N-doped Carbon Fibers Research Articles

Kilogram-Scale Synthesis and Functionalization of Carbon Dots for Superior Electrochemical Potassium Storage.

Carbon dot is a type of carbon material with an ultrasmall size of less than 10 nm for all three dimensions, which has attracted more and more attention due to its useful merits. Unfortunately, the complicated synthesis method and low yield largely limit its wide large-scale application. Herein, an inexpensive and high-efficiency aldol condensation method under ambient temperature and pressure was proposed for the large-scale synthesis of CDs, which can obtain products with 1.083 kg in 2 h and realize the functionalization of carbon dots doped with nitrogen (NCDs) and sulfur/nitrogen doubly (NSCDs), and then the mechanism and structure of CDs formation were explained. Moreover, utilizing the feature of controllable assembly of carbon dots, and combined with theoretical calculations, we have designed functionalized 1D carbon fibers (CF) to construct high-performance potassium storage anode materials through the assembly of carbon dots induced by a Zn compound. Benefitting from the microstructure and surface functional groups derived from CDs, the N-doped CF (NCF700) exhibits superior electrochemical energy storage performance for potassium ion batteries (PIBs). This study provides a low-cost and high-yield method to produce CDs and promotes the practical application of CDs in electrochemical energy storage.

N-doped hollow carbon nanoparticles encapsulated fibers derived from ZIF-8 self-sacrificed template for advanced lithium–sulfur batteries

Abstract The facile synthesis of sulfur scaffold with high electrical conductivity and strong polysulfide immobilization capability plays an important role in developing high-performance lithium sulfur batteries. Here a new type of porous N-doped carbon fiber consisting of hollow carbon nanoparticles (9 wt%-CF) is designed as sulfur scaffold through electrospinning and carbonization processes with ZIF-8 and polyacrylonitrile as precursors. The carbon fiber skeleton can provide high electrical conductivity, and interconnected hollow particles provide ample space to host active materials and to immobilize polysulfides. Moreover, the N-doping further improves the interaction between 9 wt%-CF and polysulfides. Consequently, the as-prepared 9 wt%-CF/S cathode delivers an initial discharge capacity of 1524 mAh g−1 at 0.1 C and high capacity retention of 83% after 200 cycles charge/discharge at 0.5 C with a sulfur loading of 1.9 mg cm−2.

Co-Ni alloy nanoparticles supported by carbon nanofibers for hydrogen evolution reaction

Abstract Alloying, a general strategy to improve the electrocatalytic performance of non-precious metal catalysts. Herein, we adopt a simple method to in-situ grow a cobalt-nickel alloy on a three-dimensional network of N-doped carbon fibers that put spatial restriction to the alloy particles, making the size smaller and uniformly distributed. The electronic synergy between nickel and cobalt and the confinement effect of in-situ growth can make Co-Ni/NCNFs provide more feasible reaction sites for catalytic hydrogen evolution reaction. Simultaneously, the formation of cobalt-nickel alloys inhibits the generation of oxides during the synthesis process, so as to promote the quality of alloys with better activity. Co-Ni/NCNFs exhibits excellent electrocatalytic properties with only 61 mV overpotential and 152.3 dec−1 at 10 mA cm−2 current density and excellent long-term stability due to the in-situ growth approach. This research also provides a feasible method for designing self-supporting alloy catalysts by in-situ growth.

