Effect of electronic state of ions on the electrochemical properties of layered cathode materials LiNi1−2x Co x Mn x O2

The cathode materials of the composition LiNi_{1 − 2x} Co _x Mn _x O₂ (x = 0.1, 0.2. 0.33) synthesized from the Ni, Co, Mn mixed hydroxides and LiOH by using mechanical activation method are studied. It is shown that all synthesized compounds have layered structure described by the space group R-3m. With the decreasing of the nickel content the cell volume and the degree of structure disordering decrease. According to XPS data, the electronic main state of d-ions at the prepared samples’ surfaces corresponds to Ni²⁺, Co³⁺, and Mn⁴⁺. An increase in the nickel content leads to the increase of the Ni2p _3/2 and Co2p _3/2 binding energy, which points to the change in the Me-O bond covalence. According to magnetic susceptibility measurements data, the nickel ions in LiNi_0.6Co_0.2Mn_0.2O₂ exist in the two oxidation states: Ni²⁺ and Ni³⁺. It is shown that this sample has the highest specific discharge capacity (∼170 mAh/g). The positions of redox peaks in the differential capacitance curves depend on the sample composition: with the increasing of nickel content they are shifted toward lower voltages. Based on the paper presented in the IX International Conference “Basic Problems of Energy Conversion in Lithium Electrochemical Systems” (Ufa, 2006).     

Recent advances in layered LiNi x CoyMn1−x−y O2 cathode materials for lithium ion batteries

Lithium cobalt oxide, LiCoO₂, has been the most widely used cathode material in commercial lithium ion batteries. Nevertheless, cobalt has economic and environmental problems that leave the door open to exploit alternative cathode materials, among which LiNi _x Co_yMn_{1 − x − y} O₂ may have improved performances, such as thermal stability, due to the synergistic effect of the three ions. Recently, intensive effort has been directed towards the development of LiNi _x Co _y Mn_{1 − x − y} O₂ as a possible replacement for LiCoO₂. Recent advances in layered LiNi _x Co_yMn_{1 − x − y} O₂ cathode materials are summarized in this paper. The preparation and the performance are reviewed, and the future promising cathode materials are also prospected.     

Effect of layer charge modification for CoAl layered double hydroxides: study by X-ray absorption spectroscopy

When tuning the exchange capacity of a Co²⁺, Al³⁺ containing layered double hydroxyde's (LDH's) material, a concomitant phenomenon of oxidation-migration of the cations is observed for one of the end members. X-ray absorption spectroscopy, performed at the cobalt and aluminum k-edge, shows that part of the Co²⁺ cations are oxidized to Co³⁺, while Al³⁺ cations have left the LDH's layers, leading to a [Co²⁺_xCo³⁺] intralayer composition. Interlamellar AlO₆ polyhedra are present after repetitive washing and exchange reactions, suggesting strong interactions with the LDH's layers.     

Microwave hydrothermal synthesis,characterisation, and catalytic performance of Zn1−x Mn x O in cellulose conversion

Wurtzite-type Zn_1?x Mn _x O (x = 0, 0.03, 0.05, 0.07) nanostructures were successfully synthesised using a simple microwave-assisted hydrothermal route and their catalytic properties were investigated in the cellulose conversion. The morphology of the nanocatalysts is dopant-dependent. Pure ZnO presented multi-plate morphology with a flower-like shape of nanometric sizes, while the Zn_0.97Mn_0.03O sample is formed by nanoplates with the presence of spherical nanoparticles; the Zn_0.95Mn_0.05O and Zn_0.93Mn_0.07O samples are mainly formed by nanorods with the presence of a small quantity of spherical nanoparticles. The catalyst without Mn did not show any catalytic activity in the cellulose conversion. The Mn doping promoted an increase in the density of weak acid sites which, according to the catalytic results, favoured promotion of the reaction.     

