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Fabrication of flower-like mesoporous TiO2 hierarchical spheres with ordered stratified structure as an anode for lithium-ion batteries
Accepted Manuscript Title: Fabrication of flower-like mesoporous TiO2 hierarchical spheres with ordered stratified structure as an anode for lithium-ion batteries Authors: Yujie Zheng, Bingjie Liu, Pei Cao, Hui Huang, Jing Zhang, Guowei Zhou PII: DOI: Reference:
S1005-0302(18)30289-5 https://doi.org/10.1016/j.jmst.2018.10.028 JMST 1395
To appear in: Received date: Revised date: Accepted date:
1-4-2018 2-5-2018 3-6-2018
Please cite this article as: Zheng Y, Liu B, Cao P, Huang H, Zhang J, Zhou G, Fabrication of flower-like mesoporous TiO2 hierarchical spheres with ordered stratified structure as an anode for lithium-ion batteries, Journal of Materials Science and Technology (2018), https://doi.org/10.1016/j.jmst.2018.10.028 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Fabrication of flower-like mesoporous TiO2 hierarchical spheres with ordered stratified structure as an anode for lithium-ion batteries Yujie Zheng, Bingjie Liu, Pei Cao, Hui Huang, Jing Zhang, Guowei Zhou * Key Laboratory of Fine Chemicals in Universities of Shandong, School of Chemistry and Pharmaceutical Engineering, Qilu University of Technology (Shandong Academy o f Sciences),
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Jinan 250353, China
[Received 1 April 2018; Received in revised form 2 May 2018; Accepted 3 June 2018]
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* Corresponding author. Tel.: +86 531 89631696.
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E-mail addresses: [email protected], [email protected] (Guowei Zhou).
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Graphical Abstract
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Highlights Flower-like mesoporous TiO2 hierarchical spheres (FMTHSs) were fabricated.
FMTHSs are assembled by petals, which is full of ordered stratified structure.
FMTHSs2 electrode shows initial discharge capacity of 212.4 mA h g −1 at 0.2 C.
FMTHSs electrode exhibits excellent cycling stability and rate capability.
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In this study, flower-like mesoporous TiO2 hierarchical spheres (FMTHSs) with ordered stratified structure and TiO2 nanoparticles (TNPs) were synthesized via a facile solvothermal route and an etching reaction. Multilamellar vesicles (MTSVs) and unilamellar TiO2/SiO2 vesicles (UTSVs) were prepared using cetyltrimethylammonium
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bromide and didodecyldimethylammonium bromide as structure-directing agents under
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different solvothermal conditions. FMTHSs and TNPs were obtained from the etching
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reactions of MTSVs and UTSVs, respectively, in an alkaline system. FMTHSs display
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flower-like, ordered stratified structures on each petal. The thickness of the ordered stratified structure is approximately 3–6 nm, and the number of layers is approximately 2–4. The FMTHSs2 electrode exhibits the first discharge capacity of 212.4 mA h g−1 at 0.2
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C, which is higher than that of TNPs electrode (167.6 mA h g−1). The discharge specific capacity of FMTHSs2 electrode after 200 cycles at 1 C is 105.9 mA h g−1, which is higher than that of TNPs electrode (52.2 mA h g−1) after the same number of cycles. The
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outstanding performance of FMTHSs2 electrode is attributed to the advantages of FMTHSs. In particular, their own stratified structure can provide additional active sites for
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reactions. The hierarchical structure can provide short diffusion length for Li+, large electrolyte–electrode contact area, and superior accommodation of the strain of Li +
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intercalation/deintercalation. Key words: Lithium ion batteries; Flower-like TiO2 spheres; Stratified structure; Multialmellar TiO2/SiO2 vesicles; Controllable morphology
1. Introduction Lithium-ion batteries (LIBs) have received increasing attention due to their considerable
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advantages, such as high energy density, no effect on memory, long life cycle, small self-discharge, and environmental benignity[1–4]. Anode materials with large capacity, high rate capability, and long life cycle in LIBs must be developed to improve their commercial applications, such as in cell phones and electric vehicles [5–8]. Efforts have been devoted toward the development of electrode materials, and substantial materials, such as MoS 2[9,10], Co3O4[11, 12]
, TiO2[13–15], graphene[16], and LiFePO4[17], have been widely investigated. As a
commercialized negative electrode material, graphite is widely used for LIBs; however, this
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material has relatively low theoretical capacity and poor safety, which limit its further development and do not satisfy the requirements of batteries in the future [18–20]. TiO2 has drawn attention as an important semiconductor material due to its availability, environmental
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friendliness, high chemical stability, and relatively high performance [21–25]. In addition, the Li insertion voltage of TiO 2 (more than 1.5 V vs Li/Li +) is higher than that of commercial graphite anode (below 0.2 V vs Li/Li +); this phenomenon helps avoid the formation of a solid electrolyte
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interface caused by Li electrochemical deposition during stable operation [26]. Among the
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various morphological structures, TiO 2 hierarchical nanostructures, such as nanotube [27],
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nanoflake[28], nanorob sphere[29], hollow sphere[30], and urchin-like[31] hierarchical TiO2 structures, have been successfully prepared using various techniques. In addition, the ultrathin
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nanosheets have attracted much attention by virtue of high efficient active sites on the expose d surface[32,33]. Compared with low-dimensional nanomaterials, three-dimensional (3D)
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hierarchical architectures often possess the properties of 1D or 2D nanomaterials and some additional distinctive physicochemical properties, such as high surface-to-volume ratio, high surface area, less defects, and large interspace [34,35]. Various 3D hierarchical TiO 2 structures
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have been prepared under different conditions. For example, Biswas et al. [36] used aerosol-assisted metal organic chemical vapor deposition to deposit TiO2 films containing
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hierarchical TiO2 microflowers with diameter of approximately 2–3 μm. Li et al.[35] obtained hierarchical TiO2 microstructures of approximately 1 μm) via a solvothermal approach in a mixed solvent composed of N,N-dimethylformamide and acetic acid. Fan et al. [37] found that
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the morphology of hierarchical TiO 2 is effectively controlled by the changing solvothermal temperature. In addition, rose-like, chrysanthemum-like, and sea-urchin-like hierarchical TiO2 structures with micron-scale diameters were fabricated. The micron-scale hierarchical TiO2 was produced in large quantities, whereas the nanoscale hierarchical TiO 2 was reported in few studies. However, flower-like mesoporous TiO2 hierarchical spheres (FMTHSs) with their own stratified structure have not been reported. Compared with other TiO2 nanomaterials, such as P25 and TiO2 nanofiber, hierarchical TiO 2 structure has advantages in terms of performance. Li 3
et al. [38] obtained excellent cycling stability using hierarchical TiO 2 structure as LIBs anode materials, where the retained capacity of the anode after 50 cycles at 1 C is 151 mA h g−1. In contrast, the reversible capacity of P25 is only 110 mA h g−1. It is noteworthy that the reversible capacities of the hierarchical TiO 2 are 162, 135, 110, and 80 mA h g−1 at 1 C, 2 C, 4 C, and 10 C, respectively, while the corresponding capacities of P25 are only 118, 93, 74, and 48 mA h g−1, respectively. Deepa et al. [39] reported that the charge capacities are 141.2, 115.3, 89.2, 63.5, and 55.2 mA h g−1 at current rates of 0.5 C, 1 C, 2 C, 4 C, and 5 C, respectively
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using porous TiO2 nanofiber as electrode materials.
In this study, we report the fabrication of novel FMTHSs and TiO 2 nanoparticles (TNPs)
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with ordered stratified structure in high uniformity by a controlled solvothermal reaction, a calcination process, and an etching route. Two types of cationic surfactants were applied for the synthesis of multilamellar TiO 2/SiO2 vesicles (MTSVs) and unilamellar TiO 2/SiO2 vesicles In
this
system,
cetyltrimethylammonium
bromide
(CTAB)
and
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(UTSVs).
didodecyldimethylammonium bromide (DDAB) were self-assembled into vesicle aggregation
petals
are
composed
of
layered
structures.
