Ce0.7Bi0.3O1.85-(La0.8Sr0.2)0.9MnO3-Y0.16Zr0.84O1.92 ternary cathodes for low temperature solid oxide fuel cells

The ternary cathodes of Ce_0.7Bi_0.3O_1.85-(La_0.8Sr_0.2)_0.9MnO₃-Y_0.16Zr_0.84O_1.92 (BDC-LSM-YSZ) are fabricated through infiltration for low temperature solid oxide fuel cells. The infiltrated BDC particles are 10–20 nm in size and cover on LSM and YSZ particles. The 10 wt% and 20 wt% BDC-LSM-YSZ samples show a large peak for the desorption of surface oxygen species and a large peak for the evolution of lattice oxygen, reflecting their good redox property. 0.1BDC-LSM-YSZ cell and 0.2BDC-LSM-YSZ cell give the power density at 0.6 V of 387.8 and 521.7 mWcm^?2 at 600 °C, which is 3.7 and 4.9 times higher than that of LSM-YSZ cell, respectively. 0.1BDC-LSM-YSZ cell and 0.2BDC-LSM-YSZ cell exhibit low ohmic resistance and low total polarization resistance. The DRT analysis reveals that charge transfer reaction and surface diffusion are greatly accelerated on the BDC-LSM-YSZ cathodes.     

Transformation of La0.65Sr0.35MnO3 in electrochemical water oxidation

One of the most promising approaches to produce sustainable energy is hydrogen evolution by water splitting. Since water electrolysis is limited by the high overpotential required for the water oxidation reaction, electrocatalysts are applied to reduce the activation energy necessary for this reaction. However, primary catalysts may chemically convert to other compounds during the reaction. Therefore, the physicochemical and electrochemical changes of catalysts used over a long time need to be investigated in detail to understand the real operating catalyst.In this work, we have observed long-term microstructural changes and amorphization of La_0.65Sr_0.35MnO₃ when used as a catalyst in water-electrolysis at near neutral pH. Microscopic and electrochemical analyses show that the catalyst changed at the molecular level. This study revealed that an entirely different catalyst evolved from the original material over the course of the water oxidation reaction. This observation revealed the importance of the study of the long-term stability and reactivity of La_0.65Sr_0.35MnO₃ toward the water oxidation reaction.     

Tailoring kinetics of Cr-chemisorption over La0.6Sr0.4Fe0.8Co0.2O3 cathode material through its porosity variation

The La_0.6Sr_0.4Co_0.2Fe_0.8O₃ (LSCF) ceramics with the porosity of 20% (LSCF-20) and 50% (LSCF-50) were fabricated through temperature variation. Kinetics of the Cr-adsorption has been studied at 700 °C over 345 h under air. Different dominant mechanisms of Cr chemisorption over the ceramics with different porosities were identified. The Cr–substitution into the LSCF perovskite grains will dominate in the denser LSCF-20 ceramics, whereas the growth of SrCrO₄ crystals over the LSCF perovskite phase will occur preferably in the more porous LSCF-50 ceramics. The Cr penetrates into a more porous LSCF-50 ceramics up to 12–17 μm and the total Cr amount adsorbed after 345 h over the LSCF-50 ceramics is larger by about 10 times than over the denser LSCF-20 ceramics. The revealed remarkable differences could be associated with the increase in the surface area and with a higher volume of macro- and mesoporosity.     

Effect of Mg-doping on the electrochemical performance of LiNi0.84Co0.11Mn0.05O2 cathode for lithium ion batteries

Mg-doped LiNi_0.84Co_0.11Mn_0.05O₂ cathode material is synthesized from introducing Mg by high temperature solid state method. X-ray diffraction analysis confirms the formation of ordered α-NaFeO₂ rock-salt like structure with R-3m symmetry. Rietveld refinement results confirm the expansion in ɑ and c lattice parameters as the amount of Mg increases. All the Mg-doped samples show significant improvement in structure stability and electrochemical properties, such as capacity retention and rate capability. The 1 wt% Mg-doped LiNi_0.84Co_0.11Mn_0.05O₂ delivers the high discharge capacity of 196.7 mAh g⁻¹ (0.1 C) and maintains the capacity retention of 85.95% after 80 cycles indicating outstanding cycling performance. Furthermore, at high cut-off voltage the Mg-doped samples exhibit superior electrochemical performance than the un-doped sample. Cyclic voltammetry results show that the addition of Mg has suppressed the phase transition between H2+H3.     

