High-Performance Li-Ion Capacitor Based on an Activated Carbon

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A High-Performance Li-Ion Capacitor Based on an Activated Carbon Cathode and a Well-Dispersed Ultrafine TiO Nanoparticles Embedded in Mesoporous Carbon Nanofibers Anode 2

Cheng Yang, Jin le Lan, Wenxiao Liu, Yuan Liu, Yunhua Yu, and Xiaoping Yang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • Publication Date (Web): 12 May 2017 Downloaded from http://pubs.acs.org on May 12, 2017

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ACS Applied Materials & Interfaces

A High-Performance Li-Ion Capacitor Based on an Activated Carbon Cathode and a Well-Dispersed Ultrafine TiO2 Nanoparticles Embedded in Mesoporous Carbon Nanofibers Anode Cheng Yang,†,‡ Jin-Le Lan,†,§,‡ Wen-Xiao Liu,† Yuan Liu,† Yun-Hua Yu,*,†,§ and Xiao-Ping Yang*,†,§ †

State Key Laboratory of Organic-Inorganic Composites, Beijing University of Chemical

Technology, Beijing 100029, China §

Changzhou Institute of Advanced Materials, Beijing University of Chemical Technology, Beijing

100029, China ABSTRACT: A novel Li-ion capacitor based on an activated carbon cathode and a well-dispersed ultrafine TiO2 nanoparticles embedded in mesoporous carbon nanofibers (TiO2@PCNFs) anode was reported. A series of TiO2@PCNFs anode materials were prepared via a scalable electrospinning method followed by carbonization and a post-etching method. The size of TiO2 nanoparticles and the mesoporous structure of the TiO2@PCNFs were tuned by varying amounts of tetraethyl orthosilicate (TEOS) to increase the energy density and power density of the LIC significantly. Such a subtle designed LIC displayed a high energy density of 67.4 Wh kg-1 at a power density of 75 W kg-1. Meanwhile, even when the power density was increased to 5 kW kg-1, the energy density can still maintain 27.5 Wh kg-1. Moreover, the LIC displayed a high capacitance retention of 80.5% after 10000 cycles at 10 A g-1. The outstanding electrochemical performance can be contributed to the synergistic effect of the well-dispersed ultrafine TiO2 nanoparticles, the abundant mesoporous structure and the conductive carbon networks.

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KEYWORDS: Li-ion capacitor, TiO2 nanoparticles, carbon nanofibers, mesoporous structure, electrospinning.


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1. INTRODUCTION Recently, electrochemical energy storage (EES) devices have been attractive in the fields of renewable energy and electric vehicles (EVs).1-2 High energy density, high power density and good cycling stability are really important to EES devices. Lithium-ion batteries (LIBs) have many advantages, such as high energy density, no memory effect and environmental friendliness.3 However, LIBs display low power density and cycle stability.4 In contrast, supercapacitors (SCs) display high power density and cycle stability, but low energy density.5 Therefore, a new type of EES device is strongly expected to overcome the disadvantages of LIBs and SCs. Recently, lithium-ion capacitor (LIC), a newly-emerged hybrid EES device, has been attractive due to combine the advantages of LIBs and SCs.6 In general, the cathode of a LIC is a high surface area carbonaceous electrode, and the anode of a LIC is a Li-insertion electrode.7 Owing to the two different storage mechanisms of the electrodes, LICs exhibit higher power density than LIBs and higher energy density than SCs.8,9 Obviously, the cathode and anode materials are really important to LICs.1,10 Generally, activated carbon (AC) is an excellent cathode material for LICs due to its overwhelming advantages including high specific surface area, controllable meso/microporosity, cycling stability, excellent electronic conductivity, eco-friendliness and low cost.11,12 Therefore, the electrochemical performance of LICs with an AC cathode primarily relies on a high-performance anode. Previous reports have shown that titanium-based compounds, such as Li4Ti5O12, TiO2 (B) and anatase TiO2, are excellent anode materials for LICs.13-16 Especially, the anatase TiO2 as the anode material for LICs and LIBs has been attractive due to its high cycling stability, high working voltage (∼1.5 V vs. Li+/Li), low cost, and good environmental benignity.15-23 However, the poor electrical conductivity and the slow Li-ion



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diffusion of TiO2 seriously limit its practical use.19,23 So far, various strategies have been extensively explored to overcome these disadvantages of TiO2. Constructing nanostructure TiO2 can obtain large surface area and shorten Li-ion diffusion paths.22-25 However, the high active surface of nanostructure TiO2 may lead to the serious aggregation of nanostructure TiO2, resulting in the decreased rate capability of nanostructure TiO2 anodes. Fabricating TiO2/carbon hybrids can inhibit the agglomeration of nanostructure TiO2 and increase the conductivity of TiO2.26-28 Electrospinning is an inexpensive, facile and scalable method for the fabrication of one-dimensional nanostructure metal oxide/carbon hybrids.29-31 However, the carbon usually covers the surface of metal oxide tightly and blocks the Li-ion diffusion paths, resulting in the decreased rate capability of metal oxide/carbon hybrids anodes. In this context, designing porous structure is an effective way to offer desirable large electrode-electrolyte interfacial area and numerous Li-ion diffusion paths, thus improving the rate capability of metal oxide/carbon hybrids anodes.32-34 Herein, we successfully fabricated a high-performance LIC based on an activated carbon cathode and a well-dispersed ultrafine TiO2 nanoparticles embedded in mesoporous carbon nanofibers (TiO2@PCNFs) anode. The TiO2@PCNFs were prepared by a scalable electrospinning method combined with carbonization and a post-etching method. The well-dispersed ultrafine TiO2 nanoparticles can provide short Li-ion diffusion paths and large reaction area, endowing the high energy density and power density of the LIC. Meanwhile, the abundant mesoporous structure can offer numerous Li-ion diffusion paths, endowing the power density of the LIC. Moreover, the carbon nanofibers can inhibit the agglomeration of TiO2 nanoparticles and provide conductive carbon networks for quick electron transfer, endowing the high cycling stability and power density of the


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LIC.