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their
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as structure-directing agents. The resulting FMTHSs possess uniform nanoflowers, in which These
petals
can
enlarge
the
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electrolyte–electrode interface, and the gaps between petals can accommodate the changes in volume that accompany charge/discharge. The FMTHSs2 electrode shows a higher initial
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discharge capacity of 212.4 mA h g −1 at 0.2 C than that of TNPs electrode (167.6 mA h g −1). In addition, FMTHSs electrode exhibits better cycling stability and rate capability than TNPs electrode. The morphology evolution, formation mechanism, and effects of the reaction
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conditions on the formation of FMTHSs and TNPs were investigated in detail.
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2. Experiment 2.1. Materials
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TiOSO4 and tetraethyl orthosilicate (TEOS) were purchased from Aladdin Chemical Co.,
Ltd. (Shanghai, China). CTAB and DDAB were obtained from Sigma-Aldrich (St. Louis, MO, USA). Other chemical reagents in this study were purchased from Sinopharm Chemical Reagent Co., Ltd. and directly used without further purification. Millipore water (18.2 MΩ cm, purified using aMilli-Q® Reference system) was used throughout the study. 2.2. Synthesis of samples
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MTSVs and UTSVs were prepared using CTAB and DDAB as structure-directing agents via a simple solvothermal route. First, 0.141 g of CTAB was dissolved in 35.00 mL of deionized water, followed by the addition of 0.174 g of DDAB with continuous stirring at 35 °C to form a clear solution. Afterward, 0.69 mL of ammonia was added into the solution. The mixture solution was stirred for an additional of 2 h. Second, 2.0 g of TEOS and 0.768 g of TiOSO4 were dissolved in 15 mL of ethanol solution and then added dropwise into the mixture solution under vigorous stirring. The reaction solution was constantly stirred at 35 °C for 24 h
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until a homogenous suspension was formed. This homogenous suspension was transferred onto a Teflon-lined autoclave and stored at different temperatures for 24 h under static conditions, followed by air-cooling to room temperature. White solid products were collected through
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filtration, washed with water, air-dried at room temperature, and calcined at 500 °C at a rate of 1 °C min−1 in a tube furnace for 4 h to remove the surfactant template. The final products were designated as MTSVsm, where m=1, 2 refer to the hydrothermal temperature of 100 °C and
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130 °C, respectively. UTSVs were prepared with the same conditions for MTSVsm
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preparation, except for the hydrothermal temperature of 160 °C.
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MTSVsm and UTSVs were etched with 0.5 mol L −1 NaOH at 70 °C to remove residual silica. The solid products were centrifuged and washed several times with absolute ethanol.
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FMTHSs1 and FMTHSs2 were obtained by etching MTSVs1 and MTSVs2, respectively,
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whereas TNPs were obtained by etching UTSVs.
2.3. Material characterization and electrochemical measurements The as-prepared samples were characterized by a field-emission scanning electron
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microscopy (FESEM, SUPRA TM55 microscope operated at 5 kV.) and transmission electron microscopy (TEM, JEM-2100F). The X-ray diffraction (XRD) patterns were obtained on a
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Bruker D8 Advance X-ray diffractometer with Cu Kα radiation (40 kV, 40 mA, λ = 0.15406 nm). The 2θ ranged from 10° to 80°, with a resolution step size of 0.1° s −1. N2
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adsorption-desorption experiments were performed by TriStar 3020. The surface areas and pore size distribution curves were estimated using the Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH) methods based on the adsorption isotherm. The electrochemical measurements were carried out in CR2032 coin-type cells with a lithium plate serving as the counter and reference electrode. The working electrode was prepared as described below. Polyvinylidene difluoride (PVDF) was used as a binder. The as-prepared samples were mixed with PVDF and acetylene black at a weight ratio of 70:20:10
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in N-methylpyrrolidone to form a slurry and then pasted uniformly on Cu foil and dried overnight at 110 °C to ensure solvent evaporation. Electrode discs with a diameter of 12 mm were punched from the Cu-foil which was used as current collectors, and the mass of active materials loaded on each electrode was ca. 0.1 mg. The cells were assembled in a glovebox (MIKROUNA Super) filled with high-purity argon using a polypropylene separator (Celgard 2400) and electrolyte consisted of 1.0 M LiPF 6 in ethylene carbonate, ethylene methyl carbonate and dimethyl carbonate with a volume ratio of 1:1:1. The potentiostatic impedance
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tests were performed by PARSTAT4000 with an amplitude of 10 mV in the frequency range from 100 kHz to 0.01 Hz, while the galvanostatic charge-discharge tests were performed on a
different current rates of 0.2 C, 0.5 C, 1C, 2 C, 5 C, and 10 C. 3. Results and Discussion
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3.1. Morphology and structure characterizations
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LANHE test system (CT2001A) in a voltage range of 1.0–3.0 V at room temperature at
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The morphologies of the as-obtained MTSVsm, UTSVs, FMTHSsm, and TNPs were characterized by TEM. The morphology of MTSVsm is strongly affected by the solvothermal
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temperature. Fig. 1(a, b) reveals that MTSVs1 and MTSVs2 show vesicular morphology with well-defined multilamellar structures and monodispersed vesicles. Each vesicle has uniform
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size with a diameter of approximately 60 nm. Fig. 1(c) shows that UTSVs have a high degree of particle aggregation and nonhomogeneous size distribution in terms of the diameter as compared with MTSVs1 and MTSVs2. Moreover, the multilamellar structures in UTSVs are
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nonexistent. These results indicate that the solvothermal temperature considerably influences MTSVsm formation. The FMTHSsm samples in Fig. 1(d, e) show flower hierarchical
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structures, which are constructed by self-assembly of 2D nanoplates as building block materials. FMTHSs have the size range of 100–140 nm. This hierarchical structure can significantly provide additional reaction sites and improve the specific surface area.
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Furthermore, this unique structure can provide short diffusion length for Li +, larger electrolyte–electrode contact area, and good accommodation of the strain of Li + intercalation/deintercalation [40]. Fig. 1(f) indicates that TNPs are irregular nanoparticles with size of approximately 9 nm. Therefore, high hydrothermal temperatures lead to the failure of forming a hierarchical structure. Fig. 2(a, b) indicates that the numbers of layer of MTSVs1 and MTSVs2 are
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approximately 3–5, and the thicknesses range from 6 to 8 nm. Fig. 2(c) reveals the typical TEM image of single hierarchical structure of FMTHSs2, clearly showing that the hierarchical nanostructures are self-assembled by numerous nanoplates. Fig. 2(d) shows that the nanoplates are full of layered structure. The nanoplate thickness ranges from 3 to 6 nm, and the number of layer is approximately 2–4. The structural nature of the hierarchical structure was further investigated by FESEM. As
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shown in Fig. 3(a, b, d, e), FMTHSs1 and FMTHSs2 display a 3D hierarchical morphology with uniform size distribution. The synthesized nanostructures consist of self-supported nanosheets. The distributed nanosheets are similar to the petals in a flower structure, with
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thickness of several nanometers. The size of FMTHSs1 and FMTHSs2 ranges from 100 to 140 nm in diameter. Fig. 3(c, f) indicate that TNPs are irregular nanoparticles. These findings are consistent with the TEM results.
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The crystalline phases of samples were determined by XRD. As shown in Fig. 4, the peaks
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located at 25.3°, 37.8°, 48.0°, 53.9°, 55.1°, 62.7°, 68.8°, 70.3°, and 75.0° can be assigned to the
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(101), (004), (200), (105), (211), (204), (116), (220), and (215) crystal planes of anatase TiO 2
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(JCPDS PDF No. 21-1272)[41], respectively, and no other phases are detected. The average crystalline sizes of FMTHSs1, FMTHSs2, and TNPs are 8.27, 7.71, and 8.12 nm, respectively,
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which were calculated using the Scherrer equation based on the broad XRD peaks of the (101) plane. According to the increased peak intensity, the crystallization level is improve d with the increase in hydrothermal temperature.