Dendrite-free lithium metal anode enabled by ion/electron-conductive N-doped 3D carbon fiber interlayer

Lithium metal is considered as the ultimate anode candidate for next-generation high-energy storage systems due to its ultrahigh specific capacity and low reduction potential. However, the practical application of lithium metal anode is severely impeded by uncontrollable lithium dendrite growth. In this work, a three-dimensional (3D) N-doped carbon fiber (NCF) network with ion/electron-conductivity has been fabricated by electrospinning the polyacrylonitrile solution and subsequent thermal treatment. The 3D NCF as an interlayer covering on the lithium anode is used to regulate the lithium plating/stripping behavior, accommodating partially deposited Li to realize lithium dendrite-free deposition on the lithium anode. Benefiting from these, the symmetrical cell of Li anode protected by NCF (Li@NCF) delivers long duration time (>1200 h) with a low initial nucleation overpotential (30 mV) at the current density of 1 mA cm−2. In addition, the full cell of Li@NCF||LiFePO4 exhibits excellent capacity retention of 114.6 mAh cm−2 over 360 cycles at the current density of 1 C. This strategy contributes a step forward for dendrite-free lithium metal batteries.

NiSe2/Ni5P4 nanosheets on nitrogen-doped carbon nano-fibred skeleton for efficient overall water splitting

Combining a variety of factors to optimize the performances of electrocatalysts has become a new breakthrough for the development of low-cost electrolytic catalysts. In this work, we constructed N-doped carbon fibers as the substrate, which could provide high electronic conductivity and large surface area for the load of active catalysts, as well as close incorporation. The nanosheets morphology of NiSe2/Ni5P4 is conducive to enlarging the specific surface area and exposing more active sites. The electrical conductivity is improved by the selenide and carbon nano-fiber substrate. The multiple features, including the unique structure characteristics, heterostructure of NiSe2 and Ni5P4, and high electroconductivity, endow NiSe2/Ni5P4 with superior catalytic activity towards water splitting. As a result, the overpotentials at the cathode current density of 10 and 100 mA cm−2 upon NiSe2/Ni5P4 nanosheets are 112 and 350 mV in 0.5 M H2SO4. For oxygen evolution reaction (OER), the overpotential of NiSe2/Ni5P4 nanosheets at a current density of 10 mA cm−2 in alkaline electrolyte is 316 mV. Furthermore, the bifunctional NiSe2/Ni5P4 nanosheets exhibit excellent working stability for both HER, OER and overall water splitting, showing potential application in hydrogen energy.

Rationalized atomic/clusters dispersion of Fe/Se/Al on interconnected N-doped carbon nanofibers for fast sodiation

The greater availability of sodium with large storage capacity motivates the fabrication of advanced electrodes materials for sodium ion batteries (SIBs) to promote in potential market of smart appliances. Multiple metals atomic dispersion into carbon framework can enhance the adsorption property of sodium for high performance SIBs. In this work, rationalized atomic/clusters of Fe/Se/Al are dispersed on N-doped amorphous carbon fibers through electrospinning and direct selenization (DS) processes. The developed product of DS-Fe/Se/Al@NC-650 nanofibers are employed as anode materials of SIBs, exhibitinga high specific capacity of 432 mAh g−1 at 100 mA g−1 a desirable cycling stability with a capacity retention of 99 % after 700 cycles. Such an excellent storage capacity initiates through synergistic effects of the uniformly distributed Fe/Se/Al and the interconnected nitrogen-doped carbon network. For the apprehension of capacity and stability of DS-Fe/Se/Al@NC-650 nanofibers for SIBs, the theoretical calculations were carried out and provide strong evidences which proves the electron/ion transport in experimental results.

Centrifugally spun SnSb nanoparticle/porous carbon fiber composite as high-performance lithium-ion battery anode

A SnSb alloy nanoparticle/porous carbon fiber (PCF) composite was prepared using a novel centrifugal spinning technology with subsequent thermal treatment. In SnSb/PCF composite, the SnSb nanoparticles are uniformly distributed in N-doped carbon fiber matrix due to the created porous structure. The centrifugal spinning can significantly increase the production rate of the fiber composites and the as-prepared SnSb/PCF composite demonstrated small particle size with uniform distribution, mesoporous structure which can facilitate the diffusion of electrolyte and N-doped carbon matrix that is beneficial to the acceleration of the electron transfer. Consequently, SnSb@CFs-20 exhibits a promising electrochemical performance in lithium storage.