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2. EXPERIMENTAL SECTION 2.1. Materials Synthesis. Firstly, 1 g polyvinylpylrrolidone (PVP, Mw = 1 300 000) was mixed with 10 mL of ethanol and 3 mL of acetic acid, followed by magnetic stirring for 8 h at room temperature, to obtain a PVP solution. Various amounts of tetraethyl orthosilicate (TEOS) and 1.7 g tetrabutyltitanate (TBT) were added into the PVP solution, followed by magnetic stirring for 1 h at room temperature, to obtain a solution for electrospinning. A large-scale electrospinning was performed using a nanofibers electrospinning machine (Elmarco NS Lab 2G, Czech Republic) with a substrate speed of 3 cm/min, a carriage speed of 25 cm/s, an electrostatic voltage of 45 kV, and a distance of 18 cm between electrode and substrate at room temperature. The as-spun nanofibers were carbonized at 800 °C for 1 h in N2 to obtain the hybrid carbon nanofibers containing TiO2 and SiO2 nanoparticles (TiO2-SiO2@CNFs), which were etched with 2.5 M NaOH at 60 °C for 3 h, washed with deionized water, and then dried to obtain TiO2@PCNFs. TiO2@PCNFs with different addition of TEOS (0, 4, 8, 12, and 16 mmol) were denoted as TiO2@CNFs, TiO2@PCNF-4, TiO2@PCNF-8, TiO2@PCNF-12, and TiO2@PCNF-16, respectively. 2.2. Materials Characterization. The phase analysis of TiO2@PCNFs was examined by X-ray diffraction (XRD, D8 Advance, Brucker) equipped with Cu Kα as the radiation source. The morphologies and structures of TiO2@PCNFs were examined by a field emission-scanning electron microscopy (FE-SEM, Supra55, Carl Zeiss) and a high resolution transmission electron microscopy (HR-TEM, Tecnai G2 F30 S-TWIN) with an energy dispersive X-ray (EDX) spectroscopy. The thermal behaviors of TiO2@PCNFs were examined by a thermogravimetric analysis (TGA) instrument (TA-Q50, America) with increasing temperature from 30 to 800 °C by 10 °C min-1 in air. The chemical composition and oxidation states of titanium on the surface of TiO2@PCNF-12 was


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examined by X-ray photoelectron spectroscopy (XPS) measurement on an EscaLab 250 XPS instrument (Thermo Fisher Scientific) with a monochromatic Al Kα X-ray source. The Nitrogen adsorption-desorption measurements were conducted at 77 K on a Quantachrome SI instrument, and Barrett-Joyner-Halenda (BJH) method was adopted to calculate the surface area and the pore diameters. 2.3. Electrochemical Measurements. The commercially available AC cathode was provided by Research Institute of Tsinghua University in Shenzhen. The electrochemical analysis of the TiO2@PCNFs anodes, the activated carbon (AC) cathode and the AC/TiO2@PCNFs LICs were conducted using two-electrode cells. The TiO2@PCNFs anodes were prepared by pressing slurries of TiO2@PCNFs, carbon black, and polyvinylidene fluoride (PVDF) at a weight ratio of 7:2:1 in N-methyl pyrrolidone (NMP) on Ni foils, and dried at 120 °C for 12 h in an oven. The TiO2@PCNFs/Li+ and AC/Li+ half-cells were assembled in an argon-filled glove box by using Li-metal foils as counter electrodes in 2025-type coin cells. The working electrode and Li-metal foil were separated by a polypropylene membrane with a 1 M LiPF6 solution in a 1:1 (v/v) mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) as electrolyte. The TiO2@PCNFs anodes was pre-lithiated before assembled into the LICs. The TiO2@PCNFs/Li+ half-cells were discharged from the open circuit voltage (OCV) to 1.0 V at 0.1 A g-1, and then charged to OCV at 0.1 A g-1. The TiO2@PCNFs/Li+ half-cells were discharged/charged in the same way for three cycles. The LICs were assembled as two-electrode cells using the pre-lithiated TiO2@PCNFs anodes, the AC cathode, and the same electrolyte in the half-cells. The optimized mass ratio of active materials for the cathode and anode was 3. The active materials of the AC cathode and the TiO2@PCNFs anodes were AC and TiO2@PCNFs, respectively. The mass loading of AC and TiO2@PCNFs was about 3.6 mg



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and 1.2 mg, respectively. Cyclic voltammetry (CV) and electrochemical impedance spectra (EIS) were examined by an Autolab (Metrohm) Analyzer. The charge-discharge measurements were examined by a LAND CT2001A battery measurement system. All the electrochemical tests were performed at room temperature.


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3. RESULTS AND DISCUSSION 3.1. Anode Materials: TiO2@PCNFs. The preparation process of TiO2@PCNFs is shown in Figure 1. Firstly, TiO2-SiO2@CNFs were prepared by carbonizing the as-spun nanofiber web composed of PVP with TEOS and TBT at 800℃ for 1 h in N2, and then TiO2@PCNFs were obtained by etching of the SiO2 template from TiO2-SiO2@CNFs in 2.5M NaOH.

Figure 1. Schematic illustration of the preparation process of TiO2@PCNFs.

Figure 2. XRD patterns of TiO2@PCNFs. The XRD patterns of TiO2@PCNFs are shown in Figure 2. All of the peaks in the patterns of samples can be well-indexed to the anatase phase of TiO2 (JCPDS 21-1272).22 Furthermore, no clear peaks were assigned to carbon, indicating the amorphous state of PVP-derived carbon. The average particle sizes of the TiO2 calculated by the Scherrer equation on the anatase (101) diffraction peak were 11.8, 11.0, 6.0, 3.5, and 4.3 nm for TiO2@CNFs, TiO2@PCNF-4, TiO2@PCNF-8,