Structure and properties of cathode materials for ion batteries

近年来,可充电电池以其成本低廉、操作简单、安全环保等优点引起了不少研究者的关注。与锂离子电池相比,钠、钾、镁、锌和铝等离子电池在成本和安全等方面表现出独特的优势,为电池型储能系统（BESS）和电动汽车（EVs）的发展提供了新的思路。正极材料作为离子电池的重要组成之一,其性能的优劣将直接影响整个电池系统的工作状况。本文将介绍离子电池正极材料在容量、循环寿命和能量密度方面的最新进展,以及离子的储存机制。此外,探讨了材料结构和性能间的关系,总结了各种改善离子储存性能的方法,从而使低成本的离子电池更接近可持续大规模储能系统的应用。     

Enhancing surface activity of La0.6Sr0.4CoO3-δ cathode by a simple infiltration process

Nanoscaled La_0.6Sr_0.4CoO_3?δ (LSC) prepared by infiltration has been investigated as an effective catalyst to promote oxygen reduction reaction (ORR) performance for solid-oxide fuel cell. The area specific resistance of original cathode is appreciably reduced by the infiltration of LSC nanoparticles into the porous backbones of LSC cathode. The Arrhenius plots reveal that the reduction is originated from the pre-exponential factor, not the activation energy, suggesting that the rate of ORR has been enhanced by the infiltrated LSC nanoparticles. The infiltrated cell shows a high power density of 800 mW cm^?2 at 700 °C, which is more than two times higher than those measured in the same conditions for a similar cell with pristine LSC cathode. Our results demonstrate that simple infiltration process without further heating at high temperature is a potential way to enhance electrochemical performance and to reduce the operating temperature.     

Effect of powder morphology on the microstructural characteristics of La0.6Sr0.4Co0.2Fe0.8O3 cathode: A Kinetic Monte Carlo investigation

Microstructural parameters such as triple phase boundary (TPB) density, surface area density, connectivity and tortuosity of different phases strongly influence the performance of solid oxide fuel cells (SOFCs). In this study, the effect of the powder morphology on the microstructural parameters of a La_0.6Sr_0.4Co_0.2Fe_0.8O₃ (LSCF) cathode is comprehensively examined using Kinetic Monte Carlo (KMC) simulations. A number of numerical samples consisting of spheres or clumped spheres are created using a Discrete Element Method (DEM), taking into account the powder morphology such as particle size, particle size distribution, particle aspect ratio and sphericity, and particle orientation. The DEM-generated numerical structures with different particle morphologies are submitted to the KMC simulations. Their effects on relative density, densification rate, surface area density, tortuosity factor of LSCF phase and tortuosity factor and connectivity of the pore phase are compared and analyzed.     

Li2MnO3 based Li-rich cathode materials: towards a better tomorrow of high energy lithium ion batteries

Abstract

Li₂MnO₃ based layered Li-rich materials as promising cathode candidates of Li ion batteries (LIBs) have attracted much recent attention mainly owing to their superior high specific capacity and high working voltage. To date, although researchers have put much effort to this family of materials, there are still a number of issues under debates in the fundamental understanding of the crystal structures and the electrochemical reaction mechanisms, before the materials can be ready for practical applications. In this review article, we address the recent progress of this group of Li-rich cathode materials with a good hope to better understanding of the relationships among composition, crystal structure and electrochemical reaction mechanisms. In addition, the use of advanced microscopic characterisation and the strategies of novel material designs will also be discussed for better cathode design for LIBs.     

