•We successfully prepared lignin-based interconnected welded mesoporous carbonized nanofibers (MCNFs) via simple electrospinning and thermal treatment.•Welded carbon fibers exhibited excellent mechanical strength and lower electrical resistance.•The synthesized MCNFs as free-standing and binder-free anodes materials displayed high rate performances and robust cycle life for LIBs.A novel type of renewable lignin-based mesoporous carbonized nanofibers (MCNFs) has been fabricated via electrospinning technique and thermal treatment, using lignin with polyacrylonitrile (PAN) as the carbon source and triblock copolymer Pluronic P 123 as the template. The obtained MCNFs were directly used as anodes of lithium-ion batteries (LIBs) without binder and current collector. The MCNFs anode exhibited a large reversible capacity of 384.4 mAh g− 1 at 20.0 mA g− 1 and maintain 177.7 mAh g− 1 at a current density of 1.0 A g− 1 after 400 cycles. Even at a fast (91 s) discharge condition, the MCNFs achieved a high discharge capacity of 127.7 mAh g− 1.

AbstractThe SiO2/carbon composite material used as a lithium-ion battery (LIB) anode was synthesized by aerosol spraying a mixture of polyvinyl alcohol (PVA) solution and SiO2 nanoparticles, followed by coating polyacrylonitrile (PAN) on the SiO2/PVA surface and an annealing treatment at 800 °C. The as-prepared SiO2/po-C@C has a hollow core–shell structure. The hollow section contributes to accommodate the volume expansion of SiO2 nanoparticles; the skeleton of porous carbon in the core not only enhances the electronic conductivity, but also provides the lithium-ion diffusion path; the PAN-based carbon shell benefits for forming a stable solid electrolyte interphase (SEI) film. This core–shell structure could partly alleviate the pulverization of the SiO2/po-C@C particles and also perform excellent electrochemical performances. Compared with the SiO2@C composite, the SiO2/po-C@C composite possesses a high specific charge capacity of 669.8 mA h g−1 at a current density of 100 mA g−1 after 100 charge and discharge cycles with a high capacity retention of 98.6 %. Therefore, the SiO2/po-C@C composite with a hollow core-shell structure shows great potential as an anode material for future LIBs.

•Two types of HC materials with different properties as negative electrode.•Lithium ion intercalation plateau of HC affects electrochemical performance of LIC.•The electrochemical performance of LIC is operated at different potential ranges.•The selection of HC and appropriate potential range of LIC have been proposed.Lithium-ion capacitors (LICs) are assembled with activated carbon (AC) cathode and pre-lithiated hard carbon (HC) anode. Two kinds of HC materials with different physical and electrochemical behaviors have been investigated as the negative electrodes for LIC. Compared with spherical HC, the irregular HC shows a distinct lithium ion intercalation plateau in the charge–discharge process. The existence of lithium ion intercalation plateau for irregular HC greatly affects the electrochemical behavior of HC negative electrode and AC positive electrode. The effect of working potential range on the electrochemical performance of LIC-SH and LIC-IH is investigated by the galvanostatic charging–discharging, electrochemical impedance tests and cycle performance testing. The charge–discharge potential range of the irregular HC negative electrode is lower than the spherical HC electrode due to the existence of lithium ion intercalation plateau, which is conducive to the sufficient utilization of the AC positive electrode. The working potential range of LIC should be controlled to realize the optimization of electrochemical performance of LIC. LIC-IH at the working potential range of 2.0-4.0 V exhibits the optimal electrochemical performance, high energy density up to 85.7 Wh kg−1 and power density as high as 7.6 kW kg−1 (based on active material mass of two electrodes), excellent capacity retention about 96.0% after 5000 cycles.

•MCMB with the optimal pre-lithiation capacity as negative electrode in LIC.•The capacity design of cathode affects the electrochemical performance of LIC.•The optimal designed capacity of positive electrode has been proposed.Lithium-ion capacitors (LICs) are assembled with activated carbon (AC) cathode and pre-lithiated mesocarbon microbeads (MCMB) anode. The effect of AC cathode capacity design on the electrochemical performance of LIC is investigated by the galvanostatic charging-discharging and electrochemical impedance tests. As the designed capacity of AC positive electrode is lower than 50 mAh g−1, the working potential of negative electrode is always in the low and stable plateau, which is conductive to the sufficient utilization and the working potential stability of positive electrode. When the designed capacity of positive electrode is higher than 50 mAh g−1, the instability of negative electrode directly causes the reduced utilization and shortened working potential range of the positive electrode, which is responsible for the capacity attenuation and cycle performance deterioration of LIC. The positive electrode capacity design can realize the optimization of electrochemical performance of LIC. LIC50 exhibits the optimal electrochemical performance, high energy density up to 92.3 Wh kg−1 and power density as high as 5.5 kW kg−1 (based on active material mass of two electrodes), excellent capacity retention of 97.0 % after 1000 cycles. The power density and cycle performance of LIC can be further improved by reducing the AC positive electrode designed capacity.