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TiO2@PCNF-12 and TiO2@PCNF-16, respectively. When the amount of TEOS was increased, the size of TiO2 nanoparticles was initially decreased because the SiO2 nanoparticles generated from the TEOS can effectively inhibit the growth and agglomeration of TiO2 nanoparticles during carbonization. However, when the amount of TEOS was increased to a certain extent, instead, the size of TiO2 nanoparticles was increased because the agglomeration of SiO2 nanoparticles had the weak effect of inhibiting the growth and agglomeration of TiO2 nanoparticles. It is notable that the amount of TEOS in precursor solution should be optimized to obtain the TiO2@PCNF anode material with well-dispersed ultrafine TiO2 nanoparticles. In this work the optimal TiO2@PCNFs anode material was the TiO2@PCNF-12 with the smallest size of TiO2 nanoparticles (3.5 nm). TGA revealed that the weight fractions of TiO2 in the samples were about 65 wt% (Figure S1). XPS was performed to analyze the chemical composition and oxidation states of titanium on the surface of TiO2@PCNF-12. In the general spectrum (Figure S2a), Ti, O, and C elements were clearly observed. The Ti 2p high resolution XPS spectrum of TiO2@PCNF-12 (Figure S2b) showed that the Ti 2p peaks with bonding energies of 459.2 eV and 464.7 eV, attributable to Ti 2p3/2 and Ti 2p1/2, respectively, were related to the Ti4+.32


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Figure 3. TEM images of (a) TiO2@CNFs, (b) TiO2@PCNF-4, (c) TiO2@PCNF-8, (d) TiO2@PCNF-12, and (e) TiO2@PCNF-16, (f) SEM image of TiO2@PCNF-12. The morphologies of TiO2@PCNFs are shown in Figure 3. It was found that the dark/light contrast along the axial direction became clear with increasing the amount of TEOS in precursor solution (Figure 3a-e) because more and more pores were developed by etching off SiO2 nanoparticles. These pores were exposed to the surface of carbon nanofibers, resulting in the large surface area and the rough cross section (Figure 3f). All the TiO2@PCNFs were individual and uniform with the diameters of 300-400 nm (Figure S3). These carbon nanofibers constructed conductive carbon networks as quick electron pathways to the interface of TiO2 nanoparticles. Moreover, the pores in the carbon nanofibers made electrolyte move through them and contact with the interface of TiO2 nanoparticles quickly, endowing the high rate capability of TiO2@PCNFs



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anodes and LICs.33

Figure 4. HR-TEM images of (a) and (b) TiO2@PCNF-12, (c) STEM image and (d) corresponding EDX elemental mapping images of TiO2@PCNF-12. The microstructure of TiO2@PCNF-12 was further characterized using HR-TEM. As shown in Figure 4a, TiO2 nanoparticles were ultrafine, uniform in size and well-dispersed in the porous carbon nanofibers, and the average particle size of the TiO2 observed in HR-TEM images were quite similar to that calculated by the Scherrer equation using the XRD data. Furthermore, the lattice fringes of the TiO2 nanoparticles with adjacent plane distance of 0.35 nm were clearly observed in Figure 4b, corresponding to the (101) plane of anatase TiO2.22 The selected area electron diffraction (SAED) pattern taken by focusing the electron beam on an individual fiber indicated that the TiO2@PCNF-12 was polycrystalline with the diffraction rings (inset in Figure 4b).24 The local elemental composition of TiO2@PCNF-12 was further analyzed by scanning TEM microanalysis (Figure 4c) and EDX spectroscopy (Figure 4d). It can be seen that the C, O, and Ti elements were homogenously


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distributed in TiO2@PCNF-12 along the one-dimensional nanostructure with an indicator of well-dispersion of the TiO2 nanoparticles. The well-dispersed ultrafine TiO2 nanoparticles can not only provide large surface area, but also shorten Li-ion diffusion paths, endowing the high rate capability of TiO2@PCNFs anodes and LICs.23

Figure 5. (a) Nitrogen sorption isotherms and (b) pore size distribution curves of TiO2@PCNFs. The

porous

structure

and

the

surface

area

of

all

samples

were

analyzed

by

Brunauer-Emmett-Teller (BET) measurements. As shown in Figure 5a, all isotherms showed a sharp N2 uptake at low pressures and a slightly upswept rear edge at high pressures, indicative of the presence of micropores formed by the gas released from PVP during carbonization.35 According to the IUPAC classification, TiO2@CNFs and TiO2@PCNF-4 exhibited Type I isotherms, showing the microporous characteristic, while TiO2@PCNF-8, TiO2@PCNF-12 and TiO2@PCNF-16 presented the Type Ⅳ isotherms with distinct hysteresis loops, suggesting the existence of mesopores developed by etching off the SiO2 nanoparticles generated from the TEOS.36 The particular pore size distributions were calculated from the desorption isotherm using BJH model (Figure 5b). The pore size distributions of all the samples ranged from 0.5 to 15 nm, and most of pores were mesopores in the range of 2 to 15 nm. The BET specific surface area of TiO2@CNFs, TiO2@PCNF-4,



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TiO2@PCNF-8, TiO2@PCNF-12 and TiO2@PCNF-16 was 155.06, 182.06, 297.22, 392.22, and 366.96 m2 g-1, respectively. When the amount of TEOS was increased, the specific surface area was initially increased because the mesopores formed by etching off the SiO2 nanoparticles can provide large specific surface area. However, when the amount of TEOS was increased to a certain extent, instead, the specific surface area was decreased because the agglomeration of SiO2 nanoparticles can adversely cause reduced surface area. Therefore, the specific surface area of the TiO2@PCNFs samples can be tuned by altering the amount of TEOS in precursor solution. In this work the TiO2@PCNF-12 had the highest specific surface area (392.22 m2 g-1) in all the samples. The abundant mesoporous structure and the large specific surface area of the TiO2@PCNFs can increase electrolyte/electrode contact area and shorten Li-ion diffusion paths, endowing the high rate capability of TiO2@PCNFs anodes and LICs.33


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Figure 6. (a) CV curves of TiO2@PCNFs electrodes at a scanning rate of 0.1 mV s-1, (b) charge/discharge curves of TiO2@PCNFs electrodes during the 1st cycle at 0.2 C, (c) cycling performance of TiO2@PCNFs electrodes at 0.2 C, (d) rate capability of TiO2@PCNFs electrodes, (e) cycling performance of TiO2@PCNFs electrodes at 10 C and (f) Nyquist plots of TiO2@PCNFs



