Three-dimensional mesoporous γ-Fe2O3@carbon nanofiber network as high performance anode material for lithium- and sodium-ion batteries

Constructing High-Performance Carbon Nanofiber Anodes by the Hierarchical Porous Structure Regulation and Silicon/Nitrogen Co-Doping

Due to the rapid development of bendable electronic products, it is urgent to prepare flexible anode materials with excellent properties, which play a key role in flexible lithium-ion batteries. Although carbon fibers are excellent candidates for preparing flexible anode materials, the low discharge specific capacity prevents their further application. In this paper, a hierarchical porous and silicon (Si)/nitrogen (N) co-doped carbon nanofiber anode was successfully prepared, in which Si doping can improve specific capacity, N doping can improve conductivity, and a fabricated hierarchical porous structure can increase the reactive sites, improve the ion transport rate, and enable the electrolyte to penetrate the inner part of carbon nanofibers to improve the electrolyte/electrode contacting area during the charging–discharging processes. The hierarchical porous and Si/N co-doped carbon nanofiber anode does not require a binder, and is flexible and foldable. Moreover, it exhibits an ultrahigh initial reversible capacity of 1737.2 mAh g−1, stable cycle ability and excellent rate of performance. This work provides a new avenue to develop flexible carbon nanofiber anode materials for lithium-ion batteries with high performance.

Enabling Long Cycle Life and High Rate Iron Difluoride Based Lithium Batteries by In Situ Cathode Surface Modification

Metals fluorides (MFs) are potential conversion cathodes to replace commercial intercalation cathodes. However, the application of MFs is impeded by their poor electronic/ionic conductivity and severe decomposition of electrolyte. Here, a composite cathode of FeF₂ and polymer-derived carbon (FeF₂ @PDC) with excellent cycling performance is reported. The composite cathode is composed of nanorod-shaped FeF₂ embedded in PDC matrix with excellent mechanical strength and electronic/ionic conductivity. The FeF₂ @PDC enables a reversible capacity of 500 mAh g^-1 with a record long cycle lifetime of 1900 cycles. Remarkably, the FeF₂ @PDC can be cycled at a record rate of 60 C with a reversible capacity of 107 mAh g^-1 after 500 cycles. Advanced electron microscopy reveals that the in situ formation of stable Fe₃ O₄ layers on the surface of FeF₂ prevents the electrolyte decomposition and leaching of iron (Fe), thus enhancing the cyclability. The results provide a new understanding to FeF₂ electrochemistry, and a strategy to radically improve the electrochemical performance of FeF₂ cathode for lithium-ion battery applications.

Hierarchical and Heterogeneous Porosity Construction and Nitrogen Doping Enabling Flexible Carbon Nanofiber Anodes with High Performance for Lithium-Ion Batteries

With the rapid development of flexible electronic devices, flexible lithium-ion batteries are widely considered due to their potential for high energy density and long life. Anode materials, as one of the key materials of lithium-ion batteries, need to have good flexibility, an excellent specific discharge capacity, and fast charge–discharge characteristics. Carbon fibers are feasible as candidate flexible anode materials. However, their low specific discharge capacity restricts their further application. Based on this, N-doped carbon nanofiber anodes with microporous, mesoporous, and macroporous structures are prepared in this paper. The hierarchical and heterogeneous porosity structure can increase the active sites of the anode material and facilitate the transport of ions, and N-doping can improve the conductivity. Moreover, the N-doped flexible carbon nanofiber with a porous structure can be directly used as the anode for lithium-ion batteries without adding an adhesive. It has a high first reversible capacity of 1108.9 mAh g⁻¹, a stable cycle ability (954.3 mAh g⁻¹ after 100 cycles), and excellent rate performance. This work provides a new strategy for the development of flexible anodes with high performance.

Electrospun Fe3O4-Sn@Carbon Nanofibers Composite as Efficient Anode Material for Li-Ion Batteries

Nanoscale Fe₃O₄-Sn@CNFs was prepared by loading Fe₃O₄ and Sn nanoparticles onto CNFs synthesized via electrostatic spinning and subsequent thermal treatment by solvothermal reaction, and were used as anode materials for lithium-ion batteries. The prepared anode delivers an excellent reversible specific capacity of 1120 mAh·g^-1 at a current density of 100 mA·g^-1 at the 50th cycle. The recovery rate of the specific capacity (99%) proves the better cycle stability. Fe₃O₄ nanoparticles are uniformly dispersed on the surface of nanofibers with high density, effectively increasing the electrochemical reaction sites, and improving the electrochemical performance of the active material. The rate and cycling performance of the fabricated electrodes were significantly improved because of Sn and Fe₃O₄ loading on CNFs with high electrical conductivity and elasticity.

