The article considers Ancient Halych as a medieval ethnocultural center of Ukraine. Whereas ancient Halych was one of the leading cultural centers of Kyivan Rus, its studying will help us to show the ...place of Ukraine and Ukrainians in global ethnocultural processes.
Lithium‐ and manganese‐rich layered oxides (LMLOs, ≥ 250 mAh g−1) with polycrystalline morphology always suffer from severe voltage decay upon cycling because of the anisotropic lattice strain and ...oxygen release induced chemo‐mechanical breakdown. Herein, a Co‐free single‐crystalline LMLO, that is, LiLi0.2Ni0.2Mn0.6O2 (LLNMO‐SC), is prepared via a Li+/Na+ ion‐exchange reaction. In situ synchrotron‐based X‐ray diffraction (sXRD) results demonstrate that relatively small changes in lattice parameters and reduced average micro‐strain are observed in LLNMO‐SC compared to its polycrystalline counterpart (LLNMO‐PC) during the charge–discharge process. Specifically, the as‐synthesized LLNMO‐SC exhibits a unit cell volume change as low as 1.1% during electrochemical cycling. Such low strain characteristics ensure a stable framework for Li‐ion insertion/extraction, which considerably enhances the structural stability of LLNMO during long‐term cycling. Due to these peculiar benefits, the average discharge voltage of LLNMO‐SC decreases by only ≈0.2 V after 100 cycles at 28 mA g‐1 between 2.0 and 4.8 V, which is much lower than that of LLNMO‐PC (≈0.5 V). Such a single‐crystalline strategy offers a promising solution to constructing stable high‐energy lithium‐ion batteries (LIBs).
A Li+/Na+ ion‐exchange reaction is reported to synthesize the Co‐free single‐crystalline LiLi0.2Ni0.2Mn0.6O2 (LLNMO‐SC). In situ synchrotron‐based X‐ray diffraction and absorption spectroscopy are utilized to investigate the structural evolution of LLNMO‐SC and its polycrystalline counterpart (LLNMO‐PC) during electrochemical cycling. The origin of mitigated voltage decay in LLNMO‐SC is unraveled upon long‐term cycling.
Layered alkali-containing 3d transition-metal oxides are of the utmost importance in the use of electrode materials for advanced energy storage applications such as Li-, Na-, or K-ion batteries. A ...significant challenge in the field of materials chemistry is understanding the dynamics of the chemical reactions between alkali-free precursors and alkali species during the synthesis of these compounds. In this study, in situ high-resolution synchrotron-based X-ray diffraction was applied to reveal the Li/Na/K-ion insertion-induced structural transformation mechanism during high-temperature solid-state reaction. The in situ diffraction results demonstrate that the chemical reaction pathway strongly depends on the alkali-free precursor type, which is a structural matrix enabling phase transitions. Quantitative phase analysis identifies for the first time the decomposition of lithium sources as the most critical factor for the formation of metastable intermediates or impurities during the entire process of Li-rich layered LiLi0.2Ni0.2Mn0.6O2 formation. Since the alkali ions have different ionic radii, Na/K ions tend to be located on prismatic sites in the defective layered structure (Na2/3-xNi0.25Mn0.75O2 or K2/3-xNi0.25Mn0.75O2) during calcination, whereas the Li ions prefer to be localized on the tetrahedral and/or octahedral sites, forming O-type structures.
Structure changes of a mixture of alkali-free precursor and alkali species during the synthesis of layered Li-, Na-, or K-containing 3d transition-metal oxides (ATMOs) were monitored by in situ high-resolution synchrotron-based X-ray diffraction. The intermediate phases, contributing to the ATMO formation pathway, were directly observed, which provide valuable information for the rational design and synthesis of advanced layered oxides with desirable structural and chemical properties. Display omitted
•In situ high-resolution HT-sXRD techniques was used to unveil the Li/Na/K-ion insertion induced structural evolution during heating.•The dynamics of chemical reaction between alkali-free precursor and alkali species upon calcination were systematically investigated.•High-temperature lithiation reaction pathway strongly depends on the alkali-free precursor type.•Site preferences of Li/Na/K-ion leads to the formation of various types of layered structures.
The article examines the history of the archaeological research of ancient Halych from the middle of the 19th to the end of the 20th century. Whereas ancient Halych was one of the leading cultural ...centers of Kyiv Rus, its studying will help us to show the place of Ukraine and Ukrainians in global ethno-cultural processes.
Single crystals of Li15Si4 and Li15-xAlxSi4 (x = 0.63(1)) were obtained from equilibrated melts with compositions Li100-xSix (x = 10, 15) and Li83Al13Si4, respectively, and isolated by isothermal ...centrifugation. Li15Si4 and Li14.37(1)Al0.63(1)Si4 crystallize with the Cu15Si4 structure type (I (4) over bar 3d, a(x=0) = 10.6322(9) angstrom, a(x=0.63(1)) = 10.6172(4) angstrom, Z = 4, T = 123 K). The incorporation of Al equally affects both crystallographically distinguished Li positions in the Li15Si4 structure. The replacement of about 4% of Li is firmly established by the refinement of single crystal diffraction data and NMR spectroscopy. The homogeneity range of Li15-xAlxSi4 was assessed as 0.4 < x < 0.8 from synthesis experiments using stoichiometric proportions of the elements. Differential scanning calorimetry studies confirm the metastable character of Li15Si4, decomposing exothermally at temperatures around 200 degrees C. However, the decomposition process of Li15Si4, is sluggish and appreciable rates are not observed before temperatures reach 400 degrees C. In contrast Li15-xAlxSi4 is thermodynamically stable. The decomposition temperature is at about 700 degrees C. It is speculated that the thermodynamic stability of Li15-xAlxSi4 is a consequence of the increased electron concentration, shifting the Fermi level to a pseudo-gap in the electronic density of states. Since metastable Li15Si4 plays an important role during electrochemical lithiation of a silicon anode, thermodynamically stable Li15-xAlxSi4 may have interesting properties as anode material in lithium ion batteries.
