SiOx-based anodes have attracted tremendous attention owing to their low cost, higher theoretical capacity than graphite and lower volume expansion than pure silicon. In this work, a simple and cost-effective two-step ball-milling method was proposed to fabricate Si/SiOx/C composites by using commercial SiO and graphite carbon as raw materials. The two-step ball-milling synthesis of the Si/SiOx/C composites can avoid the generation of an inert SiC phase and realize the uniform dispersion of Si/SiOx in graphite carbon, which offers good electrical conductivity and relieves the volume expansion of the Si/SiOx phase. Owing to the synergistic effect of the Si/SiOx phase and the graphite carbon, the typical Si/SiOx/C electrode exhibits a stable and high capacity of 726 mA h g−1 after 500 cycles at a current density of 0.1 A g−1 with a capacity retention of 82%. The two-step ball-milling preparation of the Si/SiOx/C composite provides a facile approach to fabricate high-performance SiOx-based anode materials.

Hollow-structured carbon nanofibers embedded with ultrafine SnOx nanoparticles (SnOx/H-CNFs) have been prepared by a simple single-spinneret electrospinning technique assisted by phase separation between polyvinylpyrrolidone and tetraethyl orthosilicate. The nitrogen adsorption–desorption isothermal analysis shows that the SnOx/H-CNFs possess a large specific surface area of 739 m2 g−1 and large amounts of mesopores. The high specific surface area provides a large electrode/electrolyte contact interface for Li+ transport and storage, while the hollow structure shortens the Li+-diffusion pathway and thus favors the rate capability. Moreover, the hollow and porous carbon matrix can act as a buffer zone to accommodate the volume change of the highly active SnOx during the lithiation/delithiation processes. Consequently, the SnOx/H-CNF electrode delivers a high reversible capacity of 732 mA h g−1 at the rate of 500 mA g−1 upon the 100th cycle, good rate performance (254 mA h g−1 at 4 A g−1), and long-term cycling stability (513 mA h g−1 at 1 A g−1 after 500 cycles).

Development of high volumetric capacitance, high rate performance and low-cost electrode materials for supercapacitors is still a significant challenge. Among the various promising candidates, carbon nanofibers (CNFs) with heteroatom functionalization have attracted increasing attention. Herein, a type of nonporous CNFs combined with a heteroatom functionalization strategy is proposed for high performance supercapacitor electrodes. Tri-heteroatom functionalization of nonporous carbon nanofibers was carried out by tetraethyl orthosilicate (TEOS) and phosphorus (H3PO4) activation of polyacrylonitrile (PAN) through electrospinning and subsequent thermal treatment. The optimal electrode material showed a high gravimetric capacitance of 243.7 F g−1 at 0.5 A g−1, superior rate capability with ∼83% retention at rates ranging from 0.5 A g−1 to 30 A g−1 and excellent cycle stability (capacitance retention rate >100% after 8000 cycles at a high current density of 30 A g−1). It is worth noting that the nonporous CNF also possesses a high packing density, which presents a maximum volumetric capacitance of 253.4 F cm−3 at 0.5 A g−1 and 209 F cm−3 at 30 A g−1. The current synthetic strategy of preparing nonporous carbon architectures with multi-heteroatom doping offers an eco-friendly, feasible, and cost-effective way for constructing high-performance electrode materials employed in supercapacitors.

•Vertically oriented polyaniline nanothorns are “grafted” on the N/P co-doped carbon nanofibers.•The phosphorus groups play a key role in the oriented growth of polyaniline.•The phosphorus groups also act as anchor sites for polyaniline.•The composite exhibits highly enhanced rate capability and cycling stability.A series of highly homogeneous polyaniline@N/P co-doped carbon nanofibers (PANI@NPCNFs) composites have been prepared by in-situ polymerization of aniline on the surface of NPCNFs. Vertically oriented PANI nanothorns are achieved by introducing phosphorus groups on the surface of NPCNFs. The optimized PANI@NPCNFs composite demonstrates outstanding electrochemical performance with high specific capacitance (436 F g−1 at 0.5 A g−1), high rate capability (79% capacitance retention at 20 A g−1 relative to that at 0.5 A g−1), and good stability (96% capacitance retention after 1000 cycles at 10 A g−1). The excellent electrochemical performance can be attributed to the surface phosphorus-oxygen groups which bridge the gaps between PANI and NPCNFs, leading to highly enhanced charge transfer dynamics.