Lithium-ion capacitors (LICs) are assembled with activated carbon (AC) cathode and pre-lithiated mesocarbon microbeads (MCMB) anode. For ensuring the electrochemical performance of LIC, the pre-lithiation capacity of MCMB anode is designed to make the anode at the two lithium ion intercalation plateaus. The utilization of the two plateaus greatly affects the charge-discharge process and behavior at different working potential ranges of LIC, which achieves the regulation of the electrochemical performance. LIC150 using the first plateau of MCMB anode exhibits higher power density and superior cycle performance, and LIC300 using the second plateau of MCMB anode shows higher energy density. The two plateaus utilization of the MCMB anode can be further increased by improving the working potential range. LIC150 and LIC300 display the optimal electrochemical performance at the working potential range of 2.0-4.0 V. LIC150 exhibits high power density of 6.3 kW kg−1 and the energy density up to 62.9 Wh kg−1, capacity retention of 93.4% after 1000 cycles. Besides, the energy density of LIC300 is up to 92.3 Wh kg−1, the power density as high as 5.5 kW kg−1 and excellent capacity retention of 97.0% after 1000 cycles.

•Phenolic Resin-based hard carbon microspheres were obtained by a hydrothermal-carbonization method.•PF-HCSs were successfully applied as electrode materials in sodium-ion batteries.•Electrochemical performances of the electrodes were high.Phenolic Resin-based hard carbon microspheres (PF-HCSs) were successfully synthesized by a simple hydrothermal route in a stainless steel autoclave and followed carbonization at different temperatures. The materials possess perfect spherule shape and interlayer spacing above that of equilibrium graphite, facilitating Na intercalation and favoring efficient ion storage. A high reversible capacity of 311 mAh g− 1 and good long-term electrochemical stability are achieved in the PF-HCS-1250 anode obtained at 1250 °C. Carbonizing the samples at higher carbonization temperature than 1250 °C results in such a decrease of the reversible capacity down to 270 mAh g− 1. That can be related to the appearing closed pore structure and the decreasing interlayer space which exceeds the limited value sodium ion can insert. Hence the most suitable hard carbon anode material for sodium ion batteries should possess a large interlayer space and a suitable pore structure.

•MCMB and HC as active materials for lithium ion capacitor anode.•The composite negative electrode dealing with the optimal pre-lithiation capacity.•Adding HC into MCMB improves the electrochemical performance of LIC.•The optimal addition of HC has been proposed.Lithium-ion capacitor (LIC) is fabricated using activated carbon (AC) as the positive electrode and a mixture of mesocarbon microbeads (MCMB) and hard carbon (HC) as the negative electrode (denoted as MH). The structure characterization of carbon materials are investigated by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM) and nitrogen adsorption apparatus. The electrochemical performances of LIC with different HC content are characterized by the charge–discharge measurements of three-electrode cell, electrochemical impedance tests and cycle performance testing. The addition of HC material greatly affects the charge–discharge process and behavior, which impacts on the comprehensive electrochemical performance of LIC. The power density and cycle stability of LIC are improved with little sacrifice of energy density. LIC with 30 wt.% HC was found to have the optimal electrochemical performance, high energy density up to 89.3 Wh kg−1 and power density as high as 7.1 kW kg−1 (based on active material mass of two electrodes), excellent capacity retention of 93.9% after 5000 cycles at 10 C rate. The power density and cycle performance of LIC can be further improved by increasing the HC content. The present work indicates such electrodes as promising candidates for the realization of LIC with high energy density, high power density and long cycle life.