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electrodes over the frequency range 100 kHz to 0.1 Hz before cycling. All measurements were performed in the voltage range of 1.0-3.0 V vs. Li+/Li. The CV curves of TiO2@PCNFs electrodes are shown in Figure 6a. The cathodic and anodic peaks were observed at 1.74 V and 1.99 V, indicating the Li+ insertion/extraction processes between the tetragonal and orthorhombic phases with lithiated reaction into anatase TiO2.25 Thanks to the smallest size of TiO2 nanoparticles (3.5 nm) and the highest specific surface area (392.22 m2 g-1), the TiO2@PCNF-12 electrode delivered a largest area surrounded by the CV curve in all the samples, indicating the highest specific capacity of the TiO2@PCNF-12 electrode. The first charge/discharge curves of TiO2@PCNFs electrodes are shown in Figure 6b. The typical voltage plateaus of discharging (1.7-1.8 V) and charging (1.9-2.0 V) processes, reflecting the Li+ insertion/extraction processes of the anatase TiO2, were not obvious. This was probably due to the well-dispersed ultrafine TiO2 nanoparticles embedded in the carbon nanofibers.32 The initial capacity loss was caused by (1) irreversible formation of the SEI films on the electrode surface due to the ultrafine TiO2 nanoparticles and the high specific surface area of TiO2@PCNFs, (2) irreversible intercalation of Li+ into TiO2, and (3) electrolyte decomposition.4 The TiO2@PCNF-12 electrode exhibited not only the highest capacity of 239.4 mAh g-1 after 100 cycles (Figure 6c), but also the highest rate capability in all the samples (Figure 6d) because its ultrafine TiO2 nanoparticles provided large reaction area and short paths for Li-ion diffusion,23 and its mesoporous structure provided the efficient transport pathways for Li-ion diffusion.33 Moreover, the carbon nanofibers inhibited the agglomeration of TiO2 nanoparticles and provided conductive carbon networks for quick electron transfer, resulting in the high rate capability of the TiO2@PCNF-12 electrode.


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As shown in Figure 6e, the TiO2@PCNF-12 electrode exhibited a superior cycling stability, maintaining a high capacity of 125.7 mAh g-1 with a capacity retention of 74.8% after 2000 cycles at 10 C between 1.0 and 3.0 V. The carbon nanofibers can mitigate the agglomeration of TiO2 nanoparticles, resulting in the high cycling stability of the TiO2@PCNF-12 electrode. The Nyquist plots of TiO2@PCNFs electrodes before cycling are shown in Figure 6f. In general, the high-frequency region is a semicircle, corresponding to the charge transfer resistance of the electrode-electrolyte interface, indicating that Li+ transfer from the electrolyte to the surface of TiO2@PCNFs electrodes.37 The low-frequency region is a inclined line, corresponding to Li-ion diffusion process in the TiO2@PCNFs electrodes, indicating the Li+ insertion/extraction processes of the TiO2 nanoparticles.37 In all the TiO2@PCNFs electrodes, the TiO2@PCNF-12 electrode exhibited the smallest resistance and the most superior Li-ion diffusion process as evidenced by the drastically reduced diameter of the semicircle at the high-frequency region and the appreciably steep slope line at the low-frequency region, respectively. The results were all in favor of the superior rate capability of TiO2@PCNF-12.



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3.2. AC/TiO2@PCNFs Li-Ion Capacitors. Considering the exceptional performance of the TiO2@PCNFs anodes as mentioned above, we designed and assembled a series of LICs by using the as-prepared pre-lithiated TiO2@PCNFs anodes and commercial AC cathodes. The assembled structure of the LICs in 1 M LiPF6 in EC-DMC electrolyte solution is shown in Figure 7. According to the principle Q+ = Q-, the mass of the two electrodes must be adjusted to equalize the capacity to achieve a high energy density of LIC.15 The specific capacity Qsp is commonly measured, and the mass balance can be expressed as m+/m- = Qsp-/Qsp+ by following the relationship Q = m·Qsp. A highly symmetrical Galvanostatic charge-discharge (GCD) curve of the AC electrode at 1.0 A g-1 between 2.0 and 4.0 V is shown in Figure S4a, indicating the characteristic of electric double layer storage mechanism.6 The AC electrode displayed a discharge capacity of 55.6 mAh g-1 without any capacity fading up to 200 cycles (Figure S4b). These results suggested that the AC electrode was an excellent cathode for LICs. Based on the capacity values of the AC cathode and the TiO2@PCNFs anodes, the mass ratio of the active materials for the cathode and the anodes in the AC/TiO2@PCNFs LICs was chosen to be 3.

Figure 7. Schematic illustration of the assembled structure of the Li-ion capacitor.


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Figure 8. (a) CV curves of AC/TiO2@PCNFs LICs at 50 mV s-1, (b) CV curves of the AC/TiO2@PCNF-12 LIC at different scan rates, (c) GCD curves of AC/TiO2@PCNFs LICs at 0.1 A g-1, and (d) GCD curves of the AC/TiO2@PCNF-12 LIC at different current densities. All measurements were performed in the voltage range of 0-3.0 V vs. Li+/Li. CV curves of AC/TiO2@PCNFs LICs are shown in Figure 8a. The LICs demonstrated non-rectangular shapes due to the two different Li-ion storage mechanisms: surface adsorption/desorption process and redox reactions.15 Additionally, the AC/TiO2@PCNF-12 LIC delivered apparently the largest area surrounded by the CV curve, indicating the highest specific capacity due to the smallest size of TiO2 nanoparticles and highest specific surface area of TiO2@PCNF-12. As shown in Figure 8b, the LIC exhibited a gradual deviation from the ideal rectangular shape with increasing scan rates because of the two different Li-ion storage mechanisms.15 As shown in Figure 8c and d, the LICs demonstrated non-linear slopes especially at



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low current densities, indicating that the Li-ion storage mechanism of LICs was based on the combination of the LIB-type and the electrochemical double layer capacitor-type behavior.1,15 In addition, the negligible IR drops indicated an excellent electrical conductivity due to the quick electron transfer and Li-ion diffusion of TiO2@PCNFs.

