Origin of the irreversible plateau (4.5 V) of Li[Li0.182Ni0.182Co0.091Mn0.545]O2 layered material

Layered LiNi_0.4Co_0.2Mn_0.4O₂, Li[Li_0.182Ni_0.182Co_0.091Mn_0.545]O₂, Li[Li_1/3Mn_2/3]O₂ powder materials were prepared by rheological phase method. XRD characterization shows that these samples all have analogous structure to LiCoO₂. Li[Li_0.182Ni_0.182Co_0.091Mn_0.545]O₂ can be considered to be the solid solution of LiNi_0.4Co_0.2Mn_0.4O₂ and Li[Li_1/3Mn_2/3]O₂. Detailed information from XRD, ex situ XPS measurement and electrochemical analysis of these three materials reveals the origin of the irreversible plateau (4.5 V) of Li[Li_0.182Ni_0.182Co_0.091Mn_0.545]O₂ electrode. The irreversible oxidation reaction occurred in the first charging above 4.5 V is ascribed to the contribution of Li[Li_1/3Mn_2/3]O₂ component, which maybe extract Li⁺ from the transition layer in Li[Li_1/3Mn_2/3]O₂ or Li[Li_0.182Ni_0.182Co_0.091Mn_0.545]O₂ through oxygen release. This step also activates Mn⁴⁺ of Li[Li_1/3Mn_2/3]O₂ or Li[Li_0.182Ni_0.182Co_0.091Mn_0.545]O₂, it can be reversibly reduced/oxidized between Mn⁴⁺ and Mn³⁺ in the subsequent cycles.     

Zur Löslichkeit von Cobalt(IV) in Li8SiO6

On the Solubility of Cobalt(IV) in Li₈SiO₆ Li₈SiO₆ dissolves up to 2 at.‐%, cobalt(IV). Crystals of such solid solutions are transparent and of deep ruby red colour. Cobalt concentrations as determined by ICP‐OES, EDX and magnetic susceptibility measurements are in good accordance. The X‐ray powder diffraction and the magnetic properties confirm integration of Co⁴⁺ into the lithiumoxosilicate. These new results are indicating that the ruby red phase, previously addressed as “Li₈CoO₆”, is in fact cobalt doped Li₈SiO₆.     

Ein neues Cobaltat mit Inselstruktur: Li6[CoO4]

A New Cobaltate with Isolated Anion Structure: Li₆[CoO₄] For the first time transparent, blue single crystals of Li₆[CoO₄] have been prepared (Li₂O/Na₂O/?CoO”? (Li:Na:Co = 1.3:1.3:1), Co-tube, 580°C, 22 d). Corresponding to Li₆□CoO; it is an ordered variant of the Li₂O-type of structure: P4₂/nmc; a = 653.6(1) pm, c = 465.4(1) pm; Z = 2; d_x = 2.75 g cm^?3, d_pyk = 2.71 g cm^?3 (4-circle-diffractometer-data (PW 1100), AgKα; 230 from 936 I₀(hkl); R = 9.58%, R_W = 5.25%). Parameters see text. The Madelung Part of Lattice Energy, MAPLE, and Effective Coordination Numbers, ECoN, these via Mean Fictive Ionic Radii, MEFIR, are calculated and discussed. The magnetic properties are measured in the temperature range of 14–297 K.     

Na2Li3CoO4, das Erste quaternäre Oxocobaltat(III) der Alkalimetalle

Na₂Li₃CoO₄, the First Quaternary Oxocobaltate(III) of the Alkali Metals For the first time we obtained Na₂Li₃CoO₄ by annealing intimate mixtures of Co₃O₄, Na₂O₂, and Li₂O [Co : Na : Li = 1 : 2.2 : 10.1; 760°C; 21 d; Ag-tube] in form of transparent red single crystals. Structure Refinement [four-circle diffractometer data; AED2; MoKα-radiation; 1016 I_o(hkl); R = 2.6%; R_w = 2.0%; space group Pnnm; Z = 4; a = 818.7(3), b = 799.4(2), c = 655.1(2) pm] confirms the isotypism to Na₂Li₃GaO₄ [2] and Na₂Li₃FeO₄ [3]. Mean Fictive Ionic Radii, MEFIR, Effective Coordination Numbers, ECoN, and the Charge Distribution were calculated. The isotypism of Na₂Li₃CoO₄ and Na₂Li₃GaO₄ is compared graphically.     

