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Pillared Structure Design of MXene with Ultralarge Interlayer Spacing for HighPerformance Lithium-Ion Capacitors Jianmin Luo,† Wenkui Zhang,† Huadong Yuan, Chengbin Jin, Liyuan Zhang, Hui Huang, Chu Liang, Yang Xia, Jun Zhang, Yongping Gan, and Xinyong Tao* College of Materials Science and Engineering, Zhejiang University of Technology, Hangzhou 310014, People’s Republic of China S Supporting Information *
ABSTRACT: Two-dimensional transition-metal carbide materials (termed MXene) have attracted huge attention in the field of electrochemical energy storage due to their excellent electrical conductivity, high volumetric capacity, etc. Herein, with inspiration from the interesting structure of pillared interlayered clays, we attempt to fabricate pillared Ti3C2 MXene (CTAB−Sn(IV)@Ti3C2) via a facile liquid-phase cetyltrimethylammonium bromide (CTAB) prepillaring and Sn4+ pillaring method. The interlayer spacing of Ti3C2 MXene can be controlled according to the size of the intercalated prepillaring agent (cationic surfactant) and can reach 2.708 nm with 177% increase compared with the original spacing of 0.977 nm, which is currently the maximum value according to our knowledge. Because of the pillar effect, the assembled LIC exhibits a superior energy density of 239.50 Wh kg−1 based on the weight of CTAB−Sn(IV)@Ti3C2 even under higher power density of 10.8 kW kg−1. When CTAB−Sn(IV)@Ti3C2 anode couples with commercial AC cathode, LIC reveals higher energy density and power density compared with conventional MXene materials. KEYWORDS: MXene, Ti3C2, lithium-ion capacitors, pillared structure, nanocomposites
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MAX phases with a formula of Mn+1AXn (M is an early transition metal, A is an III or IV A-group element, and X is C or N).19 The exfoliation process is the selective etching of the A layers from MAX phases with hydrofluoric acid (HF), leaving the 2D layers of Mn+1Xn terminated with OH, O, and F groups.20 MXenes have been applied in many areas until now, such as supercapacitors,21−25 LIBs,26−31 hydrogen storage,32,33 sewage purification,34,35 and photocatalysis,36 etc. Although MXene materials show high capacitance as supercapacitor electrodes in the aqueous electrolyte, the assembling of MXene electrode with AC electrode (LICs system) in nonaqueous electrolytes can further enhance the energy density due to the wider electrochemical stability window. Simon and Gogotsi et al. used Ti2C MXene, Nb2CTx−carbon nanotubes (CNT), and V2C MXene for LICs and Na ion capacitors (NICs).8,37,38 Wang et al. used Ti2C as negative electrode of NICs coupling with Na2Fe2(SO4)3 electrode.39 In the above-mentioned examples, pure MXenes were usually used as the electrode materials for LICs and NICs. If the interlayer space of MXenes
lectrochemical energy-storage (EES) devices with high energy and power density have various important applications, especially in electric vehicles and hybrid electric vehicles.1,2 Bridging the gap between lithium-ion batteries (LIBs) and supercapacitors (SCs),3−5 lithium-ion capacitors (LICs) combine the complementary features of LIBs and SCs with both high energy density and power density.6,7 As the hybrid energy-storage devices, LICs can be constructed from a traditional capacitor-type electrode (ions sorption) and a LIB-type electrode (Li+ insertion/intercalation) with an electrolyte containing Li salt.8−10 Until now, various configurations of LICs have been reported with inspiring performance.11−14 In all of the reported configurations, the major one is composed of insertion-type anodes (such as TiO2−B,15 Li4TiO12,16 etc.) and activated carbon (AC) cathodes. However, as the conventional anodes, insertion-type materials are still impeded by their lower capacitance and mediocre rate performance, which cannot completely satisfy the demand of high energy and power LICs.17 In recent years, the development of many materials has brought a good opportunity for the creation of high performance LICs.18 MXene, a new family of 2D earlytransition-metal carbides, was first exfoliated from threedimensional (3D) layered counterparts, which are called © 2016 American Chemical Society
Received: November 14, 2016 Accepted: December 20, 2016 Published: December 21, 2016 2459
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RESULTS AND DISCUSSION Figure 2a shows the X-ray diffraction (XRD) patterns of Ti3AlC2 before and after HF etching. The disappearing Ti3AlC2 peaks and shift of the main peak (002) in Figure 2a indicate good etching effect, and these results can also be verified by scanning electron microscopy (SEM) images (Figure 2b−e). After etching and oven-drying, many nanoparticles arise on the surface of Ti3C2, while they do not appear in the freeze-dried Ti3C2. These nanoparticles are Al2O3 nanocrystals (Figure 2a, JCPDS card: 81-2267). This phenomenon maybe because that the residual Al3+ will follow the migration of inside water to the surface and separate out during the oven-drying process, forming an Al2O3 nanocrystal. Freeze-drying will probably freeze residual Al3+ and will not form nanocrystals. To avoid the influence of Al2O3 nanocrystals, the freeze-dried Ti3C2 was used in the following experiment. It has been reported that many cations, such as Li+, Na+, Mg2+, K+, NH4+, Al3+, and organic small molecules, such as hydrazine, urea, dimethyl sulfoxidea, and isopropylamine, can intercalate between the Ti3C2 layers, causing an increase of the interlayer spacing about Ti3C2.22,24,30 However, augmentation of the layer spacing is limited due to their smaller volume. Cationic surfactant, usually used as the intercalation agent in the clay intercalation chemistry,43,44 has a larger volume due to the existence of a long-chain hydrophobic tail. When Ti3C2 was immersed in the cationic surfactant solution, cationic surfactant was self-assembled and intercalated into the interlayer of negatively charged Ti3C2 by electrostatic interaction, causing the increase of interlayer spacing about Ti3C2.24,45 The intercalation effects of cationic surfactants with different lengths of hydrophobic alkyl chain (dodecyltrimethylammonium bromide (DTAB), tetradecyltrimethylammonium bromide (TTAB), CTAB, stearyltrimethylammonium bromide (STAB), dioctadecyldimethylammonium chloride (DDAC)) at 40 °C are discussed (Figure 3a,b). After immersing Ti3C2 in cationic surfactant solution at 40 °C, all of the main peaks of Ti3C2 were shifted to a lower angle. The main peak of Ti3C2 continues to decrease when the carbon atoms in the alkyl chain of cationic surfactant increased from 12 (DTAB) to 16 (CTAB), indicating the increased interlayer spacing. This phenomenon is attributed to the intercalation of
was rationally increased and utilized, the overall energy density of MXene based LICs will be further enhanced. As is commonly known, the pillared interlayered clays (PILCs) have attracted increasing interest due to their applications in catalysis and separation.40,41 The stable pillars in the PILCs can keep the clay layers apart and increase interlayer spacing.42 Inspired by the interesting structure of PILCs, we attempted to fabricate pillared MXene, the highly conductive “clay”, via a facile liquid-phase prepillaring and pillaring method. The pillared MXene may effectively exploit the potential storage space in the interlayer and attract more Li+ to be intercalated and overcome the low capacity that pure MXene electrodes suffered. If an electrochemically active substance is used as the pillar in the pillared MXene, it will undergo volume expansion when reacting with Li+, further propping the layers open and endowing the MXene with extra storage space. Therefore, in the present study, we attempt to fabricate pillared Ti3C2 MXene via a facile liquid-phase prepillaring and pillaring method (Figure 1) and investigate its energy storage
Figure 1. Schematic illustration of preparation of CTAB−Sn(IV)@ Ti3C2 by HF etching, CTAB prepillaring, and Sn4+ pillaring methods.
