Free-standing Carbon Nanofiber Research Articles

Vertically Aligned Sulfiphilic Cobalt Disulfide Nanosheets Supported on a Free-Standing Carbon Nanofiber Interlayer for High-Performance Lithium–Sulfur Batteries

Vertically Aligned Sulfiphilic Cobalt Disulfide Nanosheets Supported on a Free-Standing Carbon Nanofiber Interlayer for High-Performance Lithium–Sulfur Batteries

High-Density Lignin-Derived Carbon Nanofiber Supercapacitors with Enhanced Volumetric Energy Density.

Supercapacitors are increasingly used in short‐distance electric transportation due to their long lifetime (≈15 years) and fast charging capability (>10 A g−1). To improve their market penetration, while minimizing onboard weight and maximizing space‐efficiency, materials costs must be reduced (<10 $ kg−1) and the volumetric energy‐density increased (>8 Wh L−1). Carbon nanofibers display good gravimetric capacitance, yet their marketability is hindered by their low density (0.05–0.1 g cm−3). Here, the authors increase the packing density of low‐cost, free‐standing carbon nanofiber mats (from 0.1 to 0.6 g cm−3) through uniaxial compression. X‐ray computed tomography reveals that densification occurs by reducing the inter‐fiber pore size (from 1–5 µm to 0.2–0.5 µm), which are not involved in double‐layer capacitance. The improved packing density is directly proportional to the volumetric performances of the device, which reaches a volumetric capacitance of 130 F cm−3 and energy density of 6 Wh L−1 at 0.1 A g−1 using a loading of 3 mg cm−2. The results outperform most commercial and lab‐scale porous carbons synthesized from bioresources (50–100 F cm−3, 1–3 Wh L−1 using 10 mg cm−2) and contribute to the scalable design of sustainable electrodes with minimal ‘dead volume’ for efficient supercapacitors.

Facile Fabrication of Flexible Carbon Nanofiber Electrodes with Both High Packing Density and Capacity for Li‐Ion Batteries

Freestanding carbon nanofiber (CNF) films are promising flexible battery electrodes because of their rich functionalities and the avoidance of the unnecessary usage of conductive additives and binders, which introduce additional interfacial resistance. However, most reported freestanding CNF electrodes have lower energy density than the metrics of practical usage. Herein, an in situ welding strategy is proposed to fabricate flexible CNF electrodes with both high packing density (0.343 g cm−3) and capacity (832.4 mA h g−1 @0.1 C) by electrospinning of a polyacrylonitrile (PAN) and poly(vinyl‐butyral) (PVB) sol followed by pyrolysis. The addition of 20 wt% of low‐thermal‐stability PVB into PAN carbon precursors endows the CNFs with mixed amorphous/graphitic carbon domains and welded structures. The former enhances the capacity and long‐cycling stability, and the latter improves the flexibility and packing density of the anodes. As a result, these flexible anodes display stable reversible capacities of 430 mA h g−1 @1 C over 1000 cycles and excellent rate performance from 0.1 to 5 C. The successful fabrication of high‐capacity CNF anodes at commercial‐level density opens a new avenue for their practical application.

Hierarchical Co3O4/CNT decorated electrospun hollow nanofiber for efficient hybrid capacitive deionization

