Substituted transition metal phospho olivines LiMM′PO4 (M = Mn,M′ = Fe,Co, Mg): Optimisation routes for LiMnPO4

Since transition metal phospho olivines gain increasing interest as cathode materials for lithium ion batteries in the last decades lots of publications appeared. Various synthesis methods were in the focus of interest as well as structural investigations of the pure LiMPO₄ and mixed Li (MM′)PO₄ phases (M, M′ = Fe, Mn, Co, Ni, Mg, Zn, Al) and their structural changes during electrochemical conversion. Lithium insertion and exsertion mechanisms have been studied with the help of e.g. structural, optical and electronic, and electrochemical characterisation methods. Likewise many efforts have been done for material optimisation concerning synthesis procedure or substitution.We tend to give an overview about Li (MM′Mn)PO₄ (M, M′ = Mg, Fe, Co) on the basis of our results. For the greater topic of enhancement of performance and energy density of LiMnPO₄ we discuss different solution approaches concerning the raise of specific capacity, redox potential and optimisation of material characteristics. Thus we consider effects due to the intrinsic conductivity, structural stability of the charged phase as well as its chemical stability against the electrolyte and the dynamic stability of the interface between charged phase and discharged phase during electrochemical conversion.For this purpose in our experimental part we focus on three different approaches: substitution with an electrochemically active transition metal, substitution with an electrochemically inactive metal in case for the manipulation of unit cell volume alternation and the substitution with electrochemically inactive metals for the purpose of providing a “lithium reservoir”. This generated “lithium reservoir” is expected to be accessible for the utilisation of a new redox step. Phase transition in mixed transition metal phospho olivines Li(MnCo)PO₄ has been investigated as example for the effect of substitution with an electrochemically active transition metal. Substitution with an electrochemically inactive metal leading to binary Li(MgMn)PO₄ has been structurally and electrochemically investigated. Promising new electrochemical characteristics of binary Li(MgMn)PO₄ phospho olivines are introduced for the first time. When charged to high potentials (>4.9 V) the activation of the Mn³⁺/Mn⁴⁺ step is reported.     

The structural and thermal stability,electrochemical hydrogenation and corrosion behavior of LaT5−xMx(T = Co,Ni and M = Al,Ge, Li) phases

The structural and thermal stability, electrochemical hydrogenation and corrosion behavior of LaT_5−x(M/Li)_x (T = Co, Ni and M = Al, Ge) alloys have been investigated using x-ray diffraction, SEM with WDS/EDX, DSC and electrochemical techniques. The prepared ternary and quaternary samples are solid solutions on the base of binary LaCo₅ and LaNi₅ compounds with hexagonal CaCu₅ structure type. By partial substitution of transition metals (Ni and Co) by Al, Ge and Li in the LaT_5−x(M/Li)_x alloys the discharge capacity increased by 25%. Doping of LaCo₅ and LaNi₅ binary phases by Al, Ge and Li improves corrosion resistance, thermal stability and absorption capacity during the electrochemical hydrogenation. These alloys passivate effectively in strong alkaline solution.     

Structural and magnetic properties of metal telluromolybdates MxM′1−xTeMoO6 (M,M′ = Mn,Co, Cd)

Synthesis, crystal structures and magnetic properties of metal telluromolybdates M_xM′_1?xTeMoO₆ (M, M′ = Mn, Co, Cd) have been investigated. Their crystal structures have two-dimensional arrays of M and M′ atoms. From the powder X-ray diffraction measurements, Mn_xCo_1?xTeMoO₆ adopt an orthorhombic structure throughout the composition range (x = 0.0–1.0). On the other hand, Mn_xCd_1?xTeMoO₆ and Co_xCd_1?xTeMoO₆ adopt two types of structures corresponding to their end members (orthorhombic for Mn- or Co-rich solid solutions; tetragonal for Cd-rich ones). In the intermediate compositions, it was found that two phases coexist with different metal components. Magnetic properties of these solid solutions were investigated. All the Mn_xCo_1?xTeMoO₆ exhibits an antiferromagnetic transition at ～23 K. The antiferromagnetic transition was also observed in Mn_xCd_1?xTeMoO₆ and Co_xCd_1?xTeMoO₆. However, the Néel temperature rapidly decreases with increasing the concentration of Cd and disappeared below x = 0.6, which is characteristic for two-dimensional magnetic system.     

