon high discharge rates.     

Study of glass formation in the Sb2O3-PbO-MnO ternary system

Vitreous systems based on antimony oxide Sb₂O₃ have been investigated. The influence of MnO substitution on the mechanical and physical properties in the (80 − x)Sb₂O₃-20PbO-xMnO and (70 − x)Sb₂O₃-(30 − x)PbO-2xMnO systems has been studied. Vickers hardness, density, molar volume, Young modulus, glass temperature transition, infrared and UV transmission spectra depend on the MnO concentration. Crack analysis of the glass surface under indentor deformation shows the tenacity changes according to concentration of the MnO.     

Mn2O3掺杂对MnO催化氧还原性能的提高

本文主要研究了纯相MnO以及Mn₂O₃掺杂MnO氧还原催化剂的结构和性能,XRD、SEM、HRTEM等测试表明,氢气还原条件下可以得到Mn₂O₃掺杂的MnO,氨气还原得到纯相MnO。循环伏安(CV)法、Tafal曲线法、时间电流曲线和线性扫描伏安等方法对其催化氧还原性能的研究表明：MnO催化氧还原的峰值电压在-0.1 V到-0.5 V之间,Mn₂O₃的掺杂提高了氧还原峰值电流强度和电压;RDE与RRDE测试表明：Mn₂O₃掺杂MnO的催化氧还原反应主要是4电子反应,而纯相MnO催化氧还原主要是2电子反应。通过本研究表明：Mn₂O₃掺杂提高了MnO的催化氧还原性能,元素不同价态离子的共存提高了催化氧还原反应的活性。     

Enhanced cycling stability of La modified LiNi0.8–xCo0.1Mn0.1LaxO2 for Li-ion battery

A series of layered LiNi_0.8–xCo_0.1Mn_0.1La_xO₂ (x=0, 0.01, 0.03) cathode materials were synthesized by combining co-precipitation and high temperature solid state reaction to investigate the effect of La-doping on LiNi_0.8Co_0.1Mn_0.1O₂. A new phase La₂Li_0.5Co_0.5O₄ was observed by XRD, and the content of the new phase could be determined by Retiveld refinement and calculation. The cycle stability of the material is obviously increased from 74.3% to 95.2% after La-doping, while the initial capacity exhibits a decline trend from 202 mA·h/g to 192 mA·h/g. The enhanced cycle stability comes from both of the decrease of impurity and the protection of newly formed La₂Li_0.5Co_0.5O₄, which prevents the electrolytic corrosion to the active material. The CV measurement confirms that La-doped material exhibits better reversibility compared with the pristine material.     

Resynthesis of LiCo<Subscript>1−x</Subscript>Mn<Subscript>x</Subscript>O<Subscript>2</Subscript> as a cathode material for lithium secondary batteries

A recycling process involving chemical, mechanical, and electrochemical steps has been applied to recover cobalt from spent lithium ion batteries and resynthesize cathode active materials. LiCo_1−xMn_xO₂ powders using Co salt including Mn from the leach liquor were resynthesized by solid-state reaction as cathode active materials. When the powder mixture with added Li salt was calcined at 950 °C for 8 hours, well crystallined LiCo_1−xMn_xO₂ was successfully obtained. The LiCo_1−xMn_xO₂ powders with a ratio of Co:Mn=10:1 has a discharge capacity of 156.3 mAh/g at a rate of 20 mA/g with no perceptible capacity loss, in sharp contrast to the pure LiCoO₂ as active materials. The resynthesized LiCo_1−xMn_xO₂ was proven to have good characteristics as cathode active materials in charge/discharge capacity and cyclic performance.     

