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The application of ceramic garnet-type Li7La3Zr2O12 electrolytes is restricted by the challenge of poor contact with metallic lithium, which results in high interfacial resistance, uneven current distribution, and severe lithium dendrite penetration. Herein, a remarkably ultra-low interfacial impedance (∼2.7 Ω cm2) is achieved by employing Si addition into molten Li, because of the realized intimate interface contact resulting from the decreased surface tension of molten Li and, most importantly, the reinforced interfacial connection as a result of the minor reaction between the Li4.4Si and Li6.4La3Zr1.4Ta0.6O12 (LLZTO), further improving charge transfer across the Li/LLZTO interface. The generated Li4.4Si at the interface (I-Li4.4Si), showing strong combination with garnet, can function as a "rivet" for the stable interface upon cycling. Moreover, the I-Li4.4Si species with Li+ diffusivity favor the reduced local current density and thus the decreased over-potential to some extent. Thus, the resulting symmetric Li–Li4.4Si‖LLZTO‖Li–Li4.4Si cell delivers a stable Li plating–stripping performance for over 1200 h at a current density of 0.1 mA cm−2 (1000 h)/0.2 mA cm−2 (200 h) and a temperature of 60 °C with a small over-potential (5.3 mV@0.1 mA cm−2; 10.2 mV@0.2 mA cm−2). The fabricated full cell with a LiFePO4 cathode delivers a high reversible capacity of ∼169 mA h g−1 at 0.05C and excellent cycling stability with a capacity decay rate of only 0.038% per cycle. [ABSTRACT FROM AUTHOR]

Conversion-alloying-type compounds offer many new possibilities as anode materials for Li-ion cells, but also show some drawbacks related to their intrinsic characteristics. To overcome those limitations, the consecutive steps of electrochemical processes occurring in the selected Zn2SnO4 inverse spinel are studied in detail i.e. by operando X-ray diffraction, ex situ X-ray absorption spectroscopy, and transmission electron microscopy. Decomposition of the spinel phase upon the 1st lithiation proceeds with the precipitation of Li2O and metallic particles, which further form LiZn and LixSn. A multicomponent matrix is created, which allows for reversible lithium storage. After dealloying upon the 1st delithiation, a Li6ZnO4/Li4ZnO3-type phase is formed in the conversion reaction, indicating reactivity between ZnO and Li2O. Initially, α-Sn is likely precipitated, which is transformed into β-Sn during the 2nd cycle, indicating aggregation. Understanding the electrochemical reaction mechanism allowed identifying essential issues, important for the practical application of the Zn2SnO4 anode: too high reaction voltage vs. Li+/Li with large hysteresis during the conversion reaction; metallic particle aggregation; large volume changes during deep (de-)alloying; mechanical problems on prolonged cycling. While the full-range capacity of the developed anodes reaches 920 mA h g−1 after 10 cycles at a current of 50 mA g−1 and over 460 mA h g−1 at 1000 mA g−1, their operation range has to be limited in order to overcome the listed problems. This can be achieved by the controlled electrochemical prelithiation of Zn2SnO4 anodes before assembling full-cells. For the first time, excellent cycling stability is reached for micrometer-sized solid-state-synthesized Zn2SnO4, working in full Li-ion cells. [ABSTRACT FROM AUTHOR]