Das erste Oxocobaltat des Typs A2CoIIO2: K2CoO2 = K4[OCoO2CoO]

The First Oxocobaltate of the Type A₂Co^IIO₂: K₂CoO₂ = K₄[OCoO₂CoO] By “reaction with the cylinder surface” of intimate mixtures of K₂O and CdO (molar ratio 1:1) in closed Co-Cylinders at 450°C during 73 d dark-red single-crystals of K₂CoO₂ were obtained. Structure solution and refinement (four-circle diffractometer-data, MoKα , 1 567 independent I_o(hkl), none was omitted, R = 3.25%, R_w = 2.67%) result in a monoclinic unit cell containing anions [Co₂O₄]^4? of two connected triangles similar to those of Rb₁₀[Co^IO₂]₂[CoO₄]. MAPLE-values and Charge-distributions are given and discussed.     

Über Oxocobaltate der Alkalimetalle. Zur Kenntnis von Li8CoO6

Oxocobaltates of Alkali Metals. On Li₈CoO₆. Hitherto unknown Li₈CoO₆, rubin- red single crystals, cristallizes according to WEISSENBERG and precession photographs (MoK_α) hexagonal with a = 5.44 Å, c = 10.87 Å; c/a = 2.0; Z = 2, space group C? P6₃cm. Atomic parameters see text. The structure derives from a closest packing of O^2?, ABACA … (The tetrahedral, ?isolated”? groups [CoO₄] show remarkable short distances Co–O (1.66 Å), comparable with [CoO₄] in Li₄CoO₄, being isotypic with Li₄SiO₄. The MADELUNG Part of Lattice Energy is calculated and discussed.     

Behavior of Co4+ ion in K2NiF4-type (Ca1+xSm1−x)CoO4

Orthorhombic K₂NiF₄-type (Ca_1+xSm_1−x)CoO₄ (0.00 ≤ x ≤0.15) with space group Bmab has been synthesized by the polymerized complex route. The cell parameters (a and b) decrease, while the cell parameter (c) increases with increasing Co⁴⁺ ion content. The global instability index (GII) indicates that the crystal stability of (Ca_1+xSm_1−x)CoO₄ is not influenced by the Co⁴⁺ ion content. (Ca_1+xSm_1−x)CoO₄ is a p-type semiconductor and exhibits hopping conductivity in the small-polaron model at low temperatures. The magnetic measurement indicates that (Ca_1+xSm_1−x)CoO₄ shows paramagnetic behavior above 5 K, and that the spin state of both the Co³⁺ and Co⁴⁺ ions is low. The Co⁴⁺ ion acts as an acceptor, and the electron transfer becomes active through the Co³⁺–O–Co⁴⁺ path as the Co⁴⁺ ions increase.     

Structure and electron density analysis of electrochemically and chemically delithiated LiCoO2 single crystals

Single crystals of Li_0.68CoO₂, Li_0.48CoO₂, and Li_0.35CoO₂ were successfully synthesized for the first time by means of electrochemical and chemical delithiation processes using LiCoO₂ single crystals as a parent compound. A single-crystal X-ray diffraction study confirmed the trigonal R3¯m space group and the hexagonal lattice parameters a=2.8107(5) Å, c=14.2235(6) Å, and c/a=5.060 for Li_0.68CoO₂; a=2.8090(15) Å, c=14.3890(17) Å, and c/a=5.122 for Li_0.48CoO₂; and a=2.8070(12) Å, c=14.4359(14) Å, and c/a=5.143 for Li_0.35CoO₂. The crystal structures were refined to the conventional values R=1.99% and wR=1.88% for Li_0.68CoO₂; R=2.40% and wR=2.58% for Li_0.48CoO₂; and R=2.63% and wR=2.56% for Li_0.35CoO₂. The oxygen-oxygen contact distance in the CoO₆ octahedron was determined to be shortened by the delithiation from 2.6180(9) Å in LiCoO₂ to 2.5385(15) Å in Li_0.35CoO₂. The electron density distributions of these Li_xCoO₂ crystals were analyzed by the maximum entropy method (MEM) using the present single-crystal X-ray diffraction data at 300 K. From the results of the single-crystal MEM, strong covalent bonding was clearly visible between the Co and O atoms, while no bonding was found around the Li atoms in these compounds. The gradual decrease in the electron density at the Li site upon delithiation could be precisely analyzed.     