Mechanical properties of mixed conducting La0.5Sr0.5Fe1−x Co x O3−δ (0≤x≤1) materials

Young’s modulus, strain–stress behavior, fracture strength, and fracture toughness of (0≤×≤1) materials have been investigated in the temperature range 20–1,000°C. Young’s moduli of and , measured by resonant ultrasound spectroscopy, were 130±1 and 133±3 GPa, respectively. The nonlinear stress–strain relationship observed by four-point bending at room temperature was inferred as a signature of ferroelastic behavior of the materials. Above the ferroelastic to paraelastic transition temperature, the materials showed elastic behavior, but due to high-temperature creep, a nonelastic respond reappeared above ∼800°C. The room temperature fracture strength measured by four-point bending was in the range 107–128 MPa. The corresponding fracture toughness of , measured by single edge V-notch beam method, was 1.16±0.12 MPa·m^1/2. The measured fracture strength and fracture toughness were observed to increase with increasing temperature. The fracture mode changed from intragranular at low temperature to intergranular at high temperature. Tensile stress gradient at the surface of the materials caused by a frozen-in gradient in the oxygen content during cooling was proposed to explain the low ambient temperature fracture strength and toughness.     

Improved electrochemical properties of chromium substituted in LiCr1 ? x Ni x O2 cathode materials for rechargeable lithium-ion batteries

Pristine- and chromium-substituted LiNiO₂ nanoparticles were synthesized by sol-gel method using nitrate precursor at 800?°C for 12?h. Physical properties of the synthesized product were analyzed using Fourier transform infrared, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive analysis X-ray. XRD studies revealed a well-defined layer structure and a linear variation of lattice parameters with the addition of chromium and no impurities. Surface morphology and particle size of synthesized materials were changed with chromium addition using SEM and TEM analyses. Assembled lithium-ion cells were evaluated for charge/discharge studies at different rates, cyclic voltammetry, and electrochemical impedance spectra. The initial discharge capacity of LiNiO₂ cathode material was found to be 168?mA hg^?1; however, discharge capacity increased in chromium substitution. Electrochemical impedance spectroscopy revealed that LiCr_0.10Ni_0.90O₂ could enhance charge transfer resistance upon cycling. The substitution of Ni with chromium, LiCr_0.10Ni_0.90O₂, had better cycle life, low irreversible capacity, and excellent electrochemical performance.     

Electrochemical study of spinel oxide systems with nominal compositions Ni1− x Cu x Co2O4 and NiCo2− y Cu y O4

Studies on the electrochemical behaviour of Ni_{1− x} Cu _x Co₂O₄ (x ≤ 0.75) and NiCo_{2− y} Cu _y O₄ (y ≤ 0.30) electrodes in 5 mol dm⁻³ KOH aqueous solutions are presented. The oxide layers have been prepared by thermal decomposition of aqueous nitrate solutions on nickel supports at 623 K. Powder samples were also prepared by thermal decomposition under the same conditions. The powder samples and the oxide layers were characterised by X-ray powder diffraction. The influence of the copper content on the voltammetric response of the electrodes and activity towards oxygen evolution reaction is analysed and correlated with the surface composition of the electrodes by means of X-ray photoelectron spectroscopy data. The analysis of the results reveals that the presence of Cu affects the electrode behaviour and its influence depends on which cation has been replaced. Received: 22 February 1999 / Accepted: 26 October 1999     

Glycolate Ti1 − x Fe x (OCH2CH2O)2 − x/2 as a precursor for the preparation of quasi-one-dimensional (1D) solid solutions Ti1 − x Fe x O2 − 2x/2 (0 ≤ x ≤ 0.1)

