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…     

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.     

Mn3−xZnxO4 spinel phases in the Zn–Mn–O system

The thermal evolution of the Zn–Mn–O system in air was studied by X-ray diffraction, transmission electron microscopy–energy dispersive spectroscopy and electron energy loss spectroscopy. The obtained results suggest that this evolution involves the formation of different Mn_3−xZn_xO₄ spinel-type phases. With increasing temperature these spinels experience phase transformations which are found to be induced by the Mn(IV) to Mn(III) reduction process. This last cation is an active Jahn–Teller ion which leads to an appreciable distortion of the Mn_3−xZn_xO₄ spinel structure, from a cubic symmetry at low temperatures to highly distorted tetragonal symmetries at high temperatures.     

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⁺.     

Investigation of structural and electrical properties of (1 − x) Bi0.5Mg0.5TiO3–(x) PbTiO3 ceramic system

A 3 V cathode material for lithium ion batteries, Li_0.33MnO₂, was synthesized by solid-state reaction. Two Mn crystallographic positions, Mn₍₁₎ and Mn₍₂₎, were determined by X-ray diffraction analysis. The [Mn₍₂₎O₆] octahedron had a lower symmetrical degree than that of [Mn₍₁₎O₆], which was attributed to the geometrical effects of the non-symmetrical environment around Mn₍₂₎. Li_0.33MnO₂ delivered a reversible discharge capacity 140 mA h g⁻¹. In situ synchrotron diffraction clearly showed a reversible phase transition of Li_0.33MnO₂ during electrochemical process. The analysis of X-ray absorption near edge spectroscopy observed the conversion of Mn⁴⁺ to Mn³⁺ with Li⁺ intercalation into Li_0.33MnO₂, accompanied by the formation of more severely distorted [MnO₆] octahedron.     

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.     

The corrosion behavior of Fe-Cr alloys containing Co,Mn, and/or Ni and of a Co-base alloy in the presence of molten (Li,K)-carbonate

The corrosion behavior or commercial Fe ana Co base alloys and Fe-Cr model alloys with different contents of Co and/or Mn was investigated by continuous exposure tests in the presence of a thin carbonate film. All alloys studied form multi-layered corrosion scales consisting of outer Li containing oxides and inner Cr rich oxides, i.e. spinels or LiCrO₂. The LiCrO₂ is formed on alloys with high Cr contents (≤ 20 wt.%), whereas mixed (Fe,M)_3-x Cr_xO₄ spinels (M = Co, Mn, Ni) were found on alloys with lower Cr content (15–20 wt.%). Insoluble Cr containing oxides occur only in the inner layers of the corrosion scale, whereas on the surface of corroded specimens soluble chromates were detected. Alloys with Mn contents greater than 15 wt.% form Mn₂O₃ in the initial stages of the experiments, this oxide reacts with the melt and formation of Li₂MnO₃ takes place. In exposure tests up to 500 h Fe-Cr alloys with low contents of Mn and Co (10 wt.% Co or Mn) form iron rich oxides (LiFeO₂ and LiFe₅O₈) with varying amounts of dissolved Mn or Co. In the later corrosion stages outward diffusion of Mn and/or Co takes place and LiCoO, and Li₂MnO₃ are formed on top of LiFeO₂, whereby the concentration of Mn and/or Co in the inner layers (LiFeO₂ and spinel) decreases. The outer Li containing oxides LiFeO₂, LiCoO₂ and Li₂MnO₃ are nearly insoluble in the melt and when present at the surface protect the metallic material from further corrosive attack. Fe-Cr model alloys containing Co and Mn form multi-layered corrosion layers after 2000 h of exposure. These layers consist of four oxides in the following sequence from the metal-scale to the scale-melt interface: (Fe,Cr,Co,Mn)₃O₄ spinel, LiFeO₂, Li₂MnO₃ and LiCoO₂.     

