SiO_x-based(0<x≤2) composites for lithium-ion batteries

Silicon(Si) materials as anode materials for applications in lithium-ion batteries(LIBs) have received increasing attention.Among the Si materials,the electrochemical properties of SiO_x-based(0x≤2)composites are the most prominent.However,due to the cycling stability of SiO_x being far from practical,there are some problems,such as Iow initial coulombic efficiency(ICE),obvious volume expansion and poor conductivity.Researchers in various countries have optimized the electrochemical properties of SiO_x-based composites by means of pore formation,surface modification,and the choice of constituents.In this review,SiO_x-based composites are classified into three categories based on the valency of Si(SiO_2 composites,SiO composites and SiO_x(0x2) composites).The synthesis,morphologies and electrochemical properties of the SiO_x-based composites that are applied in LIB are discussed.Finally,the prope rties of several common SiO_x-based composites are briefly compared and the challenges faced by SiO_x-based composites are highlight.     

锂离子电池SiO_x(0<x≤2)基负极材料

随着锂离子电池向电动汽车、可再生能源储能系统等大型应用领域发展,锂离子电池的能量密度、功率密度等性能指标需要进一步提高。在负极材料方面,传统的石墨碳负极材料的比容量有限,已经难以满足高能量密度电池的需求。以Si基材料为代表的新型高比容量负极材料受到了人们的广泛关注。其中,Si Ox材料在发挥高比容量的同时,具有相比纯Si更小的体积变化,因而在循环寿命方面更具实用潜力。本文对目前报道的Si Ox基负极材料的研究工作进行总结,系统阐述了Si Ox材料的基本电化学性能、结构模型、电化学机理及合成方法,分类介绍了改进Si Ox材料电化学性能的各类措施,并对其中Si O及无定形Si O2材料进行了重点论述。研究表明,氧含量、歧化程度、表面状态等对Si Ox材料的电化学性能具有重要影响;界面团簇混合(ICM)结构模型可更好地对其电化学机理进行理解;通过与第二相(碳、金属、金属氧化物等)复合,造孔,表面改性(包覆、刻蚀等)及其他手段(改变粘结剂及电解液)可有效提升Si Ox基材料的首次库仑效率和循环性能;部分使用Si Ox基材料的全电池具有循环600次后容量保持率达90%的优秀循环性能。Si Ox基材料已成为一种在高比能量锂离子电池中极具应用潜力的负极材料。     

Positron annihilation studies in YBa2Cu3O x (6<x≤7)

Positron lifetime and Doppler broadening of the annihilation line measurements, as a function of temperature between 14 and 300 K, have been performed on four YBa₂Cu₃O _x (6<x7) samples with different oxygen deficiency. It was found that the positron lifetime and theS parameter values increase as the oxygen deficiency increases in the YBa₂Cu₃O _x (6<x7) samples. It was also observed that the positron annihilation parameers show different temperature dependence in the YBa₂Cu₃O _x (6<x7) samples associated with their different oxygen deficiency.     

Crystal structures of chiral (R/S) (C<Subscript>8</Subscript>H<Subscript>11</Subscript>N)<Subscript>2</Subscript> · Zn(OAc)<Subscript>2</Subscript>

Two opposite configuration (R/S) of chiral complexes (C₈H₁₁N)₂ · Zn(OAc)₂ (Ia and Ib—L-(−)-) and D-(+)-isomer) were synthesized by a simple one-pot method. The crystal structures of Ia and ib determined by X-ray crystallography.     

Synthesis and study of lead(II) uranate Pb(UO<Subscript>2</Subscript>)<Subscript>2</Subscript>O<Subscript>2</Subscript>(OH)<Subscript>2</Subscript>·H<Subscript>2</Subscript>O

An individual crystalline compound Pb(UO₂)₂O₂(OH)₂·(H₂O) was obtained by reaction of synthetic schoepite UO₃·2.25H₂O with an aqueous solution of lead(II) nitrate under hydrothermal conditions. The composition and structure of this compound were determined, and the processes of its dehydration and thermal decomposition were studied by chemical analysis, X-ray diffraction, IR spectroscopy, and thermography.     