Developing high-energy-density cathodes with prolonged cycling life is crucial to the continuing success of lithium-ion batteries. In particular, nickel-rich layered LiNi0.8Mn0.1Co0.1O2 (NMC811) ...cathodes are receiving growing interest due to their high reversible capacities in the range of 160–200 mAh/g and reduced content of critical and expensive cobalt. Nevertheless, nickel-rich NMC materials still encounter several challenges limiting their long-term cyclability, such as irreversible structural rearrangements, transition-metal dissolution, high surface reactivity, and parasitic oxidation of organic electrolyte at the surface of delithiated Li1–z Ni x Mn y Co1–x–y O2 at high voltages. Here, we investigate the use of several electrolyte additives that can alleviate capacity fading through the formation of a protective layer passivating the surface of nickel-rich NMC811. Film-forming cathode additives should decompose prior to the solvents and cover the electrode surface with a protection layer which prevents further oxidative decomposition of the electrolyte and minimizes surface side reactions. We find that the addition of 1 vol. % tris(trimethylsilyl)phosphite (TMSPi) in combination with 1 vol. % vinylene carbonate (VC) to a standard electrolyte consisting of 1 M LiPF6 in ethylene carbonate (EC):dimethyl carbonate (DMC) (1:1 vol.) significantly enhances the capacity retention of NMC811/graphite full cells. Remarkably, a discharge capacity retention of 91% is achieved after 200 cycles at C/3.
Cubic Li
2
Fe
0.9
M
0.1
SO antiperovskites with M–Co
2+
, or Mn
2+
were successfully synthesized by a solid-state technique, and studied as cathode materials in Li-batteries. The influence of the Co, ...and Mn cation substitution of Fe in Li
2
FeSO on the resulting electrochemical performance was evaluated by galvanostatic cycling, while the reaction mechanism was explored by applying
operando
X-ray absorption and X-ray diffraction techniques using synchrotron radiation facilities. Even 10% Fe-substitution by these metals completely changes the structural behavior of the material upon Li-removal and insertion, in comparison to Li
2
FeSO. The Co-substitution significantly improves cyclability of the material at high current densities in comparison to the non-substituted material, reaching a specific capacity of 250 mAh/g at 1C current density. In contrast, the Mn-substitution leads to deterioration of the electrochemical performance because of the impeded kinetics, which may be caused by the appearance of a second isostructural phase due to formation of Jahn-Teller Mn
3+
cations upon delithiation.
Complex perovskite La2(Al1/2MgTa1/2)O6 (LAMT) crystallizes in a monoclinic unit cell with space group P21/n at room temperature. Its B-site cations are ordered in a rock-salt-type arrangement. ...Previously, the full occupancy of Mg on the 2c-Wyckoff position was deduced from powder X-ray diffraction (PXRD). However, conventional X-rays could not properly resolve the mixed occupation on the B-site, since there is little scattering contrast between the neighbouring elements Mg and Al of the periodic table. Hence, complementary neutron diffraction studies were carried out to verify the exact B-site cation ordering in the unit cell. In this specific configuration of the B-cations, with its occupancy ratio and the presence of a heavy element Ta as well as neighbouring elements Mg and Al, only the strategy of a combined Rietveld analysis using both the X-ray and neutron diffraction data simultaneously succeeded in elucidating an accurate B-site cation ordering in this complex perovskite system. A full occupancy of Mg on the 2c-Wyckoff position and each a half occupancy of Al and Ta on the 2d-Wyckoff position could be resolved for the rock-salt-type ordering of the B-site cations in the monoclinic unit cell of LAMT.
Single‐phase samples of the compounds K8Al8Si38 (1), Rb8Al8Si38 (2), and Cs7.9Al7.9Si38.1 (3) were obtained with high crystallinity and in good quantities by using a novel flux method with two ...different flux materials, such as Al and the respective alkali‐metal halide salt (KBr, RbCl, and CsCl). This approach facilitates the removal of the product mixture from the container and also allows convenient extraction of the flux media due to the good solubility of the halide salts in water. The products were analyzed by means of single‐crystal X‐ray structure determination, powder X‐ray and neutron diffraction experiments, 27Al‐MAS NMR spectroscopy measurements, quantum chemical calculations, as well as magnetic and transport measurements (thermal conductivity, electrical resistivity, and Seebeck coefficient). Due to the excellent quality of the neutron diffraction data, the difference between the nuclear scattering factors of silicon and aluminum atoms was sufficient to refine their mixed occupancy at specific sites. The role of variable‐range hopping for the interpretation of the resistivity and the Seebeck coefficient is discussed.
It takes two: A large‐scale synthesis of clathrate compounds is described by the reaction of an arc‐melted aluminum–silicon alloy with alkali metals in alkali‐metal halide flux media. The Si/Al ratios are determined by using X‐ray and neutron diffraction as well as 27Al‐MAS NMR spectroscopy methods. The three materials A8Al8Si38 (A=K, Rb, and Cs) are further characterized by magnetic and transport measurements.
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