An enhanced electrochemical CO2 reduction reaction on the SnOx–PdO surface of SnPd nanoparticles decorated on N-doped carbon fibers

Electrochemical reduction of CO2 to formate on SnPd–NCF. The adsorbed bicarbonate ion promotes the protonation of CO2˙− to HCO2−.

Synergy between copper and iron sites inside carbon nanofibers for superior electrocatalytic denitrification.

Developing low-cost electrocatalysts for the nitrate reduction reaction (NO3RR) with superior performance is of great significance for wastewater treatment. Herein, we synthesized bimetal Cu/Fe nanoparticles encased in N-doped carbon nanofibers (Cu/Fe@NCNFs) through simple electrospinning followed by a pyrolysis reduction strategy. Metallic copper is beneficial for reducing nitrate to nitrite, and the existence of Fe is conducive to convert nitrate and nitrite into nitrogen. Additionally, the nitrogen-doped carbon nanofibers also facilitate the adsorption of nitrate, and the continuous and complete fiber structure enhances the stability of the catalyst and prevents the corrosion of the active sites. Therefore, the synergetic effect of bimetal Cu/Fe and N-doped carbon fiber plays a key role in promoting the efficiency of nitrate reduction. The obtained Cu/Fe@NCNF catalyst exhibits a satisfactory nitrate conversion efficiency of 76%, removal capacity of 5686 mg N g-1 Cu/Fe and nitrogen selectivity of 94%.

Hollow Porous CoSnOx Nanocubes Encapsulated in One-Dimensional N-Doped Carbon Nanofibers as Anode Material for High-Performance Lithium Storage.

CoSnO3, as a high theoretical capacity electrode material (1235 mAh g-1) for lithium storage, has been limited due to its low rate performance, huge volume expansion, and an unstable solid electrolyte interface (SEI). A rational design of the material structure including carbon coating can effectively solve the problems. To buffer the volume change and achieve a superior rate capability, hollow CoSnOx nanocubes encapsulated in 1D N-doped carbon nanofibers (CNFs) were fabricated by electrospinning, showing a final discharge capacity of 733 mAh g-1 with a 96% capacity retention after 800 cycles at a current rate of 1 A g-1 and a brilliant rate performance (49% capacity maintenance with the current variation from 0.1 to 5 A g-1). Absolutely, these outstanding characteristics are ascribed to the unique structure. The N-doped carbon fibers outside not only prevent the volume expansion during Li+ intercalation/extraction but also improve the electron transport in the electrode. Most significantly, the hollow structure offers enough vacant space to buffer the internal strain, while the porous structure shortens the Li+ diffusion distance. Combined with electrospinning technology, this study shares a novel idea for designing various composites with rational structures and outstanding electrochemical properties.

Active MoSx Nanoparticle Pillars Embedded in Reduced Graphene Oxide As Anode Materials for High Performance Na-Ion Batteries

