Mg二次电池正极材料Cu2Mo6S8的合成与表征

采用CuS.H2O、MoS2、Mo为原料,用熔盐法(KCl为熔盐)合成了谢弗雷尔相的Cu2Mo6S8正极材料,并用XRD,SEM,循环伏安测试,充放电测试对材料的结构和电化学性能进行研究。XRD结果表明本Cu2Mo6S8正极材料属于R3空间群,具有良好的晶型。电化学测试表明,当材料在电压0.2～2 V范围内进行充放电时,其放电比容量在90 mAh.g-1左右,循环稳定性和可逆性均良好。该材料的充放电曲线中在1.2 V和1.9 V分别有还原峰,0.7 V和1.0 V分别有氧化峰,与伏安曲线相对应。     

One-dimensional condensation of Mo6 octahedral clusters: A new cluster,Mo12, and a new building block,Mo12S14, in M2Mo9S11

Two new Mo compounds, Tl₂Mo₉S₁₁ and K₂Mo₉S₁₁, have been found. The structure of these compounds is characterized by the presence of a completely new building block, Mo₁₂S₁₄, in addition to the well-known Mo₆S₈ unit as in the PbMo₆S₈-type compounds. The new cluster, Mo₁₂, contained in the Mo₁₂S₁₄ unit can be considered as a one-dimensional condensation of three Mo₆ octahedral clusters. These new materials, the structure of which resembles that of PbMo₆S₈, are metallic but are not superconducting above 2.1°K.     

Stabilization of Mo6S8 by halogens; new superconducting compounds: Mo6S6Br2, Mo6S6I2

We present a study of the properties of the series Mo₆X_8?xY_x (X = S, Se, Te; Y = Br, I) having the hexagonal rhombohedral structure of the PbMo₆S₈ type. For X = S we have found two new superconducting compounds Mo₆S₆Br₂ and Mo₆S₆I₂, having critical temperatures of 13.8 and 14.0°K, respectively. We further find that Mo₆Te₈ becomes superconducting (T_c ≈ 2.6°K) upon substitution of Te by small quantities of iodine, and that in the case of Mo₆Se₈ substitution of a Se atom by a halogen, raises T_c up to about 7.6°K.     

Subsolidus phase diagram of Cu2OCuOMoO3 system

Five chemical compounds, CuMoO₄, Cu₃Mo₂O₉, Cu₂Mo₃O₁₀, Cu₆Mo₄O₁₅, and Cu_4?x Mo₃O₁₂ (0.10 ? x ? 0.40), were identified in the system Cu₂OCuOMoO₃ and characterized by DTA, X-ray powder patterns, ir spectra, and magnetic properties. Cupric molybdates CuMoO₄ and Cu₃Mo₂O₉ are stable in air up to 820 and 855°C, respectively, melting at these temperatures with simultaneous decomposition (oxygen loss). Congruent mp of cuprous molybdates Cu₂Mo₃O₁₀ and Cu₆Mo₄O₁₅, in argon, are 532 and 466°C, respectively. Nonstoichiometric phase Cu_4?x Mo₃O₁₂ = Cu²⁺₃Cu⁰_1?xMo⁶⁺₃O₁₂, melts in argon between 630 and 650°C depending on the value of x and at 525–530°C undergoes polymorphic transformation. Areas of coexistence of the above-mentioned phases are determined. The μ_eff of Cu²⁺ ions and θ values are: 1.80 B.M. and 28°K for CuMoO₄, 1.71 B.M. and ? 12°K for Cu₃Mo₂O₉, and 1.74 B.M. and ? 93°K for Cu_4?xMo₃O₁₂. Below 200°K CuMoO₄ becomes antiferromagnetic. Cu₂Mo₃O₁₀ and Cu₆Mo₄O₁₅ show weak temperature-independent paramagnetism.     

Investigation of vortex dynamics close to Bc2 in Cu2Mo6S8 quasi epitaxial thin films

The Ginzburg number of superconducting Chevrel phases M_xMo₆S₈ with small coherence length (10⁻³ to 10−5) is intermediate between those obtained for conventional low T_c materials (10⁻⁸) and those of high T_c (10⁻¹) indicating that these phases may display features in the dynamics of the vortices similar to those observed in high T_c superconductors. In this work we present a detailed study of I–V measurements close to the B_c2 line carried out on quasi epitaxial thin films of Cu₂Mo₆S₈. The non-linear I–V curves show a scaling behaviour making possible to determine a transition temperature between an unpinned vortex state and a vortex glass state. However, the temperature range of the unpinned vortex state is much wider than expected.     