Phase separation in the spin-state transition system of La1−xBaxCoO3

The magnetic and electric transport properties of La_1−xBa_xCoO₃ (0<x≤0.50) have been studied systematically. Two effects of substitution divalent ions on the spin-state transition of Co³⁺ have been differentiated for the substitution of Ba²⁺ for La³⁺ in La_1−xBa_xCoO₃. The first is the transition from low-spin state to high-spin state due to lattice expansion, and the second is the transition from low-spin state to intermediate-spin state caused by the strong hybridization between ligand (oxygen) 2p and Co 3d orbital with introduction of holes in the oxygen 2p orbital. Based on the two different spin-state transition mechanisms and experimental results, a phase separation model has been developed and a very detailed magnetic and electric phase diagram of La_1−xBa_xCoO₃ has been constructed.     

Ni-Mn共掺杂高电压钴酸锂锂离子电池正极材料

以金属硫酸盐为原料,NaOH和NH₃·H₂O为沉淀剂,用共沉淀法合成了Co_0.9Ni_0.05Mn_0.05(OH)前驱体,再进行配锂并通过高温固相法合成了Ni-Mn共掺杂高电压钴酸锂锂离子电池正极材料Li(Co_0.9Ni_0.05Mn_0.05)O₂。用X射线衍射(XRD)、扫描电镜(SEM)、 循环伏安(C-V)、交流阻抗(EIS)和充放电测试研究样品的晶体结构、形貌和电化学性能。结果表明Ni-Mn共掺杂正极材料Li(Co_0.9Ni_0.05Mn_0.05)O₂有优秀的电化学性能:在3.0~4.4 V和3.0~4.5 V区间,0.5C倍率下首次放电比容量分别为162 mAh·g^-1和187 mAh·g^-1,循环100次后容量保持率分别为94%和94%。     

Electrochemical behaviour of solid lithium cobaltate (LiCoO2) and lithium manganate (LiMn2O4) in an aqueous electrolyte system

Lithium cobaltate (LiCoO₂) and lithium manganate (LiMn₂O₄) were synthesized by self-propagating high-temperature combustion and their phase purity and composition were characterized by X-ray diffraction and inductively coupled plasma spectroscopy. These transition metal oxides were mechanically immobilized on the surface of paraffin-impregnated graphite electrodes and their cyclic voltammetric behaviour in aqueous alkali electrolytes was examined. It was shown that both the oxides undergo proton insertion upon the reduction of Co³⁺ to Co²⁺ in LiCoO₂ and Mn⁴⁺ to Mn³⁺ in LiMn₂O₄, while they deintercalate protons on the reverse oxidation. Scanning electron microscopy reveals spherical LiCoO₂ particles with a very narrow size distribution. Energy dispersive X-ray detection proved the absence of metal cation intercalation. Received: 30 August 1999 / Accepted: 11 November 1999     

Crystal Structure, Electric and Magnetic Properties of Layered Cobaltite β-NaxCoO2

The layered oxide thermoelectric material β-Na_0.67CoO₂ has been studied by powder neutron diffraction, electric and magnetic measurements. This compound includes an edge-sharing CoO₆ slab and a highly vacant Na⁺ sheet in a unit cell (space group symmetry C2/m, a=4.9023(4) Å, b=2.8280(2) Å, c=5.7198(6) Å and β=105.964(6)° at 300 K). The evaluated formal valence of cobalt ion, +3.33(1), is ascribed to the coexistence of Co³⁺ and Co⁴⁺ in the ratio 2:1. Polycrystalline β-Na_0.67CoO₂, a p-type thermoelectric material, exhibits metallic behavior of the electric resistivity below 300 K. The Curie-Weiss-type magnetic susceptibility indicates antiferromagnetic interactions between magnetic cobalt ions in the edge-sharing CoO₆ slab.     

