Structural and electrochemical properties of Li1+xNi0.5Mn0.5O2+δ (0 ≤ x ≤ 0.7) cathode materials for lithium-ion batteries

A comparative analysis of the properties of LiNi_0.5Mn_0.5O₂ and Li_1+xNi_0.5Mn_0.5O₂ (0.2 ≤ x ≤ 0.7) powders, obtained by the freeze drying method, was performed. Lattice parameters of Li_1+xNi_0.5Mn_0.5O₂ decreased considerably with growing amounts of Li until x = 0.3; at x > 0.5 trace amounts of Li₂MnO₃ are observed by X-ray diffraction (XRD) patterns. X-ray photoelectron spectroscopy (XPS) analysis displayed an increase of Ni³⁺/Ni²⁺ ratio at 0.3 < x < 0.5, while Mn 2p spectra were almost identical in all samples. Rechargeable capacity values (V = 2.5–4.6 V) increased systematically with x reaching its maximum (185–190 mAh g⁻¹) at x = 0.5. Samples with superstoichiometric lithium content also demonstrated good C rate characteristics.     

Preparation and properties of LiCoyMnxNi1−x−yO2 as a cathode for lithium ion batteries

The preparation of LiCo_yMn_xNi_1−x−yO₂ from LiOH·H₂O, Ni(OH)₂ and γ-MnOOH in air was studied in detail. Single-phase LiCo_yMn_xNi_1−x−yO₂ (0y0.3 and x=0.2) is obtained by heating at 830–900°C. The optimum heating temperatures are 850°C for y=0–0.1 and 900°C for y=0.2–0.3. Excess lithium (1z1.11 for y=0.2) and the Co doping level (0.05y0.2) do not significantly affect the discharge capacity of Li_zCo_yMn_0.2Ni_0.8−yO₂. The doping of Co into LiMn_0.2Ni_0.8O₂ accelerates the oxidation of the transition metal ion, and suppresses partial cation mixing. Since the valence of the manganese ion in LiMn_0.2Ni_0.8O₂ is determined to be 4, the formation of a solid solution between LiCo_yNi_1−yO₂ and Li₂MnO₃ is confirmed.     

A new way of obtaining LixNi1−xO cathodes for molten-carbonate fuel cells

An unsintered nickel plaque containing Li₂CO₃ and an organic binder were tested as a cathode in a molten-carbonate fuel cell. Organic burnout, nickel oxidation,lithium carbonate decomposition and Li_xNi_1−xO solid-solution formation occurred during the start-up of the cell. The in-cell test showed good performance after a short time of operation, and a limited performance decay after 3500 h.     

Structural and electrochromic properties of nanosized Fe/V-oxide films with FeVO4 and Fe2V4O13 grains: comparative studies with crystalline V2O5

Various mixed Fe/V-oxides can be used as anodes in Li⁺ rocking chair batteries, however, their small optical modulation during the insertion/extraction of Li⁺ ions makes them candidates for the counter electrodes in electrochromic (EC) devices. The sol–gel route in combination with dip-coating deposition was used for the preparation of Fe/V-oxide films with molar ratios Fe:V=0.1:1, 1:2, 1:1 and 2:1. X-ray diffraction combined with Fourier transform infrared (FT-IR) spectroscopy studies of films and powders reveal that heating of xerogel films at 400°C produces films with nanosized FeVO₄ (Fe:V=1:1) and Fe₂V₄O₁₃ (Fe:V=1:2) grains, while the corresponding crystalline powders were obtained at 500°C (8 h). Charge capacities (Q) of Fe/V-oxide films (300 and 400°C) were determined using cyclic voltammetry (CV) from 1.5 to −1.5 V vs. Ag/AgCl (4.8 to 1.8 V vs. Li) in 1 M LiClO₄/propylene carbonate (PC) electrolyte. Our results revealed that Q values of Fe/V-oxide films are up to 20 mC cm⁻² depending on the thickness (40–100 nm), temperature of heating and the Fe:V molar ratio (1:2, 1:1). During the first 300 cycles the cycling stability of the Fe-containing films is better than that of V₂O₅ crystalline films. UV-visible spectra of charged/discharged films revealed that these films, similar to V₂O₅ films, exhibit a mixed anodic/cathodic electrochromism. It was established that with regard to the colouring/bleaching changes of V₂O₅ crystalline films, the Fe/V-oxide films exhibit smaller cathodic colouring at wavelengths λ>600 nm and higher visible transmittance. IR spectroscopy of charged/discharged Fe/V-oxide films confirmed that the reduction of Fe³⁺ prevents the overreduction of V⁵⁺ to V³⁺, which takes place in V₂O₅ films cycled in the same potential range.     