In this work, one-dimensional polyvinylpyrrolidone-derived porous carbon nanofibers decorated with SnOx nanoparticles (denoted as SnOx@PCNFs) were prepared by an electrospinning technique, followed by a simple one-step heat treatment and a postetching process. The structural evolution of SnOx and the morphological change of the carbon nanofiber webs during the heat treatment are investigated by varying the content of the SnOx precursor in the electrospinning solutions. The highly interconnected pores, created by etching off the in situ generated SiO2 template in the carbon nanofibers, are beneficial for the easy penetration of Li+-carrying electrolyte into the nanocomposites and thus enable the direct contact between embedded SnOx nanoparticles and electrolyte. When tested as anode materials for lithium-ion batteries, SnOx@PCNFs with optimal SnOx component show outstanding initial reversible capacity of 1057 mA h g–1 at 0.2 A g–1, long cycling capability (511 mA h g–1 at 1 A g–1 after 900 cycles), and good rate performance (323 mA h g–1 at 2 A g–1). The remarkable electrochemical properties of the nanocomposites can be attributed to the highly interconnected pores, high surface area, and well-controlled SnOx nanoparticles.Keywords: Anode; Lithium-ion battery; Polyvinylpyrrolidone; Porous carbon nanofibers; Tin oxides nanoparticles

Polydopamine-derived nitrogen-doped carbon has attracted tremendous attention owing to its huge success in improving the electrochemical properties of high-capacity lithium-storage materials (such as S, Si and Sn). In this study, we first demonstrate its excellent and durable lithium-storage capability by designing a one-dimensional hollow structure through a template-assisted method. The polydopamine-derived nitrogen-doped carbon tubes show high specific capacity, excellent rate capability and robust durability. Interestingly, the capacity gradually increased from 587 to 1103 mA h g−1 upon the 500th cycle at 500 mA g−1. The self-improvement in capacity stems from the continuous interlamellar spacing expansion of the graphene-like carbon layers as confirmed by HR-TEM. Our work offers a new insight into the electrochemical behaviour of polydopamine-derived carbon and is beneficial for its future utilization in high-performance lithium-ion battery electrode materials.

A series of carbon nanofiber-supported B2O3–SnOx glasses (0B2O3–SnOx/CNFs, 0.5B2O3–SnOx/CNFs, 1.5B2O3–SnOx/CNFs and 3B2O3–SnOx/CNFs) have been prepared by an electrospinning technique, and a subsequent stabilization and carbonization treatment. The amorphous B2O3–SnOx glass nanoparticles homogeneously dispersed in the carbon nanofibers (CNFs) matrix have been utilized as anode materials for lithium-ion batteries. The typical 1.5B2O3–SnOx/CNF nano hybrid anode material demonstrates the highest reversible capacity as well as superior cycling stability and rate performance by virtue of the special glass network structure of non-bridging oxygen (NBO: B–O⋯Sn) in the B2O3–SnOx glasses, which can not only buffer the large volume change of SnOx, but also prohibit the aggregation of Sn nanoparticles during the charge–discharge cycles.

Amorphous Cu-added tin oxides/carbon nanofiber (Cu-added SnOx/CNFs) composite webs used for lithium-ion battery anode materials are prepared by an electrospinning technique and subsequent thermal treatment. The Cu-doped SnOx particles are uniformly distributed in the CNFs and maintain the original morphology after long-term cycling. In a controlled experiment, SnOx-20%Cu/CNFs with an atomic ratio of Cu:Sn = 0.2 shows the highest electrochemical performance with a high reversible capacity of 743 mA h g−1 at a current density of 200 mA g−1 and an excellent rate capacity of 347 mA h g−1 at 5 A g−1. Moreover, the composite electrode exhibits an outstanding long-term cycling performance at 2 A g−1 even after 1000 cycles. The superior reversible lithium-ion storage capability is attributed to the uniform dispersion of the Cu2O and ultrafine SnOx particles in CNFs as well as the Cu-addition effects such as promoting electron transport and Li+ diffusion, preventing Sn from aggregation during cycling, and improving the reversibility of Sn back to SnOx in the recharge process.