Phosphasilaallenes >Si = C = P− and phosphagermaallenes >Ge = C = P−

Phosphasilaallene Tip(Ph)Si = C = PMes* (Tip = 2,4,6-triisopropylphenyl, Mes* = 2,4,6-tri-tert-butylphenyl) and phosphagermaallene Mes₂Ge = C = PMes* (Mes = 2,4,6-trimethylphenyl) have been obtained by dehalogenation of their corresponding dihalophosphametallapropenes > E(X)-C(X′) = P? by tert-butyllithium. They dimerize above ?40 °C by a cycloaddition involving two E = C double bonds or the E = C and the P = C double bonds but can be characterized at low temperature by trapping reactions and by low field shifts in ³¹P, ²⁹Si and particularly ¹³C NMR for the sp carbon atom. Owing to a small increase in the steric hindrance, phosphagermaallene Tip(t-Bu)Ge = C = PMes* can be stabilized and isolated. The Ge = C double bond undergoes nearly quantitative [2 + 1] cycloadditions with chalcogens and [2 + 2] cycloadditions with aldehydes or ketones. The surprisingly stable lithiochlorosilane R(Cl₂)Si-C(Li) = PMes* (R = 9-methylfluorenyl) behaves as a synthetic equivalent of the phosphasilaallene R(Cl)Si = C = PMes*. With two alkyl groups (t-Bu) on the germanium atom, the phosphagermaallene t-Bu₂Ge = C = PMes* is not obtained but its formal dimers 1,3-digermacyclobutanes have been isolated.     

Synthesis,characterization and thermochemistry of Cs(ASP) · nH2O (n = 0, 1)

New compounds of aspartic acid Cs(ASP) · nH₂O (n = 0, 1) have been synthesized and characterized by XRD, IR and Raman spectroscopy as well as TG. The structural formula of this new compound was Cs(ASP) · nH₂O (n = 0, 1). The enthalpy of solution of Cs(ASP) · nH₂O (n = 0, 1) in water were determined. With the incorporation of the standard molar enthalpies of formation of CsOH(aq) and ASP(s), the standard molar enthalpy of formation of −(1202.9 ± 0.2) kJ · mol⁻¹ of Cs(ASP) and −(1490.7 ± 0.2) kJ · mol⁻¹ of Cs(ASP) · H₂O were obtained.     

Hyperconjugation versus back bonding in AH3−nXn species (A = Si and Ge; X = F,Cl and Br; and n = 1, 2 and 3)

In this research two competing phenomena, back bonding and hyperconjugation, have been investigated based on Natural Bond Orbital (NBO) and Atoms in Molecules (AIM) analyses for radical AH_3?nX_n species, where A = Si and Ge, and n = 1, 2 and 3. It is demonstrated in this article that both above phenomena will be occurred significantly, while back bonding is the only event in analogous compounds with carbon and hyperconjugation is rather negligible. It was also found that only one back bonding with the help of keyword $CHOOSE in NBO analysis can be found in this type of compounds with reasonable structure, while it can be sometimes detected in AH_3?nX_n without using keyword $CHOOSE. It is also shown that there is always an increase in bond length in comparison with reference molecules in mentioned species due to existing hyperconjugation, while if the central atom is carbon, we have always a decrease of bond length due to only having back bonding. Additionally, from AIM point of view, the delocalization indices for α-spin (majority spin) is more than β-spin (minority spin) in radical species for molecules without back bonding, while the situation in our compounds is quite reverse, which can be attributed to the π back bonding in the β-spin electrons.     

Synthesis,characterization and reactions of the transition metal halogenoalkyl carbocation complexes [Cp(CO)2M{η2-CH2CH(CH2)nX}]PF6 (n = 1–8, 10, M = Fe; n = 3, 4 M = Ru; X = Br,I)

The halogenoalkyl complexes [Cp(CO)₂M{(CH₂)_nX}] (n = 3–10, 12, M = Fe; n = 5, 6, M = Ru, X = Br, I) react with Ph₃CPF₆ in dry CH₂Cl₂ to give the corresponding carbocation complexes [Cp(CO)₂M{η²-(CH₂CH(CH₂)_n?2X}]PF₆ in high yields. NMR evidence indicates that the metals form metallacyclopropane type structures with the carbocation ligand. The reactions of some of the cationic complexes with NaI, PPh₃, Na[Cp(CO)₂Fe] and Et₃N are discussed. NaI and Na[Cp(CO)₂Fe] displace the halogeno-olefin, while PPh₃ adds at the β-CH^δ+ giving the unstable phosphonium adducts [Cp(CO)₂Fe{CH₂CH(PPh₃)(CH₂)_n?2X}]PF₆ which decompose to the halogeno-olefins and the cationic PPh₃ complex [Cp(CO)₂Fe(PPh₃)]⁺. Et₃N causes allylic deprotonation forming internal olefin complexes of the type [Cp(CO)₂Fe{CH₂CHCH(CH₂)_n?3X}]PF₆.     