properties as LICs anodes coupling with AC cathode. Due to the pillar effect, the assembled LIC exhibited a superior energy density and power density, indicating the good kinetics match extent between the CTAB−Sn(IV)@Ti3C2 anode and AC cathode.
Figure 2. (a) XRD patterns of Ti3AlC2 and two kinds of Ti3C2 after freeze-drying and oven-drying. (b) SEM image of Ti3AlC2. (c, d) SEM images of freeze-dried Ti3C2. (e) SEM image of oven-dried Ti3C2. 2460
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Figure 3. (a) XRD patterns of cationic surfactants prepillaring Ti3C2 at 40 °C. (b) The magnification of XRD patterns in (a). (c) Interlayer spacing of cationic surfactants (CTAB, STAB, DDAC) prepillared Ti3C2 at different treatment temperatures (30−70 °C). (d) XRD patterns of CTAB@Ti3C2 before and after Sn4+ intercalation. (e) Magnification of XRD patterns in (d). (f) XRD patterns of Ti3C2 before and after Sn4+ loading without a CTAB prepillaring process. Inset: magnification of XRD patterns in (f). (g) Schematic drawing about the structure of CTAB. (h) Possible position of CTA+ in the interlayer space of Ti3C2 MXene.
according to our knowledge. As for the DDAC@Ti3C2, the interlayer spacing continues to increase. However, all of the interlayer spacings of DDAC@Ti3C2 are less than that of CTAB@Ti3C2 and STAB@Ti3C2 at the same temperature due to the greater steric effect of DDA+. Although STAB@Ti3C2 (50 °C, 60 °C) has larger interlayer spacings than that of CTAB@Ti3C2 (40 °C), the higher prepillaring temperature (50 °C, 60 °C) may influence the surface state of Ti3C2 and cause the partial oxidation of Ti3C2, rendering the decrease of conductivity.46−48 Furthermore, the larger volume STA+ in the interlayer may be impeditive for the intercalation of metal-ion in the interlayer. Thus, the inexpensive and commonly used CTAB was chosen as the optimal prepillaring agent, and 40 °C was chose as the optimal prepillaring temperature. The influence of different amounts of CTAB on the intercalation effect about CTAB@Ti3C2 can be found in Figure S2. The result shows that the interlayer spacings of three CTAB@Ti3C2 samples (0.05, 0.15, and 0.25 g) are the same, but the intensity of the main peak in the XRD pattern about CTAB@Ti3C2 (0.15 g) is highest. As the intercalation agent, CTA+ is deemed as the substitution of four hydrogens in the NH4+ by three methyls and one hexadecyl. The overall spatial configuration of CTA+ looks like an exceptional cylinder with slightly larger space dimension in the cation terminal. The schematic drawing about the size of CTA+ (side view) is presented in Figure 3g: the length of CTA+ is 2.5 nm, and the corresponding widths of the two sides are 0.51 and 0.46 nm, respectively.49 Since the interlayer spacing of CTAB@Ti3C2 is 2.230 nm and the
larger volume of intercalation agent with the increase of alkyl chain length. However, the interlayer spacing of Ti3C2 decreases when the number of carbon atoms in the alkyl chain continues to increase above 16. The above phenomenon can be ascribed to the need for more intercalation energy to overcome the increasing steric hindrance along with the increase carbon atoms of alkyl chain length above 16 at the same temperature, causing the greater difficulty for the intercalation of cationic surfactant between layers of Ti3C2. The interlayer spacing of three larger volume cationic surfactant prepillaring Ti3C2 (CTAB@Ti3C2, STAB@Ti3C2, DDAC@Ti3C2) based on different treatment temperatures (30−70 °C) at the same cationic surfactant amount was explored (Figure 3c and Figure S1). With the treatment temperature increase, interlayer spacing variation of CTAB@ Ti3C2 and STAB@Ti3C2 shows the same trend, increase first and then decrease. This phenomenon can be ascribed to the incremental intercalation energy to overcome the steric hindrance for the intercalation of CTA+ and STA+ with temperature increase at the beginning. With the temperature continues to increase, the intercalation energy keep on increasing, but the molecular thermal movement is intensified, causing reversible deintercalation of CTA+ and STA+ between the layers of Ti3C2. The maximum interlayer spacing of STAB@Ti3C2 is 2.708 nm (50 °C), which is bigger than that of CTAB@Ti3C2 (2.230 nm, 40 °C) due to the longer alkyl chain length of cationic surfactant. It is worth mentioning that this value (2.708 nm) is the maximum interlayer spacing of MXene until now compared with the original spacing of 0.977 nm 2461
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Figure 4. (a) SEM image of CTAB@Ti3C2. (b) SEM image of Sn(IV)@Ti3C2 without CTAB prepillaring process. (c−f) SEM and TEM images of CTAB−Sn(IV)@Ti3C2. Inset in (f): lateral size distribution of the anchored Sn(IV) nanocomplex. (g−i) STEM image of CTAB−Sn(IV)@ Ti3C2 and corresponding elemental mapping of Ti and Sn.