Structure and properties of a novel cobaltate La0.30CoO2

The layered cobaltate La_0.30CoO₂ was prepared from Na_xCoO₂ precursor by a solid-state ionic exchange and was characterized by means of X-ray and neutron diffraction, magnetic, thermal and electric transport measurements. The compound consists of hexagonal sheets of edge-sharing CoO₆ octahedra interleaved by lanthanum monolayers. Compared to Na⁺ in the parent system, the La³⁺ ions occupy only one-third of available sites, forming a 2-dimensional superstructure. The deviation from the ideal stoichiometry La_1/3CoO₂ introduces extra hole carriers into the diamagnetic LS Co³⁺ matrix making the sample Pauli paramagnetic. The temperature dependence of the electrical conductivity in La_0.30CoO₂ follows Mott's T^−1/3 law up to about 400 K, which is in contrast with the standard metallic behavior in the Na⁺ homolog possessing the same formal doping. The experiments are complemented by electronic structure calculations for La_0.30CoO₂ and related Na_xCoO₂ systems.     

Electrochemical characteristics of La0.6Sr0.4CoO3-δ, Pr0.6Sr0.4CoO3-δ and Gd0.6Sr0.4CoO3-δ on Ce0.85Sm0.15O1.925 electrolyte

Cyclic voltammetry, chronoamperometry and electro-chemical impedance have been used for the analysis of the following medium temperature half-cells: Ce_0.85Sm_0.15O_1.925| La_0.6Sr_0.4CoO_3-δ, Ce_0.85Sm_0.15O_1.925| Pr_0.6Sr_0.4CoO_3-δ and Ce_0.85Sm_0.15O_1.925| Gd_0.6Sr_0.4CoO_3-δ. The influence of the atomic mass of the A–site cation in the perovskite cathode on the oxygen reduction kinetics has been discussed. The total polarisation resistance, obtained from the Z′′, Z′-plots, increases with the rise of atomic mass of the cation in the A-site position. Two different time constants have been obtained for the oxygen electroreduction process, and the replacement of La³⁺ by Gd³⁺ in the cathode material decreases somewhat the surface catalytic activity, but the noticeably higher low-frequency series resistance, i.e. mainly diffusion-like mass transfer resistance, values have been obtained. However, the mainly diffusion-limited process at T≤773 K for Gd_0.6Sr_0.4CoO_3-δ and the kinetically mixed process (diffusion + charge transfer) for Pr_0.6Sr_0.4CoO_3-δ and La_0.6Sr_0.4CoO_3-δ have been established. At higher temperature (T≥993 K) and more negative potentials, the O₂ reduction process is limited mainly by the heterogeneous charge transfer step. Presented at the fourth Baltic Conference on Electrochemistry, Greifswald, March 13–16, 2005.     

Cobalt spin state above the valence and spin-state transition in (Pr0.7Sm0.3)0.7Ca0.3CoO3

(Pr_0.7Sm_0.3)_0.7Ca_0.3CoO₃ belongs to a class of cobalt oxides undergoing a first-order transition (T* ≈90 K) associated to a coupled change in the valence and spin-state degrees of freedom. The Curie–Weiss regime present around room temperature (T >> T*) was analyzed in detail to address the controversial issue of the cobalt spin states above the transition. This magnetic investigation indicates that the Co⁴⁺ are in an intermediate spin-state, while the Co³⁺ are in a mixed state combining low-spin and high-spin states. These results are discussed with respect to the literature on related compounds and recent results of X-ray absorption spectroscopy.     