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To investigate the pore structure of the samples, N 2 adsorption–desorption isotherms and corresponding BJH pore size distribution curves of FMTHSsm and TNPs were measured ( Fig. 5). The results show that all isotherms exhibit evident hysteresis loop, indicating that the
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samples are mainly mesoporous [42]. FMTHSs2 show the highest surface area of 171.52 m 2 g−1, while FMTHSs1 and TNPs show lower surface areas of 151.42 and 99.05 m 2 g−1, respectively.
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The pore size distributions of FMTHSs1 and FMTHSs2 are centered at ~7 nm and mainly assigned to the interspaces between nanoplates. The pore size distribution of TNPs is relatively wide, which belongs to the interparticle voids between the packed TNPs. After analyzing the above results, we proposed a possible mechanism for the formation of FMTHSsm and TNPs, as shown in Scheme 1. At a low solvothermal temperature (100 °C or 130 °C), multilamellar vesicle aggregation is formed with CTAB and DDAB. In this process,
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the range of the average packing parameter P, P = v/a0lc is 0.50–1.0[43,44], where v is the hydrophobic volume of the amphiphile, a0 is the polar head surface area, and lc is the hydrophobic chain length. The addition of TEOS and TiOSO 4 lead to the occurrence of hydrolysis and condensation reaction by using the multilamellar vesicle aggregations as templates. MTSVs are obtained by the subsequent calcination process to remove the multilamellar vesicle aggregation. Moreover, SiO 2 is removed by etching reaction. In this process, the MTSVs are broken into nanoplates, and the large number of nanoplates can further
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assemble into flower-like nanostructures, which is driven by the minimization of interfacial energy[45,46]. Meanwhile, at a relatively high solvothermal temperature (160 °C), the UTSVs is
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formed after calcination and broken in the etching process. Finally, the TNPs is formed. 3.2. Lithium storage performance of electrodes
Fig. 6(a) compares the galvanostatic charge–discharge profiles of the FMTHSsm and
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TNPs electrode in the voltage range of 1–3 V vs Li/Li+ at 0.2 C (1 C=168 mA g−1). The cells
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fabricated with FMTHSs2 yield a first charge capacity of 159.6 mA h g −1 and discharge
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capacity of 212.4 mA h g−1. The FMTHSs1 and TNPs electrodes deliver first charge capacities of 124.9 and 136.6 mA h g−1 and discharge capacities of 175.5 and 167.6 mA h g−1,
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respectively. A total of 2 clear horizontal plateaus are observed at ∼1.91 and 1.74 V in the charge and discharge curves, respectively, which correspond to the characteristics of
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intercalation and deintercalation between anatase and lithiated TiO2[47,48]. This result clearly indicates the formation of electrochemically stable TiO 2 phases in both the FMTHSsm and
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TNPs electrodes.
The cycling behaviors of FMTHSsm and TNPs electrodes were examined at 1 C, and the
CC
data are shown in Fig. 6(b). The results show that the initial reversible discharge specific capacities of the FMTHSs1, FMTHSs2, and TNPs electrodes are 156.6, 170.6, and 144.5 mA h g−1, respectively. The retained capacities after 200 cycles are 98.6, 105.9, and 52.2 mA h g −1,
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and the retention ratios are 63.0%, 62.1%, and 36.1%, respectively. Upon cycling, all samples reach a high coulombic efficiency of more than 99.0%. These results indicate that FMTHSsm electrodes are a suitable active material for LIBs. The structural benefits can be observed in the rate capabilities of the FMTHSsm and TNPs electrodes. The rate performances were examined at various current rates; the data are shown in Fig. 6(c). The results show that the FMTHSs2 electrode exhibits much better rate performances
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than FMTHSs1 and TNPs electrodes. At increasing current rates of 0.5 C, 1 C, 2 C, 5 C, and 10 C, the discharge capacities of FMTHSs2 electrode are 152.3, 128.0, 109.2, 80.9, and 66.2 mA h g−1, respectively. At a high rate of 10 C, a specific capacities of 59.7 and 66.2 mA h g −1 can be retained for the FMTHSs1 and FMTHSs2 electrodes, respectively. By contrast, the specific capacity of TNPs electrode declines quickly to 5.6 mA h g−1 at the same rate. The interspaces between petals and the gaps in FMTHSs can provide free space for strain relaxation and volume–change accommodation of the electrode materials during repeated lithium
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intercalation–deintercalation. The hierarchical structure with ordered stratified structure in FMTHSs shows high surface area, which can provide extra active sites for lithium storage. Moreover, the stratified structure in FMTHSs can provide short diffusion distances for both
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lithium ions and electrons, leading to enhanced rate performance [40]. Furthermore, FMTHSs2 electrode exhibits better rate performances than FMTHSs1 and TNPs electrodes. This result can be attributed to the high surface area (171.52 m 2 g−1) of FMTHSs2. The increase in the
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BET surface areas can provide additional surface active sites and facilitate easy charge carrier
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create high rate LIBs than the as-prepared TNPs.
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transport[40]. These results indicate that the formation of FMTHSsm is much more favorable to
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Electrochemical impedance spectroscopy (EIS) measurements were obtained to investigate the electrochemical kinetics of the FMTHSsm and TNPs electrodes. The frequency
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ranges from 100 kHz to 0.01 Hz, and the amplitude is 10 mV. Nyquist plots of all samples with their corresponding electrical circuits are presented in Fig. 7. The Nyquist plot consists of a semicircle at high-to-medium frequencies and a sloping straight line in the low frequency range, corresponding to the Rct and W, respectively. The semicircle diameter of the FMTHSs2
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electrode is the smallest, which indicates the smallest Rct (< 60 Ω) compared with those of the FMTHSs1 and TNPs electrodes. This result suggests that FMTHSs2 can facilitate rapid charge
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transfer and may possess good performance for LIBs, which may be ascribed to the high SBET of FMTHSs2, which can improve the electrolyte transport and Li-ion diffusion. As a result, the
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as-prepared FMTHSsm electrode exhibits high capacity, excellent cycling stability, and outstanding rate capability for LIBs anode compared with TNPs electrode. 4. Conclusion FMTHSs were successfully synthesized by a facile solvothermal method using CTAB/DDAB vesicle aggregation as template, followed by an etching process. Particularly, the diameter of FMTHSs is nanoscale, and FMTHSs are assembled by petals, which is full of 9
ordered stratified structure. The flower-shaped structures can shorten the diffusion length for Li+, allowing faster Li + intercalation/deintercalation. Moreover, the stratified structure can significantly provide more reaction sites. The retained capacities of the FMTHSs2 electrode after 200 cycles at 1 C is 105.9 mA h g −1, which is much higher than that of TNPs electrode (52.2 mA h g−1) after the same number of cycles. Our results clearly demonstrate that FMTHSs is more advantageous than TNPs as anode material for LIBs in the future. Thus, we believe that this strategy can potentially be extended to the other metal oxide with different compositions,
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sizes, and shapes. This controlled structure is expected to be widely used in environmental field and other applications.
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Acknowledgements
This work was supported by the National Natural Science Foundation of China (Grant
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Nos. 51372134 and 51572124).
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References
M
X. Zhang, J. Wang, H. Liu, H. Liu, B. Wei, Materials 10 (2017) 77. Y. Li, J. Li, X. Lang, Z. Wen, W. Zheng, Q. Jiang, Adv. Funct. Mater. 27 (2017) 1700447
11189−11192.
TE D
L. Hu, L. Yang, D. Zhang, X. Tao, C. Zeng, A. Cao, L. Wan, Chem. Commun. 53 (2017)
231−238.