thickness of Ti3C2 monolayer is ∼0.95 nm, a tilted manner of intercalated CTA+ with 30.8° to the broad plane (Figure 3h) is considered. The homogeneously distributed of CTA+ in Ti3C2 can be verified by the N signals in Figure S3. X-ray photoelectron spectroscopy (XPS) results (Figure S4) affirm that the intercalation of CTA+ is caused by the electrostatic interaction. Both the weaker N signal in transmission electron microscopy (TEM)/XPS testing processes is caused by partial CTA+ deintercalation and easy-sublimation of CTA+ under high vacuum and high energy electron beams/X-rays conditions.24 The increase of interlayer spacing after CTAB prepillaring process is of great benefit to the intercalation of other metal ions between Ti3C2 layers. After the CTA+ intercalation, the CTA+ cations in Ti3C2 interlayers may replace the H+ in the [Ti−O]−H+ to form [Ti−O]−CTA+, obtaining some ionexchange sites on the cation substitution of OH groups.34 To build and effectively use the pillared structure, pillar is the key factor. Tin is an ideal candidate for the pillar in the pillared MXene due to its large volume expansion during the alloying process with lithium, which will further prop the layers open and endow the pillared MXene with extra capacity. However, the sluggish electrochemical process between tin and lithium will cause the kinetic imbalance between the two electrodes and impede the realization of sufficient performance at high currents.14 Fortunately, it has been confirmed that when the dimension of nanoscale materials is less than 10 nm, the sluggish diffusion limitations will be overcame by pseudocapacitance for most reactions occur on the surface or near the
surface.4 Therefore, Sn-contained nanoparticle less than 10 nm was chosen as the pillar. The potential energy storage space and the exchangeable organic cation group in the CTAB@Ti3C2 are believed to facilitate the selectivity adsorption of Sn4+ to form Ti−OSn. Furthermore, the radius of Sn4+ (0.069 nm) is obviously smaller than the interlayer spacing of CTAB@Ti3C2 (2.230 nm), further confirming the possibility of intercalation of Sn4+. After the CTAB@Ti3C2 was immersed in SnCl4 solution, Sn4+ was successfully intercalated into the CTAB@ Ti3C2 by the ion-exchange interaction with CTA+ group. To maintain the electroneutrality, Sn4+ in the CTAB@Ti3C2 matrix combined with the anions (Cl−, OH−) in solution, forming Sn(IV) complex. This Sn(IV) complex and the hydrolysisproduced stannic hydroxide in the Ti3C2 matrix constituted CTAB−Sn(IV)@Ti3C2 nanocomposites.26 Figure 3d shows the XRD patterns of two samples (CTAB@ Ti3C2, CTAB−Sn(IV)@Ti3C2). After Sn4+ intercalation, no additional diffraction peak appears, indicating the possible amorphous structure of the Sn(IV) nanocomplex forming in the CTAB@Ti3C2 matrix. As shown in the magnified XRD patterns in the range from 3° to 7° (Figure 3e), the main peak (002) is shifted to a higher angle, indicating the decrease of interlayer spacing after Sn4+ intercalation. This phenomenon may be ascribed to the replacement of large volume CTA+ by the relatively small volume Sn4+, confirming the possible ionexchange interaction between Sn4+ and CTA+. This conjecture can be corroborated in the FT-IR spectra (Figure S5) before and after Sn4+ intercalation.50 X-ray fluorescence (XRF) testing results (Table S1) show that the element content ratio of Ti/Sn 2462
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Figure 5. (a) CV curves of CTAB−Sn(IV)@Ti3C2 at various scan rates. Inset: b-value determination of the peaks in CV curves. (b) Cycling performance of four samples (Ti3C2, CTAB@Ti3C2, Sn(IV)@Ti3C2, CTAB−Sn(IV)@Ti3C2) at 0.1 A g−1. (c) Rate performance of samples. (d) Discharge−charge curves of CTAB−Sn(IV)@Ti3C2 electrodes at different current densities. (e) Long cycling performance of CTAB− Sn(IV)@Ti3C2 at a current density of 1 A g−1.
As shown in the TEM image of CTAB−Sn(IV)@Ti3C2 (Figure 4e,f), the Sn(IV) nanocomplexes are dot-shaped and uniformly distributed in the CTAB@Ti3C2 matrix. CTAB not only acts as the prepillaring agent but also as the surfactant, which can effectively reduce the particle size and impede the agglomeration of the nanoparticles.45,51−53 The diameter of the anchored Sn(IV) nanocomplex dots is ranges from ca. 2 to 5 nm (Figure 4f). They are too small to be distinguished in the SEM testing process, so no clear particles can be detected in the SEM images (Figure 4c,d). The clearly layered structure as well as the uniform distribution of Sn(IV) nanocomplex in the interlayer can be observed in the STEM image of CTAB− Sn(IV)@Ti3C2 (Figure 4g). To further confirm the existence of the Sn(IV) nanocomplex in the interlayers of the CTAB@ Ti3C2 matrix, elemental mapping of Ti and Sn is supplied (Figure 4h,i). It is noteworthy that the signal of element Ti (Figure 4h) and element Sn (Figure 4i) is opposite. The signal of Sn is strong in the interlayer and weak in the surface of the CTAB@Ti3C2 matrix, which successfully confirms that most of the Sn4+ was intercalated in the interlayer. The electrochemical performances of CTAB−Sn(IV)@Ti3C2 were initially evaluated before constructing the LIC by assembling CR2032 coin half-cells using metal lithium as the
is 5.99 and the Sn element content is 8.41 wt % of the whole nanocomposites, demonstrating the powerful ion-exchange capacity between Sn4+ and CTA+ as well as the strong metalion intercalation ability of CTAB@Ti3C2. In the SEM image of CTAB@Ti3C2 (Figure 4a), many irregular particles are detected on the Ti3C2 matrix, which belong to the anchored CTAB, and this result can also be confirmed in the TEM images of CTAB@Ti3C2 (Figure S3). Figure 4b is the SEM image of Sn(IV)@Ti3C2 composites fabricated without the CTAB prepillaring process. Almost no obvious particles are detected, which may due to the smaller Sn4+ adsorption site without CTAB prepillaring. This conjecture can be confirmed in Figure 3f, where the main peak (002) does not shift and no additional peak appears in the XRD patterns. In Figure 4c,d, after the Sn(IV) nanocomplex loading by assist of CTAB prepillaring process, no clear particles can be detected in the CTAB@Ti3C2 matrix. Compared to the morphology of Sn(IV)@Ti3C2, the layer stripes in CTAB−Sn(IV)@Ti3C2 almost disappeared after Sn(IV) nanocomplex loading, indicating the probable intercalation of Sn4+ in the interlamination of the Ti3C2 matrix and cramming of the layer stripes. 2463
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Figure 6. (a−c) TEM and HRTEM image of CTAB−Sn(IV)@Ti3C2 charge to 3 V after 100 cycles at 0.1 A g−1. (d−f) STEM image of CTAB− Sn(IV)@Ti3C2 after 100 cycles and elemental mapping images of Ti and Sn.