Pyrazolate-bridged binuclear zinc complexes Zn<Subscript>2</Subscript>(μ-dmpz)<Subscript>2</Subscript>(Hdmpz)<Subscript>2</Subscript>(OOCR)<Subscript>2</Subscript> (R = Me,Ph; Hdmpz = 3,5-dimethylpyrazole)

Triethylamine reacts with aqueous zinc acetate and the product of its thermolysis in the presence of benzoic acid to yield the complexes [Zn₇(μ₄-O)(μ-OOCMe)₁₀][η-OC(Me)OHNEt₃]₂ (1) and [Zn₂(μOOCPh)₄][η-OC(Me)OHNEt₃]₂ (2), respectively. The reactions of 1 and 2 with 3,5-dimethylpyrazole at room temperature in benzene yield pyrazolate-bridged binuclear complexes Zn₂(μdmpz)₂(Hdmpz)₂(OOCR)₂ (R = Me (3), Ph (4)). The structures of complexes 1–4 have been determined by X-ray crystallography.     

Synthesis and structure of the [Co(NioxH)<Subscript>2</Subscript>(Thio)<Subscript>2</Subscript>]<Subscript>2</Subscript>SO<Subscript>4</Subscript>·2H<Subscript>2</Subscript>O complex compound

A new Co(III) complex of 1,2-cyclohexanedionedioxime and thiocarbamide with an SO ₄ ^2? anion and solvation water molecules in the outer sphere has been synthesized and its structure has been defined. Orthorhombic crystals, a = 11.659(2) Å, b = 26.448(5) Å, c = 30.142(6) Å, V = 9295(3) Å ³, Z = 8, d_calc = 1.599 g/cm³, space group Pbca; final R index is 0.0578 for 8221 reflections with I > 2σ(I). In the octahedral Co(III) complex, two 1,2-cyclohexanedionedioxime residues lie in the equatorial plane, while two thiocarbamide molecules are in the axial plane. Intramolecular bonds: N-H…O and O-H…O type hydrogen bonds and π-π interactions that stabilize the complex cations. In crystal, the components are linked by N-H…O and O-H…O hydrogen bonds into a 3D framework.     

Crystal structure of barium bis(nitrilotriacetato)cobaltate(III), Ba<Subscript>3</Subscript>[Co(Nta)<Subscript>2</Subscript>]<Subscript>2</Subscript> · 10H<Subscript>2</Subscript>O

Crystals of Ba₃[Co(Nta)₂]₂ · 10H₂O (Nta^3? is the ion of nitrilotriacetic acid) are obtained (monoclinic crystal system, a = 17.094(3), b = 13.1873(13), c = 21.490(3) Å, β = 98.457(18)°, Z = 4, space group I2/c). The crystal structure of the compound is determined by X-ray diffraction analysis. The crystals consist of the Ba²⁺ cations, water molecules, and [Co(Nta)₂]^3? anions in which the donor N and 2O atoms of each Nta^3? ion are located at opposite faces of the coordination octahedron. The Co(1, 2) atoms are arranged in the inversion centers. The Ba atoms of the complexes form an intricate three-dimensional framework. One of the two crystallographically nonequivalent complexes binds eight Ba atoms, and another one binds six Ba atoms. The coordination number of the Ba(1) atoms (in the general position) is nine (three O atoms of water molecules and six O atoms of the carboxyl groups of five complexes), and that of the Ba(2) atoms (on the 2 axis) is 6 (two O atoms of water molecules and four O atoms of the carboxyl groups of four complexes).     

Synthesis,properties, and molecular and crystal structure of diantipyrylmethanium Bis(μ-tartrato)dihydroxydigermanate(IV) tetrahydrate (HDAm)<Subscript>2</Subscript>[Ge<Subscript>2</Subscript>(μ-L)<Subscript>2</Subscript>(OH)<Subscript>2</Subscript>] · 4H<Subscript>2</Subscript>O