KCl熔盐法制备LiMn2O4

采用熔盐法合成了LiMn₂O₄。熔盐的使用可以使原来固相反应的高温焙烧时间缩短。合成获得的材料结晶良好，颗粒大小在数百个纳米左右，有较明显的团聚现象。该材料的初始容量为113 mAh·g^-1，循环性能优良，前100次的容量平均衰减率在0.05%左右；倍率性能亦非常优秀，8 C放电时的容量为1 C放电容量的93%以上。熔盐的用量在4倍于Li⁺以上时，对材料的结构形貌和性能都没有明显影响。     

Application of Solid-State Molybdenum Sulfide Clusters with an Octahedral Metal Framework to Catalysis: Ring-Opening of Tetrahydrofuran to Butyraldehyde

Solid-state molybdenum sulfide clusters with an octahedral metal framework, the superconducting Chevrel phases, are applied to catalysis. The cluster of copper salt, Cu _x Mo₆S₈ (x = 2.94), stored in air is treated in a hydrogen stream above 300 °C. The activated cluster exhibits catalytic activity for the ring-opening of tetrahydrofuran, yielding butyraldehyde. Cyclic ethers such as trimethylene oxide and tetrahydropyran are also converted to the corresponding aldehydes. The cluster contains nonstoichiometric defects of sulfur atoms. Oxygen atoms are incorporated at the sulfur-deficient sites upon storage in air, but they are removed from the sites by the activation in a hydrogen stream. The resulting coordinatively unsaturated molybdenum atoms are catalytically active for the ring-opening reaction. The molybdenum atom in an intermediate oxidation state around 2+ is moderately coordinated by the oxygen of tetrahydrofuran and favorably releases the produced aldehyde. The neutral cluster Mo₆S₈, which has such sulfur-deficient sites, also catalyzes the reaction.     

Synthesis of Cu2Mo6S8 powders and thin films from intermediate oxides prepared by polymeric precursor method

Powders and thin films of the copper molybdenum sulfide Cu₂Mo₆S₈ were synthesized from intermediate oxides prepared by polymeric precursor method based on Pechini process. In the case of the thin films, deposition was performed onto R-plane sapphire single crystal by spin coating. The influence of temperature and duration of the 3 step heat treatment cycle (calcination, sulfurization and reduction) were investigated to optimize the synthesis conditions. The first step of calcination under air atmosphere performed for 3 h at 450 °C and 400 °C is suitable to obtain the intermediate oxides powders and thin films, respectively. The sulfurization treatment at 600 °C for 2 h under H₂S/H₂ gas flow followed by reduction at 650 °C for 4 h under H₂ gas flow allowed to obtain Cu₂Mo₆S₈ in powder or thin film form. In the last case, a multilayer process led to dense and homogeneous films. Moreover, the insertion and superconducting behaviour of the final powders allowed to validate the Cu₂Mo₆S₈ synthesis by this moderate temperature process.     

Crystal structure and ionic conductivity of the series A2Bi24Mo8X2O68 (A = Ca, Sr and Ba and X = Cr and W) in the Bi2O3?MoO3 system

A series of A₂Bi₂₄Mo₈X₂O₆₈ compounds, Ca₂Bi₂₄Mo₈Cr₂O₆₈ (CBMC), Sr₂Bi₂₄Mo₈Cr₂O₆₈ (SBMC), Pb₂Bi₂₄Mo₈Cr₂O₆₈ (PBMC) and Ba₂Bi₂₄Mo₈W₂O₆₈ (BBMW) have been synthesized by the solid-state method and characterized by single crystal X-ray diffraction. The compounds index into the monoclinic P2/c system with a=11.687(4) ?, 5.784(2) ?, 24.728(9) ?, 101.911(6)°, Z=1; 11.673(6) ?, 5.775(3) ?, 24.670(2) ?, 101.757(8)°, Z=1; 11.638(3) ?, 5.790(1) ?, 24.655(6) ?, 101.716(4)°, Z=1 and 11.718(6) ?, 5.818(3) ?, 24.716(12) ?, 101.835(9)°, Z=1 for CBMC, SBMC, PBMC and BBMW, respectively. The structures were solved by direct methods and refined to R indices of 0.081, 0.065, 0.080 and 0.079 respectively. These compounds are isostructural with Bi₂₆Mo₁₀O₆₉ and the structure consists of columns of [Bi₁₂O₁₄] along the b-axis, surrounded by Mo/Cr/WO₄ tetrahedra. a.c. impedance studies indicate higher values of ionic conductivity for the tungsten-substituted compounds. Supplementary material The crystal data of CBMC, SBMC, PBMC and BBMW have been deposited at the Fachinformationszentrum Karlsruhe (FIZ) with the numbers CSD 415143, CSD 415145, CSD 415144 and CSD 415142, respectively.     