be restored after the increasing 50 cycles. Electrochemical impedance spectroscopy (EIS, Figure S6d) results show that CTAB−Sn(IV)@Ti3C2 has the lowest impedance among three samples (CTAB@Ti3C2, Sn(IV)@Ti3C2, and CTAB−Sn(IV)@ Ti3C2). The structural stability of the CTAB−Sn(IV)@Ti3C2 can be verified by TEM after 100 cycles at 0.1 A g−1. The clearly layered structure can be seen in TEM image of CTAB−Sn(IV) @Ti3C2 (Figure 6a), which confirms the robust structure of CTAB@Ti3C2 matrix. Although the alloying reaction process has been experienced, many individual nanoparticles, in the diameter range of 3−7 nm, are still homogeneously anchored in the CTAB@Ti3C2 matrix. In the HRTEM image of CTAB− Sn(IV)@Ti3C2 after cycling (Figure 6c), the lattice fringe is clearly showed and the d-spacing is measured to be 0.210 nm, which is in agreement with the previous report,56 belonging to the (220) planes of tetragonal Sn phase (JCPDS card no.65− 5224). To further confirm the intercalation of Sn in the interlayer of the CTAB@Ti3C2 matrix, cross-sectional STEM images of CTAB−Sn(IV)@Ti3C2 after 100 cycles combined with elemental mapping of Ti and Sn are supplied in Figure 6d−f. The corresponding results are in agreement with the results in Figure 4d−f, where the signal of Sn is strong in the interlayer and weak in the surface of the CTAB@Ti3C2 matrix. The robust structure of CTAB@Ti3C2 and the pillar effect of Sn in the interlayer of matrix endow the nanocomposites with excellent electrochemical performance. On the basis of the remarkable energy storage performance, CTAB−Sn(IV)@Ti3C2 was used as the anode electrode for LICs coupling with an ordinary commercial AC electrode (Figure 7a). The corresponding electrochemical performance of AC in the organic electrolyte over 3.0−4.5 V (vs Li+/Li) in a half-cell system is provided in Figure S7. The capacity of AC is 34 mAh g−1 at 0.2 A g−1, which is in the range of conventional AC (∼30−60 mAh g−1 at 0.1−0.3 A g−1). Before a LIC was fabricated, the CTAB−Sn(IV)@Ti3C2 electrode was first preactivated at 0.1 A g−1 for 10 cycles in a Li half-cell to obtain high efficiency and ended in a lithiated state as 0.3 V. After preactivation, the CTAB−Sn(IV)@Ti3C2
counter electrode. As shown in the CV curve of CTAB−Sn(IV) @Ti3C2 (Figure 5a), the widely cathodic and anodic current response of CTAB−Sn(IV)@Ti3C2 can be attributed to two parts: The electrochemical reaction between Li+ and Sn(IV) nanocomplex as well as Ti3C2 matrix (Figure S6). To analyze the electrochemical storage mechanism, CV curves at various scan rates ranging from 0.1 to 2 mV s−1 are presented in Figure 5a. Generally, the peak current (i) of CV curve varies with the scan rate (v), and the corresponding relationship of them obeys the power law54,55 i = avb
(1)
where a and b are appropriate values. The b value in the plot of log(i) vs log(v) (Figure 5a), which is infinitely close to 1, indicates that the current is surface controlled and the electrochemical reactions of CTAB−Sn(IV)@Ti3C2 electrodes are dominated by capacitive effect.54 After 100 cycles at 0.1 A g−1, the CTAB−Sn(IV)@Ti3C2 electrode delivers a highly reversible capacity of 765 mAh g−1 (Figure 5b), which is higher than those of Sn(IV)@Ti3C2 (218 mAh g−1) and CTAB@Ti3C2 (248 mAh g−1), confirming the excellent electrochemical performance. The corresponding discharge−charge curves of the CTAB−Sn(IV)@Ti3C2 electrode are presented in Figure S6b. All of the specific capacities were calculated on the basis of the total mass of composites in electrodes. Even when the current increases to 1 A g−1, a specific capacity of 506 mAh g−1 can still be retained, corresponding to capacity retention of 96.9% after 250 cycles. Compared with other MXene-based anode materials (Table S2), CTAB−Sn(IV)@Ti3C2 has remarkable capacity and excellent cycling stability under high current density. As for the STAB−Sn(IV)@Ti3C2 (Figure S6c), a capacity of only 408 mAh g−1 can be delivered at 1 A g−1 after 100 cycles. This phenomenon may result from the fact that larger volumetric STA+ in STAB@Ti3C2 (50 °C) hinders the intercalation of Sn4+. As shown in Figure 5c, a stable and durable capacity at different current density is observed in the rate performance of CTAB−Sn(IV)@Ti3C2. When the current density was returned to 0.1 A g−1, a reversible capacity of 765.6 mAh g−1 still could 2464
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Figure 7. (a) Charging process of CTAB−Sn(IV)@Ti3C2//AC LIC. (b) CV curves of CTAB−Sn(IV)@Ti3C2//AC LIC at different scan rates. (c) Typical charge−discharge curves of CTAB−Sn(IV)@Ti3C2//AC LIC at different current densities. (d) Long-term cycling performance of LIC at 2 A g−1. Inset in panel (d): charge−discharge curves at 2 A g−1.