Hybrid capacitive deionization (HCDI) is emerging as an energy-efficient alternative for brackish water desalination with low expenditure cost and favourable ion removal effectiveness by adopting battery-type electrodes in the traditional capacitive deionization (CDI) system. Herein, an unscalable electrospinning method is introduced to contrive cathode material for HCDI system. Co3O4 and nitrogen-doped carbon nanotube decoration are formed successfully and uniformly distributed with the hollow structure of free-standing carbon nanofibers (Co3O4@CNF@CNT). The conductive “bridges” provided by the CNF matrix significantly shorten the diffusion length of Na+ and promote the electrical conductivity of the Co3O4 nanoparticles. Moreover, benefiting from the incorporation of nitrogen-doped CNTs, the electrical conductivity is further enhanced. The as-prepared Co3O4@CNF@CNT cathode shows excellent pseudocapacitive performance of 395F g−1 at a scan rate of 1 mV s−1 and superior rate performance of 279F g−1 at 100 mV s−1. The HCDI system delivers an outstanding salt adsorption capacity (SAC) of 58.6 mg g−1 and a highest salt adsorption rate (SAR) of 12.27 mg g−1 min−1 with a potential difference of 1.4 V, indicating the great potential of applying Co3O4@CNF@CNT in the practical HCDI system.

Kraft lignin-derived free-standing carbon nanofibers mat for high-performance all-solid-state supercapacitor

In the present investigation, renewable kraft lignin-based nanofibers were synthesized by facile electrospinning technique and further converted into carbon nanofibers (CNFs) by heat treatment at different temperatures (600, 800 and 1000 °C). These different heat treated carbon nanofiber mats were characterized using SEM, Raman, FTIR, BET and electrochemical workstation. These CNFs were used as a free-standing electrode and characterized for electrochemical performance using a three-electrode system. Among different electrodes, the 800 °C heat treated CNF electrode shows higher specific capacitance (196.63 F/g @ 1 A/g) as compared to the 600 and 1000 °C heat treated CNF electrodes. Based on the electrochemical performance, 800 °C heat treated CNF electrode is selected to assemble two different types of symmetrical supercapacitor devices i.e., aqueous (using 1 M H2SO4) and solid-state electrolyte using PVA-1M H2SO4 polymer gel. The solid-state electrolyte device operating potential window of 0–2 V which is higher than that of an aqueous electrolyte based device. In addition to this, it delivers higher energy and power density as 62.6 Wh/kg and 1.25 kW/kg respectively with an efficiency of 99.5% after 10,000 cycles. These remarkable results of Kraft lignin-derived ribbon type CNF based solid-state symmetrical supercapacitor device opens new paths for the development of futuristic carbon-based free-standing mat as energy storage devices.

A Fishing‐Net‐Like 3D Host for Robust and Ultrahigh‐Rate Lithium Metal Anodes

Constructing an architectural host is demonstrated to be an effective strategy for long-life lithium metal anodes (LMAs). Herein, an integrated 3D host for stable and ultrahigh-rate LMAs is developed by a binary highly conductive network of 2D reduced graphene oxide (rGO) and 1D carbon nanofibers (CNF) anchored with 0D ultrasmall MgZnO nanoparticles (MgZnO/CNF-rGO). A facile net-fishing strategy is proposed to combine the rGO nanosheets with free-standing CNF matrix as interconnected paths for fast electron transport. Notably, serving as Li nucleation sites, the superlithiophilic MgZnO nanoparticles are uniformly distributed and tightly contacted with the conductive matrix without agglomeration due to the rGO confinement. Such a delicate nanoscale combination guarantees the effective transportation and uniform deposition of Li-ions in the inner surface of the host. The symmetric cell of Li@MgZnO/CNF-rGO exhibits a long lifespan above 1450 cycles under an ultrahigh current density of 50mAcm-2 with an areal capacity of 1.0mAhcm-2 . Impressively, it also delivers a high reversible capacity of 10mAhcm-2 at 50mAcm-2 . This work offers an avenue to promise the prospect for practical LMAs working under high rates and capacities.