Quasi-one-dimensional (1D) solid solutions Ti_{1 ? x} Fe _x (OCH₂CH₂O)_{2 ? x/2} (0 < x ≤ 0.1) with the structure of anatase were prepared by heating the glycolate Ti_{1 ? x} Fe _x (OCH₂CH₂O)_{2 ? x/2} in an atmosphere of air at a temperature of >450°C. The conditions of formation and the properties of the new glycolate Ti₃Fe₂(OCH₂CH₂O)₉ were described. It was found that the synthesized Ti_{1 ? x} Fe _x O_{2 ? 2x/2} solid solutions exhibit photocatalytic activity in the reaction of hydroquinone oxidation in an aqueous solution on irradiation with UV light. A correlation between the rate of oxidation of hydroquinone and the concentration of iron in the catalyst was established. A procedure for the preparation of titanium dioxide with the structure of anatase doped with iron and carbon (Ti_{1 ? x} Fe _x O_{(2 ? x/2) ? yCy)} and also composites on its basis, which contain an excess amount of carbon, was proposed.     

Synthesis of Li3Ni x V2−x (PO4)3/C cathode materials and their electrochemical performance for lithium ion batteries

Li₃Ni _x V_2?x (PO₄)₃/C (x?=?0, 0.02, 0.04 and 0.06) samples have been synthesized via an improved sol–gel method. X-ray diffraction patterns indicate that the structure of the prepared samples retains monoclinic, and the single phase has not been changed with Ni doping. From the analysis of electrochemical performance, the Li₃Ni_0.04?V_1.96(PO₄)₃/C sample exhibits the best electrochemical property. It delivers a discharge capacity of 112.1 mAh?g^?1 with capacity retention of 95.2 % over 300 cycles at 10 C rate in the range of 3.0–4.8 V; cyclic voltammetry and electrochemical impedance spectra testing further prove that the electrochemical reversibility and lithium ion diffusion behavior of Li₃V₂(PO₄)₃ have also been effectively improved through Ni doping.     

Sol–gel derived silica-based organic–inorganic hybrid materials as “composite precursors” for the synthesis of highly homogeneous nanostructured mixed oxides: an overview

The present contribution reports on our results concerning the synthesis of different binary and ternary oxide systems by using hybrid materials as “composite” precursors. In the last years, we have developed and explored a valuable strategy to yield a very homogeneous dispersion of nanoparticles of early metal transition oxide, MO₂ (M = Zr, Hf) inside a silica matrix. This route is based on the use of the sol–gel process to obtain organic–inorganic hybrid silica-based materials embedding the oxide precursors (Zr and/or Hf oxoclusters), which are then calcined at high (T > 500 °C) temperatures to give the desired oxides. The “precursor” hybrid materials are prepared by a modified sol–gel process, involving the copolymerisation of the organically modified oxozirconium or oxohafnium clusters (M₄O₂(OMc)₁₂ (M = Zr, Hf and OMc = methacrylate) with (methacryloxymethyl)triethoxysilane (MAMTES) or (methacryloxypropyl)trimethoxysilane (MAPTMS). Free radical copolymerisation of the 12 methacrylate groups of the oxoclusters with the methacrylate-functionalised siloxanes allows a stable anchoring of the oxoclusters to the silica network formed by the hydrolysis and condensation of the alkoxy groups. The sol–gel reactions of the two methacrylate-modified silanes methacryloxymethyltriethoxysilane and methacryloxypropyltrimethoxysilane were followed by using two independent time-resolved spectroscopic methods, viz., IR ATR and NMR with the aim to optimise their pre-hydrolysis times and consequently their use as precursors for hybrid materials. As mentioned, thermal treatment at high temperature of the hybrid yields a very homogeneous dispersion of ZrO₂ and/or HfO₂ nanoparticles in the silica matrix, since the molecular homogeneity of the starting hybrid is retained in the final mixed oxide. This route was successfully applied both to the synthesis of bulk materials and thin films characterised by different compositions (in term of M/Si molar ratios and M nature), heating route (conventional or microwave-assisted) and final temperature of annealing (from RT to 1,100 °C). The first example of the ZrO₂–HfO₂–SiO₂ ternary oxide system was also prepared by this approach. The prepared systems, both in the form of hybrid materials as well as in the final form of binary or ternary oxides, were thoroughly characterised by a wide variety of analytical tools from a compositional, structural, morphological point of view. Moreover, in the case of the binary ZrO₂–SiO₂ bulk materials, also the evolution under heating was followed by different methods. In particular, the composition of the hybrid as well as of the final oxidic materials was determined by X-Ray Photoelectron Spectroscopy and elemental analysis, whereas FT-IR and multinuclear solid-state NMR spectroscopies shed light on the changes occurring in the composition upon thermal heating and the degree of condensation of the silica network. The morphology and the microstructure of the hybrids and of the oxides were studied by nitrogen sorption and Scanning Electron Microscopy. X-Ray Diffraction, Transmission Electron Microscopy and X-ray Absorption Fine Structure Spectroscopy X-ray Absorption Fine Structure Spectroscopy were used to follow the conversion of the amorphous oxides to the final materials consisting of crystalline zirconia or hafnia dispersed in amorphous silica. On selected systems, functional properties (surface reactivity, dielectric properties) were furthermore investigated. The obtained binary oxides were also used as substrates for functionalisation experiments with (1) dialkycarbamates and (2) long alkyl chains to produce functional materials for catalysis and HPLC applications, respectively.     