Figure 9. (a) Specific discharge capacitance versus current density plots, (b) Ragone plots of AC/TiO2@PCNFs LICs. Inset: a green LED can be light up by the AC/TiO2@PCNF-12 LIC, (c) the relationship between the size of TiO2 nanoparticles and the energy densities and (d) the relationship between the specific surface area of TiO2@PCNFs and the energy densities of AC/TiO2@PCNFs LICs at different power densities. All measurements were performed in the voltage range of 0-3.0 V vs. Li+/Li.


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The specific discharge capacitance (CSP) versus current density plots of AC/TiO2@PCNFs LICs are shown in Figure 9a. The discharge capacitance (Ccell) and the CSP of LIC were calculated from the equations Ccell = (i·t/∆V)

(1)

CSP = (4Ccell/m)

(2)

where i is the applied current, t is the discharge time, m is the total mass of the active materials of the AC cathode and the TiO2@PCNFs anodes, and ∆V is the potential difference.45 When the current density was increased, the specific discharge capacitances of the AC/TiO2@PCNFs LICs were decreased due to the surface adsorption process and polarization effect. The ions were closed to the surface of the electrode material in the surface adsorption process at high current density. Therefore, the electrochemical active species were predominantly decreased，resulting in the low capacitance value at high current density.15 However, owing to the smallest size of TiO2 nanoparticles and highest specific surface area of TiO2@PCNF-12, the AC/TiO2@PCNF-12 LIC displayed the highest rate capability in the samples. The AC/TiO2@PCNF-12 LIC exhibited a specific discharge capacitance of 213.1 F g-1 at 0.05 A g-1, and still maintained 98.4 F g-1 when the current density was increased to 2.0 A g-1. The Ragone plots of AC/TiO2@PCNFs LICs are shown in Figure 9b. The energy density and the power density were calculated from the equations P = ∆E·i/m

(3)

E = P·t

(4)

where ∆E = (Emax + Emin)/2, Emax and Emin are the initial and the final potentials of Galvanostatic discharge curves at different current densities, respectively, and m is the total mass of the active



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materials of the AC cathode and the TiO2@PCNFs anodes.45 The AC/TiO2@PCNF-12 LIC displayed highest energy density and power density in the LICs. Specifically, the maximum energy density of the AC/TiO2@PCNF-12 LIC reached 67.4 Wh kg-1 at a power density of 75 W kg-1. Even when the power density was increased to 3 kW kg-1, the energy density can still maintain 30.5 Wh kg-1, indicating that the AC/TiO2@PCNF-12 LIC exhibited prominent energy density and power density. As shown in the inset of Figure 9b, a green light emitting diode (LED) with a high working voltage of 3.2 V can be easily light up by the AC/TiO2@PCNF-12 LIC. This physical demonstration further indicated the high potential of the AC/TiO2@PCNF-12 LIC for electrochemical energy storage with high energy and power density. In order to further illustrate the relationship between the structure of TiO2@PCNFs and the performance of AC/TiO2@PCNFs LICs, the energy densities of the AC/TiO2@PCNFs LICs at different power densities were plotted as a function of the size of TiO2 nanoparticles and the specific surface area of TiO2@PCNFs, which are presented in Figure 9c and d, respectively. Obviously, when the size of TiO2 nanoparticles was decreased, the energy densities of AC/TiO2@PCNFs LICs at different power densities were increased remarkably. This indicates that optimizing the size of TiO2 nanoparticles can improve the energy density and power density by shortening the Li-ion diffusion paths and enlarging the reaction area of the well-dispersed ultrafine TiO2 nanoparticles.23 Meanwhile, when the specific surface area of TiO2@PCNFs was increased, the energy densities of AC/TiO2@PCNFs LICs at different power densities were also increased significantly. This proved that the abundant mesoporous structure can endow the high power density by offering large surface area and numerous Li-ion diffusion paths from the electrolyte to the interface of TiO2 nanoparticles.33 Therefore, it can be concluded that the outstanding electrochemical performance of


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the AC/TiO2@PCNF-12 LIC are contributed to the smallest size of TiO2 nanoparticles and highest specific surface area of TiO2@PCNF-12.

Figure 10. (a) Cycling performance of AC/TiO2@PCNFs LICs at 10 A g-1 between 0 and 3.0 V and (b) Ragone plots of the AC/TiO2@PCNF-12 LIC in comparison to the other LICs from References. The long-term cycling stability of the AC/TiO2@PCNF-12 LIC at 10 A g-1 are shown in Figure 10a. It exhibited a high capacitance retention of 80.5% and a coulombic efficiency of over 97.0% after 10000 cycles at 10 A g-1 because the carbon nanofibers inhibited the agglomeration of TiO2 nanoparticles, resulting in the high cycling stability of the TiO2@PCNF-12 electrode. As shown in Figure 10b, when the power density was increased from 75 to 5000 W kg-1, the energy density of the AC/TiO2@PCNF-12 LIC was only reduced from 67.4 to 27.5 Wh kg-1. Notably, the energy density and the power density of the AC/TiO2@PCNF-12 LIC were much higher than those of the reported



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LICs in Table 1. Table 1. LICs Performances Reported in the Previous Literature Studies LIC

Energy density

Power density

Ref.