51, 42, 34, 33, 25 F g−1 based on the weight of CTAB−Sn(IV) @Ti3C2 and AC and 268, 220, 181, 173, 132 F g−1 based on the mass of CTAB−Sn(IV)@Ti3C2. Furthermore, CTAB−Sn(IV) @Ti3C2//AC LIC exhibits good cycling performance with a capacity retention of 71.1% after 4000 cycles at 2 A g−1 (Figure 7d), and the Columbic efficiency is nearly 100% during the cycling test. The Ragone plot of the CTAB−Sn(IV)@Ti3C2//AC LIC is shown in Figure 8. At a power density of 495 W kg−1, CTAB− Sn(IV)@Ti3C2//AC LIC can achieve a high energy density of 105.56 Wh kg−1. Even when the power density increases to 10.8 kW kg−1, CTAB−Sn(IV)@Ti3C2//AC LIC can still deliver 45.31 Wh kg−1 based on the weight of CTAB− Sn(IV)@Ti3C2 and AC and 239.50 Wh kg−1 based on the weight CTAB−Sn(IV)@Ti3C2 and exhibit high energy density and power density when compared with MXene materials.
anode was coupled with an AC cathode to fabricate LIC (CTAB−Sn(IV)@Ti3C 2//AC). To maintain the charge balance, the mass ratio of cathode to anode was 410,12 and the corresponding voltage testing window was chosen between 1 and 4 V to avoid the oxidative decomposition of electrolytes.12 The CV curves of CTAB−Sn(IV)@Ti3C2//AC LIC are exhibited in Figure 7b. The deviation from the ideal rectangular shape of the CV shape about CTAB−Sn(IV)@ Ti3C2//AC LIC is due to the different energy-storage mechanisms of the anode and cathode, which is different from that of the symmetric supercapacitor (rectangular CV shape). The shape of the CV can still be maintained when the sweep rate increases. The charge/discharge curves were shown in Figure 7c. These curves exhibit an almost inclined straight line. At the current density of 0.2, 0.5, 1, 2, 5 A g−1, the specific capacitance values of CTAB−Sn(IV)@Ti3C2//AC LIC were 2465
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indicating good kinetics match the extent between the CTAB− Sn(IV)@Ti3C2 anode and AC cathode. We believe that this efficient cationic surfactant prepillaring and metal-ion pillaring method will be helpful for the development of other functional pillared MXenes materials and extend the scope of MXenes for various applications such as adsorbent, separation, catalysis, gas sensing, etc.
METHODS Exfoliation of Ti3AlC2. Ti3AlC2 powders (>98 wt % purity) were used as the raw material (Shanghai Yuehuan New Materials Technology Co., Ltd.). The Ti3AlC2 powder (2 g) was first immersed in 40% HF solutions (20 mL, Aladdin) by stirring for 24 h at room temperature (rt) to obtain the Ti3C2. The obtained Ti3C2 powder was rinsed with deionized water several times until the pH of solution reached 6−7. After that, the obtained suspension was frozen in a freeze dryer at −40 °C for 24 h to eliminate the water in the solution by freeze-drying technology. The oven-dried sample was dried in the blast oven at 80 °C for 24 h. Synthesis of Prepillared Ti3C2. Freeze-dried Ti3C2 (0.35 g) was added to 40 mL of cationic surfactant solution (0.374 wt %, 0.15 g, DTAB, TTAB, CTAB, STAB, and DDAC, Aladdin, 98%) and stirred in a water bath under different temperatures for 24 h. Finally, the solid product was rinsed by DI water, collected, and dried at 80 °C to obtain prepillared Ti3C2. Synthesis of CTAB−Sn(IV)@Ti3C2 Nanocomposites. Freezedried Ti3C2 (0.35 g) was added to 40 mL of CTAB solution (0.374 wt %, 0.15 g), and then the mixture solution was kept at 40 °C in a water bath and stirred for 24 h. Finally, 2.804 g of SnCl4·5H2O was introduced to the suspension and stirred for another 24 h. The solid product was collected by filtration, rinsed with DI water several times, and vacuum-dried at 80 °C to obtain CTAB−Sn(IV)@Ti3C 2 nanocomposites. Characterization. The phase purity and crystalline structure of the products was characterized by XRD and conducted by an X’Pert Pro diffractometer using Cu Kα radiation (λ = 0.15418 nm). The morphology of the products was observed by SEM (Hitachi S4700). TEM (FEI, Tecnai G2 F30) equipped with an energy-dispersive spectroscopy (EDS) detector was used to observe the microstructure and investigate the element distribution of the products. Cross-section STEM was performed with a Reichert-Jung Ultracut E Ultramicrotome. XPS analysis was conducted using an Al Kα monochromatic X-ray source (1486.6 eV, Axis Ultra DLD, Kratos). XRF was conducted using Arl Advant’X IntelliPowerTM 4200. Fabrication of the Half Cells. The working electrodes were composed of active materials, acetylene black, and polyvinylidene fluoride (PVDF) binder in a weight ratio of 70:15:15 with N-methyl-2pyrrolidinone (NMP) as dispersant. The anode materials (CTAB@ Ti3C2, Sn(IV)@Ti3C2, CTAB−Sn(IV)@Ti3C2, and DDAC−Sn(IV)@ Ti3C2) were slurry-cast onto a copper foil. An AC electrode was fabricated by mixing AC (75 wt %) with super P (15 wt %) and polyvinylidene fluoride (PVDF, 10 wt %). The current collector of the AC electrode is Al foil. Cells were assembled into coin-type test cell (CR2032) with lithium metal working as both the counter and reference electrode. The electrolyte used was 1 M LiPF6 in ethylene carbonate (EC)/dimethyl carbonate (DEC)/ethyl methyl carbonate (EMC) (1:1:1, v/v/v) and 1 wt % fluoroethylene carbonate (FEC). The cell assembly was conducted in an argon-filled glovebox with a Celgard 2375 membrane as the separator. Fabrication of the Lithium-ion Capacitors. LICs were also assemble into coin-type test cell (CR2032) with prelithiated CTAB− Sn(IV)@Ti3C2 nanocomposites as the anode (discharged−charged for 10 cycles, and ending in a lithiated state as 0.3 V under a current density of 0.1 A g−1), AC materials as the cathode, and Celgard 2375 membrane as the separator. The electrolyte used was 1 M LiPF6 in ethylene carbonate (EC)/dimethyl carbonate (DEC)/ethyl methyl carbonate (EMC) (1:1:1, v/v/v) and 1 wt % fluoroethylene carbonate (FEC).