(Cu/Ni)–Al layered double hydroxides@Fe3O4 as efficient magnetic nanocomposite photocatalyst for visible-light degradation of methylene blue

Research on Chemical Intermediates - A new magnetic nanocomposite based on layered double hydroxides (LDHs) was synthesized by coprecipitation of (Cu/Ni)–Al LDHs and nano-Fe3O4 and...     

Two-step hydrothermal synthesis of submicron Li(1+x)Ni(0.5)Mn(1.5)O(4-δ) for lithium-ion battery cathodes (x = 0.02, δ = 0.12)

A facile two-step hydrothermal method is developed for the large-scale preparation of lithium nickel manganese oxide spinel as a cathode material for lithium ion batteries. In the reaction, nickel is introduced in a first step at neutral pH, followed by lithium insertion under base to form a product having composition Li(1.02)Ni(0.5)Mn(1.5)O(3.88). The X-ray diffraction pattern and Raman spectroscopy of the synthesized material support a cubic Fd3m structure in which Ni and Mn are disordered on the 16d Wyckoff site, necessary for good cycling characteristics. XP spectroscopy and elemental analysis confirms that Mn remains reduced in the final product (Z(Mn) = 3.82) and that two different chemical environments for Ni exist on the surface. SEM imaging shows a primary particle size of ~200 nm, and galvanostatic cycling of the material vs. Li(+/0) gives a reversible gravimetric capacity of ~120 mA h g(-1) at 1 C rate (147 mA g(-1)) with reversible cycling up to 1470 mA g(-1), supported by rapid Li(+) diffusion. The capacity fade at 1 C is substantial, 17.3% over the first 100 cycles between 3.4 and 5.0 V. However, when the voltage limits are altered, the capacity retention is excellent: nearly 100% when cycled either between 3.4 and 4.4 V (where oxygen vacancies are not electrochemically active) or 89% when cycled between 4.4 and 5.0 V (where the Jahn-Teller active Mn(4+/3+) couple is not accessed).     

On the sol–gel synthesis and catalytic activity of Ce1−xAxO2−δ (A = Pr, Sm, Gd) SOFCs anode materials for reforming of methane

A sol–gel route to synthesize nanocrystalline praseodymium-, samarium- and gadolinium-doped ceria powders for solid oxides fuel Cells SOFCs is presented. The method involves metal nitrates with propionic acid (both as chelating ligand and solvent), gel formation, liquid nitrogen quenching, drying at 150 °C/24 h, and finally decomposition at 450 °C in nitrogen followed by calcination at 650 °C in air. TG–DTA, BET, XRD, FTIR, UV–vis and catalytic tests were used to characterize the samples. Ce_0.8Pr_0.2O_2?δ sample exhibited the best catalytic performance in methane steam reforming under water deficient conditions, closely followed by Ce_0.9Gd_0.1O_2?δ, Ce_0.8Sm_0.2O_2?δ and Ce_0.8Gd_0.2O_2?δ catalysts. The superior catalytic performance of Ce_0.8Pr_0.2O_2?δ sample was attributed to the existence of praseodymium species (Pr⁴⁺/Pr³⁺) strongly interacting with ceria. The two systems act synergistically in the catalytic steam reforming of methane.     

