Metal selenides have caused widespread concern due to their high theoretical capacities and appropriate working potential; however, they suffer from large volume variation during cycling and low electrical conductivity, which limit their practical applications. In this article, a three-dimensional (3D) porous carbon framework embedded with homogeneous FeSe 2 nanoparticles (3D porous FeSe 2 /C composite) was synthesized by a facile calcined approach, following a selenized method without a template. As the uniformity of FeSe 2 nanoparticles and 3D porous structure are beneficial to accommodate volume stress upon cycling and shorten electrons/ions transport path, associated with carbon as a buffer matrix for increasing conductivity, the 3D porous FeSe 2 /C composite displays excellent electrochemical properties with high reversible capacities of 798.4 and 455.0 mA h g −1 for lithium-ion batteries and sodium-ion batteries, respectively, when the current density is 100 mA g −1 after 100 cycles. In addition, the as-prepared composite exhibits good cycling stability as compared to bare FeSe 2 nanoparticles. Therefore, the facile synthetic strategy in the current work provides a new perspective in constructing a high-performance anode.
Polyoxometalate (POM) as an "electronic sponge" can store a great number of electrons; however, shortcomings of poor conductivity and solubility in electrolytes cause a significant decrease in specific capacity and poor rate capability. To address the aforementioned disadvantages, a dual strategy was proposed, including coating the conductive polypyrrole (PPy) and utilizing nitrogenous ligands (1,10-phenanthroline monohydrate = 1,10-phen) for metal−organic frameworks (MOFs) to fabricate a [Cu(1,10-phen)(H 2 O) 2 ] 2 [Mo 6 O 20 ]@PPy (Cu-POMOF@PPy) composite, effectively confining the POM in MOFs to avoid dissolution of POM in the electrolyte and improve electrochemical stability. Simultaneously, the PPy shell could improve the conductivity, contribute extra capacity, and alleviate volume variation of Cu-POMOF during cycling. Therefore, the final Cu-POMOF@PPy composite provides an excellent specific capacity of around 769 mA h g −1 at 0.1 A g −1 after 160 cycles and good rate performance, associated with great cycling stability (319 mA h g −1 at 2 A g −1 after 500 cycles). Moreover, the electrochemical reaction mechanism of Cu-POMOF@PPy was investigated by ex situ XPS measurements, indicating that storage of electrons results from the reduction/oxidation of Mo atoms (Mo 6+ ↔ Mo 4+ ) and Cu atoms (Cu 2+ ↔ Cu 0 ). As a consequence, this work not only proposes a novel method for preparing POM-based lithium-ion batteries but also expands the variety of anode materials.
A promising anode material composed of SnS2@CoS2 flower-like spheres assembled from SnS2 nanosheets and CoS2 nanoparticles accompanied by reduced graphene oxide (rGO) was fabricated by a facile hydrothermal pathway. The presence of rGO and the combined merits of SnS2 and CoS2 endow the SnS2@CoS2–rGO composite with high conductivity pathways and channels for electrons and with excellent properties as an anode material for sodium-ion batteries (SIBs). A high capacity of 514.0 mAh g−1 at a current density of 200 mA g−1 after 100 cycles and a good rate capability can be delivered. The defined structure and good sodium-storage performance of the SnS2@CoS2–rGO composite demonstrate its promising application in high-performance SIBs.Electronic supplementary materialThe online version of this article (10.1007/s40820-018-0200-x) contains supplementary material, which is available to authorized users.
CoO-Co nanocomposite films were successfully deposited at room temperature by pulsed laser deposition as an anode material for lithium-ion batteries. The prepared nanocomposite exhibited enhanced performance, such as excellent cycling stability (830 mA h g -1 at a specific current of 500 mA g -1 after 200 cycles) and high rate capability (578 mA h g -1 at 10000 mA g -1 ). The outstanding electrochemical performance can be ascribed to the nanocrystalline structure of CoO and the presence of Co nanoparticles, which could sustain high strain, enhance reaction kinetics and improve conductivity.
Transition-metal
phosphides have a potential application in lithium-ion
batteries (LIBs) because of their high theoretical capacities and
low cost; nevertheless, they possess dramatic volumetric variation
during cycling associated with poor conductivity, limiting their practical
applications. Here, a three-dimensional (3D) hierarchical flowerlike
FeP coated with nitrogen-doped carbon layer (FeP@N,C hybrid) was constructed
through a solvothermal method, followed by a phosphating approach
under low temperature. N-doped carbon not only suppresses the volume
fluctuation of FeP, but also promotes electron transfer, accompanied
by catalyzing the decomposition of Li3P to improve the
reversibility of the FeP@N,C hybrid during cycling processes. In addition,
a 3D flowerlike architecture assembled from porous nanosheets is also
beneficial for shortening the migration path of ions as well as improving
the contact area of electrode with electrolyte, which enhances the
reaction kinetics and is proved by both experimental measurement of
Li+ diffusion coefficient and resistivity, along with the
calculation of density functional theory. Consequently, the 3D hierarchical
flowerlike FeP@N,C hybrid performs excellent cyclic stability (569
mA h g–1 at a current density of 500 mA g–1 for the 300th cycle) and rate performance (331.94 mA h g–1 at a high current density of 5 A g–1) for LIBs.
Based on above results, the fabrication strategy in this work could
offer a thought to design other high-performance metal phosphide hybrids.
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