Effect of Co content on performance of LiAl1/3−xCoxNi1/3Mn1/3O2 compounds for lithium-ion batteries

Layered LiAl_1/3−xCo_xNi_1/3Mn_1/3O₂ (0  x  1/3) compounds were studied via the combination of computational and experimental approach. The calculated voltage curve of LiNi_1/3Al_1/3Mn_1/3O₂ compound is presented, indicating it is of great potential for a cathode material of lithium-ion batteries. Unfortunately, it was found that the LiNi_1/3Al_1/3Mn_1/3O₂ compound without impurity phase could not be synthesized via a sol–gel process. To obtain a layered compound without impurity phase, partial of Al is replaced by Co in LiNi_1/3Al_1/3Mn_1/3O₂ compound in this study. Layered LiAl_1/3−xCo_xNi_1/3Mn_1/3O₂ (0  x  1/3) compounds were synthesized via sol–gel reaction at 900 °C under a oxygen stream. Single phase of the LiAl_1/3−xCo_xNi_1/3Mn_1/3O₂ in 1/6  x  1/3 region could be prepared successfully. The discharge capacity and conductivity increased with an increase in the Co-substitution content. The enhancement of the conductivity and phase purity by the introduction of Co content shows profound influence on the performance of the LiAl_1/3−xCo_xNi_1/3Mn_1/3O₂ compounds.     

Enhancing the elevated temperature performance of Li/LiMn2O4 cells by reducing LiMn2O4 surface area

Lithium-rich spinels were obtained with the same structure but different surface area by two different synthesis routes, namely the “once-annealed” and the “twice-annealed” methods. The elevated temperature performance of Li/Li_1+xMn₂O₄ cell is significantly improved using a spinel cathode with a small surface area: the cell at 50°C lost 5% of the initial capacity over the first 100 cycles based on a spinel cathode with the small surface area of 1.2 m²/g compared to 8% based on a large one of 6.2 m²/g. Also the mechanism responsible for the reaction of LiMn₂O₄ with LiOH to form lithium-rich spinel has been investigated.     

Electrochemical performance of thermally-grown SiO2 as diffusion barrier layer for integrated lithium-ion batteries

Direct integration of lithium-ion battery (LIB) with electronic devices on the same Si substrate can significantly miniaturize autonomous micro systems. For achieving direct integration, a barrier layer is essential to be inserted between LIB and the substrate for blocking Li⁺ diffusion. In this paper, the feasibility of thermal SiO₂ film as the barrier layer is investigated by electrochemical characterization and X-ray photoelectron spectroscopy (XPS). Due to the negligible side reactions of thermal SiO₂ with electrolyte, the solid electrolyte interphase (SEI) layer formed on the surface of the barrier layer is thin and the SEI content mainly consists of hydrocarbon together with slight polyethylene oxide (PEO), Li_xPO_yF_z, and Li₂CO₃. Although 8-nm thermal SiO₂ effectively prevents the substrate from alloying with Li⁺, the whole film changes to Li silicate after electrochemical cycling due to the irreversible chemical reactions of SiO₂ with electrolyte. This degrades the performance of the barrier layer against the electrolyte penetration, thus leading to the existence of Li⁺ (in the form of F-Si-Li) and solvent decompositions (with the products of hydrocarbon and PEO) near the barrier layer/substrate interface. Moreover, it is found that the reaction kinetics of thermal SiO₂ with electrolyte decrease significantly with increasing the SiO₂ thickness and no reactions are found in the bulk of the 30-nm SiO₂ film. Therefore, thermal SiO₂ with an appropriate thickness is a promising barrier layer for direct integration.     