Synthesis and structure of a new octahedral molybdenum thiocyanide cluster complex K7[Mo6(μ3-S)8(CN)6]·8H2O

The new octahedral molybdenum thiocyanide cluster complex K₇[Mo₆S₈(CN)₆]·8H₂O was synthesized by excision of the cluster core (the reaction of ZnMo₆S₈ with a melt of KCN). The structure of the complex was established by X-ray diffraction analysis. The reaction of Mo₆Se₈ with a KCN—KSCN mixture afforded the mixed-ligand cluster anions [Mo₆(Se,S)₈(CN)₆]^7–. The salt of composition K_1.5Cs_5.5[Mo₆Se_6.8S_1.2(CN)₆]·8H₂O was obtained. The complexes are isostructural to each other and to the selenium analog described previously. The magnetic properties and the electronic and IR spectra were measured and discussed.     

Photosynthesis of a cyanocomplex containing molybdenum(IV) and molybdenum(VI): Photosynthesis of K6[Mo2Mo(CN)8O6]2H2O

A photochemical method for the preparation of K₆[Mo₆[Mo₂^IVMo^IV(CN)₈O₆]2H₂O is discussed. The synthesis of this complex was achieved by photolysing aqueous solutions of K₄Mo(CN)₈ in contact with atmospheric oxygen.     

Phase control and its mechanism of CuInS2 nanoparticles

CuInS₂ nanoparticles (NPs) usually take chalcopyrite-(CP) structure. Recently, CuInS₂ NPs with pseudo-wurtzite (WZ) structure, which is thermodynamically less favored, have been synthesized. However, the formation mechanism of this metastable-phase has not been understood yet. In this report, the key issue of phase selectivity of CuInS₂ (CIS) NPs has been investigated using various metal sources and ligands. Experimental results suggested that the crystalline structure and morphology of CIS NPs were decided by the stability of indium ligand complex; the active ligand reduces the precipitation rate of In₂S₃, resulting in pre-generation of Cu₂S seed NPs. Crystallographic analogy and superionic conductivity of Cu₂S remind us that the formation of WZ CIS NPs is attributed to the pre-generation of Cu₂S seed NPs and the following cation exchange reaction. In order to confirm this hypothesis, Cu_2-xS seed NPs with various structures have been annealed in indium-ligand solution. This experiment revealed that the crystalline structure of CIS NP was determined by that of pre-generation Cu_2-xS NPs. Our results provide the important information for the phase control and synthesis of ternary chalcogenide NPs with a novel crystalline structure.     

A new increasing delocalization of M=3d-elements (Ti, Fe, Co) in the channels network of the ternary MyMo6Se8 Chevrel phases

A structural investigation on single crystals of M_yMo₆Se₈ Chevrel phases (M=3d: Ti, Fe, and Co) has been carried out. These latter compounds as well as others with Cr, Mn, and Ni atoms make part of a new original family of Chevrel phases. The M ions occupy new interstices in the tridimensional channels network never observed in the other classical Chevrel phases as Li_y, Cu_y Mo₆X₈. They occupy only cavity 2 centered on and with a progressive delocalization of the M cation versus the nature of the cation from the center of the cavity to the outside . The position in cavity 2 is different from the position of the Cu (2) atoms, the second position of the copper atoms in the channels of the Cu_yMo₆X₈ compounds. This new position reinforces the interaction with the Mo₆ cluster, and may be able to involve new remarkable physical properties as thermoelectric properties.     

Cathode Electrolyte Interphase (CEI) Endows Mo6S8 with Fast Interfacial Magnesium-Ion Transfer Kinetics

Magnesium (Mg) metal secondary batteries have attracted much attention for their high safety and high energy density characteristics. However, the significant issues of the cathode/electrolyte interphase (CEI) in Mg batteries are still being ignored. In this work, a significant CEI layer on the typical Mo₆S₈ cathode surface has been unprecedentedly constructed through the oxidation of the chloride-free magnesium tetrakis(hexafluoroisopropyloxy)borate (Mg[B(hfip)₄]₂) salt under a proper charge cut-off voltage condition. The CEI has been identified to contain B_xO_y effective species originating from the oxidation of [B(hfip)₄]⁻ anion. It is confirmed that the B_xO_y species is beneficial to the desolvation of solvated Mg²⁺, speeding up the interfacial Mg²⁺ transfer kinetics, thereby improving the Mg²⁺-storage capability of Mo₆S₈ host. The firstly reported CEI in Mg batteries will give deeper insights into the interface issues in multivalent electrochemical systems.     

Hot pressing sintered CuxMo6S8 targets for laser ablation thin films deposition

Sintering conditions of Cu₄Mo₆S₈ pellets, 20 mm in diameter and about 4 mm thick have been determined. The expulsion of copper out of the pellet for an annealing temperature of 1100 ° C has been observed, in agreement with the evolution of the phase diagram when the temperature increases. The appearance of Cu₂S cristallites on the surface of the films deposited from highly densified targets associated with a high excess of copper and sulfur can be correlated with the behavior observed on the pellets. In fact the increase of the temperature of the target under the laser beam impact is likely responsible for a copper migration on its surface, which leads to the observed composition of the film.     