Among the for the first time reported Cr-containing high entropy La1−xSrx(Co,Cr,Fe,Mn,Ni)O3−δ (x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5) perovskite-type oxides, the selected Sr-doped La0.7Sr0.3(Co,Cr,Fe,Mn,Ni)O3−δ material is documented to possess attractive properties as a candidate air electrode material for Solid Oxide Fuel Cells (SOFCs). Nanosized powders of the considered oxides are obtained using a modified Pechini sol–gel method. In the formed solid solution with a simple perovskite structure the strontium solubility limit is found to be at least x = 0.3. Room temperature (RT) structural data indicate the presence of rhombohedral structural distortion (R3¯c symmetry) in the materials. High-temperature structural studies for the selected La0.7Sr0.3(Co,Cr,Fe,Mn,Ni)O3−δ indicate the occurrence of a phase transition to an aristotype Pm3¯m structure at ca. 800 °C. The linear thermal expansion coefficient in the RT-1000 °C range is found to be moderate, 16.0(3) × 10−6 K−1. The results of impedance spectroscopy measurements support the semiconducting-type behavior of the electrical conductivity for all single-phase materials, in a temperature range of RT-1000 °C. The maximum recorded conductivity for the La0.7Sr0.3(Co,Cr,Fe,Mn,Ni)O3−δ composition exceeds 16 S cm−1 in the 900–1000 °C range, being suitable for application. Furthermore, chemical stability toward the La0.8Sr0.2Ga0.8Mg0.2O3−δ (LSGM) electrolyte is proven. Considering the presence of chromium, typically deleterious to the performance, the measured value of the total cathodic polarization resistance for the La0.7Sr0.3(Co,Cr,Fe,Mn,Ni)O3−δ-based electrode, being 0.126 Ω cm−2 at 900 °C, seems to be very attractive. The results obtained for a button-type fuel cell indicate power densities at a level of 550 mW cm−2 at 900 °C. Therefore, it can be considered that the high entropy-based approach enables to propose alternative SOFC air electrode materials, with otherwise inaccessible chemical compositions. [ABSTRACT FROM AUTHOR]

Modified by Sm0.2Ce0.8O2−δ (SDC) nanoparticles (NPs), SmBaCo2O5+δ (SBCO) double perovskite oxide is evaluated as a promising cathode material for intermediate temperature solid oxide fuel cells. The SDC NPs are epitaxially grown on the surface of SBCO with (220) planes of SDC aligning smoothly to (020) or (100) planes of SBCO, forming a tight, coherent connection at the interface. The influence of this modification on thermal expansion, oxygen diffusion, electrical conductivity and electrochemical properties is investigated thoroughly in this work. The designed SBCO–SDC cathode material demonstrates a lower thermal expansion coefficient (TEC), ∼16.4 × 10−6 K−1, than that of the unmodified SBCO, ∼20.9 × 10−6 K−1. While SDC coating results in a decreased total electrical conductivity, it facilitates oxygen bulk diffusion and improves the surface exchange reaction kinetics. Coating with SDC NPs can accelerate the rate-determining process of dissociation of the absorbed molecular oxygen, especially at intermediate temperatures. Accordingly, the constructed symmetrical cell with the La0.8Sr0.2Ga0.8Mg0.2O3−δ (LSGM) electrolyte shows lower polarization resistance values, if the SBCO–SDC cathode is utilized. Also, the LSGM electrolyte-supported (300 μm) full cell is found to deliver a high power density of 800 mW cm−2 at 800 °C. Owing to the strong and coherent interfacial connection, the developed cathode demonstrates a relatively steady electrochemical performance. [ABSTRACT FROM AUTHOR]

It is shown that appropriately doped Cu-based perovskite-type oxides exhibit high catalytic activity toward the oxygen reduction reaction at high temperatures, surprisingly making them suitable candidates for the preparation of air electrodes for solid oxide fuel cells. The proposed substitution in the La-sublattice of LaCuO3−δ by Ba and/or Sr (i.e. La4BaCu5O13±δ, La3SrCu4O10±δ and La3Sr0.6Ba0.4Cu4O10±δ compositions) allows stabilization of the perovskite-type structure at ambient pressures in a wide range of temperatures. The materials exhibit extraordinarily high total electrical conductivity associated with the presence of mixed Cu3+/Cu2+ states, limited thermal expansion due to suppressed oxygen release at high temperatures, as well as suitable thermal and chemical stability. Moreover, as derived from first principles calculations for the La4BaCu5O13±δ-based supercell, the activation energy of migration of the oxygen vacancies for La4BaCu5O13−δ is low, ca. 0.4 eV. In contrast to Co, copper is cheap, environmentally benign and thermal treatment of its oxides does not require high temperatures, and therefore, the proposed Cu-based compounds are attractive for preparation of the electrode layers. For the selected La4BaCu5O13±δ oxide the influence of sintering temperature on the cathodic polarization resistance is presented, with the lowest recorded value of 0.03 Ω cm2 at 900 °C. The performance of a button-type solid oxide fuel cell with the optimized La4BaCu5O13±δ-based air electrode screen-printed on the La0.2Ce0.8O2−δ buffer layer and La0.8Sr0.2Ga0.8Mg0.2O3−δ solid electrolyte is good, with the highest power output exceeding 1 W cm−2 at 900 °C for the cell fuelled with wet H2. [ABSTRACT FROM AUTHOR]

