Konrad Świerczek

MoS2 Nanosheets Vertically Grown on Graphene Sheets for Lithium-Ion Battery Anodes

A designed nanostructure with MoS2 nanosheets (NSs) perpendicularly grown on graphene sheets (MoS2/G) is achieved by a facile and scalable hydrothermal method, which involves adsorption of Mo7O24(6-) on a graphene oxide (GO) surface, due to the electrostatic attraction, followed by in situ growth of MoS2. These results give an explicit proof that the presence of oxygen-containing groups and pH of the solution are crucial factors enabling formation of a lamellar structure with MoS2 NSs uniformly decorated on graphene sheets. The direct coupling of edge Mo of MoS2 with the oxygen from functional groups on GO (C-O-Mo bond) is proposed. The interfacial interaction of the C-O-Mo bonds can enhance electron transport rate and structural stability of the MoS2/G electrode, which is beneficial for the improvement of rate performance and long cycle life. The graphene sheets improve the electrical conductivity of the composite and, at the same time, act not only as a substrate to disperse active MoS2 NSs homogeneously but also as a buffer to accommodate the volume changes during cycling. As an anode material for lithium-ion batteries, the manufactured MoS2/G electrode manifests a stable cycling performance (1077 mAh g(-1) at 100 mA g(-1) after 150 cycles), excellent rate capability, and a long cycle life (907 mAh g(-1) at 1000 mA g(-1) after 400 cycles).

Conduction mechanism in operating a LiMn2O4 cathode

Abstract Two series of the Li x Mn 2 O 4 spinel samples were studied at low temperatures (200–300 K) on electrical, thermal (DSC) and structural (X-ray diffraction (XRD)) properties for different lithium contents. Results obtained for deintercalated spinel samples with x ∼1 revealed the existence of a broad (100 K) phase transition that can be attributed to the molecular polaron condensation, leading to the orthorhombic distortion of the initial cubic form. The differential scanning calorimetry (DSC) measurement results enable us to regard the phase transition as a form of order–disorder one. Corresponding thermoelectric power (TEP) and electrical conductivity measurements fall within such description, moreover, indicating clear inconsistency between the measured regular DC conductivity of the spinel sample and that observed for the cathode in the working lithium cell. This discrepancy points to an alternative charge transport mechanism existing in the manganese spinel cathode, and it seems to be essential for the lithium cell performance.

High-Performance Anode Material Sr2FeMo0.65Ni0.35O6−δ with In Situ Exsolved Nanoparticle Catalyst

A metallic nanoparticle-decorated ceramic anode was prepared by in situ reduction of the perovskite Sr2FeMo0.65Ni0.35O6-δ (SFMNi) in H2 at 850 °C. The reduction converts the pure perovksite phase into mixed phases containing the Ruddlesden-Popper structure Sr3FeMoO7-δ, perovskite Sr(FeMo)O3-δ, and the FeNi3 bimetallic alloy nanoparticle catalyst. The electrochemical performance of the SFMNi ceramic anode is greatly enhanced by the in situ exsolved Fe-Ni alloy nanoparticle catalysts that are homogeneously distributed on the ceramic backbone surface. The maximum power densities of the La0.8Sr0.2Ga0.8Mg0.2O3-δ electrolyte supported a single cell with SFMNi as the anode reached 590, 793, and 960 mW cm(-2) in wet H2 at 750, 800, and 850 °C, respectively. The Sr2FeMo0.65Ni0.35O6-δ anode also shows excellent structural stability and good coking resistance in wet CH4. The prepared SFMNi material is a promising high-performance anode for solid oxide fuel cells.

Structural, Transport and Electrochemical Properties of LiFePO4 Substituted in Lithium and Iron Sublattices (Al, Zr, W, Mn, Co and Ni)

LiFePO4 is considered to be one of the most promising cathode materials for lithium ion batteries for electric vehicle (EV) application. However, there are still a number of unsolved issues regarding the influence of Li and Fe-site substitution on the physicochemical properties of LiFePO4. This is a review-type article, presenting results of our group, related to the possibility of the chemical modification of phosphoolivine by introduction of cation dopants in Li and Fe sublattices. Along with a synthetic review of previous papers, a large number of new results are included. The possibility of substitution of Li+ by Al3+, Zr4+, W6+ and its influence on the physicochemical properties of LiFePO4 was investigated by means of XRD, SEM/EDS, electrical conductivity and Seebeck coefficient measurements. The range of solid solution formation in Li1−3xAlxFePO4, Li1−4xZrxFePO4 and Li1−6xWxFePO4 materials was found to be very narrow. Transport properties of the synthesized materials were found to be rather weakly dependent on the chemical composition. The battery performance of selected olivines was tested by cyclic voltammetry (CV). In the case of LiFe1−yMyPO4 (M = Mn, Co and Ni), solid solution formation was observed over a large range of y (0 < y ≤ 1). An increase of electrical conductivity for the substitution level y = 0.25 was observed. Electrons of 3d metals other than iron do not contribute to the electrical properties of LiFe1−yMyPO4, and substitution level y > 0.25 leads to considerably lower values of σ. The activated character of electrical conductivity with a rather weak temperature dependence of the Seebeck coefficient suggests a small polaron-type conduction mechanism. The electrochemical properties of LiFe1−yMyPO4 strongly depend on the Fe substitution level.