As the use of large-scale energy storage devices (i.e. electric vehicles, smart grids.) are increased in recent years, research on the energy storage system is constantly being developed.1 Li-ion batteries are extensively used for energy applications. However, there are some obstacles to its application to large-scale energy systems, such as the limited lithium resources, unstable supply, and cost issues.2 Na-ion batteries have been considered as one of the most promising alternative to Li-ion batteries owing to the low-cost and abundance of sodium element. However, the ionic radius of Na+ (1.06 Å) is larger than Li+ (0.76 Å).3 It leads to severe structural deformation of electrode materials, accompanied by phase change or structural pulverization during cycling.4 To effectively accommodate the larger Na ion into the electrode structure and enhance the cell performance, we need to find suitable anode material for Na-ion batteries. There have been many attempts to develop the carbonaceous electrode materials for Na-ion batteries such as hard carbon, N-doped porous carbon fiber, and expanded graphite.5 , 6 Among them, the expanded graphite alternative could be a good choice due to (i) extended interlayer space for proper accommodation of large Na ions and (ii) stable structural feature with long range order for sufficient stress relaxation during Na intercalation. However, side-reactions between Na ions and a lot of anion pillars (e.g. epoxide and hydroxyl) are often found in the carbon layers, resulted in degradation of the cell performances. Therefore, proper pillar candidate should be introduced to optimize the expanded graphite anode for high performance Na-ion batteries.A representative layered 2-D molydisulfide (MoS2) has been recognized as a promising anode material for Na-ion batteries.7 The MoS2 materials operate via intercalation of sodium at the beginning and a subsequent four-electron conversion reactions.8 The S-Mo-S layer are stacked by van der Waals forces, providing a large interlayer spacing. The large interlayer spacing of MoS2 (~6.2 Å vs. 3.4 Å of graphite) could allow facile transport of Na+ during initial intercalation reaction.9 However, MoS2 has low electronic conductivity and internal strain during sodiation/desodiation. Therefore, many strategies have been considered to develop the cell performance with tailored design, morphology control, (nanocomposite, core-shell structure etc.), and hybridization with carbon materials (carbon nanofibers, amorphous carbon etc.)10 , 11.In this presentation, we introduce the expanded graphite material employing MoSx as bi-functional conversion reaction anode and pillar species between graphite interlayers. The MoSx-expanded graphite anode material synthesized via self-assembly of poly-cationic molybdenum-sulfide source and negatively charged graphite oxide flakes. We demonstrate that the morphological and structural changes of crystalline MoSx pillars under the different thermal temperature in reduction conditions. We attempt to solve the irreversible capacity problems by chemically forming SEI-layer on the electrode surface. We also elucidate the electrochemical reaction mechanisms and structural changes during charge/discharge reaction. M. D. Slater, D. Kim, E. Lee and C. S. Johnson, Adv Funct Mater, 2013, 23, 947-958.Y. Kim, K. H. Ha, S. M. Oh and K. T. Lee, Chem-Eur J, 2014, 20, 11980-11992.Y. Li, Y. Liang, F. C. R. Hernandez, H. D. Yoo, Q. An and Y. Yao, Nano Energy, 2015, 15, 453-461.J. H. Li, H. K. Wang, W. Wei and L. J. Meng, Nanotechnology, 2019, 30.E. Edison, S. Sreejith, C. T. Lim and S. Madhavi, Sustain Energ Fuels, 2018, 2.Y. Wen, K. He, Y. J. Zhu, F. D. Han, Y. H. Xu, I. Matsuda, Y. Ishii, J. Cumings and C. S. Wang, Nat Commun, 2014, 5.J. F. Mao, T. F. Zhou, Y. Zheng, H. Gao, H. K. Liu and Z. P. Guo, J Mater Chem A, 2018, 6, 3284-3303.R. Wang, S. Wang, Y. Zhang, D. Jin, X. Tao and L. Zhang, Nanoscale, 2018, 10, 11165-11175.W. H. Ryu, J. W. Jung, K. Park, S. J. Kim and I. D. Kim, Nanoscale, 2014, 6, 10975-10981.T. S. Sahu and S. Mitra, Sci Rep-Uk, 2015, 5.H. Hou, X. Qiu, W. Wei, Y. Zhang and X. Ji, Adv Energy Mater, 2017, 7, 1602898.

Spontaneously rooting carbon nanotube incorporated N-doped carbon nanofibers as efficient sulfur host toward high performance lithium-sulfur batteries

Lithium-sulfur (Li-S) battery is considered as a promising alternative for the development of battery technologies. However, shuttling behavior and sluggish reaction kinetics still impede its further development. Herein, we report a novel sulfur host material with 3D nanoporous structure consisting of Co3O4 nanoparticles and spontaneously rooting carbon nanotubes on N-doped carbon fibers (Co3O4-CNT@NCFs) to inhibit shuttling effect and promote catalytic kinetics. Both experimental and theoretical analyses show that the rooting CNT incorporated NCFs hierarchical structure establishes a conductive network favoring both long- and shot-range electron transfer. Besides, the highly polar and electrocatalytically Co3O4 nanoparticles offer improved interactions with polysulfides and exhibit enhanced catalysis performance, which mitigates the shuttling effect in sulfur cathode and promotes LiPS conversion kinetics. Benefiting from these unique superiorities, the S/Co3O4-CNT@NCFs cathode can efficiently promote and stabilize the sulfur electrochemistry, thus enabling outstanding alternative for high performance Li-S battery (682.1 mAh g−1 at 5.0 C and capacity fading rate of 0.056% over 700 cycles).