EP
Y. Hui, L. Cao, Z. Xu, J. Huang, H. Ouyang, J. Li, H. Hu, J. Mater. Sci. Technol. 33 (2017):
S. Chen, L. Shen, P. Aken, J. Maier, Y. Yu, Adv. Mater. 29 (2017) 1605650.
CC
G. Zeng, N. Shi, M. Hess, X. Chen, W. Cheng, T. Fan, M. Niederberger, ACS Nano 9 (2015) 4227−4235.
A
H. Chen, Z. He, Z. Huang, L. Song, C. Shen, J. Liu, Ceram. Int. 43 (2017) 8616−8624. Y. Wang, S Nakamura, M Ue, P Balbuena, J. Am. Chem. Soc. 123 (2001) 11708−11718. Y. Wang, L. Yu, X. Lou, Angew. Chem. Int. Edit. 55 (2016) 7423−7426.
H. Zhao, J. Li, H. Wu, T. Dong, Y. Zhang, H. Liu, ChemElectroChem. 5 (2018)
383−390.
10
J. Wang, N. Yang, H. Tang, Z. Dong, Q. Jin, M. Yang, D. Kisailus, H. Zhao, Z. Tang, D.
Wang, Angew. Chem. Int. Edit. 52 (2013) 6417−6420.
G. Huang, F. Zhang, X. Du, Y. Qin, D. Yin, L. Wang. ACS Nano 9 (2015) 1592−1599.
B. Qiu, M. Xing, J. Zhang, J. Am. Chem. Soc. 136 (2014) 5852−5855.
J. Chen, Y. Tan, C. Li, Y. Cheah, D. Luan, S. Madhavi, F. Boey, L. Archer, X. Lou, J.
IP T
Am. Chem. Soc. 132 (2010) 6124−6130. H. Liu, W. Li, D. Shen, D. Zhao, G. Wang. J. Am. Chem. Soc, 137 (2015)
13161−13166.
Y. Zhao, X. Li, B. Yan, D. Li, S. Lawes, X. Sun, J. Power Sources 274 (2015) 869−884.
B. Wang, W. Abdulla, D. Wang, X. Zhao, Energy Environ. Sci. 8 (2015) 869−875.
X. Zhu, C. Yang, F. Xiao, J. Wang, X. Su, New J. Chem. 39 (2015) 683−688.
X. Li, W. Li， M. Li, P. Cui, D. Chen, T. Gengenbach, L. Chu, H. Liu, G. Song, J.
N
U
SC R
B. Wang, Y. Tang, X. Lu, S. Fung, K. Wong, W. Aua, P. Wu, Phys. Chem. Chem. Phys.
18 (2016) 4911−4923.
F. Giordano, A. Abate, J. Baena, M. Saliba, T. Matsui, S. Im, S. Zakeeruddin, M.
TE D
M
A
Mater. Chem. A 3 (2015) 2762−2769.
Nazeeruddin, A. Hagfeldt, M. Graetzel, Nat. Commun. 7 (2016) 10379. S. Selcuk, A. Selloni, Nat. Mater. 15 (2016), 1107–1112.
H. Wei, E. Rodriguez, A. Hollenkamp, A. Bhatt, D. Chen, R. Caruso, Adv. Funct. Mater.
EP
27 (2017) 1703270.
C. Yi, X. Li, J. Luo, S. Zakeeruddin, M. Grätzel, Adv. Mater. 28 (2016) 2964−2970.
C. Wang, F. Wang, Y. Zhao, Y. Li, Q. Yue, Y. Liu, Y. Li, A. Elzatahry, A. Enizi, Y. Wu,
CC
A
Y. Deng, D. Zhao, Nano Res. 9 (2016) 165−173.
X. Tong, M. Zeng, J. Li, F. Li, Appl. Surf. Sci. 392 (2017) 897−903.
F. Zhuge, J. Qiu, X. Li, X. Gao, X. Gan, W. Yu, Adv. Mater. 23 (2011) 1330−1334.
Y. Tang, P. Wee, Y. Lai, X. Wang, D. Gong, P. Kanhere, T. Lim, Z. Dong, Z. Chen, J.
Phys. Chem. C 116 (2012) 2772−2780.
H. Bai, Z. Liu, L. Liu, D. Sun, Chem. Eur. J. 19 (2013) 3061−3070. 11
X. Lü, S. Ding, Y. Xie, F. Huang, Eur. J. Inorg. Chem. 18 (2011) 2879−2883.
L. Xiang, X. Zhao, J. Yin, B. Fan, J. Mater. Sci. 47 (2012) 1436−1445.
J. Liu, X. Wei, X. Wang, X. Liu, Chem. Commun. 47 (2011), 6135–6137.
J. Liu, J. Chen, X. Wei, X. Lou, X. Liu, Adv. Mater. 23 (2011), 998–1002.
Y. Chen, A. Li, Q. Li, X. Hou, L. Wang, Z. Huang, J. Mater. Sci. Technol. 34 (2018)
IP T
955-960. Z. Li, L. Mo, W. Chen, X. Shi, N. Wang, L. Hu, T. Hayat, A. Alsaedi, S. Dai, ACS Appl.
SC R
Mater. Int. 9 (2017) 32026−32033.
S. Biswas, C. Jiménez, A. Khan, S. Forissier, A. Kar1, D. Rojas, J. Deschanvres, Cryst.
Eng. Comm. 19 (2017) 1535−1544.
Z. Fan, F. Meng, M. Zhang, Z. Wu, Z. Sun, A. Li, Appl. Surf. Sci. 360 (2016) 298−305.
Y Li, X Yan, W Yan, X. Lai, N. Li, Y. Chi, Y. Wei, X. Li, Chem. Eng. J. 232 (2013)
N
U
T. Deepa, S. Mohapatra, S. Nair, A. Nair, A. Rai, Sustainable Energy Fuels. 1 (2017)
M
A
356−363.
138−144.
B. Guo, K. Yu, H. Fu, Q. Hua, R. Qi, H. Li, H. Song, S. Guo, Z. Zhu, J. Mater. Chem. A
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3 (2015) 6392‒6401.
B. Wang, F. Zhao, G. Du, S. Porter, Y. Liu, P. Zhang, Z. Cheng, H. Liu, Z. Huang, ACS
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Appl. Mater. Int. 8 (2016) 16009−16015. M. Kruk, M. Jaroniec, Chem. Mater. 13 (2001) 3169−3183.
Y. Zhang, G. Zhou, B. Sun, M. Zhao, J. Zhang, F. Chen, Chem. Commun. 50 (2014)
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2907−2909.
A
G. Zhou, K. Fung, L. Wong, Y. Chen, R. Renneberg, S. Yang, Talanta 84 (2011)
659−665.
L. Zhu, G. Liao, Y. Yang, H. Xiao, J. Wang, S. Fu, Nanoscale Res. Lett. 4 (2009) 550.
C. Yang, F. Xiao, J. Wang, X. Su, Sensor. Actuat. B-Chem. 207 (2015) 177−185.
Z. Zhang, L. Zhang, W. Li, A. Yu, P. Wu. ACS Appl. Mater. Int. 7 (2015)
10395−10400. 12
S. Lee, J. Ha, J. Choi, T. Song, J. Lee, U. Paik. ACS Appl. Mater. Int. 5 (2013)
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11525−11529.
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Figure list:
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Fig. 1. TEM images of MTSVs1 (a), MTSVs2 (b), UTSVs (c), FMTHSs1 (d), FMTHSs2 (e), and TNPs
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(f).
Fig. 2. High-magnification TEM images of MTSVs1 (a), MTSVs2 (b), and FMTHSs2 (c, d).
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Fig. 3. FESEM images of FMTHSs1 (a, d), FMTHSs2 (b, e) and TNPs (c, f).
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Fig. 4. XRD patterns of FMTHSsm and TNPs.
Fig. 5. The N2 adsorption-desorption isotherms and corresponding BJH pore size distribution curves of FMTHSsm and TNPs.
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Scheme 1. Schematic representation for formation of FMTHSsm and TNPs.
Fig. 6. Electrochemical properties of FMTHSsm and TNPs electrode: (a) first charge-discharge voltage profiles at 0.2 C, (b) cycling performance and coulombic efficiency, and (c) rate capabilities.
