Comparative structural and electrochemical properties of mixed P2/O′3-layered sodium nickel manganese oxide prepared by sol-gel and electrospinning methods:Effect of Na-excess content

The effect of Na-excess content in the precursor on the structural and electrochemical performances of sodium nickel manganese oxide(NNMO)prepared by sol-gel and electrospinning methods is investigated in this paper.X-ray diffraction results of the prepared NNMO without adding Na-excess content indicate sodium loss,while the mixed phase of P2/O′3-type layered NNMO presented after adding Na-excess content.Compared with the sol-gel method,the secondary phase of NiO is more suppressed by using the electrospinning method,which is further confirmed by field emission scanning electron microscope images.N_(2) adsorption-desorption isotherms show no remarkably difference in specific surface areas between different preparation methods and Na-excess contents.The analysis of X-ray absorption near edge structure indicates that the oxidation states of Ni and Mn are+2 and+4,respectively.For the electrochemical properties,superior electrochemical performance is observed in the NNMO electrode with a low Na-excess content of 5wt%.The highest specific capacitance is 36.07 F·g^(-1)at0.1 A·g^(-1)in the NNMO electrode prepared by using the sol-gel method.By contrast,the NNMO electrode prepared using the electrospinning method with decreased Na-excess content shows excellent cycling stability of 100%after charge-discharge measurements for 300 cycles.Therefore,controlling the Na excess in the precursor together with the preparation method is important for improving the electrochemical performance of Na-based electrode materials in supercapacitors.

High-performance aqueous asymmetric supercapacitors based on the cathode of one-step electrodeposited cracked bark-shaped nickel manganese sulfides on activated carbon cloth

In this work,we report a high-performance self-standing supercapacitor electrode of mixed nickel manganese sulfides (NMSs)with a cracked-bark shape grown by one-step electrochemical deposition on activated carbon cloth (ACC).The electrode possesses outstanding electrochemical properties,including a high specific capacitance of up to 3142.8 F g^(-1)at 1.0 A g^(-1),the high-rate performance (~1206.8 F g^(-1)at 60.0 A g^(-1)),and cycle stability (~92.3%capacitance retention after 8000 cycles at8 A g^(-1)).An asymmetric supercapacitor assembled using NMSs on ACC as the cathode,activated carbon on carbon cloth as the anode and 1.0 mol L;KOH as the electrolyte delivers a high energy density of 111.2 W h kg^(-1)at 800.0 W kg^(-1)and the prominent cycling performance of~93.2%capacitance retention after 10000 cycles at 5 A g^(-1)with the Columbic efficiency of around 100%during these 10000 cycles.The high performance and facile preparation indicate that the NMSs on ACC hold a huge potential as the electrode for supercapacitors.

Effects of chromium doping on performance of LiNi_(0.5)Mn_(1.5)O_4 cathode material

In order to improve the cycle and rate performance of LiNi0.5Mn1.5O4, LiCr2 Ni0.5 Mn1.5 O （0≤Y≤0.15） particles were Y -Y -Y 4 synthesized by the sucrose-aided combustion method. The effects of Cr doping in LiNi0.5Mn1.5O4 on the structures and electrochemical properties were investigated. The samples were characterized by X-ray diffractometry （XRD）, scanning electron microscopy （SEM）, cyclic voltammetry （CV）, galvanostatic charge-discharge test and electrochemical impedance spectrum （EIS）. The results indicate that the LiCr2 Ni0.5 Mn1.5 O possess a spinel structure and small particle size, and LiCr0.2Ni0.4Mn1.4O4exhibits Y -Y -Y 4 the best cyclic and rate performance. It can deliver discharge capacities of 143 and 104 mA·h/g at 1C and 10C, respectively, with good capacity retention of 96.5% at 1C after 50 cycles.

Improving Interfacial Electrochemistry of LiNi0.5Mn1.5O4 Cathode Coated by Mn3O4

In this work the surface of LiNi0.5Mn1.5O4(LMN)particles is modified by Mn3O4 coating through a simple wet grinding method,the electronic conductivity is significantly improved from 1.53×10^-7 S/cm to 3.15×10^-5 S/cm after 2.6 wt%Mn3O4 coating.The electrochemical test results indicate that Mn3O4 coating dramatically enhances both rate performance and cycling capability(at 55℃)of LNM.Among the samples,2.6 wt%Mn3O4-coated LNM not only exhibits excellent rate capability(a large capacity of 108 m Ah/g at 10 C rate)but also shows 78%capacity retention at 55 ℃ and 1 C rate after 100 cycles.