Cyclic voltammetry studies on 4 V and 5 V plateaus of non-stoichiometric spinel Li1＋xMn2-yO4

1 Introduction As one of the most promising cathode materials for lithium ion batteries, spinel LiMn2O4 has received much attention in recent years. This material has reversible capacities at both 3 V and 4 V plateaus[1]. However, the Li insertion and ex…     

Luminescence and energy transfer of Mn and Tb in Y3Al5O12 phosphors

Mn²⁺ is an excellent luminescent ion with variable color from green, yellow to red in different hosts and has been widely utilized in recent years. The luminescent intensity of Mn²⁺ in many hosts is so low that the correlative application is restricted. In the present paper, two methods, i.e. employing a charge compensator and introducing a sensitizer, were adopted to enhance the luminescence of Mn²⁺ in Y₃Al₅O₁₂ (YAG). By employing Si⁴⁺ as a charge compensator, the doping content of Mn²⁺ (x) in Y₃Mn_xAl_5−2xSi_xO₁₂ can be lifted up to 0.4. Mn²⁺ in YAG emits orange light in a broad band. The peak wavelength shifts from 586 to 593 nm with the increasing x. The luminescent intensity of Mn²⁺ reaches its maximum when x = 0.1. Co-doping Tb³⁺ into Mn²⁺ doped YAG, the sensitization effect of Tb³⁺ on Mn²⁺ was observed clearly. The resonance energy transfer from Tb³⁺ to Mn²⁺ occurs because there is a well overlapping between emission spectrum of Tb³⁺ and excitation spectrum of Mn²⁺. A reasonable explanation for the sensitization effect of Tb³⁺ on the luminescence of Mn²⁺ was brought forward.     

Hydrothermal synthesis of MnCO3 nanorods and their thermal transformation into Mn2O3 and Mn3O4 nanorods with single crystalline structure

MnCO₃ nanorods with diameters of 50-150 nm and lengths of about 1-2 μm have been prepared for the first time by a facile hydrothermal method. Mn₂O₃ and Mn₃O₄ nanorods were obtained via the heat-treatment of the MnCO₃ nanorods in air and nitrogen atmosphere, respectively. The morphology and structure of the as-synthesized MnCO₃, Mn₂O₃ and Mn₃O₄ nanorods were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and selected area electron diffraction. It was found that the MnCO₃ nanorods are single-crystalline, and their morphology and single-crystalline characteristic can be sustained after thermal transformation into Mn₂O₃ and Mn₃O₄. The corresponding growth directions for MnCO₃, Mn₂O₃ and Mn₃O₄ nanorods were [2 1 4], [1 0 0] and [1 1 2], respectively. When applied as anode materials for lithium ion batteries, the Mn₂O₃ and Mn₃O₄ nanorods exhibited a reversible lithium storage capacity of 998 and 1050 mAh/g, respectively, in the first cycles.     

Effect of the impurity LixNi1−xO on the electrochemical properties of 5 V cathode material LiNi0.5Mn1.5O4

The formation of impurity Li_xNi_1−xO when synthesizing spinel LiNi_0.5Mn_1.5O₄ using solid state reaction method, and its influence on the electrochemical properties of product LiNi_0.5Mn_1.5O₄ were studied. The secondary phase Li_xNi_1−xO emerges at high temperature due to oxygen deficiency for LiNi_0.5Mn_1.5O₄ and partial reduction of Mn⁴⁺ to Mn³⁺ in LiNi_0.5Mn_1.5O₄. Annealing process can diminish oxygen deficiency and inhibit impurity Li_xNi_1−xO. The impurity reduces the specific capacity of product, but it does not have obvious negative effect on cycle performance of product. The capacity of LiNi_0.5Mn_1.5O₄ that contains Li_xNi_1−xO can deliver about 120 mAh g⁻¹.     

Structural characterization of layered LiNi0.85−xMnxCo0.15O2 with x = 0, 0.1, 0.2 and 0.4 oxide electrodes for Li batteries