Figure 8. Ragone plots of CTAB−Sn(IV)@Ti3C2//AC LIC. The energy and power densities are compared with other LICs: TiO2rGO//AC, G-LTO//G-SU, Nb 2 O 5 −C//AC, Ti 2 C//AC, H2Ti6O13//CMK-3, LiCrTiO4//AC, V2O5−CNTs//AC.
Furthermore, the Ragone plots show that the energy and power densities of CTAB−Sn(IV)@Ti3C2//AC LIC are higher than those of TiO2-rGO//AC,57 G-LTO//G-SU,58 Nb2O5−C// AC,11 Ti2C//AC,8 H2Ti6O13//CMK-3,59 LiCrTiO4//AC,60 and V2O5−CNTs//AC.61 The superior electrochemical performance of CTAB−Sn(IV)@Ti3C2//AC LIC can be ascribed to two aspects. (i) The pillared nanostructure endows the electrode with preferably electrochemical kinetics. CTAB used in this work not only prepillared the Ti3C2 matrix but promoted the facile synthesis of nanosized Sn(IV) nanocomplex. The highly conductive Ti3C2 combines with Sn4+ nanoparticles to give the CTAB−Sn(IV)@Ti3C2 nanocomposite with high electrical conductivity, especially after the formation of the Li−Sn alloy. Due to the pillared nanostructure, energy storage space between the layers of Ti3C2 can be exploited and massive Li+ can be intercalated in the interlayer of Ti3C2 matrix, endowing the CTAB−Sn(IV)@Ti3C2//AC LIC with high energy density. (ii) The Sn(IV) nanocomplex (ca. 2− 5 nm) can effectively shorten the ion-diffusion path and reduced the resistance of ionic diffusion and charge transfer.
SUMMARY AND CONCLUSIONS In summary, pillared highly conductive Ti3C2 MXene has been fabricated by a facile liquid-phase prepillaring and pillaring method based on electrostatic adherence and ion-exchange interaction. Compared to our early work,26 the pillared Ti3C2 MXene has two distinguishing features: (i) when cationic surfactants were used as the prepillaring agent during the liquidphase pillaring process, the cationic surfactants were successfully intercalated into the interlayer of negative charged Ti3C2 due to the electrostatic interactions.43,44 The large volumetric CTAB and STAB will effectively increase the interlayer spacing of Ti3C2 (2.230 and 2.708 nm, repectively), endowing the Ti3C2 matrix with larger spacing for Sn4+ intercalation by ionexchange interaction.45 (ii) Sn4+ in the form of a Sn(IV) nanocomplex are successfully intercalated and homogeneously anchored in the Ti3C2 matrix with the particle size less than 5 nm, which can remit the diffusion-controlled processes during lithiation/delithiation. Due to the “pillar effect”, more Li+ can be intercalated in the interlayers of Ti3C2 MXene, endowing the CTAB−Sn(IV)@Ti3C2 anode with good cycling and rate performance. When the CTAB−Sn(IV)@Ti3C2 anode was coupled with an AC cathode, the assembled LIC confirmed a superior energy density even under higher power density, 2466
DOI: 10.1021/acsnano.6b07668 ACS Nano 2017, 11, 2459−2469
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ACS Nano Electrochemical Measurements. All of the electrochemical tests were implemented at room temperature. Cyclic voltammogram (CV) measurements and electrochemical impedance spectroscopy (EIS) measurements were carried out using a CHI660D electrochemical workstation. The galvanostatic charge−discharge performance of the half cells was performed on a Neware battery test system at room temperature, and the galvanostatic charge−discharge performance of the lithium-ion capacitors was carried out using a Land battery test system (Land CT2001A model, Wuhan Land Electronics. Ltd.). Specific capacitance (C, F g−1) was calculated through the following equations
C = I /[(dE /dt ) × m] ≈ I /[(ΔE /Δt ) × m] (F g −1)
(3) Simon, P.; Gogotsi, Y. Materials for Electrochemical Capacitors. Nat. Mater. 2008, 7, 845−854. (4) Simon, P.; Gogotsi, Y.; Dunn, B. Where Do Batteries End and Supercapacitors Begin? Science 2014, 343, 1210−1211. (5) Gogotsi, Y.; Simon, P. True Performance Metrics in Electrochemical Energy Storage. Science 2011, 334, 917−918. (6) Naoi, K.; Ishimoto, S.; Miyamoto, J.-i.; Naoi, W. Second Generation ’Nanohybrid Supercapacitor’: Evolution of Capacitive Energy Storage Devices. Energy Environ. Sci. 2012, 5, 9363−9373. (7) Aravindan, V.; Gnanaraj, J.; Lee, Y. S.; Madhavi, S. Insertion-Type Electrodes for Nonaqueous Li-Ion Capacitors. Chem. Rev. 2014, 114, 11619−11635. (8) Come, J.; Naguib, M.; Rozier, P.; Barsoum, M. W.; Gogotsi, Y.; Taberna, P. L.; Morcrette, M.; Simon, P. A Non-Aqueous Asymmetric Cell with a Ti2C-Based Two-Dimensional Negative Electrode. J. Electrochem. Soc. 2012, 159, A1368−A1373. (9) Khomenko, V.; Raymundo-Piñero, E.; Béguin, F. High-Energy Density Graphite/AC Capacitor in Organic Electrolyte. J. Power Sources 2008, 177, 643−651. (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) Lim, E.; Kim, H.; Jo, C.; Chun, J.; Ku, K.; Kim, S.; Lee, H. I.; Nam, I.