Free-Standing Carbon Nanofibers Protected by a Thin Metallic Iridium Layer for Extended Life-Cycle Li–Oxygen Batteries

It is evident that the exhaustive use of fossil fuels for decades has significantly contributed to global warming and environmental pollution. To mitigate the harm on the environment, lithium-oxygen batteries (LOBs) with a high theoretical energy density (3458 Wh kg-1Li2O2) compared to that of Li-ion batteries (LIBs) have been considered as an attractive alternative to fossil fuels. For this purpose, porous carbon materials have been utilized as promising air cathodes owing to their low cost, lightness, easy fabrication process, and high performance. However, the challenge thus far lies in the uncontrollable formation of Li2CO3 at the interface between carbon and Li2O2, which is detrimental to the stable electrochemical performance of carbon-based cathodes in LOBs. In this work, we successfully protected the surface of the free-standing carbon nanofibers (CNFs) by coating it with a layer of iridium metal through direct sputtering (CNFs@Ir), which significantly improved the lifespan of LOBs. Moreover, the Ir would play a secondary role as an electrochemical catalyst. This all-in-one cathode was evaluated for the formation and decomposition of Li2O2 during (dis)charging processes. Compared with bare CNFs, the CNFs@Ir cathode showed two times longer lifespan with 0.2 VLi lower overpotentials for the oxygen evolution reaction. We quantitatively calculated the contents of CO32- in Li2CO3 formed on the different surfaces of the bare CNFs (63% reduced) and the protected CNFs@Ir (78% reduced) cathodes after charging. The protective effects and the reaction mechanism were elucidated by ex situ analyses, including scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy.

Porous nitrogen-enriched hollow carbon nanofibers as freestanding electrode for enhanced lithium storage

One-dimensional porous carbons bearing high surface areas and sufficient heteroatom doped functionalities are essential for advanced electrochemical energy storage devices, especially for developing freestanding film electrodes. Here we develop a porous, nitrogen-enriched, freestanding hollow carbon nanofiber (PN-FHCF) electrode material via filtration of polypyrrole (PPy) hollow nanofibers formed by in situ self-degraded template-assisted strategy, followed by NH3-assisted carbonization. The PN-FHCF retains the freestanding film morphology that is composed of three-dimensional networks from the entanglement of 1D nanofiber and delivers 3.7-fold increase in specific surface area (592 m2·g−1) compared to the carbon without NH3 treatment (FHCF). In spite of the enhanced specific surface area, PN-FHCF still exhibits comparable high content of surface N functionalities (8.8%, atom fraction) to FHCF. Such developed hierarchical porous structure without sacrificing N doping functionalities together enables the achievement of high capacity, high-rate property and good cycling stability when applied as self-supporting anode in lithium-ion batteries, superior to those of FHCF without NH3 treatment.

Flexible Cross-Linked Electrospun Carbon Nanofiber Mats Derived from Pitch as Dual-Functional Materials for Supercapacitors

Freestanding and binder-free electrospun carbon nanofiber mats with a cross-linked structure (CLCF) were fabricated by using pitch as the precursor. The cross-linked structure can be tuned easily b...

Electrospun-cellulose derived free-standing carbon nanofibers as lightweight, ultrathin, and stackable interlayers for lithium-sulfur batteries

The insertion of an interlayer between the separator and cathode is considered a promising strategy to improve the conductivity as well as suppress the polysulfide shuttling effect in lithium-sulfur batteries (LSBs). However, the fundamental disadvantages of loss in weight/volume capacity and high cost upon the addition of an interlayer brings significant challenges. Herein, we report free-standing carbon nanofibers based on electrospun-cellulose (ACCF) as a lightweight (0.38 mg cm−2) and ultrathin (10 μm) interlayer for LSBs. The unique semi-carbonization of cellulose precursors provides a large surface area (2665.2 m2 g−1) and high conductivity (6.5 S cm−1) to overcome the conductivity–surface area trade-off in conventional interlayers. Interestingly, the high wettability of ACCF is induced by the functional groups in cellulose, which decreases the electrolyte demand and enables the material to be stacked into multiple layers. This allows a conceptual study providing the scientific clue for the critical material factor in the LSB interlayer. Benefitting from its multi-functional characteristics, ACCF-modified cell provides a high specific capacity of 1403 mA h g−1 and a remarkable areal capacity 4.83 mA h cm−2 (S loading 4.6 mg cm−2) at 0.1C. Therefore, this innovative, cheap, and scalable ACCF can be used as a practical interlayer toward the commercialization of high-energy LSBs.