Na3V2(PO4)3 with a 3D open NASICON framework can accommodate a wide range of Na contents, which makes it capable of working as both a cathode and anode material. However, severe capacity degradation and inferior rate capability resulting from low electronic/ionic conductivities and poor structural stability have hindered its practical implementation. Herein, excellent sodium storage performance of Na3V2(PO4)3 is realized by delicate lattice modulation. Aliovalent Ca2+ substitution for V3+ increases both the electronic and ionic conductivities by producing electronic defects and enlarging the sodium ion migration channels. DFT calculations reveal that the fifth Na ion intercalation/deintercalation produces a large lattice volume change, which is possibly the origin of the poor redox reaction reversibility of Na3V2(PO4)3 at low potential (∼0.3 V vs. Na+/Na). The Ca2+ doping enhances significantly the structural stability to suppress the large crystal lattice distortion during the anode reaction process. The multiple effects enable superior rate-capability and ultralong cycle-life of Ca-doped Na3V2(PO4)3 as both a cathode and anode material. The symmetric full cell constructed with the optimized Na3V1.95Ca0.05(PO4)3@C electrode delivers a very high energy density of 166 W h kg−1 and an exceptional cycling stability (0.02% capacity decay per cycle over 2000 cycles at 10C rate). This study provides a feasible strategy for obtaining high-rate and long cycle-life electrode materials for high-efficiency energy storage. [ABSTRACT FROM AUTHOR]

The oxygen storage capacity, structure and thermodynamic stability were studied for hexagonal Y0.7Tb0.3MnO3+δ in oxygen and air to assess its applicability for oxygen separation from air by a temperature-swing adsorption process. We show that large amounts of oxygen excess can be reversibly incorporated into and extracted from small particle-size samples of Y0.7Tb0.3MnO3+δ prepared by sol–gel synthesis for fixed oxygen partial pressures. The hyperstoichiometric material, with δ≥ 0.45 prepared in oxygen or high-pressure oxygen atmospheres, assumes a new hexagonal structure with interstitial oxygen defects near the nominally five coordinated Mn site as determined by neutron diffraction and supported by scanning and transmission electron microscopy. Thermogravimetric measurements demonstrate reversible intercalation of oxygen in a pure O2 atmosphere at around 300 °C, but more importantly, also in air over a remarkably narrow temperature range of ∼20 °C, albeit producing smaller oxygen amounts δ≤ 0.25. Comparison of samples' properties obtained by the sol–gel and solid-state synthesis methods confirms enhanced oxygen storage capacity and oxygen exchange kinetics for the small particle-size samples which exhibit larger specific surface areas. Sequential temperature-swing absorption and long-term annealing experiments demonstrate the high practical potential of Y0.7Tb0.3MnO3 compounds for the industrial production of oxygen enriched gases by utilization of waste heat at 250–350 °C. [ABSTRACT FROM AUTHOR]

The effects of A-site substitutions on the interstitial oxygen formation energy and the migration energy in layered A2−xA′xNiO4+δ (A = selected lanthanides, A′ = Ba, Sr, Ca) are investigated by first principles calculations. The interstitial oxygen formation energy is negative, in the range of −4.81 eV to −3.45 eV, strongly supporting easiness of formation of the interstitial oxygen defects in the (A,A′)O rock salt plane. The Pr2NiO4+δ compound shows the lowest formation energy, indicating the highest amount of interstitial oxygen. Doping with alkaline earth cations (A′) increases the formation energy of the interstitial oxygen, which prefers to be located far away from the dopants. Nevertheless, Ca seems to be the best choice, due to relatively low formation energy. Calculations for the four kinds of diffusion paths allow it to be predicted that the oxygen transport in A2−xA′xNiO4+δ is governed by the interstitialcy mechanism in the ab plane, because of the significantly lower energy barriers for this mechanism. An interesting finding is achieved for A2NiO4+δ (A = Pr, Nd, Sm), for which the energy barriers for the interstitialcy transport are negative (−0.47 eV, −0.33 eV and −0.02 eV, respectively), implying that the transition state is more stable than the assumed initial state. A new structural configuration is proposed in this work, with the adjacent apical oxygen located at the adjacent interstitial site, which shows ca. 0.5 eV lower free energy than that of the initial model. This result provides a new understanding for the location of the interstitial and the adjacent apical oxygens from an energetic point of view and supports previously published experimental data. It is found that alkaline earth doping at the A-site deteriorates the interstitial oxygen diffusion in La2−xA′xNiO4.25 materials, but concerning overall transport properties, Ca seems to be a good dopant from an energetic point of view, when compared with Ba and Sr. [ABSTRACT FROM AUTHOR]