A Bio-Inspired Nanotubular Na2MoO4/TiO2 Composite as a High-Performance Anodic Material for Lithium-Ion Batteries

A train of bio-inspired nanotubular Na₂MoO₄/TiO₂ composites were synthesized by using a natural cellulose substance (e.g., commercial ordinary filter paper) as the structural template. The TiO₂ gel films were coated on the cellulose nanofiber surfaces via a sol-gel method firstly, followed with the deposition of the poly(diallyldimethylammonium chloride)/Na₂MoO₄ (PDDA/Na₂MoO₄) bi-layers several times, through the layer-by-layer self-assembly route, yielding the (PDDA/Na₂MoO₄)_n/TiO₂-gel/cellulose composite, which was calcined in air to give various Na₂MoO₄/TiO₂ nanocomposites containing different Na₂MoO₄ contents (15.4, 24.1, and 41.4%). The resultant nanocomposites all inherited the three-dimensionally porous network structure of the premier cellulose substance, which were formed by hierarchical TiO₂ nanotubes anchored with the Na₂MoO₄ layers. When employed as anodic materials for lithium-ion batteries, those Na₂MoO₄/TiO₂ nanocomposites exhibited promoted electrochemical performances in comparison with the Na₂MoO₄ powder and pure TiO₂ nanotubes, which was resulted from the high capacity of the Na₂MoO₄ component and the buffering effects of the TiO₂ nanotubes. Among all the nanotubular Na₂MoO₄/TiO₂ composites, the one with a Na₂MoO₄ content of 41.4% showed the best electrochemical properties, such as the cycling stability with a capacity of 180.22 mAh g⁻¹ after 200 charge/discharge cycles (current density: 100 mA g⁻¹) and the optimal rate capability.

Superior lithium-storage properties derived from a g-C3N4-embedded honeycomb-shaped meso@mesoporous carbon nanofiber anode loaded with Fe2O3 for Li-ion batteries

In this work, a honeycomb-shaped meso@mesoporous carbon nanofiber material incorporating homogeneously dispersed ultra-fine Fe2O3 nanoparticles (denoted as Fe2O3@g-C3N4@H-MMCN) is synthesised through a pyrolysis process. The honeycomb-shaped configuration of the meso@mesoporous carbon nanofiber material derived from a natural bio-carbon source (crab shell) acts as a support for an anode material for Li-ion batteries. Graphitic carbon nitride (g-C3N4) is produced via the one-step pyrolysis of urea at high temperature under an N2 atmosphere without the assistance of additives. The resulting favorable electrochemical performance, with superior rate capabilities (1067 mA h g-1 at 1000 mA g-1), a remarkable specific capacity (1510 mA h g-1 at 100 mA g-1), and steady cycling performance (782.9 mA h g-1 after 500 cycles at 2000 mA g-1), benefitted from the advantages of both the host material and the Fe2O3 nanoparticles, which play an important role due to their ultra-fine particle size of 5 nm. The excellent cycle life and high capacity demonstrate that this strategy of strong synergistic effects represents a new pathway for pursuing high-electrochemical-performance materials for lithium-ion batteries.

Structural design toward functional materials by electrospinning: A review

Electrospinning as one of the most versatile technologies have attracted a lot of scientists’ interests in past decades due to its great diversity of fabricating nanofibers featuring high aspect ratio, large specific surface area, flexibility, structural abundance, and surface functionality. Remarkable progress has been made in terms of the versatile structures of electrospun fibers and great functionalities to enable a broad spectrum of applications. In this article, the electrospun fibers with different structures and their applications are reviewed. First, several kinds of electrospun fibers with different structures are presented. Then the applications of various structural electrospun fibers in different fields, including catalysis, drug release, batteries, and supercapacitors, are reviewed. Finally, the application prospect and main challenges of electrospun fibers are discussed. We hope that this review will provide readers with a comprehensive understanding of the structural design and applications of electrospun fibers in different fields.