Effect of titanium substitution in layered LiNiO2 cathode material prepared by molten-salt synthesis

LiNi_1−xTi_xO₂ (0 ≤ x ≤ 0.1) compounds have been synthesized by a direct molten-salt method that uses a eutectic mixture of LiNO₃ and LiOH salts. According to X-ray diffraction analysis, these materials have a well-developed layered structure (R3-m) and are an isostructure of LiNiO₂. The LiNi_1−xTi_xO₂ (0 ≤ x ≤ 0.1) compounds have average particle sizes of 1–5 μm depending on the amount of Ti salt. Charge–discharge tests show that a LiNi_1−xTi_xO₂ (0 ≤ x ≤ 0.1) cathode prepared at 700 °C has an initial discharge capacity as high as 171 mA h g⁻¹ and excellent capacity retention in the range 4.3–2.8 V at a current density of 0.2 mA cm⁻².     

Performance of (La,Sr)MnO3 cathode based solid oxide fuel cells: Effect of bismuth oxide sintering aid in silver paste cathode current collector

Effects of a bismuth oxide (Bi₂O₃) sintering aid in the silver paste cathode current collectors on the electrochemical performance of solid oxide fuel cells with (La,Sr)MnO₃ cathode is investigated. Anode-supported single cells are prepared and applied with pure and Bi₂O₃-added silver pastes for cathode current collecting. Cell performances are evaluated using a current-voltage test and electrochemical impedance spectroscopy. The results indicate that the Bi₂O₃-added silver paste cathode current collector artificially increases the power density and lowers the polarization resistance of single cell, which may be attributed to the observation of the improved cathode current collector surface morphology and enhanced contact at the cathode-current collector interface, as well as the migration of the Bi₂O₃ and silver into the cathode from the Bi₂O₃ contained silver paste cathode current collector.     

Ni/La2O3 catalysts for dry reforming of methane: Effect of La2O3 synthesis conditions on the structural properties and catalytic performances

10 wt%Ni/La₂O₃ catalysts for dry reforming of methane (DRM) were synthesized by wetness impregnation of lanthana supports prepared using sol-gel citric method with and without NH₃ addition (Ni–La CA-NH₃ and Ni–La CA, respectively). The support preparation conditions affect the nature, phase composition, and distribution of Ni phases (LaNiO₃, NiO and La₃Ni₂O₆). The gradient temperature DRM tests (400–800 °C) reveal higher catalytic activity of Ni–La CA (at 650 °C, X(CO₂) = 65.7%, X(CH₄) = 54.6%, H₂/CO = 0.71). The Ni–La CA-NH₃ shows higher stability (at 650 °C and 24 h, X(CO₂): 73.7% => 76.4%, X(CH₄): 64.7% => 64.6%, H₂/CO: 0.77 => 0.72). For both catalysts, La₂O₂CO₃ phase is formed after long run tests at 650 °C 24 h, with the greater TGA weight loss and stronger deactivation being observed for Ni–La CA. The H₂-reduced Ni La CA-NH₃ features ultrasmall (1–2 nm) Ni NPs strongly interacting with the support. Catalyst nature affects the amount of carbon coke formed.     

Effect of mechanical activation process parameters on the properties of LiFePO4 cathode material

Pure, nano-sized LiFePO₄ and carbon-coated LiFePO₄ (LiFePO₄/C) positive electrode (cathode) materials are synthesized by a mechanical activation process that consists of high-energy ball milling and firing steps. The influence of the processing parameters such as firing temperature, firing time and ball-milling time on the structure, particle size, morphology and electrochemical performance of the active material is investigated. An increase in firing temperature causes a pronounced growth in particle size, especially above 600 °C. A firing time longer than 10 h at 600 °C results in particle agglomeration; whereas, a ball milling time longer than 15 h does not further reduce the particle size. The electrochemical properties also vary considerably depending on these parameters and the highest initial discharge capacity is obtained with a LiFePO₄/C sample prepared by ball milling for 15 h and firing for 10 h at 600 °C. Comparison of the cyclic voltammograms of LiFePO₄ and LiFePO₄/C shows enhanced reaction kinetics and reversibility for the carbon-coated sample. Good cycle performance is exhibited by LiFePO₄/C in lithium batteries cycled at room temperature. At the high current density of 2C, an initial discharge capacity of 125 mAh g⁻¹ (73.5% of theoretical capacity) is obtained with a low capacity fading of 0.18% per cycle over 55 cycles.     