Bimetallic zeolitic imidazolate framework-derived substrate-free anode with superior cyclability for high-capacity lithium-ion batteries

Freestanding carbon nanofibers loaded with bimetallic hollow nanocage structures were synthesized. The nanocages inherited the rhombic dodecahedral morphology of the zeolitic imidazolate framework (ZIF) precursors, ZIF-8 and ZIF-67. As anode materials for lithium-ion batteries (LIBs), the bimetallic nanocage-loaded freestanding carbon nanofibers effectively buffered volume expansions and alleviated pulverization through their different reduction and oxidation potentials. The higher capacities of the composite anodes arose via the formation of the LixZn alloy and Li2O by Zn and Co ions, respectively, and the enhanced conductivity conferred by the carbon nanofibers. A synergistic effect of the composite components toward the strong electrochemical performance (688 mA h·g−1 at 1200 mA·g−1) of the bimetallic nanocage-loaded fibers was demonstrated through the superior long-term stability of the anode (1048 mA h·g−1 after 300 cycles at 100 mA·g−1), suggesting that the fabricated anode can be a promising material for use in portable LIBs.

N-doped porous carbon nanofibers sheathed pumpkin-like Si/C composites as free-standing anodes for lithium-ion batteries

Abstract Dramatic capacity fading and poor rate performance are two main obstacles that severely hamper the widespread application of the Si anode owing to its large volume variation during cycling and low intrinsic electrical conductivity. To mitigate these issues, free-standing N-doped porous carbon nanofibers sheathed pumpkin-like Si/C composites (Si/C-ZIF-8/CNFs) are designed and synthesized by electrospinning and carbonization methods, which present greatly enhanced electrochemical properties for lithium-ion battery anodes. This particular structure alleviates the volume variation, promotes the formation of stable solid electrolyte interphase (SEI) film, and improves the electrical conductivity. As a result, the as-obtained free-standing Si/C-ZIF-8/CNFs electrode delivers a high reversible capacity of 945.5 mA h g−1 at 0.2 A g−1 with a capacity retention of 64% for 150 cycles, and exhibits a reversible capacity of 538.6 mA h g−1 at 0.5 A g−1 over 500 cycles. Moreover, the full cell composed of a free-standing Si/C-ZIF-8/CNFs anode and commercial LiNi1/3Co1/3Mn1/3O2 (NCM) cathode shows a capacity of 63.4 mA h g−1 after 100 cycles at 0.2 C, which corresponds to a capacity retention of 60%. This rational design could provide a new path for the development of high-performance Si-based anodes.

Construct pseudo-capacitance of a flexible 3D-entangled carbon nanofiber film as freestanding anode for dual-ion full batteries

We construct a remarkable freestanding and porous carbon nanofibers (FPCNFs) as anode materials in the dual-ion full battery. The dual-ion battery (DIB) based on electrolyte including the Li+ and PF6− has a high operating voltage from 3.0 to 5.0 V. The entangled and crossed carbon nanofiber film creates plenty of porous with a high specific surface area (200 m2g−1) to contribute to the pseudo-capacitance effect. The dual-ion full batteries exhibit a stable long-life property up to 500 cycles, an approximately above 4.0V high operating average discharge voltage and an energy density delivering almost 185 W h kg−1 at 0.1 A g−1. The FPCNFs can be a potential alternative toward a cost-efficient high energy density battery anode.