•Nano-SiO2/C was prepared by simple electrospinning and thermal treatment.•SiO2 content influences the morphology and the chemical reactions in LIBs.•The 15%-SiO2/C exhibits high capacity of 658 mAh g−1 after 100 cycles at 50 mA g−1.•The 15%-SiO2/C has good rate performance and retains 356 mAh g−1 at 1000 mA g−1.A series of nanostructured silica–carbon composites containing different contents of SiO2 nanoparticles have been prepared from SiO2 nanoparticles-incorporated polyacrylonitrile (PAN) fibers via electrospinning and subsequent thermal treatment. The SiO2/C composites as negative material for lithium ion batteries benefit from both the high capacity of nano-SiO2 and the good performance of stable 3D nanostructured carbonaceous matrix. The nanostucture can effectively resist large volume changes and accelerate both the lithium ions diffusion and the electronic migration. The SiO2 content significantly affects on both the morphology and the electrochemical performance of the SiO2/C composites. It is found that the composite obtained from the SiO2/PAN fibers with 15 wt% SiO2 exhibits a large capacity of 658 mAh g−1 after 100 cycles at a current density of 50 mA g−1 and retains 356 mAh g−1 at 1000 mA g−1, showing the best performance with high capacity, good rate capability and excellent cycling stability.

•A composite nanofibers were prepared by simple electrospinning method.•The obtained CNFs web were flexible and bendable.•The CNFs were studied as free-standing and binder-free anode for Li-ion batteries.•The CNFs shows good cycling and high rate performance.A new kind of soft carbon and hard carbon composite nanofibers were fabricated from isotropic pitch and polyacrylonitrile via simple electrospinning followed by stabilization and carbonization. The obtained fibrous mat was directly used as anodes of lithium-ion batteries without binder added and current collector. The composite nanofibers electrodes display a large reversible capacity of 452 mA h g−1 at a current density of 20 mA g−1 and a capacity of 255 mA h g−1 at 200 mA g−1 after 200 cycles. The improved electrochemical performance can be attributed to the unique fibrous structure which will facilitate electrons and ions transfer and the porous structure which will accommodate quantities of lithium ions.

Activated carbon is heat-treated in a H2 atmosphere at 600, 800, and 1000 °C for 1 h, respectively, to be used as electrode material for electrical double layer capacitors (EDLCs). After heat treatment, the surface morphology has no obvious change as compared with the raw material. The specific surface area and pore volume of sample treated at 600 °C have a slightly increase while those of samples treated at higher temperature decrease. XPS and elemental analysis indicate that oxygen containing functional groups on the sample are significantly reduced after treatment. The electrochemical performance of samples was evaluated using cyclic voltammetry and galvanostatic charge–discharge tests in 1 M TEABF4/PC electrolyte. The sample treated at 600 °C shows the optimized electrochemical performance with increase capacitance, enhanced stability, and improved energy density. Its initial specific capacitance is near 127 F/g, and initial coulombic efficiency is about 52 %. At 3.0 V, its energy density reaches 32 Wh/kg and specific capacitance is about 70 F/g at 1 A/g even after 10,000 charge–discharge cycles. Thus, heat treatment at 600 °C under H2 atmosphere is an effective method to improve electrochemical properties of EDLCs based on activated carbon material.

•Sulfonated pitch was utilized to synthesize hierarchical porous carbon.•High BET specific surface area of 2602 m2 g−1 was obtained with an activation agent to precursor ration of 1.5.•The specific capacitance could be maintained at 157 F g−1 even at 100 A g−1.•Outstanding cyclic stability with a super high capacitance retention ratio of 98.4% after 10,000 cycles.Hierarchical porous carbon (HPC) has been synthesized using sulfonated pitch as a precursor with a simple KOH activation process. Sulfonated pitch has a high content of oxygen-containing groups which enable it to be easily wetted in KOH solution and facilitate the activation process. The effect of the activation agent to precursor ratio on the porosity and the specific surface area is studied by nitrogen adsorption–desorption. A maximum specific surface area of 3548 m2 g−1 is achieved with a KOH to sulfonated pitch ratio of 3 and this produces a structure with micro-, meso- and macropores. Among the various HPC samples, the sample prepared with an activation agent to precursor ratio of 1.5 exhibits the best electrochemical performance as an electrode in an electrical double layer capacitor (EDLC) in 6 M KOH electrolyte. Its gravimetric specific capacitance is 157 F g−1 at a current density of 100 A g−1 and it has a capacitance retention ratio of 98.4% even after 10,000 cycles. The sample also presents outstanding electrochemical performance in 1 M Li2SO4 and 1 M TEA BF4/PC electrolytes. Thus, HPC derived from sulfonated pitch is a promising electrode material for EDLCs.