Synthesis and electrical properties of variable-composition phases Rb1 − x A1 − x R1 + x (MoO4)3 (0 ≤ x ≤ 0.2; A = Mg, Mn, Co, Ni; R = Sc, Yb, Lu)

Subsolidus region of the ternary systems Rb₂MoO₄-AMoO₄-R₂(MoO₄)₃, in which variable-composition phases Rb_{1 ? x} A_{1 ? x} R_{1 + x} (MoO₄)₃ crystallizing in the monoclinic system (space group C2) are formed, was studied. Their crystallographic parameters were calculated; temperature dependences of the electrical conductivity, dielectric constant, and dielectric loss tangent were analized.     

The role of Li2MO2 structures (M=metal ion) in the electrochemistry of (x)LiMn0.5Ni0.5O2·(1−x)Li2TiO3 electrodes for lithium-ion batteries

The electrochemical reactions of lithium with layered composite electrodes (x)LiMn_0.5Ni_0.5O₂·(1−x)Li₂TiO₃ were investigated at low voltages. The metal oxide 0.95LiMn_0.5Ni_0.5O₂·0.05Li₂TiO₃ (x=0.95) which can also be represented in layered notation as Li(Mn_0.46Ni_0.46Ti_0.05Li_0.02)O₂, can react with one equivalent of lithium during an initial discharge from 3.2 to 1.4 V vs. Li⁰. The electrochemical reaction, which corresponds to a theoretical capacity of 286 mAh/g, is hypothesized to form Li₂(Mn_0.46Ni_0.46Ti_0.05Li_0.02)O₂ that is isostructural with Li₂MnO₂ and Li₂NiO₂. Similar low-voltage electrochemical behavior is also observed with unsubstituted, standard LiMn_0.5Ni_0.5O₂ electrodes (x=1). In situ X-ray absorption spectroscopy (XAS) data of Li(Mn_0.46Ni_0.46Ti_0.05Li_0.02)O₂ electrodes indicate that the low-voltage (<1.8 V) reaction is associated primarily with the reduction of Mn⁴⁺ to Mn²⁺. Symmetric rocking-chair cells with the configuration Li(Mn_0.46Ni_0.46Ti_0.05Li_0.02)O₂/Li(Mn_0.46Ni_0.46Ti_0.05Li_0.02)O₂ were tested. These electrodes provide a rechargeable capacity in excess of 300 mAh/g when charged and discharged over a 3.3 to −3.3 V range and show an insignificant capacity loss on the initial cycle. These findings have implications for combating the capacity-loss effects at graphite, metal–alloy, or intermetallic negative electrodes against lithium metal-oxide positive electrodes of conventional lithium-ion cells.     

12-Tungstosilicic Acid (12-TSA) as a Tungsten Precursor in Alcoholic Solution for Deposition of xWO3(1 − x)SiO2 Thin Films (x ≤ 0.7) Exhibiting Electrochromic Coloration Ability

The preparation of stable alcoholic solution of tungstosilicic acid and silicon alkoxide, which can be used for xWO3 (1 – x)SiO2 thin film deposition by dipping, is described. After thermal treatment at temperatures 440 to 500°C in nitrogen films with x higher than 0.6 exhibit electrochromic coloration ability. After coloring the film by H+ imtercalation (by contact with an indium wire trough a drop of aqueous solution of H2SO4) the luminous transmittance (illuminant D65, wavelength range from 380 to 780 nm, summation at 10 nm intervals) of glass coated with 90 nm thick xWO3(1 – x)SiO2 thin film decreases from 71.7 to 28.6% and the IR reflection increases to over 30%. At the same time the surface resistance decreases from a few M/ to about 400/. The thermal decomposition of tungstosilic acid embedded in alkoxy-hydroxy-oxy-silicon matrix is investigated with DTA, TGA, XRD and FTIR spectroscopy.     