Free-standing N-doped hollow carbon fibers as high-performance anode for potassium ion batteries

A novel hierarchical architecture—N-doped hollow carbon fibers decorated with N-doped carbon clusters (NHCF@NCC)—was synthesized for high-performance anode material of potassium ion batteries (PIBs). The material is formulated with porous N-doped hollow carbon fibers as the backbone, which effectively shortens the diffusion length of potassium ion and increases the interface between the electrode and electrolyte. In addition, the N-doped carbon clusters attached on the hollow carbon fibers can provide abundant reactive sites. Specially, NHCF@NCC could form a free-standing electrode with a three dimensional interconnected conductive network owing to the ultrahigh aspect ratio. In this way, NHCF@NCC delivers an excellent electrochemical performance as free-standing anode materials of PIBs, exhibiting a high reversible capacity of 310 mA h g−1 at a current density of 100 mA g−1, a long cycling stability of 1000 cycles with negligible degradation, and a superior rate performance of 153 mA h g−1 at a large current density of 2000 mA g−1.

MnSe nanoparticles encapsulated into N-doped carbon fibers with a binder-free and free-standing structure for lithium ion batteries

Poor electrical conductivity and large volume changes are two disadvantages of metal selenides. In this work, MnSe nanoparticles encapsulated into N-carbon fibers are designed and prepared using electrospinning and calcination methods. When calcined at 700 °C, the composite has a high reversible capacity of 684 mAh g−1 after 100 cycles at 0.1 A g−1, owing to the improved conductivity and protection provided by carbon fibers. Furthermore, the in situ electrochemical impedance measurements reveal the process kinetics of the composites. This work will provide the basis for the further development of the application of metal selenides in the field of flexible electrodes.

Heterogeneous CoSe2–CoO nanoparticles immobilized into N-doped carbon fibers for efficient overall water splitting

The rational construction of heterogeneous interface is considered as a promising approach to improve the electrocatalytic performance of non-noble metal materials. Herein, an electrospinning–pyrolysis–partial selenization strategy is proposed to construct the heterostructure nanoparticles of CoSe2CoO, which are encapsulated into N-doped carbon fibers (CoSe2CoO/NCF). The assembled CoSe2CoO/NCF hybrid enables to integrate and optimize the multicomponent features from different components through electronic coupling effects. The heterojunction between CoO and CoSe2 owns abundant nanointerface, which could induce the electron rearrangement to enhance the charge transfer ability and optimize the adsorption towards reaction intermediates. As a result, CoSe2CoO/NCF presents superior cathodic hydrogen evolution reaction (HER) and anodic oxygen evolution reaction (OER) activities with low overpotentials, small Tafel slopes and robust durability. Impressively, the overpotentials to afford 10 mA cm−2 current density for acidic HER, alkaline HER and OER upon CoSe2CoO/NCF are 72, 117 and 279 mV, respectively, much lower than those counterparts. Further, the full water splitting device with CoSe2CoO/NCF as both cathode and anode requires a low voltage of 1.604 V to attain 10 mA cm−2. The current work proposes a new insight for interface engineering to improve the electrocatalytic performance of transition metal-based materials.