Confining sulfur in intact freestanding scaffold of yolk-shell nanofibers with high sulfur content for lithium-sulfur batteries

Abstract Nanostructure design holds great potential in fabricating sulfur electrodes that host a high sulfur loading and still attain high electrochemical utilization for the developing of high-energy-density lithium-sulfur (Li-S) batteries. In this contribution, we introduce the yolk-shell structure into a freestanding carbon nanofibers film and construct a complete hollow yolk-shell TiO2/carbon nanofibers@void@TiN@carbon (TiO2-CNFs@void@TiN@C) composite. With inherent double conductive network and strong adsorption capability for polysulfides, the TiO2-CNFs@void@TiN@C composite can not only provide sufficient electrical contact for the insulating sulfur, but also effectively entrap polysulfides for prolonged cycle life. As a result, an excellent capacity retention ratio of 60.9% after 1000 cycles at 1 C as well as a high capacity of 688.5 mAh g−1 at 5 C rate is accomplished with the cells employing TiO2-CNFs@void@TiN@C as a cathode substrate for sulfur. Moreover, the TiO2-CNFs@void@TiN@C composite, with a high S mass loading of 9.5 mg cm−2, delivers a superb areal capacity of 8.2 mAh cm−2.

Iron and silicon oxide doped/PAN-based carbon nanofibers as free-standing anode material for Li-ion batteries

The advanced rechargeable batteries have been upgraded by the production of free-standing electrodes through electrospinning technology. This study aimed to introduce a novel hybrid composition to design a free-standing carbon nanofiber (CNF) based anode by the addition of iron acetylacetonate Fe(AcAc)3 as active material and TEOS(tetraethoxysilane)/APTES(aminopropyl triethoxysilane) as an additive for Li-ion batteries. Polyacrylonitrile(PAN) was used as the polymer matrix in the spin dope, and the inclusion of Fe(AcAc)3 and TEOS/APTES resulted in compositional change, producing iron oxide and silica nanoparticles throughout the matrix. Different oxidation states and the presence of embedded iron oxide nanoparticles in CNF were identified by XPS and EDX elemental mapping analysis. PAN-TEOS-APTES-Fe(AcAc)3 based anode material was capable of enhancing the reversible specific capacity as much as 732 mAhg−1 at 500 mAg−1 lasting for 300 cycles, along with the rate capability as high as 815 mAhg−1 at 200 mAg−1. Furthermore, EIS analysis and EX-situ FESEM showed decreased impedance after cycling with the stable morphology of PAN-TEOS-APTES-Fe(AcAc)3 CNF-film. Conclusively, non-woven, binder-free, current collector free, free-standing CNF anode film doped with iron-oxide and silica nanoparticles was indeed a novel approach for Li-ion batteries and can be considered for other batteries particularly for Li-S batteries.

Free-standing interconnected carbon nanofiber electrodes: new structural designs for supercapacitor application

This work aims to develop and characterize a new design of free-standing interconnected carbon nanofiber electrodes for supercapacitor application. The fibers are obtained via carbonization of three components of electrospun nanofiber mats based on a polyacrylonitrile polymer (as a carbon backbone precursor), polyvinylalcohol (as a sacrificial copolymer), and 0–1.0 wt% multi-walled carbon nanotubes. Carbonizing these ternary composites results in fibers with about twice as large in surface area and one order of magnitude higher in electrical conductivity than those obtained by the carbonization of neat polyacrylonitrile and/or binary polyacrylonitrile-0–1.0 wt% carbon nanotube mats. The carbonized polyacrylonitrile-polyvinylalcohol-0.3 wt% carbon nanotube mat reveals the highest surface area and electrical conductivity and best capacitive performance. It exhibits energy and power densities of 27.8 Wh kg−1 and 110.59 kW kg−1, respectively, and cyclic stability of 95% after 2000 charge–discharge cycles at a charging current of 1.0 Ag−1. The nanotubes’ alignment along the fiber’s axis, the formation of fiber–fiber interconnected morphology with more mesopore pollution, and changes in the graphitization degree and defect features of fiber crystallites are the reasons for the observed increase in the electrical conductivity, surface area, and capacitive performance of the carbon fibers. Therefore, the new design represents a potential free-standing carbon nanofiber electrode for future electrochemical double layer capacitor (EDLC) device fabrication.