Activated carbons are regarded as the most important electrode materials for commercial supercapacitors because of their low cost, high surface area, and good electrical conductivity. The environmentally friendly, low-cost and renewable biomass is a promising raw material for the high-performance carbon electrode material. Herein, a series of activated carbon fibers (ACFs) are fabricated by one-step carbonization and activation of wood-derived fibers with different activation times. The micropore surface area, mesopore/micropore ratio and pore size of the ACF series are successfully controlled by adjusting the levels of burn-off in order to study the effects of these parameters on specific capacitance and rate capability. Electrochemical measurements show that the electrochemical performance of the ACF series increases with the progress of gasification unless excessive burn-off occurs. The sample with optimal structure exhibits an outstanding specific capacitance of 280 F g−1 at 0.5 A g−1 and excellent rate capability (81.8% capacitance retention at 10 A g−1) in 1 M H2SO4. Furthermore, it demonstrates good cyclic stability, showing a high capacitance retention of 99.3% over 2000 charge–discharge cycles. The excellent electrochemical performance of this sample is attributed to the large micropore surface area, a proportion of mesopores in the range of 3–4 nm, good electrical conductivity and fast charge transfer.

Hybrid nanocomposites composed of carbon nanofibers and Ti-doped SnOx nanoparticles with varied molar ratios of Ti/Sn (=0.05, 0.1 and 0.2) have been prepared through electrospinning technique and subsequent thermal treatments. High-resolution transmission electron microscopy showed that the Ti-doped SnOx nanoparticles with a very small particle size of 2∼4 nm were uniformly encapsulated in the carbon nanofibers (CNFs). Among the as-prepared samples, the electrode with the Ti/Sn molar ratio of 0.1 delivered the best reversible capacity of 670.7 mAh g−1 at the 60th cycle, which was 17.9% higher than that of the pristine SnOx/CNFs (SOC). What is more, the optimal electrode presented good rate performance (302.1 mAh g−1 at 2 A g−1). The enhanced lithium storage properties of Ti-doped SnOx/CNFs (TSOC) can be attributed to the uniform encapsulation of ultrafine SnOx nanoparticles in the conductive CNFs as well as the doping with Ti4+.

Hydrothermal treatments of electrospun titanium dioxide/carbon nanofibers (TiO2/CNFs) in LiOH solution were performed in a temperature range of 130–190 °C, and then followed by a thermal treatment at 600 °C in N2 atmosphere. The changes in morphologies, microstructures and compositions as well as the electrochemical performances with hydrothermal temperatures were investigated for all samples. The morphological and compositional characterizations showed that the surfaces of the CNFs-matrix were covered by numerous nanoparticles with size distributions of 25–100 nm. For the sample hydrothermally treated at 150 °C (denoted as LC-150), these nanoparticles (∼25 nm) were composed of well-crystalline spinel Li4Ti5O12 and anatase TiO2 with abundant phase interfaces and grain boundaries, which can induce the interfacial pseudocapacitive effect. Therefore, the as-prepared dual-phase structured Li4Ti5O12–TiO2–CNFs sample as a binder-free anode for lithium-ion batteries (LIBs) presented a greatly enhanced reversible capacity (203.8 mA h g−1 at 100 mA g−1 after 200 cycles) and a favored rate capability (114.3 mA h g−1 at 2000 mA g−1) compared with the single-phase Li4Ti5O12–CNFs sample.

The capacitive properties of nitrogen/phosphorus co-doped nonporous carbon nanofibers and nitrogen doped nonporous carbon nanofibers are comprehensively and comparatively investigated in different aqueous electrolytes in order to identify the role of phosphorus groups in improving the capacitive performance of carbon. The introduction of phosphorus groups is favourable for the adsorption of electrolyte ions onto the carbon surface, especially protons, and thus greatly enhances the electric double layer capacitance.

SiOx-rich overlayed carbon nanofibers (SiOx-CNFs) are facilely fabricated through the electrospinning of tetraethyl orthosilicate (TEOS) and polyacrylonitrile (PAN) solution and subsequent hydrolyzation and heat treatments. The SiOx-rich overlayer is apparently observed by high-resolution transmission electron microscopy (HR-TEM), which is also identified using X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDX). The SiOx-CNF electrode shows greatly improved cycle stability and rate capability, remaining 84.2% of its initial discharge capacity in contrast to only 61.4% for pure CNFs and exhibiting a reversible capacity of 288 mAh g−1 at 2 A g−1 compared with that (218 mAh g−1) of pure CNFs. This result is ascribed to the formation of a dense and stable SEI film and the highly improved ionic conductivity of SiOx-CNFs during the Li+ insertion/extraction processes. These results suggest that the introduction of SiOx-rich overlayer onto electrodes is an effective strategy to enhance the stability of SEI film and facilitate the surface Li-ion transfer of electrodes, and thus to improve their cycle stability and rate capability.