(Wh kg-1)

(W kg-1)

AC/LTO-1

11

800

38

AC/TiO2-B needle shaped grains

45

420

13

AC/LiTi2(PO4)3

15

1000

39

AC/Li2FeSiO4

43

200

40

AC/Li2MnSiO4

54

150

41

AC/LiCrTiO4

23

4000

42

CNF/PLTO-C

27.5

3000

43

CNT/TiO2-B nanowires

12.5

2.52

44

AC/TiO2-B nanorods

23

2800

45

MWCNT/TiO2-B nanotubes

19.3

2520

46

AC/LTO-2

10

2000

47

AC/F-Fe2O3

28

550

48

AC/TiP2O7

13

371

49

AC/TiO2@PCNF-12

67.4-27.5

75-5000

This work

According to the aforementioned results, the superior electrochemical performance of the AC/TiO2@PCNF-12 LIC can be ascribed to the following reasons. On the one hand, the well-dispersed ultrafine TiO2 nanoparticles can improve the energy density and power density of the AC/TiO2@PCNF-12 LIC by offering Li-ion diffusion paths and large reaction area. On the other


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hand, the abundant mesoporous structure can provide numerous Li-ion diffusion paths from the electrolyte to the interface of TiO2 nanoparticles, endowing the high power density of the AC/TiO2@PCNF-12 LIC. Additionally, the carbon nanofibers can mitigate the agglomeration of TiO2 nanoparticles and provide continuous pathways for electron transport, resulting in the high cycling stability and power density of the AC/TiO2@PCNF-12 LIC. 4. CONCLUSION We have successfully fabricated a well-dispersed ultrafine TiO2@PCNFs anode via a scalable electrospinning technique combined with carbonization and a post-etching method. On this basis, a high performance LIC based on a commercial AC cathode and the as-prepared TiO2@PCNFs anode have been designed and fabricated. The results indicate that the size of TiO2 nanoparticles, the mesoporous structure and the specific surface area of the TiO2@PCNFs can be tuned to improve both energy density and power density of LICs by varying the amount of TEOS in the electrospinning solution. Among all the TiO2@PCNFs samples, the optimized TiO2@PCNFs-12 anode with the smallest size of TiO2 nanoparticles (~3.5nm) and the highest specific surface area (~392.22 m2 g-1) exhibits the most superior lithium storage performance. Moreover, the LIC based on the TiO2@PCNF-12 anode and the AC cathode (AC/TiO2@PCNF-12) displayed high energy density vs. power density (67.4 Wh kg-1 vs. 75 W kg-1, 27.5 Wh kg-1 vs. 5 kW kg-1) as well as a superior cycling stability with a capacitance retention of 80.5% after 10000 cycles at 10 A g-1. Such superior electrochemical behavior can be attributed to the synergistic effect of the well-dispersed ultra-small TiO2 nanoparticles, the numerous mesoporous structure and the conductive carbon networks. This synergistic effect created a series of enhancements in the function, including the short Li-ion diffusion paths, the quick electron transfer, the large accessible surface area and reaction area,



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and the mitigation of the agglomeration of TiO2 nanoparticles. This work provided a novel high-performance LIC device as well as a promising anode material for advanced LIBs and LICs. ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website at DOI: TGA patterns of TiO2@PCNFs, Survey-scan XPS spectra and Ti 2p high-resolution XPS spectra of TiO2@PCNF-12, SEM images of TiO2@PCNFs, Galvanostatic charge-discharge curve and cycling performance of the AC electrode (PDF) AUTHOR INFORMATION Corresponding Authors *E-mail: [email protected] (Y.-H. Y.). *E-mail: [email protected] (X.-P. Y.). Author Contributions

‡C. Y. and J.-L. L. contributed equally to this work. Notes The authors declare no competing financial interest. ACKNOWLEDGEMENTS This work was financially supported by National Natural Science Foundation of China (No. 51072013, 51272021 and 51142004) and Natural Science Foundation of Jiangsu Province (BK20140270). We also thanked Research Institute of Tsinghua University in Shenzhen for providing the AC cathode.


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REFERENCES (1) Leng, K.; Zhang, F.; Zhang, L.; Zhang, T. F.; Wu, Y. P.; Lu, Y. H.; Huang, Y.; Chen, Y. S. Graphene-Based Li-Ion Hybrid Supercapacitors with Ultrahigh Performance. Nano Res. 2013, 6, 581-592. (2) Wu, R. F.; Shen, S. Y.; Xia, G. F.; Zhu, F. J.; Lastoskie, C.; Zhang, J. L. Soft-Templated Self-Assembly of Mesoporous Anatase TiO2/Carbon Composite Nanospheres for High-Performance Lithium Ion Batteries. ACS Appl. Mater. Interfaces 2016, 8, 19968-19978. (3) Hassan, F. M.; Batmaz, R.; Li, J.; Wang, X.; Xiao, X.; Yu, A.; Chen, Z. Evidence of Covalent Synergy in Silicon-Sulfur-Graphene Yielding Highly Efficient and Long-Life Lithium-Ion Batteries.

Nat. Commun. 2015, 6, 8597-8607. (4) Shen, L. F.; Uchaker, E.; Yuan, C. Z.; Nie, P.; Zhang, M.; Zhang, X. G.; Cao, G. Z. Three-Dimensional Coherent Titania-Mesoporous Carbon Nanocomposite and Its Lithium-Ion Storage Properties. ACS Appl. Mater. Interfaces 2012, 4, 2985-2992. (5) Simon, P.; Gogotsi, Y.; Dunn, B. Where Do Batteries End and Supercapacitors Begin. Science 2014, 343, 1210-1211. (6) Arun, N.; Jain, A.; Aravindan, V.; Jayaraman, S.; Ling, W. C.; Srinivasan, M. P.; Madhavi, S. Nanostructured Spinel LiNi0.5Mn1.5O4 as New Insertion Anode for Advanced Li-Ion Capacitors with High Power Capability. Nano Energy 2015, 12, 69-75. (7) Cericola, D.; Novák, P.; Wokaun, A.; Kötz, R. Hybridization of Electrochemical Capacitors and Rechargeable Batteries: An Experimental Analysis of the Different Possible Approaches Utilizing Activated Carbon, Li4Ti5O12 and LiMn2O4. J. Power Sources 2011, 196, 10305-10313. (8) Liu, C.; Li, F.; Ma, L. P.; Cheng, H. M. Advanced Materials for Energy Storage. Adv. Mater. 2010,



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

22, E28-E62. (9) Simon, P.; Gogotsi, Y. Materials for Electrochemical Capacitors. Nat. Mater. 2008, 7, 845-854. (10) Zhang, F.; Zhang, T.; Yang, X.; Zhang, L.; Leng, K.; Huang, Y.; Chen, Y. A High-Performance Supercapacitor-Battery Hybrid Energy Storage Device Based on Graphene-Enhanced Electrode Materials with Ultrahigh Energy Density. Energy Environ. Sci. 2013, 6, 1623-1632. (11) Su, D. S.; Schlögl, R. Nanostructured Carbon and Carbon Nanocomposites for Electrochemical Energy Storage Applications. ChemSusChem 2010, 3, 136-168. (12) Inagaki, M.; Konno, H.; Tanaike, O. Carbon Materials for Electrochemical Capacitors. J. Power