Few-layer MoS2 embedded in N-doped carbon fibers with interconnected macropores for ultrafast sodium storage

Sodium-ion battery has been considered as one of the most promising next-generation rechargeable energy storage devices. However, it remains a great challenge to exploit suitable electrode materials for sodium storage owing to relatively large radius of Na+. In this study, a novel 1D fiber-like electrode material integrating few-layer MoS2, ultrathin carbon continuous framework, doped N atoms and well-defined 3D connected macropores is developed by electrospinning (denoted as MoS2/NCF-MP). When used as anode in sodium ion battery, its unique structural hierarchy is able to maximumly diminish the solid-state diffusion length, lower electrochemical resistance, accelerate Na+ transfer from bulk to electrode, and relieve the volume variation during sodiation/desodiation process, thus displays highly reversible capacity, long-term durability, along with ultrafast sodium storage capability. The stable reversible capacity of MoS2/NCF-MP reaches 480 mAh g−1 at 0.1 A g−1 after 100 cycles, and undergoes a long cycling life of 300 cycles at 1 A g−1, no visible capacity degradation is observed. More importantly, even under a very high current density of 30 A g−1, the MoS2/NCF-MP can deliver a commendable capacity of 217 mAh g−1, which means the charge/discharge step can be completed within a very short time of 26 s.

Free-standing SiOC/nitrogen-doped carbon fibers with highly capacitive Li storage

Silicon oxycarbide (SiOC) as a prospective electrode material for next-generation lithium ion batteries (LIBs) was restricted by the unsatisfactory discharge capacity and inflexibility used in flexible and wearable electronics. Herein, freestanding flexible SiOC/nitrogen-doped carbon fiber films are constructed through electrospinning process followed by carbonizing in NH3 atmosphere. In this way, SiOC particles are tightly embedded in N-doped carbon fibers, forming a 3D conductive network to promote electron transport and faster reaction kinetics. The nitrogen dopants create more defects in carbon fibers matrix, which improve the electronic conductivity and electrochemical active sites of the electrodes. Owing to the above synergistic effect, SiOC/nitrogen-doped carbon fiber electrodes exhibit a high initial Coulombic efficiency of 73 % and a reversible remaining capacity of 595 mA h g−1 at 200 mA g−1 even after 200 cycles. The electrodes with good flexibility can successfully drive a light-emitting diode even when the package battery is bended to 180°.

A general method for large-scale fabrication of metal nanoparticles embedded N-doped carbon fiber cloth with highly efficient hydrogen production in all pH range

Ion implantation is a facile surface modification technology for greatly tailoring the surface electron structure of materials, which is very important for catalytic activity. Here we report a new universal synthesis of stable, large-scale N-doped carbon fiber cloth embedded with non-noble metal nanoparticles (CN@(Ni, Fe and Co)) by ion implantation for largely enhanced hydrogen evolution reaction (HER) activity under acidic (0.5 M H2SO4), neutral (0.5 M phosphate buffer, PH = 7) and basic solution (1M KOH). From the polarization curves, the overpotentials of current density for CN@Ni at 10 mA/cm2 decrease obviously from 710, 838 and 717 mV to 381, 589 and 532 mV in acidic, neutral and basic solution, respectively. Density functional theory (DFT) calculations also demonstrate that the Gibbs free energy (ΔGH∗) for H∗ adsorption of CN@Ni is much closer to the optimal value of ΔGH∗ = 0.15 eV compared with 1.84 eV of C and 0.86 eV of CN. The method is general and we demonstrate it using Fe+ and Co+ ions implantation into carbon fiber cloth to fabricate metal nanoparticles embedded carbon fiber cloth. Furthermore, this controlled technique is promising for industrial production of noble-metal-free HER electrocatalysts with large scale, low cost and high efficiency.