Nanosized anatase titanium dioxide loaded porous carbon nanofibers (TiO2/PCNFs) were prepared from electrospun TiO(OAc)2/PAN/PMMA composite precursor fibers with different amount of PMMA porogen, which were sequentially heat-treated in different environments. Electrochemical measurement results show that these as-prepared TiO2/PCNFs present higher cyclic reversible capacity than the TiO2/CNFs counterpart (without PMMA porogen in its precursor fibers). Among the as-prepared TiO2/PCNFs samples, the representative TiO2/PCNFs (the mass ratio of PAN to PMMA is 3:1) exhibits the best high-rate performance with a high stable capacity retention about 200 mAhg− 1 at a current density as high as 800 mAg− 1. This novel TiO2/PCNFs composite material opens up a promising application in high-power lithium-ion batteries.Highlights► Nanosized anatase TiO2 loaded porous carbon nanofiber (TiO2/PCNFs ) web as a direct anode material for LIBs is first reported. ► Facile electrospinning method and thermal treatments are employed. ► TiO2/PCNFs delivers excellent high-rate performance.

Hollow-structured carbon nanofibers embedded with ultrafine SnOx nanoparticles (SnOx/H-CNFs) have been prepared by a simple single-spinneret electrospinning technique assisted by phase separation between polyvinylpyrrolidone and tetraethyl orthosilicate. The nitrogen adsorption–desorption isothermal analysis shows that the SnOx/H-CNFs possess a large specific surface area of 739 m2 g−1 and large amounts of mesopores. The high specific surface area provides a large electrode/electrolyte contact interface for Li+ transport and storage, while the hollow structure shortens the Li+-diffusion pathway and thus favors the rate capability. Moreover, the hollow and porous carbon matrix can act as a buffer zone to accommodate the volume change of the highly active SnOx during the lithiation/delithiation processes. Consequently, the SnOx/H-CNF electrode delivers a high reversible capacity of 732 mA h g−1 at the rate of 500 mA g−1 upon the 100th cycle, good rate performance (254 mA h g−1 at 4 A g−1), and long-term cycling stability (513 mA h g−1 at 1 A g−1 after 500 cycles).

Activated carbons are regarded as the most important electrode materials for commercial supercapacitors because of their low cost, high surface area, and good electrical conductivity. The environmentally friendly, low-cost and renewable biomass is a promising raw material for the high-performance carbon electrode material. Herein, a series of activated carbon fibers (ACFs) are fabricated by one-step carbonization and activation of wood-derived fibers with different activation times. The micropore surface area, mesopore/micropore ratio and pore size of the ACF series are successfully controlled by adjusting the levels of burn-off in order to study the effects of these parameters on specific capacitance and rate capability. Electrochemical measurements show that the electrochemical performance of the ACF series increases with the progress of gasification unless excessive burn-off occurs. The sample with optimal structure exhibits an outstanding specific capacitance of 280 F g−1 at 0.5 A g−1 and excellent rate capability (81.8% capacitance retention at 10 A g−1) in 1 M H2SO4. Furthermore, it demonstrates good cyclic stability, showing a high capacitance retention of 99.3% over 2000 charge–discharge cycles. The excellent electrochemical performance of this sample is attributed to the large micropore surface area, a proportion of mesopores in the range of 3–4 nm, good electrical conductivity and fast charge transfer.

Polydopamine-derived nitrogen-doped carbon has attracted tremendous attention owing to its huge success in improving the electrochemical properties of high-capacity lithium-storage materials (such as S, Si and Sn). In this study, we first demonstrate its excellent and durable lithium-storage capability by designing a one-dimensional hollow structure through a template-assisted method. The polydopamine-derived nitrogen-doped carbon tubes show high specific capacity, excellent rate capability and robust durability. Interestingly, the capacity gradually increased from 587 to 1103 mA h g−1 upon the 500th cycle at 500 mA g−1. The self-improvement in capacity stems from the continuous interlamellar spacing expansion of the graphene-like carbon layers as confirmed by HR-TEM. Our work offers a new insight into the electrochemical behaviour of polydopamine-derived carbon and is beneficial for its future utilization in high-performance lithium-ion battery electrode materials.