Synthesis and electrochemical characteristics of xLi2MnO3–(1−x)Li(Mn0.375Ni0.375Co0.25)O2 (0.0 ≤ x ≤ 1.0) thin film cathode for lithium rechargeable micro batteries

We have compared the structure, microstructure, and electrochemical characteristics of xLi₂MnO₃–(1−x)Li(Mn_0.375Ni_0.375Co_0.25)O₂ (0.0 ≤ x ≤ 1.0) thin films with their bulk cathode laminate counterparts of identical compositions. Pure Li(Mn_0.375Ni_0.375Co_0.25)O₂ as well as the synthesized composite films partially transform into cubic spinel structure during charge–discharge cycling. In contrast, such layered to spinel phase transformation has only been identified in bulk cathode laminates with x ≥ 0.75. At a current density 0.05 mAcm⁻², the discharge capacity of Li(Mn_0.375Ni_0.375Co_0.25)O₂ thin film was measured to be ∼60 μAhcm⁻². The discharge capacity (∼217 μAhcm⁻²) was markedly improved in x∼0.5 composite thin film. The capacity retention after 20 charge discharge cycles are improved in composite films; however, their capacity fading could not be eliminated completely.     

Layered xLiMO2·(1−x)Li2M′O3 electrodes for lithium batteries: a study of 0.95LiMn0.5Ni0.5O2·0.05Li2TiO3

The electrochemical properties of 0.95LiMn_0.5Ni_0.5O₂·0.05Li₂TiO₃ have been investigated as part of a study of xLiMO₂·(1−x)Li₂M^′O₃ electrode systems for lithium batteries in which M=Co, Ni, Mn and M^′=Ti, Zr, Mn. The data indicate that the electrochemically inactive Li₂TiO₃ component contributes to the stabilization of LiMn_0.5Ni_0.5O₂ electrodes, which improves the coulombic efficiency of Li/xLiMn_0.5Ni_0.5O₂·(1−x)Li₂TiO₃ cells for x<1. The 0.95LiMn_0.5Ni_0.5O₂·0.05Li₂TiO₃ electrodes provide a rechargeable capacity of approximately 175 mAh/g at 50 °C when cycled between 4.6 and 2.5 V; there is no indication of spinel formation during electrochemical cycling.     

The pillared layered framework of Ba3(In1−xMx)2(HXO4)6 (0≤x≤1; M=Fe,Cr; X=P,As): synthesis,crystal structure,thermal stability and Mössbauer spectroscopy

The hydrothermal synthesis, single crystal structure analysis, spectroscopic and thermal stability studies of the compounds Ba₃(In_1−xM_x)₂(HXO₄)₆ (0≤x≤1; M=Cr, Fe; X=P, As) are reported. The 3D framework of these new phosphates can be described as a pillared layered framework. The metal cations (In³⁺, Fe³⁺, and Cr³⁺) occupy two crystallographically independent octahedral sites, M(1) and M(2). The layers are formed of M(2)O₆ octahedra and (HPO₄) tetrahedra sharing corners, with M(1)O₆ octahedra serving as pillars between adjacent layers. Single crystal study of Ba₃(In_0.5Fe_0.5)(HPO₄)₆ shows that indium and iron segregate between the two metal sites with Fe occupying primarily the site M(1) and In located primarily in M(2) site. Interactions between the building units within the layers occur through hydrogen bonding. Barium cations are located between the pillars, in 8-membered ring tunnels and are coordinated by 12 oxides. The phases loose three water molecules through condensation of six HXO₄ groups to form Ba₂M₂(X₂O₇)₃ at temperatures between 480 and 600 °C. Mössbauer spectroscopy shows the presence of high-spin Fe³⁺ in octahedral coordination.