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Fig. 7. EIS of the FMTHSsm and TNPs electrodes. The inset is the equivalent circuit model of the studied system (Rs, external resistance; Rct, charge transfer resistance; CPE, constant phase element; W,
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Warburg impedance).
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S1005-0302(18)30289-5 https://doi.org/10.1016/j.jmst.2018.10.028 JMST 1395
To appear in: Received date: Revised date: Accepted date:
1-4-2018 2-5-2018 3-6-2018
Please cite this article as: Zheng Y, Liu B, Cao P, Huang H, Zhang J, Zhou G, Fabrication of flower-like mesoporous TiO2 hierarchical spheres with ordered stratified structure as an anode for lithium-ion batteries, Journal of Materials Science and Technology (2018), https://doi.org/10.1016/j.jmst.2018.10.028 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Fabrication of flower-like mesoporous TiO2 hierarchical spheres with ordered stratified structure as an anode for lithium-ion batteries Yujie Zheng, Bingjie Liu, Pei Cao, Hui Huang, Jing Zhang, Guowei Zhou * Key Laboratory of Fine Chemicals in Universities of Shandong, School of Chemistry and Pharmaceutical Engineering, Qilu University of Technology (Shandong Academy o f Sciences),
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Jinan 250353, China
[Received 1 April 2018; Received in revised form 2 May 2018; Accepted 3 June 2018]
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* Corresponding author. Tel.: +86 531 89631696.
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E-mail addresses: [email protected], [email protected] (Guowei Zhou).
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Graphical Abstract
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Highlights Flower-like mesoporous TiO2 hierarchical spheres (FMTHSs) were fabricated.
FMTHSs are assembled by petals, which is full of ordered stratified structure.
FMTHSs2 electrode shows initial discharge capacity of 212.4 mA h g −1 at 0.2 C.
FMTHSs electrode exhibits excellent cycling stability and rate capability.
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In this study, flower-like mesoporous TiO2 hierarchical spheres (FMTHSs) with ordered stratified structure and TiO2 nanoparticles (TNPs) were synthesized via a facile solvothermal route and an etching reaction. Multilamellar vesicles (MTSVs) and unilamellar TiO2/SiO2 vesicles (UTSVs) were prepared using cetyltrimethylammonium
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bromide and didodecyldimethylammonium bromide as structure-directing agents under
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different solvothermal conditions. FMTHSs and TNPs were obtained from the etching
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reactions of MTSVs and UTSVs, respectively, in an alkaline system. FMTHSs display
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flower-like, ordered stratified structures on each petal. The thickness of the ordered stratified structure is approximately 3–6 nm, and the number of layers is approximately 2–4. The FMTHSs2 electrode exhibits the first discharge capacity of 212.4 mA h g−1 at 0.2
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C, which is higher than that of TNPs electrode (167.6 mA h g−1). The discharge specific capacity of FMTHSs2 electrode after 200 cycles at 1 C is 105.9 mA h g−1, which is higher than that of TNPs electrode (52.2 mA h g−1) after the same number of cycles. The
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outstanding performance of FMTHSs2 electrode is attributed to the advantages of FMTHSs. In particular, their own stratified structure can provide additional active sites for
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reactions. The hierarchical structure can provide short diffusion length for Li+, large electrolyte–electrode contact area, and superior accommodation of the strain of Li +
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intercalation/deintercalation. Key words: Lithium ion batteries; Flower-like TiO2 spheres; Stratified structure; Multialmellar TiO2/SiO2 vesicles; Controllable morphology
1. Introduction Lithium-ion batteries (LIBs) have received increasing attention due to their considerable
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advantages, such as high energy density, no effect on memory, long life cycle, small self-discharge, and environmental benignity[1–4]. Anode materials with large capacity, high rate capability, and long life cycle in LIBs must be developed to improve their commercial applications, such as in cell phones and electric vehicles [5–8]. Efforts have been devoted toward the development of electrode materials, and substantial materials, such as MoS 2[9,10], Co3O4[11, 12]
, TiO2[13–15], graphene[16], and LiFePO4[17], have been widely investigated. As a
commercialized negative electrode material, graphite is widely used for LIBs; however, this
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material has relatively low theoretical capacity and poor safety, which limit its further development and do not satisfy the requirements of batteries in the future [18–20]. TiO2 has drawn attention as an important semiconductor material due to its availability, environmental
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friendliness, high chemical stability, and relatively high performance [21–25]. In addition, the Li insertion voltage of TiO 2 (more than 1.5 V vs Li/Li +) is higher than that of commercial graphite anode (below 0.2 V vs Li/Li +); this phenomenon helps avoid the formation of a solid electrolyte
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interface caused by Li electrochemical deposition during stable operation [26]. Among the
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various morphological structures, TiO 2 hierarchical nanostructures, such as nanotube [27],
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nanoflake[28], nanorob sphere[29], hollow sphere[30], and urchin-like[31] hierarchical TiO2 structures, have been successfully prepared using various techniques. In addition, the ultrathin
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nanosheets have attracted much attention by virtue of high efficient active sites on the expose d surface[32,33]. Compared with low-dimensional nanomaterials, three-dimensional (3D)
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hierarchical architectures often possess the properties of 1D or 2D nanomaterials and some additional distinctive physicochemical properties, such as high surface-to-volume ratio, high surface area, less defects, and large interspace [34,35]. Various 3D hierarchical TiO 2 structures
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have been prepared under different conditions. For example, Biswas et al. [36] used aerosol-assisted metal organic chemical vapor deposition to deposit TiO2 films containing
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hierarchical TiO2 microflowers with diameter of approximately 2–3 μm. Li et al.[35] obtained hierarchical TiO2 microstructures of approximately 1 μm) via a solvothermal approach in a mixed solvent composed of N,N-dimethylformamide and acetic acid. Fan et al. [37] found that
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the morphology of hierarchical TiO 2 is effectively controlled by the changing solvothermal temperature. In addition, rose-like, chrysanthemum-like, and sea-urchin-like hierarchical TiO2 structures with micron-scale diameters were fabricated. The micron-scale hierarchical TiO2 was produced in large quantities, whereas the nanoscale hierarchical TiO 2 was reported in few studies. However, flower-like mesoporous TiO2 hierarchical spheres (FMTHSs) with their own stratified structure have not been reported. Compared with other TiO2 nanomaterials, such as P25 and TiO2 nanofiber, hierarchical TiO 2 structure has advantages in terms of performance. Li 3
et al. [38] obtained excellent cycling stability using hierarchical TiO 2 structure as LIBs anode materials, where the retained capacity of the anode after 50 cycles at 1 C is 151 mA h g−1. In contrast, the reversible capacity of P25 is only 110 mA h g−1. It is noteworthy that the reversible capacities of the hierarchical TiO 2 are 162, 135, 110, and 80 mA h g−1 at 1 C, 2 C, 4 C, and 10 C, respectively, while the corresponding capacities of P25 are only 118, 93, 74, and 48 mA h g−1, respectively. Deepa et al. [39] reported that the charge capacities are 141.2, 115.3, 89.2, 63.5, and 55.2 mA h g−1 at current rates of 0.5 C, 1 C, 2 C, 4 C, and 5 C, respectively
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using porous TiO2 nanofiber as electrode materials.
In this study, we report the fabrication of novel FMTHSs and TiO 2 nanoparticles (TNPs)
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with ordered stratified structure in high uniformity by a controlled solvothermal reaction, a calcination process, and an etching route. Two types of cationic surfactants were applied for the synthesis of multilamellar TiO 2/SiO2 vesicles (MTSVs) and unilamellar TiO 2/SiO2 vesicles In
this
system,
cetyltrimethylammonium
bromide
(CTAB)
and
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(UTSVs).
didodecyldimethylammonium bromide (DDAB) were self-assembled into vesicle aggregation
petals
are
composed
of
layered
structures.
