Explore the vast range of titles available.

FeSe2 is an attractive anode candidate for lithium-ion batteries (LIBs) owing to its high theoretical capacity based on a unique conversion mechanism and low cost. However, the practical application of FeSe2 is hindered by the fast capacity attenuation and the poor ion/electron transfer kinetics. Herein, a yolk-shell N-doped graphene-embedded hollow FeSe2 nanocube/carbon composite (NG/FeSe2/C) is designed to address these issues, which exhibits high specific capacity and outstanding rate performance in half cells. The interaction mechanism between FeSe2 and NG is systematically investigated by combining spectral characterizations, electrochemical measurements, and density functional theory calculations, revealing that NG enhances the electrical conductivity, elongates the Fe-Se bond, and decreases the valence of Fe species in FeSe2 by delocalizing the charge distribution of Se, which are essential to high initial Coulombic efficiency and fast reaction kinetics. Moreover, the practicality of NG/FeSe2/C in a full cell is demonstrated by pairing it with a commercial LiNi0.5Mn0.3Co0.2O2 cathode, showing high capacity and acceptable electrochemical performance. This work could offer guidance for the design of high-performance conversion-type anode materials for LIBs. N-doping induces delocalized charge distribution in the NG/FeSe2/C hetero-interface and enables the yolk-shell NG/FeSe2/C nanostructure with decreased Fe valence and elongated Fe-Se bond, demonstrating superior electrochemical performance. [Display omitted]

Rechargeable magnesium (Mg)-based energy storage has attracted extensive attention in electrochemical storage systems with high theoretical energy densities. The Mg metal is earth-abundant and dendrite-free for the anode. However, there is a strong Coulombic interaction between Mg2+ and host materials that often inhibits solid-state diffusion, resulting in a large polarization and poor electrochemical performances. Herein, we develop a Mg–Li hybrid battery using a Mg-metal anode, an FeSe2 powder with uniform size and a morphology utilizing a simple solution-phase method as the counter electrode and all-phenyl-complex/tetrahydrofuran (APC)-LiCl dual-ion electrolyte. In the Li+-containing electrolyte, at a current density of 15 mA g−1, the Mg–Li hybrid battery (MLIB) delivered a satisfying initial discharge capacity of 525 mAh g−1. Moreover, the capacity was absent in the FeSe2|APC|Mg cell. The working mechanism proposed is the “Li+-only intercalation” at the FeSe2 and the “Mg2+ dissolved or deposited” at the Mg foil in the FeSe2|Mg2+/Li+|Mg cell. Furthermore, ex situ XRD was used to investigate the structural evolution in different charging and discharging states.

Iron-based anode materials, such as Fe2O3 and FeSe2 have attracted widespread attention for lithium-ion batteries due to their high capacities. However, the capacity decays seriously because of poor conductivity and severe volume expansion. Designing nanostructures combined with carbon are effective means to improve cycling stability. In this work, ultra-small Fe2O3 nanoparticles loaded on a carbon framework were synthesized through a one-step thermal decomposition of the commercial C15H21FeO6 [Iron (III) acetylacetonate], which could be served as the source of Fe, O, and C. As an anode material, the Fe2O3@C anode delivers a specific capacity of 747.8 mAh g−1 after 200 cycles at 200 mA g−1 and 577.8 mAh g−1 after 365 cycles at 500 mA g−1. When selenium powder was introduced into the reaction system, the FeSe2 nano-rods encapsulated in the carbon shell were obtained, which also displayed a relatively good performance in lithium storage capacity (852 mAh g−1 after 150 cycles under the current density of 100 mA·g−1). This study may provide an alternative way to prepare other carbon-composited metal compounds, such as FeNx@C, FePx@C, and FeSx@C, and found their applications in the field of electrochemistry.

Sodium-ion batteries （SIBs） have great promise for sustainable and economicalenergy-storage applications. Nevertheless, it is a major challenge to developanode materials with high capacity, high rate capability, and excellent cyclingstability for them. In this study, FeSe2 clusters consisting of nanorods weresynthesized by a facile hydrothermal method, and their sodium-storage propertieswere investigated with different electrolytes. The FeSe2 clusters delivered highelectrochemical performance with an ether-based electrolyte in a voltage rangeof 0.5-2.9 V. A high discharge capacity of 515 mAh.g-1 was obtained after 400 cyclesat 1 A.g-1, with a high initial columbic efficiency of 97.4%. Even at an ultrahighrate of 35 A-g-1 a specific capacity of 128 mAh.g-1 was achieved. Using calculations,we revealed that the pseudocapacitance significantly contributed to the sodium-ionstorage, especially at high current rates, leading to a high rate capability. Thehigh comprehensive performance of the FeSe2 clusters makes them a promisinganode material for SIBs.

Some transition-metal dichalcogenides have been actively studied recently owing to their potential for use as thermoelectric materials due to their superior electronic transport properties. Iron-based chalcogenides, FeTe2, FeSe2 and FeS2, are narrow bandgap (~1 eV) semiconductors that could be considered as cost-effective thermoelectric materials. Herein, the thermoelectric and electrical transport properties FeSe2–FeS2 system are investigated. A series of polycrystalline samples of the nominal composition of FeSe2−xSx (x = 0, 0.2, 0.4, 0.6, and 0.8) samples are synthesized by a conventional solid-state reaction. A single orthorhombic phase of FeSe2 is successfully synthesized for x = 0, 0.2, and 0.4, while secondary phases (Fe7S8 or FeS2) are identified as well for x = 0.6 and 0.8. The lattice parameters gradually decrease gradually with S content increase to x = 0.6, suggesting that S atoms are successfully substituted at the Se sites in the FeSe2 orthorhombic crystal structure. The electrical conductivity increases gradually with the S content, whereas the positive Seebeck coefficient decreases gradually with the S content at 300 K. The maximum power factor of 0.55 mW/mK2 at 600 K was seen for x = 0.2, which is a 10% increase compared to the pristine FeSe2 sample. Interestingly, the total thermal conductivity at 300 K of 7.96 W/mK (x = 0) decreases gradually and significantly to 2.58 W/mK for x = 0.6 owing to the point-defect phonon scattering by the partial substitution of S atoms at the Se site. As a result, a maximum thermoelectric figure of merit of 0.079 is obtained for the FeSe1.8S0.2 (x = 0.2) sample at 600 K, which is 18% higher than that of the pristine FeSe2 sample.

We conducted an in situ crystal structure analysis of ferroselite at non-ambient conditions. The aim is to provide a solid ground to further the understanding of the properties of this material in a broad range of conditions. Ferroselite, marcasite-type FeSe2, was studied under high pressures up to 46 GPa and low temperatures, down to 50 K using single-crystal microdiffraction techniques. High pressures and low temperatures were generated using a diamond anvil cell and a cryostat respectively. We found no evidences of structural instability in the explored P-T space. The deformation of the orthorhombic lattice is slightly anisotropic. As expected, the compressibility of the Se-Se dumbbell, the longer bond in the structure, is larger than that of the Fe-Se bonds. There are two octahedral Fe-Se bonds, the short bond, with multiplicity two, is slightly more compressible than the long bond, with multiplicity four; as a consequence the octahedral tetragonal compression slightly increases under pressure. We also achieved a robust structural analysis of ferroselite at low temperature in the diamond anvil cell. Structural changes upon temperature decrease are small but qualitatively similar to those produced by pressure.