Preparation and property of spinel LiMn2O4 material by co-doping anti-electricity ions

1 Introduction At present, LiCoO2 is almost the only cathode material of Li-ion batteries, which can be used in large-scale commercialization, because such material possesses high specific capacity, ease of preparation, high discharging flat and favorable…     

Effects of Na+ doping on crystalline structure and electrochemical performances of LiNi0.5Mn1.5O4 cathode material

Pristine LiNi_0.5Mn_1.5O₄ and Na-doped Li_0.95Na_0.05Ni_0.5Mn_1.5O₄ cathode materials were synthesized by a simple solid-state method. The effects of Na⁺ doping on the crystalline structure and electrochemical performance of LiNi_0.5Mn_1.5O₄ cathode material were systematically investigated. The samples were characterized by XRD, SEM, FT-IR, CV, EIS and galvanostatic charge/discharge tests. It is found that both pristine and Na-doped samples exhibit secondary agglomerates composed of well-defined octahedral primary particle, but Na⁺ doping decreases the primary particle size to certain extent. Na⁺ doping can effectively inhibit the formation of Li_xNi_1–xO impurity phase, enhance the Ni/Mn disordering degree, decrease the charge-transfer resistance and accelerate the lithium ion diffusion, which are conductive to the rate capability. However, the doped Na⁺ ions tend to occupy 8a Li sites, which forces equal amounts of Li⁺ ions to occupy 16d octahedral sites, making the spinel framework less stable, therefore the cycling stability is not improved obviously after Na⁺ doping.     

Influence of MnO2 on the sintering behavior and magnetic properties of NiFe2O4 ferrite ceramics

The samples with small amounts of MnO₂ (0, 0.5, 1.0, 1.5, 2.0, and 2.5 wt%, respectively) were prepared via ball-milling process and two-step sintering process from commercial powders (i.e. Fe₂O₃, NiO and MnO₂). Microstructural features, phase transformation, sintering behavior and magnetic properties of Mn-doped NiFe₂O₄ composite ceramics have been investigated by means of scanning electron microscopy (SEM), differential thermal analyzer, X-ray diffraction (XRD), thermal dilatometer and vibrating sample magnetometer (VSM) respectively. The XRD analysis and the result of differential thermal analysis indicate that the reduction of MnO₂ into Mn₂O₃ and the following reduction of Mn₂O₃ into MnO existed in sintering process. No new phases are detected in the ceramic matrix, the crystalline structure of the ceramic matrix is still NiFe₂O₄ spinel structure. Morphology and the detecting result of thermal dilatometer show that MnO₂ can promote the sintering process, the temperature for 1 wt% MnO₂-doped samples to reach the maximum shrinkage rate is 59 °C lower than that of un-doped samples. For 1 wt% MnO₂-doped samples, the value of the saturation magnetization (M_s) and coercivity (H_c) is 15.673 emu/g and 48.316 Oe respectively.     

LixZrS2 intercalation compounds

The disulfide ZrS₂ has been intercalated with lithium by means of the butyllithium method. Two phases have been characterized. The first (0? x < 0.20), of the NiAs type, presents no parameter variation. The second (0.30 < x ? 1) is rhombohedral at room temperature but undergoes a phase transition to a spinel structure in the 0.30 < x < 0.50 range at 250°C. Electrical and magnetic measurements have shown that the first phase is semiconducting, the second being of a metallic type. Comparisons are made with the Li_xZrSe₂ system.     

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.     

Oxidation of Fe–10Cr in O2 and in O2 + H2O environment at 600 °C: A microstructural investigation

Oxidation of Fe–10Cr in dry and wet O₂ was studied at 600 °C for up to 168 h. Oxide microstructure was investigated by STEM/EDX, FIB/SEM and TEM. Oxidation in dry O₂ gives a Cr-rich protective (Fe_1−xCr_x)₂O₃ scale. The same protective oxide initially forms in O₂ + H₂O environment, but after an incubation period scale breakdown is triggered by CrO₂(OH)₂ evaporation that depletes the substrate in Cr and converts (Fe_1−xCr_x)₂O₃ to FeCr spinel oxide. Internal oxidation occurs after breakaway. Alternating external and internal oxidation result in the inward-growing scale showing a characteristic banded morphology.     

掺F锂离子电池正极材料Li1.03Co0.10Mn1.90FzO4-z的制备及电化学性能

以Li2CO3、Mn2O3、Co2O3及LiF为原料,采用高温固相法合成了掺F的Li1.03Co0.10Mn1.90FzO4?z锂电池正极材料。通过离子发射光谱(ICP)和电位分析法确定了材料的化学组成,用X-射线衍射(XRD)、扫描电子显微镜(SEM)和电化学测试仪分析了 F 掺杂量对材料结构、形貌和电池性能的影响。结果表明,掺 F 的Li1.03Co0.10Mn1.90FzO4?z正极材料为尖晶石结构,在F掺入量z≤0.10时,随着掺杂量的增加晶胞参数逐渐增加,当F掺杂量继续增加时,晶胞参数的增幅有所减小。适量的F?与金属离子Li+、Co+的复合掺杂提高了材料的放电比容量,同时增强了材料结构的稳定性。电化学性能测试表明,Li1.03Co0.10Mn1.90F0.15O3.85的首次放电比容量达到111.0 mA·h/g,0.2C倍率下30次循环后容量保持率为97.0%。     