In this work, a novel series of Mn-containing ReBaCo1.5Mn0.5O5+δ (Re: selected rare earth elements) perovskite-type oxides is studied, with systematic measurements of physicochemical properties being reported. Comparison with the very well-studied, parent ReBaCo2O5+δ allows determination of the role of the introduced manganese concerning modification of the crystal structure at room temperature and its evolution at high temperatures, variation of the oxygen content, thermal stability of the materials, and total electrical conductivity, as well as thermal and chemical expansion. Generally, the presence of Mn cations does not affect the tendency for A-site cation ordering, resulting in an increased unit cell volume of the compounds, as well as causing an increase of the oxygen content. Reduced thermal expansion, together with high values of electrical conductivity and suitable thermal stability, makes the compounds containing larger Re3+ cations attractive from the point of view of application as cathode materials in solid oxide fuel cells. Chemical compatibility studies reveal the sufficient stability of the considered perovskites in relation to Ce0.8Gd0.2O2−δ solid electrolyte, while unexpected, somewhat increased reactivity towards La0.8Sr0.2Ga0.8Mg0.2O3−δ and La0.4Ce0.6O2−δ is also reported. Furthermore, the electrochemical tests of the symmetric cells show strong dependence of the polarization resistance of the electrode on the synthesis and sintering temperatures. For the selected and optimized NdBaCo1.5Mn0.5O5+δ layer employed in the electrolyte-supported (LSGM) symmetric cell with a CGO buffer layer, the cathodic polarization resistance is 0.043 Ω cm2 at 900 °C. A wet hydrogen-fuelled button-type cell with the NdBaCo1.5Mn0.5O5+δ-based cathode is also prepared, delivering the maximum power density exceeding 1.3 W cm−2 at 850 °C. [ABSTRACT FROM AUTHOR]

Ca-doping at the Y-site of Y1−xCaxBaCo2O5+δ (YCBC) double perovskites is shown as an effective strategy to develop a highly efficient, stable, lanthanide-free cathode material for intermediate temperature solid oxide fuel cells (IT-SOFCs). The proposed Ca-doping has a beneficial influence on the structural stability, thermal expansion coefficient, electronic and ionic transport, and electrochemical properties of YCBC oxides. The phase stability and durability at evaluated temperature are greatly enhanced by Ca-doping. The thermal expansion coefficients of Y1−xCaxBaCo2O5+δ are calculated to be 18.1–18.7 × 10−6 K−1. At 800 °C, the conductivity is as high as 220 S cm−1 for the Y0.8Ca0.2BaCo2O5+δ sample. Area specific resistances as low as 0.010, 0.018, 0.032, 0.068 and 0.142 Ω cm2 at 850, 800, 750, 700 and 650 °C, respectively, are delivered by the Y0.8Ca0.2BaCo2O5+δ cathode in a La0.8Sr0.2Ga0.8Mg0.2O3−δ electrolyte supported symmetric cell. The maximum power densities of a full cell with the Y0.8Ca0.2BaCo2O5+δ/Ce0.9Gd0.1O2−δ composite cathode are registered to be 1066, 841, 634 and 430 mW cm−2 at 850, 800, 750 and 700 °C, respectively. All the results clearly demonstrate that Ca-doped Y1−xCaxBaCo2O5+δ double perovskites are highly stable and effectively working candidate cathodes for IT-SOFCs. [ABSTRACT FROM AUTHOR]