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their
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as structure-directing agents. The resulting FMTHSs possess uniform nanoflowers, in which These
petals
can
enlarge
the
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electrolyte–electrode interface, and the gaps between petals can accommodate the changes in volume that accompany charge/discharge. The FMTHSs2 electrode shows a higher initial
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discharge capacity of 212.4 mA h g −1 at 0.2 C than that of TNPs electrode (167.6 mA h g −1). In addition, FMTHSs electrode exhibits better cycling stability and rate capability than TNPs electrode. The morphology evolution, formation mechanism, and effects of the reaction
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conditions on the formation of FMTHSs and TNPs were investigated in detail.
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2. Experiment 2.1. Materials
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TiOSO4 and tetraethyl orthosilicate (TEOS) were purchased from Aladdin Chemical Co.,
Ltd. (Shanghai, China). CTAB and DDAB were obtained from Sigma-Aldrich (St. Louis, MO, USA). Other chemical reagents in this study were purchased from Sinopharm Chemical Reagent Co., Ltd. and directly used without further purification. Millipore water (18.2 MΩ cm, purified using aMilli-Q® Reference system) was used throughout the study. 2.2. Synthesis of samples
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MTSVs and UTSVs were prepared using CTAB and DDAB as structure-directing agents via a simple solvothermal route. First, 0.141 g of CTAB was dissolved in 35.00 mL of deionized water, followed by the addition of 0.174 g of DDAB with continuous stirring at 35 °C to form a clear solution. Afterward, 0.69 mL of ammonia was added into the solution. The mixture solution was stirred for an additional of 2 h. Second, 2.0 g of TEOS and 0.768 g of TiOSO4 were dissolved in 15 mL of ethanol solution and then added dropwise into the mixture solution under vigorous stirring. The reaction solution was constantly stirred at 35 °C for 24 h
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until a homogenous suspension was formed. This homogenous suspension was transferred onto a Teflon-lined autoclave and stored at different temperatures for 24 h under static conditions, followed by air-cooling to room temperature. White solid products were collected through
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filtration, washed with water, air-dried at room temperature, and calcined at 500 °C at a rate of 1 °C min−1 in a tube furnace for 4 h to remove the surfactant template. The final products were designated as MTSVsm, where m=1, 2 refer to the hydrothermal temperature of 100 °C and
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130 °C, respectively. UTSVs were prepared with the same conditions for MTSVsm
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preparation, except for the hydrothermal temperature of 160 °C.
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MTSVsm and UTSVs were etched with 0.5 mol L −1 NaOH at 70 °C to remove residual silica. The solid products were centrifuged and washed several times with absolute ethanol.
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FMTHSs1 and FMTHSs2 were obtained by etching MTSVs1 and MTSVs2, respectively,
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whereas TNPs were obtained by etching UTSVs.
2.3. Material characterization and electrochemical measurements The as-prepared samples were characterized by a field-emission scanning electron
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microscopy (FESEM, SUPRA TM55 microscope operated at 5 kV.) and transmission electron microscopy (TEM, JEM-2100F). The X-ray diffraction (XRD) patterns were obtained on a
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Bruker D8 Advance X-ray diffractometer with Cu Kα radiation (40 kV, 40 mA, λ = 0.15406 nm). The 2θ ranged from 10° to 80°, with a resolution step size of 0.1° s −1. N2
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adsorption-desorption experiments were performed by TriStar 3020. The surface areas and pore size distribution curves were estimated using the Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH) methods based on the adsorption isotherm. The electrochemical measurements were carried out in CR2032 coin-type cells with a lithium plate serving as the counter and reference electrode. The working electrode was prepared as described below. Polyvinylidene difluoride (PVDF) was used as a binder. The as-prepared samples were mixed with PVDF and acetylene black at a weight ratio of 70:20:10
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in N-methylpyrrolidone to form a slurry and then pasted uniformly on Cu foil and dried overnight at 110 °C to ensure solvent evaporation. Electrode discs with a diameter of 12 mm were punched from the Cu-foil which was used as current collectors, and the mass of active materials loaded on each electrode was ca. 0.1 mg. The cells were assembled in a glovebox (MIKROUNA Super) filled with high-purity argon using a polypropylene separator (Celgard 2400) and electrolyte consisted of 1.0 M LiPF 6 in ethylene carbonate, ethylene methyl carbonate and dimethyl carbonate with a volume ratio of 1:1:1. The potentiostatic impedance
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tests were performed by PARSTAT4000 with an amplitude of 10 mV in the frequency range from 100 kHz to 0.01 Hz, while the galvanostatic charge-discharge tests were performed on a
different current rates of 0.2 C, 0.5 C, 1C, 2 C, 5 C, and 10 C. 3. Results and Discussion
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3.1. Morphology and structure characterizations
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LANHE test system (CT2001A) in a voltage range of 1.0–3.0 V at room temperature at
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The morphologies of the as-obtained MTSVsm, UTSVs, FMTHSsm, and TNPs were characterized by TEM. The morphology of MTSVsm is strongly affected by the solvothermal
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temperature. Fig. 1(a, b) reveals that MTSVs1 and MTSVs2 show vesicular morphology with well-defined multilamellar structures and monodispersed vesicles. Each vesicle has uniform
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size with a diameter of approximately 60 nm. Fig. 1(c) shows that UTSVs have a high degree of particle aggregation and nonhomogeneous size distribution in terms of the diameter as compared with MTSVs1 and MTSVs2. Moreover, the multilamellar structures in UTSVs are
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nonexistent. These results indicate that the solvothermal temperature considerably influences MTSVsm formation. The FMTHSsm samples in Fig. 1(d, e) show flower hierarchical
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structures, which are constructed by self-assembly of 2D nanoplates as building block materials. FMTHSs have the size range of 100–140 nm. This hierarchical structure can significantly provide additional reaction sites and improve the specific surface area.
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Furthermore, this unique structure can provide short diffusion length for Li +, larger electrolyte–electrode contact area, and good accommodation of the strain of Li + intercalation/deintercalation [40]. Fig. 1(f) indicates that TNPs are irregular nanoparticles with size of approximately 9 nm. Therefore, high hydrothermal temperatures lead to the failure of forming a hierarchical structure. Fig. 2(a, b) indicates that the numbers of layer of MTSVs1 and MTSVs2 are
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approximately 3–5, and the thicknesses range from 6 to 8 nm. Fig. 2(c) reveals the typical TEM image of single hierarchical structure of FMTHSs2, clearly showing that the hierarchical nanostructures are self-assembled by numerous nanoplates. Fig. 2(d) shows that the nanoplates are full of layered structure. The nanoplate thickness ranges from 3 to 6 nm, and the number of layer is approximately 2–4. The structural nature of the hierarchical structure was further investigated by FESEM. As
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shown in Fig. 3(a, b, d, e), FMTHSs1 and FMTHSs2 display a 3D hierarchical morphology with uniform size distribution. The synthesized nanostructures consist of self-supported nanosheets. The distributed nanosheets are similar to the petals in a flower structure, with
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thickness of several nanometers. The size of FMTHSs1 and FMTHSs2 ranges from 100 to 140 nm in diameter. Fig. 3(c, f) indicate that TNPs are irregular nanoparticles. These findings are consistent with the TEM results.
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The crystalline phases of samples were determined by XRD. As shown in Fig. 4, the peaks
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located at 25.3°, 37.8°, 48.0°, 53.9°, 55.1°, 62.7°, 68.8°, 70.3°, and 75.0° can be assigned to the
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(101), (004), (200), (105), (211), (204), (116), (220), and (215) crystal planes of anatase TiO 2
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(JCPDS PDF No. 21-1272)[41], respectively, and no other phases are detected. The average crystalline sizes of FMTHSs1, FMTHSs2, and TNPs are 8.27, 7.71, and 8.12 nm, respectively,
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which were calculated using the Scherrer equation based on the broad XRD peaks of the (101) plane. According to the increased peak intensity, the crystallization level is improve d with the increase in hydrothermal temperature.