Effect of MnO2 Addition on Sintering Properties of 18NiO-NiFe2O4 Composite Ceramics: Preliminary Results

NiFe₂O₄ samples with small amounts of MnO₂ were prepared via ball-milling process and two-step sintering process from commercial powders. Sintered density, average grain size, and microstructure of Mn-doped 18NiO-NiFe₂O₄ composite ceramics have been investigated by means of x-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy. Bending strength was measured by three-point method. The results show that the crystalline structures of the ceramic matrix are still NiFe₂O₄ spinel structure and Mn ions homogeneously distribute in both the grains interiors and the grain boundaries. When 1 wt.% MnO₂ was added, the values of relative density and bending strength of composite ceramics reached their respective maximum of 93.6% and 38.75 MPa, respectively. It is preliminarily found that MnO₂ can reduce the sintering temperature obviously because of partial substitution of Fe³⁺ with Mn⁴⁺ in NiFe₂O₄ lattice.     

Co2MnO4 spinel-palladium co-infiltrated La0.7Ca0.3Cr0.5Mn0.5O3−δ cathodes for intermediate temperature solid oxide fuel cells

The effect of co-infiltration of Co₂MnO₄ (CM) spinel oxides and Pd on the electrochemical activity and microstructure stability of La_0.7Ca_0.3Cr_0.5Mn_0.5O_3−δ (LCCM) cathodes for the O₂ reduction reaction of intermediate temperature solid oxide fuel cells (IT-SOFCs) has been investigated in detail. The microstructure, thermal stability, electrochemical activity and stability of the Co₂MnO₄-Pd/PdO powders and Co₂MnO₄-Pd/PdO co-impregnated LCCM cathode were measured using thermal gravimetric analysis, X-ray diffraction, scanning electron microscopy and electrochemical impedance spectroscopy. The results indicate that the addition of spinel oxides effectively inhibits the growth and coalescence of the Pd/PdO nanoparticles and stabilizes the microstructure of the Pd/PdO at high temperatures. The best electrochemical activity and stability of LCCM cathodes were obtained on the cathode co-infiltrated with 50 wt% PdO/50 wt% Co₂MnO₄. The enhancement is due to the significantly improved stability of the microstructure as a result of the inhibited grain growth and agglomeration of Pd/PdO nanoparticles by the co-infiltrated Co₂MnO₄ spinel phase.     

High-temperature ferromagnetism observed in facing-target reactive sputtered MnxTi1−xO2 films

The crystal structure of reactive sputtered Mn_xTi_1−xO₂ films turns from anatase to rutile as x increases. All the films are ferromagnetic, with a Curie temperature above 340 K. Vacuum annealing enhances the ferromagnetism of the films, but O₂ annealing weakens it, indicating that the ferromagnetism is related to the oxygen-vacancy defects created by Mn⁺² dopants at Ti⁺⁴ cations. The average room-temperature moment per Mn decreases from 0.482 μ_B at x = 0.026 to 0.078 μ_B at x = 0.375. Meanwhile, the optical band gaps value decreases linearly from 3.35 eV at x = 0 to 1.73 eV at x = 0.375, suggesting that Mn ions substitute for Ti ions uniformly and the ferromagnetism is not from magnetic Mn oxide impurities. The high-temperature ferromagnetism makes the Mn_xTi_1−xO₂ films useful for the applications in spintronic devices.     

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.     

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.     

Phase diagram study for the CaO-SiO2-Cr2O3-5 mass.%MgO-10 mass.%MnO system

The phase diagram of the CaO-SiO₂-CrO_x-MgO-MnO system at moderately reducing oxygen partial pressure was calculated using a commercial thermochemical program and compared with the phase analysis for converter slags taken from the stainless steelmaking process. It was found that a (Mn,Mg)Cr₂O₄ solid solution and Ca₂SiO₄ phase are in equilibrium with the oxidation slags after the oxygen blowing period, which is consistent with thermodynamic calculations. Furthermore, it could be proposed that the thermodynamic properties of a MgCr₂O₄-MnCr₂O₄ binary spinel make it close to an ideal solution.