-S.; Yoon, S.; Kang, K.; Lee, J. Advanced Hybrid Supercapacitor Based on a Mesoporous Niobium Pentoxide/Carbon as HighPerformance Anode. ACS Nano 2014, 8, 8968−8978. (12) Yi, R.; Chen, S.; Song, J.; Gordin, M. L.; Manivannan, A.; Wang, D. High-Performance Hybrid Supercapacitor Enabled by a High-Rate Si-Based Anode. Adv. Funct. Mater. 2014, 24, 7433−7439. (13) Wang, H.; Xu, Z.; Li, Z.; Cui, K.; Ding, J.; Kohandehghan, A.; Tan, X.; Zahiri, B.; Olsen, B. C.; Holt, C. M.; Mitlin, D. Hybrid Device Employing Three-Dimensional Arrays of MnO in Carbon Nanosheets Bridges Battery−Supercapacitor Divide. Nano Lett. 2014, 14, 1987− 1994. (14) Yang, M.; Zhong, Y.; Ren, J.; Zhou, X.; Wei, J.; Zhou, Z. Electrochemical Capacitors: Fabrication of High-Power Li-Ion Hybrid Supercapacitors by Enhancing the Exterior Surface Charge Storage. Adv. Energy Mater. 2015, 5, 1500550. (15) Vlad, A.; Singh, N.; Rolland, J.; Melinte, S.; Ajayan, P. M.; Gohy, J. F. Hybrid Supercapacitor-Battery Materials for Fast Electrochemical Charge Storage. Sci. Rep. 2014, 4, 4315. (16) Jain, A.; Aravindan, V.; Jayaraman, S.; Kumar, P. S.; Balasubramanian, R.; Ramakrishna, S.; Madhavi, S.; Srinivasan, M. P. Activated Carbons Derived from Coconut Shells as High Energy Density Cathode Material for Li-Ion Capacitors. Sci. Rep. 2013, 3, 3002. (17) Augustyn, V.; Simon, P.; Dunn, B. Pseudocapacitive Oxide Materials for High-Rate Electrochemical Energy Storage. Energy Environ. Sci. 2014, 7, 1597−1614. (18) Geim, A.; Novoselov, K. The Rise of Graphene. Nat. Mater. 2007, 6, 183−191. (19) Naguib, M.; Kurtoglu, M.; Presser, V.; Lu, J.; Niu, J.; Heon, M.; Hultman, L.; Gogotsi, Y.; Barsoum, M. W. Two-Dimensional Nanocrystals Produced by Exfoliation of Ti3AlC2. Adv. Mater. 2011, 23, 4248−4253. (20) Naguib, M.; Mashtalir, O.; Carle, J.; Presser, V.; Lu, J.; Hultman, L.; Gogotsi, Y.; Barsoum, M. Two-Dimensional Transition Metal Carbides. ACS Nano 2012, 6, 1322−1331. (21) Ghidiu, M.; Lukatskaya, M. R.; Zhao, M. Q.; Gogotsi, Y.; Barsoum, M. W. Conductive Two-Dimensional Titanium Carbide ’Clay’ with High Volumetric Capacitance. Nature 2014, 516, 78−81. (22) Lukatskaya, M. R.; Mashtalir, O.; Ren, C. E.; Dall’Agnese, Y.; Rozier, P.; Taberna, P. L.; Naguib, M.; Simon, P.; Barsoum, M. W.; Gogotsi, Y. Cation Intercalation and High Volumetric Capacitance of Two-Dimensional Titanium Carbide. Science 2013, 341, 1502−1505. (23) Zhao, M. Q.; Ren, C. E.; Ling, Z.; Lukatskaya, M. R.; Zhang, C.; Van Aken, K. L.; Barsoum, M. W.; Gogotsi, Y. Flexible MXene/
(2)
where I (A), ΔE (V), Δt (s), and m (g) denote the constant discharge current, the voltage change after a full discharge, the time period for a full discharge, and mass of active materials. The power density (P, W kg−1) and energy density (E, Wh kg−1) of LICs can be calculated from the following equations
P = ΔV × I /m
(3)
E = P × t/3600
(4)
ΔV = (Emax + Emin)/2
(5)
where Emax and Emin are the maximum and minimum potentials during discharge process, respectively, I is the discharge/charge current (A), m is the mass of electrode materials (g), and t is the discharge time (s).
ASSOCIATED CONTENT S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsnano.6b07668. XRD patterns of cationic surfactant prepillared MXene, TEM, XPS, and FT-IR characterization of CTAB@Ti3C2, supplementary electrochemical data, and XRF measurement of CTAB−Sn(IV)@Ti3C2 (PDF)
AUTHOR INFORMATION Corresponding Author
*E-mail:
[email protected]. ORCID
Xinyong Tao: 0000-0002-6233-4140 Author Contributions †
J.L. and W.Z. contributed equally to this work.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS We thank Prof. Yury Gogotsi from Drexel University for providing the structural information about Ti3C2 and valuable discussions. We acknowledge financial support from the National Natural Science Foundation of China (Grant Nos. 51002138 and 51572240), the Natural Science Foundation of Zhejiang Province (Grant Nos. LR13E020002, LY13E020010, and LY15B030003), Scientific Research Foundation of Zhejiang Provincial Education Department (Grant No. Y201432424), and Ford Motor Company. REFERENCES (1) Armand, M.; Tarascon, J.-M. Building Better Batteries. Nature 2008, 451, 652−657. (2) Whittingham, M. S. Lithium Batteries and Cathode Materials. Chem. Rev. 2004, 104, 4271−4301. 2467
DOI: 10.1021/acsnano.6b07668 ACS Nano 2017, 11, 2459−2469
Article