A new low-temperature synthesis and electrochemical properties of LiV3O8 hydrate as cathode material for lithium-ion batteries

LiV₃O₈, synthesized from V₂O₅ and LiOH, by heating of a suspension of V₂O₅ in a LiOH solution at a low-temperature (100-200 °C), exhibits a high discharge capacity and excellent cyclic stability at a high current density as a cathode material of lithium-ion battery. The charge-discharge curve shows a maximum discharge capacity of 228.6 mAh g⁻¹ at a current density of 150 mA g⁻¹ (0.5 C rate) and the 100 cycles discharge capacity remains 215 mAh g⁻¹. X-ray diffraction indicates the low degree of crystallinity and expanding of inter-plane distance of the LiV₃O₈ phase, and scanning electronic microscopy reveals the formation of nano-domain structures in the products, which account for the enhanced electrochemical performance. In contrast, the LiV₃O₈ phase formed at a higher temperature (300 °C) consists of well-developed crystal phases, and coherently, results in a distinct reduction of discharge capacity with cycle numbers. Thus, an enhanced electrochemical performance has been achieved for LiV₃O₈ by the soft chemical method via a low-temperature heating process.     

One-step synthesis of nanoblocks@nanoballs NiMnO3/Ni6MnO8 nanocomposites as electrode material for supercapacitors

A novel nanoblocks@nanoballs NiMnO₃/Ni₆MnO₈ electrode material was synthesized by one-step solvothermal–hydrothermal method, followed by thermal annealing. At the same time, electrode materials with different nanostructure were prepared by changing the volume ratio of deionied water and ethylene glycol. The results show that different structure has been gained including nanospheres, nanosheets and nanoblocks. When the deionied water: ethylene glycol = 1:1 (nanoblocks@nanoballs NiMnO₃/Ni₆MnO₈ composite structure), the electrode material has a maximum specific surface area of 55.3 m² g⁻¹. The electrode material exhibited outstanding electrochemical performance with specific capacitance reached 494.4 F g⁻¹ at a current density of 1 A g⁻¹ as well as superior cycling performance of 88.0% capacitance retention after 5000 cycles at 3 A g⁻¹. Such excellent performance was due to the synergistic effective between the Ni₆MnO₈ nanoballs and NiMnO₃ nanoblocks. Nanoballs structure will increase in specific surface area and redox reaction active sites, and the blocks structure acts as a holder to improved the cycle performance. The NiMnO₃/Ni₆MnO₈ become a promising candidate as next-generation electrode material for high-performance supercapacitors.     

Sulfur poisoning of La(Ni0.6Fe0.4)O3 cathode material for solid oxide fuel cells

Sulfur poisoning of cathode materials is one of the important factors to cause cathode performance degradation resulting in shortening lifetime of SOFC. The sulfur attacks alkali earth components of the rare earth-transition metal perovskite oxides, such as Ba, Ca, Sr, which reacts with SO₂ to form sulfates. In this work, the La(Ni_0.6Fe_0.4)O₃ (LNF) cathode material without alkali earth elements was employed to investigate the sulfur poisoning behavior by flowing 30 ppm SO₂ at different temperatures of 500 °C–800 °C. It was found that SO₂ readily reacts with the La₂O₃ component in LNF to form La₂O₂SO₄ at 700 °C and 800 °C. The extent of the chemical reaction is temperature dependent. These results confirm that sulfur poisoning also occurs in cathode materials free of alkali earth components. The study prompts the exploration of new materials and new strategies for the developing new cathode materials with high sulfur tolerance.     

Combustion synthesis of Sm0.5Sr0.5CoO3−x and La0.6Sr0.4CoO3−x nanopowders for solid oxide fuel cell cathodes

Nanopowders of Sm_0.5Sr_0.5CoO_3−x (SSC) and La_0.6Sr_0.4CoO_3−x (LSC) compositions, which are being investigated as cathode materials for intermediate temperature solid oxide fuel cells (SOFC), were synthesized by a solution–combustion method using metal nitrates and glycine as fuel. Development of crystalline phases in the as-synthesized powders after heat treatments at various temperatures was monitored by X-ray diffraction (XRD). Perovskite phase in LSC formed more readily than in SSC. Single-phase perovskites were obtained after heat treatment of the combustion synthesized LSC and SSC powders at 1000 and 1200 °C, respectively. The as-synthesized powders had an average particle size of ∼12 nm as determined from X-ray line broadening analysis using the Scherrer equation. Average grain size of the powders increased with increase in calcination temperature. Morphological analysis of the powders calcined at various temperatures was done by scanning electron microscopy (SEM).     