Kinetics of discontinuous precipitation in Cu–20Ni–20Mn alloy

The morphology and growth kinetics of discontinuous precipitation （DP） in a Cu-20Ni-20Mn alloy were investigated in the tem- perature range of523-573 K by optical microscopy, scanning electron microscopy, and transmission electron microscopy. A lamellar mixed structure consisting of alternating larnellae of a matrix and NiMn phase was observed in DP colonies. The volume fraction of regions formed by a DP reaction was determined by quantitative metallographic measurements. The kinetics of DP was evaluated on the basis of the John- son-MehI-Avrami Kohnogorov equation, which resulted in a time exponent of approximately 1.5. We confirmed that the nucleation of the discontinuous precipitate was confined to grain edges or boundaries at an early stage of the reaction. The activation energy of DP process was determined to be approximately （72.7 ± 7.2） kJ/mol based on the Arrhenius equation; this result suggests that DP is controlled by gn-ain boundary diffusion. The hardness values exhibited good correlation with the volume fraction of DP; this correlation was attributed to the plvsence of the ordered N iMn phase.

Effect of Solution Heat Treatment in α+β Phase Region on Shape Memory Characteristics of Cu-Al-Ni-Mn-Ti Alloys

The effect of aluminium content and solution heat treatment in α+β phase region on the shape memory characteristics and mechanical properties of cold wrought Cu-Al-Ni-Mn-Ti alloy are studied in this paper. Results indicate that the transformation temperature (Tt) of Cu-Al-Ni-Mn-Ti alloy reduces obviously with the increase of the amount of α-phase. During aging at 623 K, Tt increases at first up to a peak value, then decreases with prolongation of aging time. Life time of heat resistance of the alloy at high temperatures is improved with increase of the amount of α-phase, this life time becomes poor with Bainite precipitation. When the amount of α-phase is less than 5%, the ratio of shape recovery brought about by the solution heat treatment in α+β phase region is almost not effected. However, plasticity of the alloy increases obviously as aluminium content decreases. We believe that improving cold workability of Cu-Al-Ni-Mn-Ti alloy and keeping good heat resistant property and shape memory effects are possible by means of reducing the content of aluminium and solulion heat treatment in α+β phase region.

Gas Generation Mechanism in Li-Metal Batteries

Gas generation induced by parasitic reactions in lithium-metal batteries(LMB)has been regarded as one of the fundamental barriers to the reversibility of this battery chemistry,which occurs via the complex interplays among electrolytes,cathode,anode,and the decomposition species that travel across the cell.In this work,a novel in situ differential electrochemical mass spectrometry is constructed to differentiate the speciation and source of each gas product generated either during cycling or during storage in the presence of cathode chemistries of varying structure and nickel contents.It unambiguously excludes the trace moisture in electrolyte as the major source of hydrogen and convincingly identifies the layer-structured NCM cathode material as the source of instability that releases active oxygen from the lattice at high voltages when NCM experiences H2→H3 phase transition,which in turn reacts with carbonate solvents,producing both CO_(2)and proton at the cathode side.Such proton in solvated state travels across the cell and becomes the main source for hydrogen generated at the anode side.Mechanisms are proposed to account for these irreversible reactions,and two electrolyte additives based on phosphate structure are adopted to mitigate the gas generation based on the understanding of the above decomposition chemistries.

Direct smelting process for stainless steel crude alloy recovery from mixed low-grade chromite, nickel laterite and manganese ores

Stainless steel crude alloy recovery from direct smelting of low-grade chromite, nickel laterite and manganese ores was investigated. The mixed low-grade ores were directly smelted in an elevator furnace at smelting temperatures ranging from 1550 to 1600 ℃. Smelting experiments were conducted in a laboratory elevator furnace equipped with 8 U-shaped high- quality molybdenum disilicide heating elements. A low-grade coal was used as the reductant. Experimental results showed that the recovery of Fe, Cr, Ni, Mn and Si within the alloy increased from 34.22, 60.27, 57.14, 25.42 and 13.02% to 69.91, 99.26, 86.02, 60.8 and 34.21%, respectively, when the temperature was increased from 1550 to 1600 ℃. There was a general increase in the total recoveries of Fe, Cr, and Ni in the alloy with CaO addition increasing from 0.4 g up to 1.2 g. However, the recoveries of Mn and Si vividly decreased as the CaO contents were increased. In general, the recoveries of the metal contents of the crude alloy increase with the increase in the amount of manganese ore. Compared to the recoveries of Fe, Cr, and Ni when CaO was added, the recoveries of Fe, Cr and Ni were lower when manganese ore was used as an additive.