The complex (HDam)₂[Ge₂(μ-L)₂(OH)₂] · 4H₂O (I) (H₄L is tartaric acid, Dam is diantipyrylmethane) was synthesized for the first time. The individual character and composition of I was established by elemental analysis and X-ray diffraction. The thermal stability of I was studied. The coordination sites of H₄L in the germanium complex were determined by IR spectroscopy. The structure of I was determined by X-ray crystallography. The crystals of I are triclinic: a = 9.3098(10) Å, b = 9.8088(10) Å, c = 17.6869(10) Å, α = 84.009(10)°, β = 77.926(10)°, γ = 67.088(5)°, V = 1454.3(2) ų, Z = 2, space group P \(\bar 1\), R = 0.0628 for 6343 reflections with I > 2σ(I). The compound is composed of the complex anions [Ge₂(μ-L)₂(OH)₂]^2?, the HDam⁺ cations, and crystal water molecules. In the dimeric anion, the metal atoms are bound to two completely deprotonated ligands L^4?. The latter are coordinated to the metal through the carboxyl (av. Ge-O, 1.911(6) Å) and hydroxyl (av. Ge-O, 1.768(6) Å) oxygen atoms. The coordination of each Ge atom is completed to trigonalbipyramidal by the O atom of the hydroxy ligand in the axial position (av. Ge-O, 1.748(7) Å). Both L^4? ligands are D isomers. In the crystal, the complex anions and crystal water molecules are combined by a system of hydrogen bonds.     

Synthesis and Structure of Cobalt(III) α-Dimethylglyoximate [Co(DH)<Subscript>2</Subscript>(Py)<Subscript>2</Subscript>][H<Subscript>2</Subscript>F<Subscript>3</Subscript>]

The [Co(DH)₂(Py)₂][H₂F₃] complex (DH^? is the dimethylglyoxime residue) is synthesized and studied by X-ray diffraction analysis. Structural units of the crystal are complex cations [Co(DH)₂(Py)₂]⁺ and anions [H₂F₃]^?. Two residues of α-dimethylglyoxime linked by intramolecular hydrogen bonds O-H?O lie in the equatorial plane of the octahedral Co(III) complex, and two pyridine molecules occupy the apical positions. The H₂F ₃ ^? anion is formed due to the association of the F^? ion with two HF molecules through hydrogen bonds F-H?F. Weak intermolecular interactions C-H?F and C-H?O are observed in the crystal. The problem of the influence of these interactions on the packing of the complexes in crystal is discussed.     

Synthesis and crystal structure of a cyanide-bridged one-dimensional nickel(II) complex with alternating [Ni(En)<Superscript>2</Superscript>]<Superscript>2+</Superscript> and [Ni(CN)<Subscript>4</Subscript>]<Superscript>2−</Superscript> ions

The complex [Ni(En)₂][Ni(CN)₄] · 3.5H₂O (I) (En = ethylenediamine) was synthesized by the reaction of [Ni(En)₂](ClO₄)₂ and K₂[Ni(CN)₄] in an H-shaped tube. The crystal structure of I has been determined by single-crystal X-ray analysis. The crystal of complex I is orthorhombic, space group Pnna with a = 28.151(3), b = 8.3946(8), c = 14.5441(13)Å, M =404.76, Z = 8, V = 3437.0(5)ų. The structure of complex I reveals infinite zigzag chains shaped structure are formed by cis-Ni(En)₂-μ-(NC)₂, cis-μ-(NC)₂Ni(CN)₂, and trans-μ-(CN)₂Ni(En)₂.     

Erbium(III) and lutecium(III) complexes [Ln(H<Subscript>2</Subscript>O)<Subscript>8</Subscript>][Cr(NCS)<Subscript>6</Subscript>] · 5H<Subscript>2</Subscript>O: Synthesis and crystal structure

[Ln(H₂O)₈][Cr(NCS)₆] · 5H₂O aqua complexes, where Ln = Er (1), Lu (2), have been found in an aqueous solution instead of binary complex salts with an organic ligand in their cation, when crystal products of the reaction between Ln(NO₃)₃ · 6H₂O (Ln = Er, Lu), K₃[Cr(NCS)₆] · 4H₂O, and 8-oxyquinoline (C₉H₇NO) were studied by X-ray diffraction. Crystals of complexes 1 and 2 are isostructural and crystallize in triclinic system, space group P\(\bar 1\), Z = 2. For complex 1: a = 9.0677(4) Å, b = 9.3115(4) Å, c = 16.9595 Å, α = 81.526(2)°, β = 86.153(2)°, γ = 83.879(2)°, V = 1406.33(10) ų, ρ_calc = 1.894 g/cm³; for complex 2: a = 9.0438(3) Å, b = 9.2880(3) Å, c = 16.9181(3) Å, α = 81.7250(10)°, β = 86.1600(10)°, γ = 83.8850(10)°, V = 1396.38(7) ų, ρ_calc = 1.926 g/cm³.     