Enhancing the rate capability of high capacity xLi2MnO3 · (1 − x)LiMO2 (M = Mn,Ni, Co) electrodes by Li–Ni–PO4 treatment

The rate capability of high capacity xLi₂MnO₃ · (1 ? x)LiMO₂ (M = Mn, Ni, Co) electrodes for lithium-ion batteries has been significantly enhanced by stabilizing the electrode surface by reaction with a Li–Ni–PO₄ solution, followed by a heat-treatment step. Reversible capacities of 250 mAh/g at a C/11 rate, 225 mAh/g at C/2 and 200 mAh/g at C/1 have been obtained from 0.5Li₂MnO₃ · 0.5LiNi_0.44Co_0.25Mn_0.31O₂ electrodes between 4.6 and 2.0 V. The data bode well for their implementation in batteries that meet the 40-mile range requirement for plug-in hybrid vehicles.     

Helical chains of [MO5Cl] octahedra – Three compounds in the new family AEM2Te3O8Cl2 (AE = Ca,Sr and M = Co,Ni)

The compounds CaCo₂Te₃O₈Cl₂, SrCo₂Te₃O₈Cl₂ and SrNi₂Te₃O₈Cl₂ were synthesized via solid–gas reactions and investigated using single-crystal X-ray diffraction. While the compound CaCo₂Te₃O₈Cl₂ formed large enough single crystals to allow for a detailed structural analysis, crystals of the Sr-containing compounds yielded evidence that they are isostructural. CaCo₂Te₃O₈Cl₂ crystallizes in the monoclinic system, space group P2₁/c, a = 6.537(2) Å, b = 9.088(2) Å, c = 19.500(9) Å, β = 113.36(4)°, Z = 4. It exhibits [CoO₅Cl] helical chains along the [010] direction, connected by [CaO₈] polyhedra, [TeO₃E] tetrahedra and [TeO₄E] trigonal bipyramids (the lone pair of electrons on Te^IV is designated as E) to form a layer. The layers are held together only by weak van der Waals forces; the shortest interlayer distance is a Te?Cl contact of 3.432(4) Å.     

(Solid + liquid) equilibria for the ternary system (CsBr + LnBr3 + H2O) (Ln = Pr,Nd, Sm) at T = 298.2 K and atmospheric pressure,thermal and fluorescent properties of Cs2LnBr5·10H2O

The (solid + liquid) phase equilibria of the ternary systems (CsBr + LnBr₃ + H₂O) (Ln = Pr, Nd, Sm) at T = 298.2 K were studied by the isothermal solubility method. The solid phases formed in the systems were determined by the Schreinemakers wet residues technique, and the corresponding phase diagrams were constructed based on the measured data. Each of the phase diagrams, with two invariant points, three univariant curves, and three crystallization regions corresponding to CsBr, Cs₂LnBr₅·10H₂O and LnBr₃·nH₂O (n = 6, 7), respectively, belongs to the same category. The new solid phase compounds Cs₂LnBr₅·10H₂O are incongruently soluble in water, and they were characterized by chemical analysis, XRD and TG-DTG techniques. The standard molar enthalpies of solution of Cs₂PrBr₅·10H₂O, Cs₂NdBr₅·10H₂O and Cs₂SmBr₅·10H₂O in water were measured to be (52.49 ± 0.48) kJ · mol⁻¹, (49.64 ± 0.49) kJ · mol⁻¹ and (50.17 ± 0.48) kJ · mol⁻¹ by microcalorimetry under the condition of infinite dilution, respectively, and their standard molar enthalpies of formation were determined as being −(4739.7 ± 1.4) kJ · mol⁻¹, −(4728.4 ± 1.4) kJ · mol⁻¹ and −(4724.4 ± 1.4) kJ · mol⁻¹, respectively. The fluorescence excitation and emission spectra of Cs₂PrBr₅·10H₂O, Cs₂NdBr₅·10H₂O and Cs₂SmBr₅·10H₂O were measured. The results show that the upconversion spectra of the three new solid phase compounds all exhibit a peak at 524 nm when excited at 785 nm.     

Crystal growth of inter-lanthanide LaLn′O3 (Ln′ = Y,Ho–Lu) perovskites from hydroxide fluxes

In this article, we report the growth of single crystals of the inter-lanthanide series LaLn′O₃ (Ln′ = Y, Ho–Lu) using molten hydroxide fluxes. Inter-lanthanide oxides, LnLn′O₃ (where Ln and Ln′ = lanthanides) typically crystallize in the A-, B- or C-Ln₂O₃ or in the ABO₃ perovskite structure types, depending on the relative sizes of the lanthanide cations involved. The inter-lanthanide oxides, LaLn′O₃ (Ln′ = Y, Ho–Lu), reported herein were determined to crystallize in the orthorhombic (Pnma) perovskite-type structure. A discussion on the effect of cation radii on the resultant crystal structure for LaLn′O₃ (Ln′ = Y, Ho–Lu) and other reported inter-lanthanide oxides is presented herein.     