•The high voltage electrolyte salt SBP-BF4 was synthesized.•SBP-BF4/PC and TEMA-BF4/PC were used as electrolyte and compared.•The highest withstand voltage for carbon/SBP-BF4–PC system has been observed.A novel quaternary ammonium salt based on spiro-(1,1′)-bipyrolidinium tetrafluoroborate (SBP-BF4) has been synthesized and dissolved in propylene carbonate (PC) with 1.5 mol L−1 (M) concentration for electric double-layer capacitors (EDLCs). The physic-chemical properties and electrochemical performance of SBP-BF4/PC electrolyte are investigated. Compared with the standard electrolyte 1.5 M TEMA-BF4 in PC, the novel SBP-BF4/PC electrolyte exhibited much better electrochemical performance due to its smaller cation size, lower viscosity and higher conductivity. The specific discharge capacitance of activated carbon electrode based EDLCs using SBP-BF4/PC electrolyte is 120 F g−1, the energy density and power density can reach 31 kW kg−1 and 6938 W kg−1, respectively, when the working voltage is 2.7 V and current density is 50 mA g−1. The withstand voltage of activated carbon based EDLCs with SBP-BF4/PC electrolyte can reach to 3.2 V, where the stable discharge capacitance and energy density are 121 F g−1 and 43 Wh kg−1, respectively.

•MCMB with different pre-lithiation capacity as negative electrode in LIC.•Pre-lithiation improves the electrochemical performance of LIC.•The optimal pre-lithiation capacity has been proposed.Lithium ion capacitors are assembled with pre-lithiated mesocarbon microbeads (LMCMB) anode and activated carbon (AC) cathode. The effect of pre-lithiation degrees on the crystal structure of MCMB electrode and the electrochemical capacitance behavior of LIC are investigated by X-ray diffraction (XRD) and the charge-discharge test of three-electrode cell. The structure of graphite still maintained when the pre-lithiation capacity is less than 200 mAh g−1, phase transition takes place with the increase of pre-lithiation capacity from 250 mAh g−1 to 350 mAh g−1. Pre-lithiation degrees of MCMB anode greatly affect the charge-discharge process and behavior, which impact on the electrochemical performance of LIC. The LIC with pre-lithiation capacity of 300 mAh g−1 has the optimal electrochemical performance. The energy density of LIC300 is up to 92.3 Wh kg−1, the power density as high as 5.5 kW kg−1 and the capacity retention is 97.0% after 1000 cycles. The excellent electrochemical performance benefits from the appropriate pre-lithiation capacity of negative electrode. The appropriate pre-lithiation ensures the working voltage of negative electrode in low and relative stable charge-discharge platform corresponding to the mutual phase transition from the second stage graphite intercalation compound (LiC12) to the first stage graphite intercalation compound (LiC6). The stable charge-discharge platform of negative electrode is conductive to the sufficient utilization of AC positive electrode.

•Electrospun carbon nanofiber webs were prepared by pyrolysis of polyacrylonitrile.•The webs as binder-free and current collector-free electrodes for SIBs and LIBs.•Different layer spacing and pore size for Li and Na lead different electrochemical behavior.•Electrochemical performances of the electrodes were high.A series of hard carbon nanofiber-based electrodes derived from electrospun polyacrylonitrile (PAN) nanofibers (PAN-CNFs) have been fabricated by stabilization in air at about 280 °C and then carbonization in N2 at heat treatment temperatures (HTT) between 800 and 1500 °C. The electrochemical performances of the binder-free, current collector-free carbon nanofiber-based anodes in lithium-ion batteries and sodium-ion batteries are systematically investigated and compared. We demonstrate the presence of similar alkali metal insertion mechanisms in both cases, but just the differences of the layer spacing and pore size available for lithium and sodium ion lead the discharge capacity delivered at sloping region and plateau region to vary from the kinds of alkali elements. Although the anodes in sodium-ion batteries show poorer rate capability than that in lithium-ion batteries, they still achieve a reversible sodium intercalation capacity of 275 mAh g−1 and similar cycling stability due to the conductive 3-D network, weakly ordered turbostratic structure and a large interlayer spacing between graphene sheets. The feature of high capacity and stable cycling performance makes PAN-CNFs to be promising candidates as electrodes in rechargeable sodium-ion batteries and lithium-ion batteries.