Investigation of In-doped BaFeO3−δ perovskite-type oxygen permeable membranes

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.

Crystallographic and electronic properties of Li1+δMn2−δO4 spinels prepared by HT synthesis

Abstract The aim of this study was to determine an influence of lithium excess in Li 1+ δ Mn 2− δ O 4 spinels (in the 0≤ δ ≤0.32 range) on their transport and structural properties. The additional lithium atoms take Mn positions causing in the lattice parameter diminution and disappearance of the phase transition observed for the stoichiometric Li 1 Mn 2 O 4 manganese spinel. Low-temperature (230–330 K) measurements of electrical conductivity and thermoelectric power indicate rather minor influence of the excess lithium on transport properties in this system.

Evaluation of La0.3Sr0.7Ti1−xCoxO3 as a potential cathode material for solid oxide fuel cells

Perovskites La0.3Sr0.7Ti1−xCoxO3 (LSTCs, x = 0.3–0.6) are systematically evaluated as potential cathode materials for solid oxide fuel cells. The effects of Co substitution for Ti on structural characteristics, thermal expansion coefficients (TECs), electrical conductivity, and electrochemical performance are investigated. All of the synthesized LSTCs exhibit a cubic structure. With Rietveld refinement on the high-temperature X-ray diffraction data, the TECs of LSTCs are calculated to be 20–26 × 10−6 K−1. LSTC shows good thermal cycling stability and is chemically compatible with the LSGM electrolyte below 1250 °C. The substitution of Co for Ti increases significantly the electrical conductivity of LSTC. The role of doping on the conduction behavior is discussed based on defect chemistry theory and first principles calculation. The electrochemical performances of LSTC are remarkably improved with Co substitution. The area specific resistance of sample La0.3Sr0.7Ti0.4Co0.6O3 on the La0.8Sr0.2Ga0.8Mg0.2O3−δ (LSGM) electrolyte in symmetrical cells is 0.0145, 0.0233, 0.0409, 0.0930 Ω cm2 at 850, 800, 750 and 700 °C, respectively, and the maximum power density of the LSGM electrolyte (400 μm)-supported single cell with the Ni–GDC anode, LDC buffer layer and LSTC cathode reaches 464.5, 648, and 775 mW cm−2 at 850 °C for x = 0.3, 0.45, and 0.6, respectively. All these results suggest that LSTC are promising candidate cathode materials for SOFCs.

Electronic structure and reactivity of Li1−xMn2O4 cathode

Abstract The investigations of low temperature electrical and structural properties of the Li 1− x Mn 2 O 4 cathode as a function of lithium concentration are presented. Structure studies of deintercalated spinel revealed the existence of a broad (300–200 K) phase transition from cubic into orthorhombic phase also confirmed by DSC results. Thermoelectric power and electrical conductivity measurements indicate that the manganese spinel undergoes a modification of electronic structure during intercalation process.

Hierarchically structured lithium titanate for ultrafast charging in long-life high capacity batteries

High-performance Li-ion batteries require materials with well-designed and controlled structures on nanometre and micrometre scales. Electrochemical properties can be enhanced by reducing crystallite size and by manipulating structure and morphology. Here we show a method for preparing hierarchically structured Li4Ti5O12 yielding nano- and microstructure well-suited for use in lithium-ion batteries. Scalable glycothermal synthesis yields well-crystallized primary 4–8 nm nanoparticles, assembled into porous secondary particles. X-ray photoelectron spectroscopy reveals presence of Ti+4 only; combined with chemical analysis showing lithium deficiency, this suggests oxygen non-stoichiometry. Electron microscopy confirms hierarchical morphology of the obtained material. Extended cycling tests in half cells demonstrates capacity of 170 mAh g−1 and no sign of capacity fading after 1,000 cycles at 50C rate (charging completed in 72 s). The particular combination of nanostructure, microstructure and non-stoichiometry for the prepared lithium titanate is believed to underlie the observed electrochemical performance of material.

Comparison of magnetic and thermoelectric properties of (Nd,Ca)BaCo2O5.5 and (Nd,Ca)CoO3

Magnetic and thermoelectric properties of Nd1−xCaxBaCo2O5.5 and Nd1−xCaxCoO3 have been studied. Ca doping in Nd1−xCaxBaCo2O5.5 (x ≤ 0.2) preserves the metal to insulator transition (MIT) at 340–360 K. While the antiferromagnetic state disappears upon doping, the Curie temperature is increasing and becomes close to MIT for x > 0.12. The magnetic susceptibility of Nd1−xCaxCoO3 is paramagnetic for x up to 0.2, similar to the parent compound, with some indication of cluster-glass-like behavior at temperatures below 30 K. The increasing effective paramagnetic moments with doping suggest a low spin state of Co3+ and a high spin state of Co4+. Maximum observed ZT reaches a value close to 0.2 for x = 0.15 at 800 K, which is one of the highest values for perovskite cobaltites.