We report the synthesis of LiNi_0.85−xCo_0.15Mn_xO₂ positive electrode materials from Ni_0.85−xCo_0.15Mn_x(OH)₂ and Li₂CO₃. XRD and XPS are used to study the effect of Mn-doping on the microstructures and oxidation states of the LiNi_0.85−xCo_0.15Mn_xO₂ materials. The analysis shows that Mn-doping promotes the formation of a single phase. With increasing substitution of Mn ions for Ni ions, the lattice parameter a decreases, while the lattice parameters c and c/a increase. XPS revealed that the oxidation states of Ni, Co and Mn in LiNi_0.85−xCo_0.15Mn_xO₂ compounds (where x = 0.1, 0.2 and 0.4) were +2/+3, +3 and +4. The substitution of Mn ions for Ni ions induces a decrease in the average oxidation state of Ni. Because the substitution of Mn for Ni ions is complex, the extent of the changes between the lattice parameter and L_M-O differ. The occupation of Ni in Li sites is affected by the ordering of Mn⁴⁺ with Ni²⁺ and Mn⁴⁺ with Li⁺.     

Spectroscopic and crystal field analysis of absorption and photoluminescence properties of red phosphor CaAl12O19:Mn modified by MgO

The spectroscopic properties of a series of red phosphors with general composition of CaAl₁₂O₁₉:yMn⁴⁺ and (Ca_1−xAl₁₂O₁₉, xMgO):yMn⁴⁺ (x = 0-1, y = 0.001-1.5%) synthesized by a modified solid state method in air have been investigated in detail. Addition of MgO is necessary for Mn⁴⁺ charge compensation and leads to the formation of separate crystal phases of Al₂O₃ and MgAl₂O₄, which was confirmed by the XRD studies. Enhancement of Mn⁴⁺ luminescence with increasing content of MgO was observed and a mechanism for explanation of this phenomenon is suggested. For an analysis of the crystal phases and luminescent efficiency of the phosphors in the prepared series, crystal field calculations of the Mn⁴⁺ energy levels have been performed. This theoretical approach allowed for assigning the observed excitation and emission spectra. Red shift of the Mn⁴⁺ luminescence with increasing concentration of Mg ions is explained from the point of view of enhanced nephelauxetic effect after doping.     

Synthesis of LiNi1/3CO1/3Mn1/3O2 cathode material via oxalate precursor

Using oxalic acid and stoichiometrically mixed solution of NiCl2, CoCl2, and MnCl2 as starting materials, the triple oxalate precursor of nickel, cobalt, and manganese was synthesized by liquid-phase co-precipitation method. And then the LiNi1/3Co1/3Mn1/3O2 cathode materials for Li-ion battery were prepared from the precursor and LiOH-H2O by solid-state reaction. The precursor and LiNi1/3Co1/3Mn1/3O2 were characterized by chemical analysis, XRD, EDX, SEM and TG-DTA. The results show that the composition of precursor is Ni1/3Co1/3Mn1/3C2O4·2H2O. The product LiNi1/3Co1/3Mn1/3O2, in which nickel, cobalt and manganese are uniformly distributed, is well crystallized with a-NaFeO2 layered structure. Sintering temperature has a remarkable influence on the electrochemical performance of obtained samples. LiNi1/3Co1/3Mn1/3O2 synthesized at 900 ℃ has the best electrochemical properties. At 0.1C rate, its first specific discharge capacity is 159.7 mA·h/g in the voltage range of 2.75-4.30 V and 196.9 mA·h/g in the voltage range of 2.75-4.50 V; at 2C rate, its specific discharge capacity is 121.8 mA·h/g and still 119.7 mA·h/g after 40 cycles. The capacity retention ratio is 98.27%.     

DC magnetization investigations in Ti1−xMnxO2 nanocrystalline powder

In the present paper, DC magnetization investigation on the insulating nanocrystalline powder samples of Ti_1−xMn_xO₂ (x = 0, 0.05, 0.10, and 0.15) prepared by simple chemical route is reported. Structural measurements revealed phase pure anatase structure of TiO₂ when x ≤ 0.05 and a mixture of anatase and rutile TiO₂ along with the signature of Mn₃O₄ phase for x > 0.05. Magnetic measurements exhibited the presence of ferromagnetic ordering at room temperature in samples having either small fraction of Mn or no Mn at all. This ferromagnetic signature is accompanied with paramagnetic contribution which is found to dominate with increase in Mn concentration. The Ti_1−xMn_xO₂ sample having highest Mn concentration of x = 0.15 showed nearly paramagnetic behavior. However, at low temperatures, additional ferrimagnetic ordering arising due to Mn₃O₄ (T_C = 42 K) is evidenced in the doped samples. Consistent with the XRD investigations, the isofield DC-magnetization measurements under field cooled and zero field cooled (FC-ZFC) histories corroborated the presence of Mn₃O₄ phase. Also, distinct thermomagnetic irreversibility has been observed above 42 K. These results are suggestive of presence of weak ferromagnetic ordering possibly due to defects related with oxygen vacancies.     