Cobalt nanoparticles embedded into free-standing carbon nanofibers as catalyst for room-temperature sodium-sulfur batteries

Room-temperature sodium-sulfur (RT Na-S) batteries are seriously limited because of poor conductivity of sulfur and sluggish reaction kinetics of polysulfide intermediates. Here, we design a free-standing film, constructed from Co nanoparticles onto nitrogen-doped porous carbon nanofibers (Co@NPCNFs), to load sulfur for RT Na-S batteries. Experiment result shows that Co as catalyst can enable the rapid sodium intercalation and fast reduction reaction of the polysulfides during cycling. Hence, the prepared Co@NPCNFs/S cathode exhibits a remarkable capacity of 906 mAh g−1 at 0.1 C and long cycling life up to 800 cycles with a slow capacity decay of 0.038% per cycle at 1 C.

Coaxial electrospun free-standing and mechanically stable hierarchical porous carbon nanofiber membranes for flexible supercapacitors

The preparation of electrode materials with superior electrochemical performance and excellent mechanical properties are essential for the fabrication of flexible supercapacitors. However, the compatibility of the porosity and flexibility for the electrode materials remains challenging. Herein, free-standing porous coaxial carbon nanofiber (PCCNF) membranes with large specific surface area (648 m2 g−1) and suitable pore size distribution were fabricated by a facile coaxial electrospinning technique and template method. PCCNF possesses superb capacitance of 261 and 48 F g−1 (1 A g−1) in three-electrode and two-electrode system, respectively, result in remarkable energy density (48.6 ± 3 Wh kg−1) and power density (67.5 ± 1 Wh kg−1). Moreover, supercapacitor devices based on PCCNF show superb flexibility as well as excellent electrochemical and mechanical stability. PCCNF-based high performance supercapacitors may be suitable for flexible electronic energy storage devices.

Origin of the extra capacity in nitrogen-doped porous carbon nanofibers for high-performance potassium ion batteries

The origin of the extra capacity of freestanding and porous N-doped carbon nanofibers was clearly revealed by systematic experimental analysis and theoretical calculations.

A Dual-Functional Conductive Framework Embedded with TiN-VN Heterostructures for Highly Efficient Polysulfide and Lithium Regulation toward Stable Li-S Full Batteries.

Lithium-sulfur (Li-S) batteries are strongly considered as next-generation energy storage systems because of their high energy density. However, the shuttling of lithium polysulfides (LiPS), sluggish reaction kinetics, and uncontrollable Li-dendrite growth severely degrade the electrochemical performance of Li-S batteries. Herein, a dual-functional flexible free-standing carbon nanofiber conductive framework in situ embedded with TiN-VN heterostructures (TiN-VN@CNFs) as an advanced host simultaneously for both the sulfur cathode (S/TiN-VN@CNFs) and the lithium anode (Li/TiN-VN@CNFs) is designed. As cathode host, the TiN-VN@CNFs can offer synergistic function of physical confinement, chemical anchoring, and superb electrocatalysis of LiPS redox reactions. Meanwhile, the well-designed host with excellent lithiophilic feature can realize homogeneous lithium deposition for suppressing dendrite growth. Combined with these merits, the full battery (denoted as S/TiN-VN@CNFs || Li/TiN-VN@CNFs) exhibits remarkable electrochemical properties including high reversible capacity of 1110 mAh g-1 after 100 cycles at 0.2 C and ultralong cycle life over 600 cycles at 2 C. Even with a high sulfur loading of 5.6 mg cm-2 , the full cell can achieve a high areal capacity of 5.5 mAh cm-2 at 0.1 C. This work paves a new design from theoretical and experimental aspects for fabricating high-energy-density flexible Li-S full batteries.