Sources 2010, 195, 7880-7903. (13) Brousse, T.; Marchand, R.; Taberna, P.; Simon, P. TiO2 (B)/Activated Carbon Non-Aqueous Hybrid System for Energy Storage. J. Power Sources 2006, 158, 571-577. (14) Ye, L.; Liang, Q.; Lei, Y.; Yu, X.; Han, C.; Shen, W.; Huang, Z.; Kang, F.; Yang, Q. A High Performance Li-Ion Capacitor Constructed with Li4Ti5O12/C Hybrid and Porous Graphene Macroform. J. Power Sources 2015, 282, 174-178. (15) Wang, H.; Guan, C.; Wang, X.; Fan, H. J. A High Energy and Power Li-Ion Capacitor Based on a TiO2 Nanobelt Array Anode and a Graphene Hydrogel Cathode. Small 2015, 11, 1470-1477. (16) Que, L.; Wang, Z.; Yu, F.; Gu, D. 3D Ultralong Nanowire Arrays with a Tailored Hydrogen Titanate Phase as Binder-Free Anodes for Li-Ion Capacitors. J. Mater. Chem. A 2016, 4, 8716-8723. (17) Zhu, G. N.; Wang, Y. G.; Xia, Y. Y. Ti-Based Compounds as Anode Materials for Li-Ion Batteries. Energy Environ. Sci. 2012, 5, 6652-6667. (18) Han, H.; Song, T.; Bae, J. Y.; Nazar, L. F.; Kim, H.; Paik, U. Nitridated TiO2 Hollow Nanofibers as an Anode Material for High Power Lithium Ion Batteries. Energy Environ. Sci. 2011, 4,


Page 28 of 33

Page 29 of 33

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


4532-4536. (19) Yang, S. B.; Feng, X. L.; Mullen, K. Sandwich-Like, Graphene-Based Titania Nanosheets with High Surface Area for Fast Lithium Storage. Adv. Mater. 2011, 23, 3575-3579. (20) Chen, Z. H.; Belharouak, I.; Sun, Y. K.; Amine, K. Titanium-Based Anode Materials for Safe Lithium-Ion Batteries. Adv. Funct. Mater. 2013, 23, 959-969. (21) Luo, J. S.; Xia, X. H.; Luo, Y. S.; Guan, C.; Liu, J. L.; Qi, X. Y.; Ng, C. F.; Yu, T.; Zhang, H.; Fan, H. J. Rationally Designed Hierarchical TiO2@Fe2O3 Hollow Nanostructures for Improved Lithium Ion Storage. Adv. Energy Mater. 2013, 3, 737-743. (22) Chen, J. S.; Tan, Y. L.; Li, C. M.; Cheah, Y. L.; Luan, D.; Madhavi, S.; Boey, F. Y. C.; Archer, L. A.; Lou, X. W. Constructing Hierarchical Spheres from Large Ultrathin Anatase TiO2 Nanosheets with Nearly 100% Exposed (001) Facets for Fast Reversible Lithium Storage. J. Am. Chem. Soc. 2010, 132, 6124-6130. (23) Sondergaard, M.; Dalgaard, K. J.; Bojesen, E. D.; Wonsyld, K.; Dahl, S.; Iversen, B. B. In Situ Monitoring of TiO2 (B)/Anatase Nanoparticle Formation and Application in Li-Ion and Na-Ion Batteries. J. Mater. Chem. A 2015, 3, 18667-18674. (24) Chen, D.; Cao, L.; Huang, F.; Imperia, P.; Cheng, Y. B.; Caruso, R. A. Synthesis of Monodisperse Mesoporous Titania Beads with Controllable Diameter, High Surface Area, and Variable Pore Diameters (14-23 nm). J. Am. Chem. Soc. 2010, 132, 4438-4444. (25) Liu, J.; Chen, J. S.; Wei, X.; Lou, X. W.; Liu, X. W. Sandwich-Like, Stacked Ultrathin Titanate Nanosheets for Ultrafast Lithium Storage. Adv. Mater. 2011, 23, 998-1002. (26) Goriparti, S.; Miele, E.; Prato, M.; Scarpellini, A.; Marras, S.; Monaco, S.; Toma, A.; Messina, G. C.; Alabastri, A.; Angelis, F. D.; Manna, L.; Capiglia, C.; Zaccaria, R. P. Direct Synthesis of



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Carbon-Doped TiO2-Bronze Nanowires as Anode Materials for High Performance Lithium-Ion Batteries. ACS Appl. Mater. Interfaces 2015, 7, 25139-25146. (27) Brumbarov, J.; Vivek, J. P.; Leonardi, S.; Valero-Vidal, C.; Portenkirchner, E.; Kunze-Liebhauser, J. Oxygen Deficient, Carbon Coated Self-Organized TiO2 Nanotubes as Anode Material for Li-Ion Intercalation. J. Mater. Chem. A 2015, 3, 16469-16477. (28) Tan, L.; Pan, L.; Cao, C. Y.; Wang, B. F.; Li, L. Nitrogen-Doped Carbon Coated TiO2 Nanocomposites as Anode Material to Improve Cycle Life for Lithium-Ion Batteries. J. Power

Sources 2014, 253, 193-200. (29) Li, X. Y.; Chen, Y. M.; Wang, H. T.; Yao, H. M.; Huang, H. T.; Mai, Y. W.; Hu, N.; Zhou, L. M. Inserting Sn Nanoparticles into the Pores of TiO2-x-C Nanofibers by Lithiation. Adv. Funct. Mater. 2016, 26, 376-383. (30) Tran, T.; McCormaca, K.; Li, J. L.; Bi, Z. H.; Wu, J. Electrospun SnO2 and TiO2 Composite Nanofibers for Lithium Ion Batteries. Electrochim. Acta 2014, 117, 68-75. (31) Yang, X. j.; Teng, D. H.; Liu, B. X.; Yu, Y. H.; Yang, X. P. Nanosized Anatase Titanium Dioxide Loaded Porous Carbon Nanofiber Webs as Anode Materials for Lithium-Ion Batteries. Electrochem.