Effect of lithium content on electrochemical property of Li1+x(Mn0.6Ni0.2Co0.2)1-xO2 (0≤x≤0.3) composite cathode materials for rechargeable lithium-ion batteries

In order to confirm the optimal Li content of Li-rich Mn-based cathode materials (a fixed mole ratio of Mn to Ni to Co is 0.6:0.2:0.2), Li_1+x(Mn_0.6Ni_0.2Co_0.2)_1-xO₂ (x=0, 0.1, 0.2, 0.3) composites were obtained, which had a typical layered structure with and C2/m space group observed from X-ray powder diffraction (XRD). Electron microscopy micrograph (SEM) reveals that the particle sizes in the range of 0.4-1.1 μm increase with an increase of x value. Li_1.2(Mn_0.6Ni_0.2Co_0.2)_0.8O₂ sample delivers a larger initial discharge capacity of 275.7 mA·h/g at the current density of 20 mA/g in the potential range of 2.0–4.8 V, while Li_1.1(Mn_0.6Ni_0.2Co_0.2)_0.9O₂ shows a better cycle performance with a capacity retention of 93.8% at 0.2C after 50 cycles, showing better reaction kinetics of lithium ion insertion and extraction.     

CO+CO2 mixtures and diffusional transport in MnO

Studies of MnO at high temperatures (1000–1200?C) suggest that diffusional transport can be different when the oxide is exposed to carbon-free environments and to CO/CO₂ mixtures, respectively. In the phase field of MnO near the MnO/Mn₃O₄ boundary it is concluded that defect clusters (consisting of four manganese vacancies + one interstitial manganese ion) are the important defects. Under these conditions it is proposed that carbon can dissolve in the oxide in association with the defect clusters. A defect structure model is proposed to account for the differences in properties. In keeping with this interpretation it is shown that parabolic rate constant for growth of MnO scales in CO/CO₂ mixtures is not only dependent upon the oxygen activity, but also up on the carbon activity in the gas. The electrical conductivity is also affected by changes in the carbon activity.     

Effects of Grit Blasting and Annealing on the High-Temperature Oxidation Behavior of Austenitic and Ferritic Fe-Cr Alloys

Grit blasting (corundum) of an austenitic AISI 304 stainless steel (18Cr-8Ni) and of a low-alloy SA213 T22 ferritic steel (2.25Cr-1Mo) followed by annealing in argon resulted in enhanced outward diffusion of Cr, Mn, and Fe. Whereas 3 bar of blasting pressure allowed to grow more Cr₂O₃ and Mn _x Cr_3?x O₄ spinel-rich scales, higher pressures gave rise to Fe₂O₃-enriched layers and were therefore disregarded. The effect of annealing pre-oxidation treatment on the isothermal oxidation resistance was subsequently evaluated for 48 h for both steels and the results were compared with their polished counterparts. The change of oxidation kinetics of the pre-oxidized 18Cr-8Ni samples at 850 °C was ascribed to the growth of a duplex Cr₂O₃/Mn _x Cr_3?x O₄ scale that remained adherent to the substrate. Such a positive effect was less marked when considering the oxidation kinetics of the 2.25Cr-1Mo steel but a more compact and thinner Fe _x Cr_3?x O₄ subscale grew at 650 °C compared to that of the polished samples. It appeared that the beneficial effect is very sensitive to the experimental blasting conditions. The input of Raman micro-spectroscopy was shown to be of ground importance in the precise identification of multiple oxide phases grown under the different conditions investigated in this study.