Thermodynamic characteristics of europium pivalate binuclear complexes Eu<Subscript>2</Subscript>(Piv)<Subscript>6</Subscript> and [Eu<Subscript>2</Subscript>(Piv)<Subscript>6</Subscript> · (Phen)<Subscript>2</Subscript>]

Sublimation of europium pivalate binuclear complexes Eu₂(Piv)₆ and [Eu₂(Piv)₆ · (Phen)₂] (Piv = (CH₃)₃CCOO, Phen = C₁₂H₈N₂) in the temperature range of 383–660 K is studied by the Knudsen effusion method with mass-spectrometric analysis of the gas phase. The vaporization of Eu₂(Piv)₆ is shown to be accompanied by polymerization and the formation of Eu₂(Piv)₆ and Eu₄(Piv)₁₂ molecules. The saturated vapor over the mixed-ligand complex of europium pivalate with o-phenanthroline consists of Phen, Eu₂(Piv)₆, and Eu₄(Piv)₁₂ molecules. The partial pressures of the gas components, as well as the standard enthalpies of sublimation and dissociation of the reaction proceeding with removal of phenanthroline have been determined.     

Crystal structure and thermal properties of [Au(en)<Subscript>2</Subscript>]<Subscript>2</Subscript>[Cu(C<Subscript>2</Subscript>O<Subscript>4</Subscript>)<Subscript>2</Subscript>]<Subscript>3</Subscript>·8H<Subscript>2</Subscript>O

The crystal structure of a double complex salt of the composition [Au(en)₂]₂[Cu(C₂O₄)₂]₃·8H₂O (en = ethylenediamine) at 150 K is determined by single crystal X-ray diffraction. The crystal data for C₂₀H₄₈Au₂Cu₃N₈O₃₂ are: a = 9.1761(3) Å, b = 16.9749(6) Å, c = 13.4475(5) Å, β = 104.333(1)°, V = 2029.43(12) ų, P2₁/c space group, Z = 2, d _x = 2.450 g/cm³. It is demonstrated that the thermal decomposition of the double complex salt in a helium or hydrogen atmosphere affords the solid solution Au_0.4Cu_0.6.     

Kinetic and mechanistic studies on the reaction of thiosemicarbazide with [(H<Subscript>2</Subscript>O)(tap)<Subscript>2</Subscript>RuORu(tap)<Subscript>2</Subscript>(H<Subscript>2</Subscript>O)]<Superscript>2+</Superscript> {tap = 2-(m-tolylazo)pyridine}

The interaction of thiosemicarbazide with the title complex has been studied spectrophotometrically in aqueous medium as a function of [complex], [thiosemicarbazide], pH and temperature at constant ionic strength. At pH 7.4, the reaction shows two distinct paths; both of which are [thiosemicarbazide] dependent. A parallel reaction scheme fits well with the experimental findings. An associative interchange mechanism is proposed for both the paths; the activation parameters calculated from Eyring plots are ΔH₁^≠ = 14.2 ± 0.8 kJ mol⁻¹, ΔS₁^≠ = −241 ± 2 JK⁻¹ mol⁻¹, ΔH₂^≠ = 30.8 ± 1.4 kJ mol⁻¹ and ΔS₂^≠ = −236 ± 4 JK⁻¹ mol⁻¹. From the temperature dependence of the outer sphere association complex equilibrium constants, the thermodynamic parameters calculated are ΔH₁^° = 34.25 ± 1.9 kJ mol⁻¹, ΔS₁^° = 146 ± 6 J K⁻¹ mol⁻¹ and ΔH₂^° = 9.4 ± 1.1 kJ mol⁻¹, ΔS₂^° = 71 ± 3 JK⁻¹ mol⁻¹, which gives a negative ΔG° at all temperatures studied, supporting the spontaneous formation of an outer sphere association complex.     