The gasochromic properties of sol–gel WO3 films with sputtered Pt catalyst

Gasochromic films are receiving considerable attention, stimulated by the need for switchable windows that compete with more complex electrochromic ‘smart’ windows for building applications. The latest development of WO₃ films, prepared by the sol–gel route and dip-coating deposition overlaid by a thin layer of sputtered Pt metal, are presented. Colouring/bleaching kinetics of WO₃ films and WO₃ films in which a hybrid organic/inorganic sol–gel precursor (ormosil) has been added are evaluated. Results revealed that with respect to velocity of coloration, sol–gel WO₃ gasochromic films compete with the sputtered ones. Many aspects of the colouring/bleaching behaviour of the films resemble that of sputtered Pt/WO₃ films and thus confirm the similarity in the colouring/bleaching mechanisms. IR spectroscopy revealed the presence of well-defined W=O and the breaking of W–O bonds indicating the formation of H⁺… ⁻OW- and WO_3−x species in coloured films.     

Behavior of the monophosphate tungsten bronzes (PO2)4(WO3)2m (m = 4 and 6) in electrochemical lithium insertion

The electrochemical lithium insertion process has been studied in the family of monophosphate tungsten bronzes (PO₂)₄(WO₃)_2m, where m = 4 and 6. Structural changes in the pristine oxides were followed as lithium insertion proceeded. Through potentiostatic intermittent technique, the different processes which take place in the cathode during the discharge of the cell were analysed. The nature of the bronzes Li_x(PO₂)₄(WO₃)_2m formed was determined by in situ X-ray diffraction experiments. These results have allowed establishment of a correlation with the reversible/irreversible processes detected during the electrochemical lithium insertion. Measurements of resistivity showed that upon lithium insertion, the metallic pristine oxides become insulating.     

High-temperature superconductor, YBa2Cu307-x as all- solid-state lithium cell

The utility of the high-temperature superconductor, YBa₂Cu₃O_7-itx, as the cathode material for an all-solid-state lithium cell has been examined. The capacity of YBa₂Cu₃O₇-x, is 223 mA h g⁻¹ and the discharge efficiency is> 92%. Measurements of a.c. impedance show that the charge-transfer resistance at the interface of the electrolyte/cathode is very low and increases with the depth-of-discharge of the battery. Studies using X-ray photoelectron spectroscopy (XPS) reveal that the cathode becomes doped with Li⁺ ions as the cell discharges.     

Electrochemical supercapacitor behavior of nanoparticulate rutile-type Ru1−xVxO2

Rutile-type Ru_1−xV_xO₂ nanoparticles possessing high surface area were prepared by a polymerizable-complex method and its electrochemical supercapacitor behavior was studied. X-ray diffractometry, energy-dispersive X-ray analysis, and N₂ adsorption/desorption measurements were used to characterize the structure of the products. The electrochemical supercapacitor behavior of thick and thin films was studied by cyclic voltammetry in various acidic, neutral, and alkaline electrolytes. Ru_1−xV_xO₂ exhibited extremely enhanced supercapacitive properties compared to pure RuO₂. The highest surface redox activity was achieved with an acidic electrolyte. Ru_1−xV_xO₂ showed negligible surface redox activity in neutral electrolytes.     