Structural and oxygen content changes of hexagonal HoMnO3+δ manganite at the stability boundary in the perovskite phase have been studied by X-ray diffraction and thermogravimetry using in situ oxidation and reduction processes at elevated temperatures in oxygen and air. The oxygen storage properties during structural transformation between stoichiometric Hex0 and oxygen-loaded Hex1 phases, transition temperatures and kinetics of the oxygen incorporation and release are reported for materials prepared by the solid-state synthesis and high-impact mechanical milling. Long-term annealing experiments have shown that the Hex0 (δ = 0) → Hex1 (δ≈ 0.28) phase transition is limited by the surface reaction and nucleation of the new phase for HoMnO3+δ 15MM. The temperatures of Hex0 ↑ Hex1 transitions have been established at 290 °C and 250 °C upon heating and cooling, respectively, at a rate of 0.1° min−1, also indicating that the temperature hysteresis of the transition could possibly be as small as 10 °C in the equilibrium. Ball-milling of HoMnO3+δ has only a small effect on improving the speed of the reduction/oxidation processes in oxygen, but importantly, allowed for considerable oxygen incorporation in air at a temperature range of 220–255 °C after prolonged heating. The Mn 2p XAS results of the Mn valence in oxygen loaded samples support the oxygen content determined by the TG method. The magnetic susceptibility data of the effective Mn valence gave inconclusive results due to dominating magnetism of the Ho3+ ions. Comparison of HoMnO3+δ with previously studied DyMnO3+δ indicates that a tiny increase in the ionic size of lanthanide has a huge effect on the redox properties of hexagonal manganites and that practical properties could be significantly improved by synthesizing the larger average size (Y,Ln)MnO3+δ manganites. [ABSTRACT FROM AUTHOR]

A cost-effective doping strategy was developed to enhance the oxygen permeability and structural stability of BaFeO3−δ. We demonstrated that the alkaline earth metal element Ca, which is usually considered an A-site dopant for perovskite oxides, can be successfully introduced into the B-site of BaFeO3−δ. The cubic perovskite structure of BaFe1−xCaxO3−δ was stabilized down to room temperature for the Ca-doping concentration range from 5 to 15 at%. First principles calculations not only proved the preference of Ca at the B-site with lower defect formation energies than the A-site, but also demonstrated that the migration of the oxygens located greater distances from the Ca position is characterized by lower barrier energies than those in the Ca vicinity and even lower than that for the undoped BaFeO3−δ. We found that these favourable, low energy barrier paths away from the Ca sites exert more pronounced effects on the oxygen migration at diluted dopant concentrations, and hence, the material with x = 0.05 level of substitution shows a higher oxygen permeability with a lower activation energy compared to the undoped or highly-doped BaFeO3−δ. The BaFe0.95Ca0.05O3−δ membrane is characterized by a high oxygen permeability of 1.30 mL cm−2 min−1 at 950 °C and good long-term stability at 800/900 °C, as obtained over 200 h. Therefore, the feasibility and applicability of Ca-doping at the B-site of the perovskite can be highlighted, which allows for the enhancement of the oxygen migration ability, originating from the appropriate tuning of the lattice structure. [ABSTRACT FROM AUTHOR]

Molybdenum dioxide is an attractive material for anodes of lithium ion batteries due to its high theoretical capacity, more than twice that of graphite. However, slow electrode reaction kinetics and structural degradation caused by large volume changes and phase separation during cycling hinder its practical application. To solve these problems, we design and fabricate a novel, 3-D hierarchical MoO2/Ni/C architecture by a combination of a hydrothermal method with chemical vapor deposition. The nickel nanoparticles are in situ formed and disperse uniformly with flower-like MoO2 particles, which are coated by thin carbon layers. The Ni particles act as a catalyst during the carbon coating process to promote the in situ growth of graphene in the carbon layer. Together, MoO2 and nickel nanoparticles, as well as amorphous carbon and graphene sheets build a 3-D hierarchical robust MoO2/Ni/C structure with a good electronically conductive network and lots of void space. Such a 3-D hierarchical structure combines multiple advantageous features, including an enhanced 3-D electronically conductive network, plenty of tunnels for electrolyte solution penetration, void space for volume change accommodation, and more surface areas for the electrode reaction. The manufactured MoO2/Ni/C composite exhibits a high reversible capacity, and excellent rate capability of 576 and 463 mA h g−1 at current densities of 100 and 1000 mA g−1, respectively. The excellent cycling performance is recorded with a capacity of 445 mA h g−1 maintained at 1000 mA g−1 after 800 cycles. The proposed synthesis process is simple and the design concept can be broadly applied, providing a novel, general approach towards manufacturing of metal oxide/metal/carbon (graphene) composites for high energy density storage or other electrochemical uses. [ABSTRACT FROM AUTHOR]