Synthesis and properties of LiNiO2 as cathode material for secondary batteries

The optimum preparation condition and electrochemical properties of LiNiO₂ as the cathode material for lithium secondary batteries were investigated. LiNiO₂ samples were prepared from Li(OH)₂·H₂O and Ni(OH)₂ in the range from 500 to 900 °C. The compound prepared in an oxygen atmosphere at 700 °C exhibited the highest discharge capacity of 200 mAh/g in the voltage range from 3.0 to 4.3 V. The structure and charge-transfer resistance of the Li_1−xNiO₂ compound were examined at each state-of-charge by X-ray diffractometry and a.c. impedance spectroscopy. The charge-transfer resistances were low in the range of 0.15<x<0.75, which was related to the expansion of the interlayer distance between NiO₂ layers.     

Effect of cathode material on the morphology and photoelectrochemical properties of vertically oriented TiO2 nanotube arrays

We report, for the first time, on the effect of the cathode material in controlling the morphology and properties of TiO₂ nanotube arrays fabricated by electrochemical anodization of Ti foil in both aqueous and ethylene glycol (EG) electrolytes. Some of the alternative less-expensive cathode materials result in TiO₂ nanotube architectures and photoelectrochemical properties similar to or in some cases superior to those obtained using a Pt cathode.     

Performance of a novel La(Sr)MnO3-Pd composite current collector for solid oxide fuel cell cathode

The electrochemical performance of LSM-Pd composite material as current collector of SOFC cathode is studied on (La_0.8Sr_0.2)_0.9MnO₃ (LSM90) cathode. The influence of Pd content on contact resistance is investigated. The investigation shows that the contact resistance of LSM-Pd is about 20 mΩ cm² at 750 °C when the composite contains 8 wt% Pd, and it could be comparable to pure Pt. The ohmic resistance of a single cell using LSM-Pd composite is about 255 mΩ cm² that contains 4 wt% Pd as current collector, this value is close to that of a cell using expensive Pt paste as current collector.     

Behavior of lanthanum-doped ceria and Sr-, Mg-doped LaGaO3 electrolytes in an anode-supported solid oxide fuel cell with a La0.6Sr0.4CoO3 cathode

Anode-supported solid oxide fuel cells (SOFCs) with lanthanum-doped ceria (LDC)/Sr-, Mg-doped LaGaO₃ (LSGM) bilayered or LDC/LSGM/LDC trilayered electrolyte films were fabricated with a pure La_0.6Sr_0.4CoO₃ (LSC) cathode. The behaviors of the two electrolytes in cells were investigated by using scanning electron microscopy, impedance spectroscopy and cell performance measurements. The reactions between LSGM and anode material can be suppressed by applying a ca. 15 μm LDC film. Due to the Co diffusion from the LSC cathode to the LSGM electrolyte during high temperature sintering, the electronic conductivity of the LDC electrolyte cannot be completely blocked with an LSGM layer below 50 μm, which leads to open-circuit potentials of these cells of ca. 0.988 V at 800 °C. The electrical conductivities of LDC and LSGM electrolytes in the cells under operation conditions are obtained from the dependence of the cell ohmic resistance on the electrolyte thickness. The electrical conductivity of LDC electrolyte is ca. 0.117 S cm⁻¹ at 800 °C on the bilayered electrolyte cells with a 50 μm LSGM layer. The bilayer electrolyte cells with a 25 μm LDC layer at 800 °C, had a cell ohmic resistance two-stage linear dependence on the LSGM layer thickness, which showed the electrical conductivity of ca. 1.9 S cm⁻¹ for the LSGM layer below 50 μm and 0.22 S cm⁻¹ for the LSGM layer above 100 μm. With a LDC/LSGM/LDC trilayered electrolyte film for the anode-supported cell, an open-circuit potential of 1.043 V was achieved.