Boron-rich environment boosting ruthenium boride on B, N doped carbon outperforms platinum for hydrogen evolution reaction in a universal pH range

Developing cost-effective and stable electrocatalysts for hydrogen evolution reaction (HER) in a universal pH range is highly desirable toward renewable energy systems but remains a great challenge. In this work, we report a novel B-rich diruthenium triboride electrocatalyst homogeneously dispersed on the B, N doped carbon nanofiber (Ru 2 B 3 @BNC) synthesized at a moderate temperature (600 °C). Electrochemical tests reveal that such a Ru 2 B 3 @BNC electrocatalyst owns surprising HER performance with ultralow overpotentials (η) of 7, 41, and 58 mV to achieve 10 mA cm −2 in 1 M KOH, 0.5 M H 2 SO 4 , and 1 M PBS (pH = 7) solutions, respectively, outperforming commercial Pt/C and all reported state-of-the-art electrocatalysts, as well as superior durability. Combining density functional theory (DFT) computational Results, it unveils that the electron-deficient B atom can contribute to the local electronic redistribution, leading to the anchoring preference effect of H* on Ru atoms for Ru–B bonds in Ru 2 B 3 . Thus, our work highlights a new type of cheap noble-metal-based electrocatalysts for high-efficiency HER electrocatalysis. In this work, for the first time, we report a novel non-Pt B-rich noble metal diruthenium triboride (Ru 2 B 3 ) electrocatalyst homogeneously dispersed on the B, N doped carbon nanofiber (Ru 2 B 3 @BNC), which demonstrates impressive HER performances outperform the commercial Pt/C electrocatalyst over a wide pH range. • We synthesized a Ru 2 B 3 NPs anchored on B, N-doped carbon fibers (Ru2B3@BNC) as highly efficient HER electrocatalystsd. • Ru 2 B 3 @BNC merely needs 7, 41, and 58 mV to deliver 10 mA cm −2 in 1 M KOH, 0.5 M H 2 SO 4 , and 1 M PBS solutions, respectively. • DFT calculations suggest that the Ru-B bonds in Ru 2 B 3 possesses the more optimal balance of H*-adsorption-H2-desorption capacity than Ru.

Highly active Fe7S8 encapsulated in N-doped hollow carbon nanofibers for high-rate sodium-ion batteries

NHCFs/Fe 7 S 8 is rationally designed by combining high active Fe 7 S 8 with high conductivity N-doped carbon. The robust structure with hollow carbon fibers and ultrathin carbon coating layer enables improved charge transfer kinetics and relieved volume expansion. • The Fe/S atomic ratio in iron sulfides controls sodium-ion storage property. • Fe 7 S 8 endows high electron conductivity, reaction reversibility and Na + transport. • The structure with an ultrathin carbon coating layer to protect the Fe 7 S 8 . • The NHCFs/Fe 7 S 8 as electrode shows high-rate capability in DME electrolyte. Nanostructured iron sulfides are regarded as a potential anode material for sodium-ion batteries in virtue of the rich natural abundance and remarkable theoretical capacity. However, poor rate performance and inferior cycling stability caused by sluggish kinetics and volume swelling represent two main obstacles at present. The previous research mainly focuses on nanostructure design and/or hybridizing with conductive materials. Further boosting the property by adjusting Fe/S atomic ratio in iron sulfides is rarely reported. In this work, Fe 7 S 8 and FeS 2 encapsulated in N-doped hollow carbon fibers (NHCFs/Fe 7 S 8 and NHCFs/FeS 2 ) are constructed by a combined chemical bath deposition and subsequent sulfidation treatment. The well-designed NHCFs/Fe 7 S 8 electrode displays a remarkable capacity of 517 mAh g −1 at 2 A g −1 after 1000 cycles and a superb rate capability with a capability of 444 mAh g −1 even at 20 A g −1 in ether-based electrolyte. Additionally, the rate capability of NHCFs/Fe 7 S 8 is superior to that of the contrast NHCFs/FeS 2 electrode and also much better than the values of the most previously reported iron sulfide-based anodes. The in-depth mechanism explanation is explained by further experimental analysis and theoretical calculation, revealing Fe 7 S 8 displays improved intrinsic electronic conductivity and faster Na + diffusion coefficient as well as higher reaction reversibility.