Synthesis,magnetic properties and X-ray analysis of Zn0.97X0.03O nanoparticles (X = Mn,Ni, and Co) using Scherrer and size–strain plot methods

Un-doped and doped ZnO nanoparticles (Zn_0.97X_0.03O-NPs, X = Mn, Co, and Ni) were synthesized from a metal acetate precursor and acetic acid by a modified sol–gel combustion method. The compounds were synthesized at calcination temperatures of 650 °C for 1 h. The synthesized un-doped/doped ZnO-NPs were characterized by X-ray diffraction analysis (XRD) and high-magnification transmission electron microscopy (TEM). The XRD results revealed that the sample product was crystalline with a hexagonal wurtzite phase. The TEM showed ZnO-NPs nearly spherical shapes and a non-uniform shape for doped ZnO-NPs. The crystalline development in the ZnO-NPs was investigated by X-ray peak broadening. The size–strain plot (SSP) method was used to study the individual contributions of crystallite sizes and lattice strain on the peak broadening of the un-doped and doped ZnO-NPs. Physical parameters such as strain, stress and energy density values were calculated more precisely for all reflection peaks of XRD corresponding to the wurtzite hexagonal phase of ZnO lying in the range of 20–80° from the SSP results. The vibrating sample magnetometer (VSM) was also used to study the magnetic behavior of the samples in the ceramic form. The obtained results showed that strain play an important role in peak broadening; moreover, the mean crystalline size of the un-doped and doped ZnO-NPs estimated from the TEM and the SSP method were highly inter-correlated.     

Thermodynamics of formation of double salts M2SO4 · M′SO4 · 6H2O and M2SeO4 · M′SeO4 · 6H2O where M denotes Rb,or Cs and M′ denote Co,Ni, or Zn

This paper describes a chemical model that calculates (solid + liquid) equilibria in the (m₁Rb₂SO₄ + m₂CoSO₄)(aq), (m₁Rb₂SeO₄ + m₂CoSeO₄)(aq), (m₁Rb₂SO₄ + m₂NiSO₄)(aq), (m₁Rb₂SO₄ + m₂ZnSO₄)(aq), (m₁Rb₂SeO₄ + m₂ZnSeO₄)(aq), (m₁Cs₂SO₄ + m₂CoSO₄)(aq), (m₁Cs₂SeO₄ + m₂CoSeO₄)(aq), (m₁Cs₂SO₄ + m₂NiSO₄)(aq), (m₁Cs₂SeO₄ + m₂NiSeO₄)(aq), (m₁Cs₂SO₄ + m₂ZnSO₄)(aq), and (m₁Cs₂SeO₄ + m₂ZnSeO₄)(aq) systems, where m denotes molality at the temperature T=298.15 K. The Pitzer ion-interaction model has been used for thermodynamic analysis of the experimental osmotic and solubility data presented in the literature. The thermodynamic functions needed (binary and ternary parameters of ionic interaction, thermodynamic solubility products) have been calculated and the theoretical solubility isotherm has been plotted. The mixing parameters {θ(MN) and ψ(MNX)} have been chosen on the basis of the compositions of saturated ternary solutions and data on the binary solubility of the sulfate M₂SO₄. M^′SO₄ · 6H₂O double salts in water. To validate the mixing solutions model two different approaches have been used in evaluation of the ternary parameters: (I) preserving the same value of the binary mixing θ(MN) for the corresponding chloride, bromide, sulfate, and selenate systems with the same cations, and (II) with constant θ(MN) value (set equal to −0.05) for the all 11 sulfate and selenate systems. Very good agreement between experimentally determined and model predicted solubilities has been found. Important thermodynamic characteristics (thermodynamic solubility products, standard molar Gibbs free energy of formation) of the solid phases (simple salts, six sulfate – M₂SO₄ · M^′SO₄ · 6H₂O, and five selenate – M₂SeO₄ · M^′SeO₄ · 6H₂O – double salts) crystallizing in the systems under consideration are determined.     

Solubilities,densities and refractive indices for the ternary systems ethylene glycol + MCl + H2O (M = Na,K, Rb,Cs) at (15 and 35) °C

The solubilities, densities and refractive indices data for the four ternary systems ethylene glycol + MCl + H₂O (M = Na, K, Rb, Cs) at different temperatures were measured, with mass fractions of ethylene glycol in the range of 0 to 1.0. In all cases, the presence of ethylene glycol significantly reduces the solubility of the salts in aqueous solution. The experimental data of density, refractive index and solubility of saturated solutions for these systems were correlated using polynomial equations as a function of the mass fraction of ethylene glycol. On the other hand, the refractive index and density of unsaturated solutions was also determined for the four ternary systems with varied unsaturated salt concentrations. Values for both the properties were correlated with the salt concentrations and proportions of ethylene glycol in the solutions.