Hollow SnS/TiO2@C nanospheres with high-performance originating from the built-in electric field introduced by SnS/TiO2 heterostructures for fast ion diffusion.
Hierarchical CoFeO (CFO) hollow spheres were successfully synthesized via solvothermal method and calcination treatment. The obtained CFO completely inherited the hollow structure and spherical morphology of its precursor of cobalt-based ferrocenyl coordination polymers (Co-Fc-CPs). The three-dimensional (3D) porous hierarchical hollow structure can not only promote the permeation of electrolyte and shorten the lithium-ion transfer distance but also provide a cushion for the volume change during insertion/extraction of lithium ions. To improve the electrochemical properties, the CFO was combined with two forms of carbonaceous materials to controllably obtain 3D CoFeO@C (CFO@C) and CoFeO@reduced graphene oxide (CFO@rGO) composites. Compared with bare CFO and CFO@C, CFO@rGO exhibited a superior electrochemical performance, achieving a high specific capacity of 933.1 mA h g at a current density of 100 mA g after 100 cycles and showing an outstanding cycling life with a capacity of 615.6 mA h g at 1000 mA g after 600 cycles. In situ X-ray diffraction technique was applied to investigate the lithium storage mechanism during discharge/charge processes. This work provides a new approach to prepare hierarchical hollow bimetallic oxides composites for lithium-ion anode materials.
The development of advanced hierarchical anode materials
has recently
become essential to achieving high-performance sodium-ion batteries.
Herein, we developed a facile and cost-effective scheme for synthesizing
graphene-wrapped, nitrogen-rich carbon-coated iron sulfide nanofibers
(FeS@NCG) as an anode for SIBs. The designed FeS@NCG can provide a
significant reversible capacity of 748.5 mAh g–1 at 0.3 A g–1 for 50 cycles and approximately 3.9-fold
higher electrochemical performance than its oxide analog (Fe2O3@NCG, 192.7 mAh g–1 at 0.3 A g–1 for 50 cycles). The sulfur- and nitrogen-rich multilayer
package structure facilitates efficient suppression of the porous
FeS volume expansion during the sodiation process, enabling a long
cycle life. The intimate contact between graphene and porous carbon-coated
FeS nanofibers offers strong structural barriers associated with charge-transfer
pathways during sodium insertion/extraction. It also reduces the dissolution
of polysulfides, enabling efficient sodium storage with superior stable
kinetics. Furthermore, outstanding capacity retention of 535 mAh g–1 at 5 A g–1 is achieved over 1010
cycles. The FeS@NCG also exhibited a specific capacity of 640 mAh
g–1 with a Coulombic efficiency of above 99.8% at
5 A g–1 at 80 °C, indicating its development
prospects in high-performance SIB applications.
Due to their high theoretical capacities, metal sulfides have been considered as promising electrode materials for lithium‐ion batteries (LIBs). Heavy‐duty applications of metal sulfides for LIBs, however, are still restricted by the unavoidable volume change, resulting in poor rate capability and cycling stability. In this work, a Ni−Co‐ZIF derived Ni0.2Co0.8S hollow nanocage@reduced graphene oxide (Ni0.2Co0.8S@rGO) composite was fabricated through facile self‐assembly followed by freeze‐drying. The highly porous architecture of Ni0.2Co0.8S hollow nanocages wrapped by flexible reduced graphene oxide (rGO) is shown to not only validly inhibit the huge volume expansion during repeated charge/discharge cycling, but also accelerate lithium‐ion and electron transport through the 3D rGO network. The as‐obtained Ni0.2Co0.8S@rGO exhibits excellent electrochemical performance with a high specific capacity of 1585 mA h g−1 after 250 cycles at a current density of 1 A g−1. It is shown that the increasing reversible capacity during cycling can be attributed to the electrochemical activation of porous Ni0.2Co0.8S‐2.5@rGO, the pseudocapacitive behavior, and the highly reversible formation/decomposition of the solid electrolyte interface layer during lithiation/de‐lithiation. The sulfidation and reduction syntheses were operated at a relative low temperature of 90 °C, which is beneficial to inherit the unique morphology of precursor.
Unravelling the lithium-ion transport mechanism in α-Fe2O3 nanofibers through in situ electrochemical impedance studies is crucial for realizing their application in high-performance anodes in lithium-ion batteries. Herein, we report the effect of heat treatment conditions on the structure, composition, morphology, and electrochemical properties of α-Fe2O3 nanofibers as an anode for lithium-ion batteries. The α-Fe2O3 nanofibers were synthesized via electrospinning and post-annealing with differences in their annealing temperature of 300, 500, and 700 °C to produce FO300, FO500, and FO700 nanofibers, respectively. Improved electrochemical performance with a high reversible specific capacity of 599.6 mAh g−1 at a current density of 1 A g−1 was achieved after 50 cycles for FO700. The in situ electrochemical impedance spectroscopy studies conducted during the charge/discharge process revealed that the charge transfer and Li-ion diffusion behaviors were related to the crystallinity and structure of the as-synthesized α-Fe2O3 nanofibers. The surfaces of the α-Fe2O3 nanofibers were converted into Fe metal during the charging/discharging process, which resulted in improved electrical conductivity. The electron lifetime, as determined by the time constant of charge transfer, revealed that, when a conversion reaction occurred, the electrons tended to travel through the iron metal in the α-Fe2O3 nanofibers. The role of iron as a pseudo-resistor with negligible capacitance was revealed by charge transfer resistance analysis.
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