Commun. 2011, 13, 1098-1101. (32) Song, L. H.; Li, L.; Gao, X.; Zhao, J. X.; Lu, T.; Liu, Z. A Facile Synthesis of a Uniform Constitution of Three-Dimensionally Ordered Macroporous TiO2-Carbon Nanocomposites with Hierarchical Pores for Lithium Ion Batteries. J. Mater. Chem. A 2015, 3, 6862-6872. (33) Zeng, L. X.; Zheng, C.; Xia, L. C.; Wang, Y. X.; Wei, M. D. Ordered Mesoporous TiO2-C Nanocomposite as an Anode Material for Long-Term Performance Lithium-Ion Batteries. J. Mater.

Chem. A 2013, 1, 4293-4299.


Page 30 of 33

Page 31 of 33

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(34) Song, L.; Li, L.; Gao, X.; Zhao, J.; Lu, T.; Liu, Z. A Facile Synthesis of a Uniform Constitution of Three-Dimensionally Ordered Macroporous TiO2-Carbon Nanocomposites with Hierarchical Pores for Lithium Ion Batteries. J. Mater. Chem. A 2015, 3, 6862-6872. (35) Liu, Y.; Yan, X.; Yu, Y.; Yang, X. Eco-Friendly Fabricated Porous Carbon Nanofibers Decorated with Nanosized SnOx as High-Performance Lithium-Ion Battery Anodes. ACS Sustainable Chem.

Eng. 2016, 4, 2951-2959. (36) Liu, Y.; Yan, X. D.; Lan, J. L.; Yu, Y. H.; Yang, X. P.; Lin, Y. H. Phase-Separation Induced Hollow/Porous Carbon Nanofibers with in-situ Generated Ultrafine SnOx as Anode Materials for Lithium-Ion Batteries. Mater. Chem. Front. 2017, DOI: 10.1039/c6qm00377j. (37) Li, H.; Shen, L.; Yin, K.; Ji, J.; Wang, J.; Wang, X.; Zhang, X. Facile Synthesis of N-Doped Carbon-Coated Li4Ti5O12 Microspheres Using Polydopamine as a Carbon Source for High Rate Lithium Ion Batteries. J. Mater. Chem. A 2013, 1, 7270-7276. (38) Pasquier, A. D.; Plitz, I.; Gural, J.; Menocal, S.; Amatucci, G. Characteristics and Performance of 500 F Asymmetric Hybrid Advanced Supercapacitor Prototypes. J. Power Sources 2003, 113, 62-71. (39) Luo, J. Y.; Xia, Y. Y. Electrochemical Profile of an Asymmetric Supercapacitor Using Carbon-Coated LiTi2(PO4)3 and Active Carbon Electrodes. J. Power Sources 2009, 186, 224-227. (40) Karthikeyan, K.; Aravindan, V.; Lee, S. B.; Jang, I. C.; Lim, H. H.; Park, G. J.; Yoshio, M.; Lee, Y. S. A Novel Asymmetric Hybrid Supercapacitor Based on Li2FeSiO4 and Activated Carbon Electrodes. J. Alloys Compd. 2010, 504, 224-227. (41) Karthikeyan, K.; Aravindan, V.; Lee, S. B.; Jang, I. C.; Lim, H. H.; Park, G. J.; Yoshio, M.; Lee, Y. S. Electrochemical Performance of Carbon-Coated Lithium Manganese Silicate for Asymmetric



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Hybrid Supercapacitors. J. Power Sources 2010, 195, 3761-3764. (42) Aravindan, V.; Chuilinga, W.; Madhavi, S. High Power Lithium-Ion Hybrid Electrochemical Capacitors Using Spinel LiCrTiO4 as Insertion Electrode. J. Mater. Chem. 2012, 22, 16026-16031. (43) Xu, H. H.; Hu, X. L.; Sun, Y. M.; Luo, W.; Chen, C. J.; Liu, Y.; Huang, Y. H. Highly Porous Li4Ti5O12/C Nanofibers for Ultrafast Electrochemical Energy Storage. Nano Energy 2014, 10, 163-171. (44) Wang, Q.; Wen, Z.; Li, J. A Hybrid Supercapacitor Fabricated with a Carbon Nanotube Cathode and a TiO2-B Nanowire Anode. Adv. Funct. Mater. 2006, 16, 2141-2146. (45) Aravindan, V.; Shubha, N.; Ling, W. Chui; Madhavi, S. Constructing High Energy Density Non-Aqueous Li-Ion Capacitors Using Monoclinic TiO2-B Nanorods as Insertion Host. J. Mater.

Chem. A 2013, 1, 6145-6151. (46) Wang, G.; Liu, Z. Y.; Wu, J. N.; Lu, Q. Preparation and Electrochemical Capacitance Behavior of TiO2-B Nanotubes for Hybrid Supercapacitor. Mater. Lett. 2012, 71, 120-122. (47) Pasquier, A. D.; Plitz, I.; Menocal, S.; Amatucci, G. A Comparative Study of Li-Ion Battery, Supercapacitor and Nonaqueous Asymmetric Hybrid Devices for Automotive Applications. J. Power

Sources 2013, 115, 171-178. (48) Karthikeyan, K.; Amaresh, S.; Lee, S. N.; Aravindan, V.; Lee, Y. S. Fluorine-Doped Fe2O3, as High Energy Density Electroactive Material for Hybrid Supercapacitor Applications. Chem. Asian J. 2014, 9, 852-857. (49) Aravindan, V.; Reddy, M. V.; Madhavi, S.; Mhaisalkar, S. G.; Rao, G. V. Subba; Chowdari, B. V. R. Hybrid Supercapacitor with Nano-TiP2O7, as Intercalation Electrode. J. Power Sources 2011, 196, 8850-8854.


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Table of Contents Graphic


High-Performance Li-Ion Capacitor Based on an Activated Carbon

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