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To investigate the pore structure of the samples, N 2 adsorption–desorption isotherms and corresponding BJH pore size distribution curves of FMTHSsm and TNPs were measured ( Fig. 5). The results show that all isotherms exhibit evident hysteresis loop, indicating that the
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samples are mainly mesoporous [42]. FMTHSs2 show the highest surface area of 171.52 m 2 g−1, while FMTHSs1 and TNPs show lower surface areas of 151.42 and 99.05 m 2 g−1, respectively.
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The pore size distributions of FMTHSs1 and FMTHSs2 are centered at ~7 nm and mainly assigned to the interspaces between nanoplates. The pore size distribution of TNPs is relatively wide, which belongs to the interparticle voids between the packed TNPs. After analyzing the above results, we proposed a possible mechanism for the formation of FMTHSsm and TNPs, as shown in Scheme 1. At a low solvothermal temperature (100 °C or 130 °C), multilamellar vesicle aggregation is formed with CTAB and DDAB. In this process,
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the range of the average packing parameter P, P = v/a0lc is 0.50–1.0[43,44], where v is the hydrophobic volume of the amphiphile, a0 is the polar head surface area, and lc is the hydrophobic chain length. The addition of TEOS and TiOSO 4 lead to the occurrence of hydrolysis and condensation reaction by using the multilamellar vesicle aggregations as templates. MTSVs are obtained by the subsequent calcination process to remove the multilamellar vesicle aggregation. Moreover, SiO 2 is removed by etching reaction. In this process, the MTSVs are broken into nanoplates, and the large number of nanoplates can further
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assemble into flower-like nanostructures, which is driven by the minimization of interfacial energy[45,46]. Meanwhile, at a relatively high solvothermal temperature (160 °C), the UTSVs is
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formed after calcination and broken in the etching process. Finally, the TNPs is formed. 3.2. Lithium storage performance of electrodes
Fig. 6(a) compares the galvanostatic charge–discharge profiles of the FMTHSsm and
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TNPs electrode in the voltage range of 1–3 V vs Li/Li+ at 0.2 C (1 C=168 mA g−1). The cells
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fabricated with FMTHSs2 yield a first charge capacity of 159.6 mA h g −1 and discharge
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capacity of 212.4 mA h g−1. The FMTHSs1 and TNPs electrodes deliver first charge capacities of 124.9 and 136.6 mA h g−1 and discharge capacities of 175.5 and 167.6 mA h g−1,
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respectively. A total of 2 clear horizontal plateaus are observed at ∼1.91 and 1.74 V in the charge and discharge curves, respectively, which correspond to the characteristics of
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intercalation and deintercalation between anatase and lithiated TiO2[47,48]. This result clearly indicates the formation of electrochemically stable TiO 2 phases in both the FMTHSsm and
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TNPs electrodes.
The cycling behaviors of FMTHSsm and TNPs electrodes were examined at 1 C, and the
CC
data are shown in Fig. 6(b). The results show that the initial reversible discharge specific capacities of the FMTHSs1, FMTHSs2, and TNPs electrodes are 156.6, 170.6, and 144.5 mA h g−1, respectively. The retained capacities after 200 cycles are 98.6, 105.9, and 52.2 mA h g −1,
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and the retention ratios are 63.0%, 62.1%, and 36.1%, respectively. Upon cycling, all samples reach a high coulombic efficiency of more than 99.0%. These results indicate that FMTHSsm electrodes are a suitable active material for LIBs. The structural benefits can be observed in the rate capabilities of the FMTHSsm and TNPs electrodes. The rate performances were examined at various current rates; the data are shown in Fig. 6(c). The results show that the FMTHSs2 electrode exhibits much better rate performances
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than FMTHSs1 and TNPs electrodes. At increasing current rates of 0.5 C, 1 C, 2 C, 5 C, and 10 C, the discharge capacities of FMTHSs2 electrode are 152.3, 128.0, 109.2, 80.9, and 66.2 mA h g−1, respectively. At a high rate of 10 C, a specific capacities of 59.7 and 66.2 mA h g −1 can be retained for the FMTHSs1 and FMTHSs2 electrodes, respectively. By contrast, the specific capacity of TNPs electrode declines quickly to 5.6 mA h g−1 at the same rate. The interspaces between petals and the gaps in FMTHSs can provide free space for strain relaxation and volume–change accommodation of the electrode materials during repeated lithium
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intercalation–deintercalation. The hierarchical structure with ordered stratified structure in FMTHSs shows high surface area, which can provide extra active sites for lithium storage. Moreover, the stratified structure in FMTHSs can provide short diffusion distances for both
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lithium ions and electrons, leading to enhanced rate performance [40]. Furthermore, FMTHSs2 electrode exhibits better rate performances than FMTHSs1 and TNPs electrodes. This result can be attributed to the high surface area (171.52 m 2 g−1) of FMTHSs2. The increase in the
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BET surface areas can provide additional surface active sites and facilitate easy charge carrier
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create high rate LIBs than the as-prepared TNPs.
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transport[40]. These results indicate that the formation of FMTHSsm is much more favorable to
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Electrochemical impedance spectroscopy (EIS) measurements were obtained to investigate the electrochemical kinetics of the FMTHSsm and TNPs electrodes. The frequency
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ranges from 100 kHz to 0.01 Hz, and the amplitude is 10 mV. Nyquist plots of all samples with their corresponding electrical circuits are presented in Fig. 7. The Nyquist plot consists of a semicircle at high-to-medium frequencies and a sloping straight line in the low frequency range, corresponding to the Rct and W, respectively. The semicircle diameter of the FMTHSs2
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electrode is the smallest, which indicates the smallest Rct (< 60 Ω) compared with those of the FMTHSs1 and TNPs electrodes. This result suggests that FMTHSs2 can facilitate rapid charge
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transfer and may possess good performance for LIBs, which may be ascribed to the high SBET of FMTHSs2, which can improve the electrolyte transport and Li-ion diffusion. As a result, the
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as-prepared FMTHSsm electrode exhibits high capacity, excellent cycling stability, and outstanding rate capability for LIBs anode compared with TNPs electrode. 4. Conclusion FMTHSs were successfully synthesized by a facile solvothermal method using CTAB/DDAB vesicle aggregation as template, followed by an etching process. Particularly, the diameter of FMTHSs is nanoscale, and FMTHSs are assembled by petals, which is full of 9
ordered stratified structure. The flower-shaped structures can shorten the diffusion length for Li+, allowing faster Li + intercalation/deintercalation. Moreover, the stratified structure can significantly provide more reaction sites. The retained capacities of the FMTHSs2 electrode after 200 cycles at 1 C is 105.9 mA h g −1, which is much higher than that of TNPs electrode (52.2 mA h g−1) after the same number of cycles. Our results clearly demonstrate that FMTHSs is more advantageous than TNPs as anode material for LIBs in the future. Thus, we believe that this strategy can potentially be extended to the other metal oxide with different compositions,
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sizes, and shapes. This controlled structure is expected to be widely used in environmental field and other applications.
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Acknowledgements
This work was supported by the National Natural Science Foundation of China (Grant
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Nos. 51372134 and 51572124).
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References
M
X. Zhang, J. Wang, H. Liu, H. Liu, B. Wei, Materials 10 (2017) 77. Y. Li, J. Li, X. Lang, Z. Wen, W. Zheng, Q. Jiang, Adv. Funct. Mater. 27 (2017) 1700447
11189−11192.
TE D
L. Hu, L. Yang, D. Zhang, X. Tao, C. Zeng, A. Cao, L. Wan, Chem. Commun. 53 (2017)
231−238.
EP
Y. Hui, L. Cao, Z. Xu, J. Huang, H. Ouyang, J. Li, H. Hu, J. Mater. Sci. Technol. 33 (2017):
S. Chen, L. Shen, P. Aken, J. Maier, Y. Yu, Adv. Mater. 29 (2017) 1605650.
CC
G. Zeng, N. Shi, M. Hess, X. Chen, W. Cheng, T. Fan, M. Niederberger, ACS Nano 9 (2015) 4227−4235.
A
H. Chen, Z. He, Z. Huang, L. Song, C. Shen, J. Liu, Ceram. Int. 43 (2017) 8616−8624. Y. Wang, S Nakamura, M Ue, P Balbuena, J. Am. Chem. Soc. 123 (2001) 11708−11718. Y. Wang, L. Yu, X. Lou, Angew. Chem. Int. Edit. 55 (2016) 7423−7426.
