RESUMEN
NASICON-type NaNbV(PO4)3 electrode material synthesized by the Pechini sol-gel technique undergoes a reversible three-electron reaction in a Na-ion cell which corresponds to the Nb5+/Nb4+, Nb4+/Nb3+, and V3+/V2+ redox processes and provides a reversible capacity of 180 mAh·g-1. The sodium insertion/extraction takes place in a narrow potential range at an average potential of 1.55 V versus Na+/Na. Structural characterization by operando and ex situ X-ray diffraction disclosed the reversible evolution of the NaNbV(PO4)3 polyhedron framework during cycling, while XANES measurements in the operando regime confirmed the multielectron transfer upon sodium intercalation/extraction into NaNbV(PO4)3. This electrode material demonstrates extended cycling stability and excellent rate capability maintaining the capacity value of 144 mAh·g-1 at 10 C current rates. It can be regarded as a superior anode material suitable for application in high-power and long-life sodium-ion batteries.
RESUMEN
The Li1.17Ni0.17Mn0.50Co0.17O2 Li-rich NMC positive electrode (cathode) for lithium-ion batteries has been coated with nanocrystals of the LiMn1.5Co0.5O4 high-voltage spinel cathode material. The coating was applied through a single-source precursor approach by a deposition of the molecular precursor LiMn1.5Co0.5(thd)5 (thd = 2,2,6,6-tetramethyl-3,5-heptanedionate) dissolved in diethyl ether, followed by thermal decomposition at 400 °C inair resulting in a chemically homogeneous cubic spinel. The structure and chemical composition of the coatings, deposited on the model SiO2 spheres and Li-rich NMC crystallites, were analyzed using powder X-ray diffraction, electron diffraction, high angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), and energy-dispersive X-ray (EDX) mapping. The coated material containing 12 wt.% of spinel demonstrates a significantly improved first cycle Coulombic efficiency of 92% with a high first cycle discharge capacity of 290 mAhg-1. The coating also improves the capacity and voltage retention monitored over 25 galvanostatic charge-discharge cycles, although a complete suppression of the capacity and voltage fade is not achieved.
RESUMEN
The incommensurate modulated crystal structure of Bi2.27Sr1.73CuO6â +â δ (2201) phase [a = 5.3874â (5), b = 5.3869â (4), c = 24.579â (3)â Å; ß = 90.01â (1)°, q = 0.2105â (3)a(*)â +â 0.538â (4)c(*), Z = 4, the (3â +â 1)-dimensional monoclinic A2/a(α0γ) group] has been refined with R = 0.041, wR = 0.052 from X-ray single-crystal data including up to third-order satellite reflections. The same structure has also been considered as incommensurate composite with a2 = 2.437, b2 = 5.387, c2 = 24.614, ß2 = 93.06, q2 = 0.4524a2(*)-0.243c2(*) and the (3â +â 1)-dimensional A2/m(α0γ)0s group for the second component. Both approaches give quite similar results. The structure possesses oxygen disorder in the oxygen-rich region of the BiO layer. An extra O atom is determined in the bridging position shifted â¼â 0.6â Å from BiO towards the SrO layer. Its presence is the cause of the tremendous increase of the bismuth U(11) atomic displacement parameter in â¼â 20% of the unit cells (t = -0.05-0.15). Vacancies are determined in the oxygen site of the SrO layer, which may result in the oxygen content variation with annealing at different oxygen pressures. The total refined oxygen content 6.18â (1) corresponds to the results of chemical analysis.
RESUMEN
To satisfy the needs of rapidly growing applications, Li-ion batteries require further significant improvements of their key properties: specific energy and power, cyclability, safety and costs. The first generation of cathode materials for Li-ion batteries based on mixed oxides with either spinel or rock-salt derivatives has already been widely commercialized, but the potential to improve the performance of these materials further is almost exhausted. Li and transition metal inorganic compounds containing different polyanions are now considered as the most promising cathode materials for the next generation of Li-ion batteries. Further advances in cathode materials are considered to lie in combining different anions [such as (XO4) (n-) and F(-)] in the anion sublattice, which is expected to enhance the specific energy and power of these materials. This review focuses on recent advances related to the new class of cathode materials for Li-ion batteries containing phosphate and fluoride anions. Special attention is given to their crystal structures and the relationships between structure and properties, which are important for their possible practical applications.
RESUMEN
In the search for high-energy materials, novel 3D-fluorophosphates, Li2Co1- x Fe x PO4F and Li2Co1- x Mn x PO4F, have been synthesized. X-ray diffraction and scanning electron microscopy have been applied to analyze the structural and morphological features of the prepared materials. Both systems, Li2Co1- x Fe x PO4F and Li2Co1- x Mn x PO4F, exhibited narrow ranges of solid solutions: x ≤ 0.3 and x ≤ 0.1, respectively. The Li2Co0.9Mn0.1PO4F material demonstrated a reversible electrochemical performance with an initial discharge capacity of 75 mA·h·g(-1) (current rate of C/5) upon cycling between 2.5 and 5.5 V in 1 M LiBF4/TMS electrolyte. Galvanostatic measurements along with cyclic voltammetry supported a single-phase de/intercalation mechanism in the Li2Co0.9Mn0.1PO4F material.
RESUMEN
A new potassium palladate KPd(2)O(3) was synthesized by the reaction of KO(2) and PdO at elevated oxygen pressure. Its crystal structure was solved from powder X-ray diffraction data in the space group R3m (a = 6.0730(1) A, c = 18.7770(7) A, and Z = 6). KPd(2)O(3) represents a new structure type, consisting of an alternating sequence of K(+) and Pd(2)O(3)(-) layers with ordered Pd(2+) and Pd(4+) ions. The presence of palladium ions in di- and tetravalent low-spin states was confirmed by magnetic susceptibility measurements.
RESUMEN
A first rare-earth phosphide silicide Ce4(P(1-x)Si(x))(3-z) and its analogues with La, Pr, and Nd were synthesized and characterized. The compounds crystallize in the anti-Th3P4 structure type. The cerium compound shows a mixed occupation of the 12a site with Si and P and possesses a wide homogeneity range with respect to x and z variation. The electronic configuration of Ce, deduced from magnetic susceptibility and X-ray absorption spectroscopy data, remains 4f(1) (Ce3+) independently from x and z. The cerium valence and the phase stability region are discussed employing electronic band-structure calculation and chemical bonding analysis with electron localization function. Atomic interactions are shown to remain nearly unchanged, while the change of the excess electron concentration with P/Si substitution is considered to play the main role for the stabilization of the structural motif.