Cobalt-free BaFe1−xInxO3−δ perovskites, with Fe partially substituted by indium at the B-site, were synthesized by a conventional solid state reaction and systematically characterized in terms of their phase composition, crystal structure, thermal reducibility, oxygen permeability, as well as structural stability in order to evaluate their application as oxygen permeation membranes. Introduction of more than 10 at.% of In into BaFe1−xInxO3−δ causes the formation of a single phase material with a cubic perovskite structure, which exhibits no phase transition during the cooling process. The thermal reducibility and thermal expansion coefficient are effectively reduced by indium doping, owing to the less changes of concentration of the oxygen vacancies in these compounds. However, the In occupying B-site breaks the B–O–B double exchange mechanism, and thus results in a gradual decrease of the electrical conductivity upon doping. Rietveld refinement and first principles calculation were performed to get an insight into the In influence on the lattice structure, oxygen migration energy and electron conduction behaviour of BaFe1−xInxO3−δ. When using He/Air as sweep/feed gas, the BaFe0.9In0.1O3−δ dense membrane with 1.0 mm thickness features a high oxygen permeation flux of 1.11 mL cm−2 min−1 at 950 °C. The observed good performance is attributed to the relatively high concentration of oxygen vacancies and low energy barrier for oxygen ion migration. It is also found that for membranes thinner than 0.8 mm, the oxygen flux is no longer limited by the bulk diffusion, while the oxygen surface exchange process becomes the dominant factor. [ABSTRACT FROM AUTHOR]

In this paper we would like to show a new approach to an explanation of the nature of the discharge–charge curve of Na/Na+/NaxCoO2−y batteries, which can justify the existence of the step-like characteristics. This is still an open problem, which until now had no proper description in the literature. On the basis of comprehensive experimental studies of physicochemical properties of NaxCoO2−y cathode material (XRD, electrical conductivity, thermoelectric power, electronic specific heat) supported by calculations performed using the DFT method with accounting for chemical disorder, it has been shown that the observed step-like character of the discharge curve reflects the variation of the chemical potential of electrons (Fermi level) in the density of states of NaxCoO2−y, which is anomalously perturbed by the presence of the oxygen vacancy defects and sodium ordering. Our studies of structural, electronic and thermal properties of NaxCoO2−y cathode material as a function of concentration of electrochemically intercalated sodium document strong and step-like shift of the position of the Fermi level during introduction of electrons in this process. This effect is coherently supported by the shape of calculated density of states (DOS) of NaxCoO2−y having included oxygen defects and sodium ordering. [ABSTRACT FROM AUTHOR]

In this paper we would like to show a new approach to an explanation of the nature of the discharge-charge curve of Na/Na(+)/NaxCoO2-y batteries, which can justify the existence of the step-like characteristics. This is still an open problem, which until now had no proper description in the literature. On the basis of comprehensive experimental studies of physicochemical properties of NaxCoO2-y cathode material (XRD, electrical conductivity, thermoelectric power, electronic specific heat) supported by calculations performed using the DFT method with accounting for chemical disorder, it has been shown that the observed step-like character of the discharge curve reflects the variation of the chemical potential of electrons (Fermi level) in the density of states of NaxCoO2-y, which is anomalously perturbed by the presence of the oxygen vacancy defects and sodium ordering. Our studies of structural, electronic and thermal properties of NaxCoO2-y cathode material as a function of concentration of electrochemically intercalated sodium document strong and step-like shift of the position of the Fermi level during introduction of electrons in this process. This effect is coherently supported by the shape of calculated density of states (DOS) of NaxCoO2-y having included oxygen defects and sodium ordering.