H. Zhao, J. Li, H. Wu, T. Dong, Y. Zhang, H. Liu, ChemElectroChem. 5 (2018)
383−390.
10
J. Wang, N. Yang, H. Tang, Z. Dong, Q. Jin, M. Yang, D. Kisailus, H. Zhao, Z. Tang, D.
Wang, Angew. Chem. Int. Edit. 52 (2013) 6417−6420.
G. Huang, F. Zhang, X. Du, Y. Qin, D. Yin, L. Wang. ACS Nano 9 (2015) 1592−1599.
B. Qiu, M. Xing, J. Zhang, J. Am. Chem. Soc. 136 (2014) 5852−5855.
J. Chen, Y. Tan, C. Li, Y. Cheah, D. Luan, S. Madhavi, F. Boey, L. Archer, X. Lou, J.
IP T
Am. Chem. Soc. 132 (2010) 6124−6130. H. Liu, W. Li, D. Shen, D. Zhao, G. Wang. J. Am. Chem. Soc, 137 (2015)
13161−13166.
Y. Zhao, X. Li, B. Yan, D. Li, S. Lawes, X. Sun, J. Power Sources 274 (2015) 869−884.
B. Wang, W. Abdulla, D. Wang, X. Zhao, Energy Environ. Sci. 8 (2015) 869−875.
X. Zhu, C. Yang, F. Xiao, J. Wang, X. Su, New J. Chem. 39 (2015) 683−688.
X. Li, W. Li， M. Li, P. Cui, D. Chen, T. Gengenbach, L. Chu, H. Liu, G. Song, J.
N
U
SC R
B. Wang, Y. Tang, X. Lu, S. Fung, K. Wong, W. Aua, P. Wu, Phys. Chem. Chem. Phys.
18 (2016) 4911−4923.
F. Giordano, A. Abate, J. Baena, M. Saliba, T. Matsui, S. Im, S. Zakeeruddin, M.
TE D
M
A
Mater. Chem. A 3 (2015) 2762−2769.
Nazeeruddin, A. Hagfeldt, M. Graetzel, Nat. Commun. 7 (2016) 10379. S. Selcuk, A. Selloni, Nat. Mater. 15 (2016), 1107–1112.
H. Wei, E. Rodriguez, A. Hollenkamp, A. Bhatt, D. Chen, R. Caruso, Adv. Funct. Mater.
EP
27 (2017) 1703270.
C. Yi, X. Li, J. Luo, S. Zakeeruddin, M. Grätzel, Adv. Mater. 28 (2016) 2964−2970.
C. Wang, F. Wang, Y. Zhao, Y. Li, Q. Yue, Y. Liu, Y. Li, A. Elzatahry, A. Enizi, Y. Wu,
CC
A
Y. Deng, D. Zhao, Nano Res. 9 (2016) 165−173.
X. Tong, M. Zeng, J. Li, F. Li, Appl. Surf. Sci. 392 (2017) 897−903.
F. Zhuge, J. Qiu, X. Li, X. Gao, X. Gan, W. Yu, Adv. Mater. 23 (2011) 1330−1334.
Y. Tang, P. Wee, Y. Lai, X. Wang, D. Gong, P. Kanhere, T. Lim, Z. Dong, Z. Chen, J.
Phys. Chem. C 116 (2012) 2772−2780.
H. Bai, Z. Liu, L. Liu, D. Sun, Chem. Eur. J. 19 (2013) 3061−3070. 11
X. Lü, S. Ding, Y. Xie, F. Huang, Eur. J. Inorg. Chem. 18 (2011) 2879−2883.
L. Xiang, X. Zhao, J. Yin, B. Fan, J. Mater. Sci. 47 (2012) 1436−1445.
J. Liu, X. Wei, X. Wang, X. Liu, Chem. Commun. 47 (2011), 6135–6137.
J. Liu, J. Chen, X. Wei, X. Lou, X. Liu, Adv. Mater. 23 (2011), 998–1002.
Y. Chen, A. Li, Q. Li, X. Hou, L. Wang, Z. Huang, J. Mater. Sci. Technol. 34 (2018)
IP T
955-960. Z. Li, L. Mo, W. Chen, X. Shi, N. Wang, L. Hu, T. Hayat, A. Alsaedi, S. Dai, ACS Appl.
SC R
Mater. Int. 9 (2017) 32026−32033.
S. Biswas, C. Jiménez, A. Khan, S. Forissier, A. Kar1, D. Rojas, J. Deschanvres, Cryst.
Eng. Comm. 19 (2017) 1535−1544.
Z. Fan, F. Meng, M. Zhang, Z. Wu, Z. Sun, A. Li, Appl. Surf. Sci. 360 (2016) 298−305.
Y Li, X Yan, W Yan, X. Lai, N. Li, Y. Chi, Y. Wei, X. Li, Chem. Eng. J. 232 (2013)
N
U
T. Deepa, S. Mohapatra, S. Nair, A. Nair, A. Rai, Sustainable Energy Fuels. 1 (2017)
M
A
356−363.
138−144.
B. Guo, K. Yu, H. Fu, Q. Hua, R. Qi, H. Li, H. Song, S. Guo, Z. Zhu, J. Mater. Chem. A
TE D
3 (2015) 6392‒6401.
B. Wang, F. Zhao, G. Du, S. Porter, Y. Liu, P. Zhang, Z. Cheng, H. Liu, Z. Huang, ACS
EP
Appl. Mater. Int. 8 (2016) 16009−16015. M. Kruk, M. Jaroniec, Chem. Mater. 13 (2001) 3169−3183.
Y. Zhang, G. Zhou, B. Sun, M. Zhao, J. Zhang, F. Chen, Chem. Commun. 50 (2014)
CC
2907−2909.
A
G. Zhou, K. Fung, L. Wong, Y. Chen, R. Renneberg, S. Yang, Talanta 84 (2011)
659−665.
L. Zhu, G. Liao, Y. Yang, H. Xiao, J. Wang, S. Fu, Nanoscale Res. Lett. 4 (2009) 550.
C. Yang, F. Xiao, J. Wang, X. Su, Sensor. Actuat. B-Chem. 207 (2015) 177−185.
Z. Zhang, L. Zhang, W. Li, A. Yu, P. Wu. ACS Appl. Mater. Int. 7 (2015)
10395−10400. 12
S. Lee, J. Ha, J. Choi, T. Song, J. Lee, U. Paik. ACS Appl. Mater. Int. 5 (2013)
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CC
EP
TE D
M
A
N
U
SC R
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11525−11529.
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Fig. 1. TEM images of MTSVs1 (a), MTSVs2 (b), UTSVs (c), FMTHSs1 (d), FMTHSs2 (e), and TNPs
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(f).
Fig. 2. High-magnification TEM images of MTSVs1 (a), MTSVs2 (b), and FMTHSs2 (c, d).
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Fig. 3. FESEM images of FMTHSs1 (a, d), FMTHSs2 (b, e) and TNPs (c, f).
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Fig. 4. XRD patterns of FMTHSsm and TNPs.
Fig. 5. The N2 adsorption-desorption isotherms and corresponding BJH pore size distribution curves of FMTHSsm and TNPs.
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Scheme 1. Schematic representation for formation of FMTHSsm and TNPs.
Fig. 6. Electrochemical properties of FMTHSsm and TNPs electrode: (a) first charge-discharge voltage profiles at 0.2 C, (b) cycling performance and coulombic efficiency, and (c) rate capabilities.
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Fig. 7. EIS of the FMTHSsm and TNPs electrodes. The inset is the equivalent circuit model of the studied system (Rs, external resistance; Rct, charge transfer resistance; CPE, constant phase element; W,
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Warburg impedance).
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