•The MgO template mesoporous carbon is the first time used in Li/S batteries.•MC is synthesized by a one-step process without catalyst and activation.•The empty pore space of MC/S composites can accommodate the polysulfide anions.•The mesoporous carbon improves the electrochemical performance of Li/S batteries.•The optimal sulfur/carbon ratio has been proposedMesoporous carbon (MC) materials with large pore volume and high surface area have been synthesized as the conductive matrix in the sulfur cathode for the lithium sulfur (Li/S) batteries using a simultaneous templating and carbonization method. The magnesium citrate is used as the precursor of the carbon and provides nanometer sized MgO particles template. Wide-angle X-ray diffraction (WA-XRD), high-resolution transmission electron microscopy (HR-TEM) and N2 sorption analysis show that the resultant carbon material possesses mesopores structure (about 6.5 nm), high surface area (1432 m2 g−1), and large pore volumes (2.894 cm3 g−1) after pyrolysis (1000 °C). Elemental maps confirm that sulfur is homogeneously dispersed in the MC framework after encapsulation. Electrochemical measurements performed on this mesoporous carbon used as an electrode material for Li/S batteries show excellent discharge capacity (1083.6 mAh g−1) at current density 200 mA g−1. The mesopores with large volume and high surface area are crucial in loading insulated sulfur, which provide enough space and good conducting networks for active materials. Meanwhile, mesoporous structure with high adsorption capacity can both effectively accommodate the polysulfide anions and improve the electrochemical performance of Li/S batteries.

•A hard carbon microsphere material was prepared by a stabilization–carbonization method.•Such carbon microsphere has a uniform walnut kernel structure.•The anode material presents excellent rate capability and cycling stability.A hard carbon microsphere (HCS) material with a uniform walnut kernel structure was prepared using polyacrylonitrile (PAN) asa a carbon precursor by a stabilization–carbonization method. The PAN–HCS preserves the original ellipsoidal shapes of natural polyacrylonitrile granules. Structural analysis shows that PAN–HCS is a kind of disordered carbon containing micropores and graphite-like micro-crystallites. The effects of heat-treatment temperature varying from 800 to 1500 °C on electrochemical performance were systemically studied. PAN–HCS–1250 obtained at 1250 °C as a negative material for lithium-ion batteries exhibits a reversible capacity of about 350 mAh g− 1 at 20 mA g− 1 with an excellent rate capability and cycling stability.

Lithium-ion capacitors (LICs) were fabricated using mesocarbon microbeads (MCMB) as a negative electrode and a mixture of activated carbon (AC) and LiFePO4 as a positive electrode (abbreviated as LAC). The phase structure and morphology of LAC samples were characterized by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). The electrochemical performance of the LICs was studied using cyclic voltammetry, charge-discharge rate measurements, and cycle performance testing. A LIC with 30 wt% LiFePO4 was found to have the best electrochemical performance with a specific energy density of 69.02 W h kg−1 remaining at 4 C rate after 100 cycles. Compared with an AC-only positive electrode system, the ratio of practical capacity to theoretical calculated capacity of the LICs was enhanced from 42.22% to 56.59%. It was proved that adding LiFePO4 to AC electrodes not only increased the capacity of the positive electrode, but also improved the electrochemical performances of the whole LICs via Li+ pre-doping.

To investigate the influence of expansion pretreatment for materials on carbon structure, activated carbons (ACs) were prepared from corncob with/without expansion pretreatment by KOH activation, the structure properties of which were determined based on N2 adsorption isotherm at 77 K. The results show that the expansion pretreatment for corncobs is beneficial to the preparation of ACs with high surface area. The specific surface area of the AC derived from corncob with expansion pretreatment (AC-1) is 32.5% larger than that without expansion pretreatment (AC-2). Furthermore, to probe the potential application of corncob-based ACs in electric double-layer capacitor (EDLC), the prepared ACs were used as electrode materials to assemble EDLC, and its electrochemical performance was investigated. The results indicate that the specific capacitance of AC-1 is 276 F/g at 50 mA/g, which increases by 27% compared with that of AC-2 (217 F/g). As electrode materials, AC-1 presents a better electrochemical performance than AC-2, including a higher voltage maintenance ratio and a lower leakage current.