Cryoscopic studies in molten salts. Dissociation state of some alkali isopolymolybdates and some related molybdenum(VI) compounds in molten K2Cr2O7and KNO3

The dissociation state of the solutes M₂MoO₄, M₂Mo₃O₁₀, M₂Mo₄O₁₃, M₂Mo₅O₁₆ (MRb or Cs), Na₂CrO₄·MoO₃, K₂CrO₄·2 MoO₃, Cr₂Mo₃O₁₂ and V₂MoO₈ was studied cryoscopically in molten K₂ Cr₂O₇ and KNO₃ solvents. The freezing point depression, ΔT, of the solvents was obtained by measuring the cooling curves of the binary salt mixtures over unlimited range of solute concentration. The number of foreign ions obtained ν, showed that the solutes were either simply dissociated in the melt into the probable stable species (MoO₄)^2?, (Mo₃O₁₀)^2?, (Mo₄O₁₃)^2? and (Mo₅O₁₆)^2? or, in some cases after reactions and rearrangements, into (CrMo₂O₁₀)^2? heteropolyions. The solute V₂MoO₈, on the other hand, was found to dissolve without any apparent dissociation. An agreement between the experimental and calculated values of activity, a, based on the Temkin and Random Mixing models and that of Van't Hoff's equation support the proposed simple dissocia- tion scheme for K₂Cr₂O₇Cs₂MoO₄ system.     

Microwave-Assisted Elemental-Direct-Reaction Route to Nanocrystalline Copper Sulfides Cu9S8 and Cu7S4

Non-stoichiometric copper sulfides Cu₉S₈ and Cu₇S₄ nanocrystallites were synthesized by the reaction between elements S and Cu under microwave radiation for several minutes. The products were analyzed by using XRD, TEM, XPS, ICP and PL.     

Bi2n+4MonO6(n+1) with n=3, 4, 5, 6: A new series of low-temperature stable phases in the mBi2O3 - MoO3 system (1.0<m<1.7): Structural relationships and conductor properties

Four low-temperature phases with compositions Bi₁₀Mo₃O₂₄, Bi₆Mo₂O₁₅, Bi₁₄Mo₅O₃₆ and Bi₈Mo₃O₂₁ have been prepared by the n-butylamine wet synthesis method. They have been characterized by powder X-ray diffraction and transmission electron microscopy, mainly by selected area electron diffraction. The four phases present a close structural relationship and a common basic fluorite-type structure and are members of a homologous series of phases with general formula Bi_2n+4Mo_nO_6(n+1), being n=3, 4, 5 and 6, respectively. The matrices relating their superstructures and the basic fluorite type unit cell are given, as well as a general one for the whole series. The conductor behavior of these phases is characterized by impedance spectroscopy being all these materials very good ionic conductors.     

Free electron model in cluster structure theory. Electronic structures of [Mo6S8(CN)6]6?, [Mo6Se8(CN)6]6?, [Re6S8(CN)6]4?, and Rh6(CO)16 clusters

The results of quantum chemical calculations of the electronic structure and geometry of octahedral clusters [Mo₆S₈(CN)₆]⁶⁻, [Mo₆Se₈(CN)₆]⁶⁻, [Re₆S₈(CN)₆]⁴⁻, and Rh₆(CO)₁₆ by the ab initio SCF (RHF) and DFT (B3LYP) methods with various basis sets are presented. The electronic states of the clusters under study in ideal spherically symmetric potential were classified in the orbital quantum number l (1s, 1p, 1d, 1f, 1g, 1h, 1i), l = 0–6. In real crystal field with O_h symmetry these states are split. The calculated new electronic states were matched to the irreducible representations of the point symmetry group O_h. The polarizabilities of the compounds considered are 55–65 ų. A new model for the electronic structure of octahedral clusters containing M₆ groups was proposed. The model is based on the idea of free electrons moving in spherically symmetric potential field. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2617–2624, December, 2005.     

A novel route to nanosized molybdenum boride and carbide and/or metallic molybdenum by thermo-synthesis method from MoO3, KBH4, and CCl4

Nanosized molybdenum boride and carbide were synthesized from MoO₃, KBH₄, and CCl₄ by thermo-synthesis method at lower temperature. The relative content of Mo, Mo₂C, and molybdenum boride in the product was decided by the molar ratio between MoO₃, KBH₄, and CCl₄. Increasing the molar ratio of CCl₄ to MoO₃ was favorable to the production of Mo₂C. Increasing the molar ratio of KBH₄ to MoO₃ was favorable to the production of molybdenum boride. By carefully adjusting the reaction conditions and annealing in Ar at 900°C, a single phase of MoB could be obtained.