Heat Capacities and Thermodynamic Properties of a H2O + Li2B4O7 Solution in the Temperature Range from 80 to 356 K

The molar heat capacities of an aqueous Li₂B₄O₇ solution were measured with a precision automated adiabatic calorimeter in the temperature range from 80 to 356 K at a concentration of 0.3492 mol⋅kg⁻¹. The occurrence of a phase transition was determined based on the changes in the curve of the heat capacity with temperature. A phase transition was observed at 271.72 K corresponding to the solid-liquid phase transition; the enthalpy and entropy of the phase transition were evaluated to be Δ H _m = 4.110 kJ⋅mol⁻¹ and Δ S _m = 15.13 J⋅K⁻¹⋅mol⁻¹, respectively. Using polynomial equations and thermodynamic relationship, the thermodynamic functions [H _T −H _298.15] and [S _T −S _298.15] of the aqueous Li₂B₄O₇ solution relative to 298.15 K were calculated in temperature range 80 to 355 K at intervals of 5 K. Values of the relative apparent molar heat capacities of the aqueous Li₂B₄O₇ solution, C _p,φ, were calculated at every 5 K in temperature range from 80 to 355 K from the experimental heat capacities of the solution and the heat capacities of pure water.     

Rb3CoO2, a Novel Oxocobaltate(I) Synthesized via the Azide/Nitrate Route

Rb₃CoO₂ was prepared via the azide/nitrate route. Stoichiometric mixtures of the precursors (Co₃O₄, RbN₃ and RbNO₃) were heated in a special regime up to 500 °C and annealed at this temperature for 100 h in silver crucibles. The crystal structure of the obtained red product was solved and refined by powder methods (Pnma, Z = 4, 12.3489(2), 7.6648(1), 6.2251(1) Å). Rb₃CoO₂ is isostructural with K₃CoO₂ and contains Co¹⁺, which is coordinated by two oxygen atoms forming a slightly distorted dumb‐bell. Rb₃CoO₂ decomposes at 580 °C to Rb₂O, Co and CoO.     

Transition Metal Ion-binding Properties of a 14-Membered N2O2S2- Macrobicyclic Ligand

The selective liquid–liquid extraction of various transition metal cations from the aqueous phase to the organic phase was carried out using a 14-membered N₂O₂S₂-macrobicycle. Metal picrates such as Pb²⁺, Co²⁺, Zn²⁺, Ni²⁺,Cu²⁺ and Cd²⁺ were used in this extraction studies. It was found that the ligand showed moderate selectivity towards Pb²⁺ only among the other metals. The extraction constant (log K _ex) was determined to be 13.8 for Pb²⁺ complex.     

Doping studies of the magnetic cobaltocuprate CoSr2Y2−xCexCu2O9±δ

A structural, magnetic and electronic study of the cobaltocuprate CoSr₂Y_2−xCe_xCu₂O_9±δ (x=0.5-0.8) has been performed. All materials crystallise in the orthorhombic Cmcm symmetry space group in which chains of corner linked CoO₄ tetrahedra run parallel to the 1 1 0 direction. An antiferromagnetic transition is observed for x=0.5-0.8; T_M increases with x. A change in the dimensionality of the magnetic order occurs at x=0.8 as the interchain distance increases to a critical value. There is charge transfer between the cuprate planes and cobaltate layer as Ce doping increases, so that Co³⁺ is partially oxidised to Co⁴⁺ with a concomitant reduction in the valence of Cu. Superconductivity is not observed in any of the samples and a crossover from Mott to Efros and Shklovskii variable range hopping behaviour is evidenced as x increases from 0.5 to 0.8.     

In situ electrochemical studies for Li+ ions dissociation from the LiCoO2 electrode by the substrate-generation/tip-collection mode in SECM

This work presents the transportation of Li⁺ ions at the interface of a charging LiCoO₂ electrode through the substrate-generation/tip-collection (SG/TC) feedback mode of scanning electrochemical microscopy (SECM). The TC current, due to the reduction of the ethylene carbonate (EC) supermolecule, is collected more strongly at 1.8 V than that of the Li⁺(DEC) _n at 2.5 V near at the substrate because of the increased concentration of the supermolecule Li⁺(EC)_m, which means that the electrolyte is not uniformly distributed over the substrate. The smooth SG/TC current loop is formed at the probe position optimized by the probe scan curve technique between the LiCoO₂ substrate with 4.0 V and the probe with 1.8 V, which is applied to analyze the Li⁺ ion transport at the interface of the LiCoO₂ electrode. Moreover, the LiCoO₂ substrate, which has a flat surface, is imaged to the nonuniform surface electrochemically by the SECM. We infer that these experimental techniques will help analyze transporting Li⁺ ions at the interface and the electrochemical uniformity of the electrode.