Calorimetric study of molecular superconductor κ-(BEDT-TTF)<Subscript>2</Subscript>Ag(CN)<Subscript>2</Subscript>H<Subscript>2</Subscript>O which contains water in the anion layers

Thermodynamic investigation of an organic superconductor κ-(BEDT-TTF)₂Ag(CN)₂H₂O in which the BEDT-TTF dimers are arranged in the κ-type structure in the donor layers is performed by the relaxation calorimetric technique at low temperatures and under magnetic fields. A thermal anomaly related to the superconductive phase transition was observed at 5 K. The existence of residual γ^* in the superconductive state is about 18% of the normal state γ value, which is larger than those of κ-(BEDT-TTF)₂Cu(NCS)₂, and κ-(BEDT-TTF)₂Cu[N(CN)₂]Br salt. The lattice heat capacity reflected on the β-term in the low-temperature heat capacity was found to be affected by the cooling rate. The disorder produced in the network structure constructed by hydrogen bond in the insulating layer is considered to give low-energy phonon excitations reflected in the heat capacity.     

Two crystalline modifications of Pd<Subscript>2</Subscript>(μ-ac)<Subscript>2</Subscript>(acac)<Subscript>2</Subscript>

Crystal structures of two modifications of a binuclear Pd₂(μ-ac)₂(acac)₂ complex are studied at 150 K and 297 K (ac = acetate; acac = acetylacetonate). It is demonstrated that in both cases, the packing of the complexes can be considered as pseudohexagonal, the molecules forming infinite chains by interactions between chelate rings with the shortest contacts Pd...C _γ ～ 3.3 Å.     

Crystal structure of Mg pivalate hydrate Mg(H<Subscript>2</Subscript>O)<Subscript>6</Subscript>(Piv)<Subscript>2</Subscript> · 3H<Subscript>2</Subscript>O

Single crystals of Mg pivalate hydrate, Mg(H₂O)₆(Piv)₂ · 3H₂O (HPiv = (CH₃)₃CCOOH) are synthesized and their structure is determined by X-ray diffraction method. The crystals are rhombic: a = 10.917(2) Å, b = 12.625(2) Å, c = 31.394(8) Å, Z = 8, space group Pbca, R ₁ = 0.0525. The Mg atom has octahedral surrounding of the O atoms of water molecules (Mg-O 2.044–2.137 Å). The cationic chains of [Mg(H₂O)₆] _∞ ²⁺ lie in the voids of doubled network anionic layers of [(H₂O)₃(Piv)₂] _∞∞ ^2? . Inside the layer, the pivalate anions alternate with water molecules in the xy plane, being bonded to them by hydrogen bonds. The cationic chains and the anionic layers are united into layered packs by hydrogen bonds between coordinated water molecules and pivalate anions and between coordinated and crystal hydrate water molecules.     

Hydrothermal synthesis and crystal structure of a novel nickel(II) complex: [Ni(H<Subscript>2</Subscript>Bibzim)<Subscript>3</Subscript>Cl<Subscript>2</Subscript> · 2H<Subscript>2</Subscript>O] (H<Subscript>2</Subscript>Bibzim = 2,2-Bibenzimidazole)

A novel organic-inorganic hybrid compound based on weak intermolecular interactions formulated as Ni(H₂Bibzim)₃Cl₂ · 2H₂O (H₂Bibzim = 2,2-bibenzimidazole, formula, C₁₄H₁₀N₄) has been synthesized under hydrothermal conditions and characterized by elemental analysis, single-crystal X-ray diffraction analyses, and IR spectra. It crystallizes in the orthorhombic system, space group Pbcn, Z = 2, a = 20.8530(19), b = 15.7838(14), c = 12.3159(11) Å, V = 4053.7(6) ų, M _r = 1736.84, ρ_c = 1.423g/cm³, λ = 0.71073 Å, μ(MoK _α) = 0.664 mm^?1, F(000) = 1792, R = 0.0283 and wR = 0.0707 for 3746 observed reflections with I > 2σ(I). The complex is composed of mononuclear cations [Ni(H₂Bibzim)₃]²⁺, chlorine anions, and lattice water molecules, which are linked into a two-dimensional supramolecular architectures via hydrogen bonds and π-π-stacking interactions.