Ag/Al2O3(Li2O)/g-C3N4光催化乙醇制取环氧乙烷

本文制备了一系列Ag/Al₂O₃(Li₂O)/g-C₃N₄复合催化剂,考察了其可见光催化乙醇制取环氧乙烷的性能。Li₂O可调变Al₂O₃表面的酸性,从而降低了主要副产物乙醛的选择性。Ag/Al₂O₃(Li₂O) 在g-C₃N₄上的负载量对产物环氧乙烷的选择性有较大影响,当Ag/Al₂O₃(Li₂O) 负载量为5wt%时,乙醇具有较高的转换率,且环氧乙烷的选择性高达100%。     

Preparation of Culn(SxSe1−x)2 thin films by sulfurization and selenization

A CuIn(S_xSe_1−x)₂ alloy thin-film was prepared by selenization of CuInS₂: its composition ratio x can be controlled by the number of selenization cycles implemented. Crystallinity of the films was improved by annealing in vacuum. The resistivity of the film was about 1 Ω cm and increased by one to two orders of magnitude after KCN treatment. An 8.1 % efficiency solar cell was obtained by using this annealed alloy thin-film.     

The effect of annealing on the electrochemical properties of Zr0.5Ti0.5Mn0.5V0.3Co0.2Ni1.1 alloy electrodes

The annealing treatment was found to result in the improvement in the cyclic stability but the degradation of discharge capacity, activation and high-rate dischargeability for Zr_0.5Ti_0.5Mn_0.5V_0.3Co_0.2Ni_1.1 alloy electrode. A lower discharge potential in the annealed alloy electrode was found owing to a more homogeneous alloy, which is consistent with the pressure–composition isotherms (P–C–T) measurement. We found that the annealed alloy also had lower and flatter pressure plateaus, and larger pressure hysteresis. At high discharge rates, the hydrogen diffusion in the bulk of the alloy was the rate-determining step. The diffusion coefficients for hydrogen in the annealed and as-cast alloys were calculated to be 1.4×10⁻¹² cm² s⁻¹ and 4.3×10⁻¹² cm² s⁻¹, respectively. The lowering of high-rate discharge capacity can be ascribed to the reason that the hydrogen diffusion coefficient is lower due to homogeneous microstructure in the annealed alloy.     

Characterization of Cu(InxGa1−x)2Se3.5 thin films prepared by rf sputtering

Cu(In_xGa_1−x)₂Se_3.5 thin films were fabricated by rf sputtering from CuIn_xGa_1−xSe₂ and Na mixture target by controlling the mixture ratio. X-ray diffraction analyses show that the structure of Cu(In_xGa_1−x)₂Se_3.5, thin films is different from chalcopyrite structure: especially, CuIn₂Se_3.5 thin films have a defect chalcopyrite structure. The lattice parameters for Cu(In_xGa_1−x)₂Se_3.5 thin film are slightly smaller than those for CuIn_xGa_1−xSe₂ thin film and linearly decreased with increasing Ga content. The optical absorption coefficients for Cu(In_xGa_1−x)₂Se_3.5, thin films exceed 2 × 10⁴ cm⁻¹ in energy region above the fundamental band edge. The band gap for Cu(In_xGa_1−x)₂Se_3.5 thin films is larger than that for CuIn.Ga_1−x2Se₂ with the same Ga content and increased with increasing Ga content.     

Selective removal of CO from hydrogen-rich stream over CuO/CexSn1−xO2–Al2O3 catalysts

The solid solutions of Ce_xSn_1−xO₂ incorporated with alumina to form Ce_xSn_1−xO₂–Al₂O₃ mixed oxides, by the suspension/co-precipitation method, were used to prepare CuO/Ce_xSn_1−xO₂–Al₂O₃ catalysts for the selective oxidation of CO in excess hydrogen. Incorporating Al₂O₃ increased the dispersion of Ce_xSn_1−xO₂, but did not change their main structures and did not weaken their redox properties. Doping Sn⁴⁺ into CeO₂ increased the mobility of lattice oxygen and enhanced the activity of the 7%CuO/Ce_xSn_1−xO₂–Al₂O₃ catalyst in the selective oxidation of CO. The selective oxidation of CO was weakened as the doped fraction of Sn⁴⁺ exceeded 0.5. Incorporating appropriate amounts of Sn⁴⁺ and Al₂O₃ could obtain good candidates 7%CuO/Ce_xSn_1−xO₂–Al₂O₃(20%), 1–x=0.1–0.5, for a preferential oxidation (PROX) unit in a polymer electrolyte membrane fuel cell system for removing CO. Its activity was comparable with, and its selectivity was much larger than, that of the noble catalyst 5%Pt/Al₂O₃.     

Preparation and electrochemical characteristics of LiNi1/3Mn1/3Co1/3O2 coated with metal oxides coating

LiNi_1/3Mn_1/3Co_1/3O₂ prepared by a spray drying method exhibited poor cyclic performance when it was operated at rates of 0.5C and 2C in 3–4.6 V. A metal oxide (ZrO₂, TiO₂, and Al₂O₃) coating (3 wt%) could effectively improve its cyclic performance at both 0.5C and 2C. Electrochemical impedance spectroscopy (EIS) studies suggested that both the surface resistance and the charge transfer resistance of the bare LiNi_1/3Mn_1/3Co_1/3O₂ significantly increase after 100 cycles, whose origin is mainly related to the change in both the particle surface and electrode morphologies. The presence of a thin metal oxide layer could remarkably suppress the increase in the total resistance (sum of the surface resistance and the charge transfer resistance), which was attributed to the improvement in good cyclic performances.     

The effect of multivalent cation dopants on lithium manganese spinel cathodes

The cycling stability of 4 V Li_xMn₂O₄ electrodes in lithium, flooded electrolyte glass cells has been improved by the addition of multivalent cation dopants (Mg²⁺, Zn²⁺ and Al³⁺). Optimal dopant levels to achieve maximum capacity and the greatest stability with repeated cycling have been determined. The effect of doping the oxygen-rich spinel Li₂Mn₄O₉, was also determined and shown to make no significant improvement in the life cycle stability in the 3 V region.     

A screen-printed Ce0.8Sm0.2O1.9 film solid oxide fuel cell with a Ba0.5Sr0.5Co0.8Fe0.2O3−δ cathode

Screen-printing technology was developed to fabricate Ce_0.8Sm_0.2O_1.9 (SDC) electrolyte films onto porous NiO–SDC green anode substrates. After sintering at 1400 °C for 4 h, a gas-tight SDC film with a thickness of 12 μm was obtained. A novel cathode material of Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ was subsequently applied onto the sintered SDC electrolyte film also by screen-printing and sintered at 970 °C for 3 h to get a single cell. A fuel cell of Ni–SDC/SDC (12 μm)/Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ provides the maximum power densities of 1280, 1080, 670, 370, 180 and 73 mW cm⁻² at 650, 600, 555, 505, 455 and 405 °C, respectively, using hydrogen as fuel and stationary air as oxidant. When dry methane was used as fuel, the maximum power densities are 876, 568, 346 and 114 mW cm⁻² at 650, 600, 555 and 505 °C, respectively. The present fuel cell shows excellent performance at lowered temperatures.     

Cycle characterizations of LiMxMn2−xO4 (M=Co, Ni) materials for lithium secondary battery at wide voltage region

LiM_xMn_2−xO₄ (M=Co, Ni) materials have been synthesized by a melt-impregnation method using γ-MnOOH as the manganese source. Highly crystallized LiM_xMn_2−xO₄ compounds were synthesized at a calcination temperature of 800°C for 24 h in air. All compounds show a single phase except for LiNi_0.5Mn_1.5O₄ based on the X-ray diffraction (XRD) diagram. With the increase of the doping content from 0.1 to 0.5, the capacity of doping materials decreases mainly in the 4 V region.

Although LiM_0.5Mn_1.5O₄ (M=Co, Ni) compound shows a small capacity in the (3+4) V region compared with parent LiMn₂O₄, it is a very effective material in reducing capacity loss in the 3 V region that is caused by the Jahn–Teller distortion. The doping of Co and Ni ions in the LiMn₂O₄ cathode material promotes the stability of this structure and provides an excellent cyclability.