ACS Nano Carbon Nanotube Composite Paper with High Volumetric Capacitance. Adv. Mater. 2015, 27, 339−345. (24) Mashtalir, O.; Lukatskaya, M. R.; Zhao, M. Q.; Barsoum, M. W.; Gogotsi, Y. Amine-Assisted Delamination of Nb2C MXene for Li-Ion Energy Storage Devices. Adv. Mater. 2015, 27, 3501−3506. (25) Zhu, M.; Huang, Y.; Deng, Q.; Zhou, J.; Pei, Z.; Xue, Q.; Huang, Y.; Wang, Z.; Li, H.; Huang, Q.; Zhi, C. Highly Flexible, Freestanding Supercapacitor Electrode with Enhanced Performance Obtained by Hybridizing Polypyrrole Chains with MXene. Adv. Energy Mater. 2016, 6, 1600969. (26) Luo, J.; Tao, X.; Zhang, J.; Xia, Y.; Huang, H.; Zhang, L.; Gan, Y.; Liang, C.; Zhang, W. Sn4+ Ion Decorated Highly Conductive Ti3C2 MXene: Promising Lithium-Ion Anodes with Enhanced Volumetric Capacity and Cyclic Performance. ACS Nano 2016, 10, 2491−2499. (27) Liang, X.; Garsuch, A.; Nazar, L. F. Sulfur Cathodes Based on Conductive MXene Nanosheets for High-Performance Lithium-Sulfur Batteries. Angew. Chem., Int. Ed. 2015, 54, 3907−3911. (28) Tang, Q.; Zhou, Z.; Shen, P. Are MXenes Promising Anode Materials for Li Ion Batteries? Computational Studies on Electronic Properties and Li Storage Capability of Ti3C2 and Ti3C2X2 (X = F, OH) Monolayer. J. Am. Chem. Soc. 2012, 134, 16909−16916. (29) Sun, D.; Wang, M.; Li, Z.; Fan, G.; Fan, L.-Z.; Zhou, A. TwoDimensional Ti3C2 as Anode Material for Li-Ion Batteries. Electrochem. Commun. 2014, 47, 80−83. (30) Mashtalir, O.; Naguib, M.; Mochalin, V. N.; Dall’Agnese, Y.; Heon, M.; Barsoum, M. W.; Gogotsi, Y. Intercalation and Delamination of Layered Carbides and Carbonitrides. Nat. Commun. 2013, 4, 1716. (31) Xie, Y.; Naguib, M.; Mochalin, V. N.; Barsoum, M. W.; Gogotsi, Y.; Yu, X.; Nam, K. W.; Yang, X. Q.; Kolesnikov, A. I.; Kent, P. R. Role of Surface Structure on Li-Ion Energy Storage Capacity of TwoDimensional Transition-Metal Carbides. J. Am. Chem. Soc. 2014, 136, 6385−6394. (32) Hu, Q.; Wang, H.; Wu, Q.; Ye, X.; Zhou, A.; Sun, D.; Wang, L.; Liu, B.; He, J. Two-Dimensional Sc2C: A Reversible and HighCapacity Hydrogen Storage Material Predicted by First-Principles Calculations. Int. J. Hydrogen Energy 2014, 39, 10606−10612. (33) Hu, Q.; Sun, D.; Wu, Q.; Wang, H.; Wang, L.; Liu, B.; Zhou, A.; He, J. MXene: A New Family of Promising Hydrogen Storage Medium. J. Phys. Chem. A 2013, 117, 14253−14260. (34) Peng, Q.; Guo, J.; Zhang, Q.; Xiang, J.; Liu, B.; Zhou, A.; Liu, R.; Tian, Y. Unique Lead Adsorption Behavior of Activated Hydroxyl Group in Two-Dimensional Titanium Carbide. J. Am. Chem. Soc. 2014, 136, 4113−4116. (35) Ying, Y.; Liu, Y.; Wang, X.; Mao, Y.; Cao, W.; Hu, P.; Peng, X. Two-Dimensional Titanium Carbide for Efficiently Reductive Removal of Highly Toxic Chromium(VI) from Water. ACS Appl. Mater. Interfaces 2015, 7, 1795−1803. (36) Mashtalir, O.; Cook, K. M.; Mochalin, V. N.; Crowe, M.; Barsoum, M. W.; Gogotsi, Y. Dye Adsorption and Decomposition on Two-Dimensional Titanium Carbide in Aqueous Media. J. Mater. Chem. A 2014, 2, 14334−14338. (37) Dall’Agnese, Y.; Taberna, P. L.; Gogotsi, Y.; Simon, P. TwoDimensional Vanadium Carbide (MXene) as Positive Electrode for Sodium-Ion Capacitors. J. Phys. Chem. Lett. 2015, 6, 2305−2309. (38) Byeon, A.; Glushenkov, A. M.; Anasori, B.; Urbankowski, P.; Li, J.; Byles, B. W.; Blake, B.; Van Aken, K. L.; Kota, S.; Pomerantseva, E.; Lee, J. W.; Chen, Y.; Gogotsi, Y. Lithium-Ion Capacitors with 2D Nb2CTx (MXene)-Carbon Nanotube Electrodes. J. Power Sources 2016, 326, 686−694. (39) Wang, X.; Kajiyama, S.; Iinuma, H.; Hosono, E.; Oro, S.; Moriguchi, I.; Okubo, M.; Yamada, A. Pseudocapacitance of MXene Nanosheets for High-Power Sodium-Ion Hybrid Capacitors. Nat. Commun. 2015, 6, 6544. (40) Kloprogge, J. T. Synthesis of Smectites and Porous Pillared Clay Catalysts: A Review. J. Porous Mater. 1998, 5, 5−41. ́ L. M.; Vicente, M. A. Recent Advances in the (41) Gil, A.; GandIA, Synthesis and Catalytic Applications of Pillared Clays. Catal. Rev.: Sci. Eng. 2000, 42, 145−212.
(42) Cheng, J.; Ming Yu, S.; Zuo, P. Horseradish Peroxidase Immobilized on Aluminium-Pillared Interlayered Clay for the Catalytic Oxidation of Phenolic Waste Water. Water Res. 2006, 40, 283−290. (43) Wang, L.; Wang, A. Adsorption Properties of Congo Red from Aqueous Solution onto Surfactant-Modified Montmorillonite. J. Hazard. Mater. 2008, 160, 173−180. (44) Senturk, H. B.; Ozdes, D.; Gundogdu, A.; Duran, C.; Soylak, M. Removal of Phenol from Aqueous Solutions by Adsorption onto Organomodified Tirebolu Bentonite: Equilibrium, Kinetic and Thermodynamic Study. J. Hazard. Mater. 2009, 172, 353−362. (45) Wang, Z.; Chen, T.; Chen, W.; Chang, K.; Ma, L.; Huang, G.; Chen, D.; Lee, J. Y. CTAB-Assisted Synthesis of Single-Layer MoS2Graphene Composites as Anode Materials of Li-Ion Batteries. J. Mater. Chem. A 2013, 1, 2202−2210. (46) Dall'Agnese, Y.; Lukatskaya, M. R.; Cook, K. M.; Taberna, P. L.; Gogotsi, Y.; Simon, P. High Capacitance of Surface-Modified 2D Titanium Carbide in Acidic Electrolyte. Electrochem. Commun. 2014, 48, 118−122. (47) Halim, J.; Cook, K. M.; Naguib, M.; Eklund, P.; Gogotsi, Y.; Rosen, J.; Barsoum, M. W. X-Ray Photoelectron Spectroscopy of Select Multi-Layered Transition Metal Carbides (MXenes). Appl. Surf. Sci. 2016, 362, 406−417. (48) Ghassemi, H.; Harlow, W.; Mashtalir, O.; Beidaghi, M.; Lukatskaya, M. R.; Gogotsi, Y.; Taheri, M. L. In Situ Environmental Transmission Electron Microscopy Study of Oxidation of TwoDimensional Ti3C2 and Formation of Carbon-Supported TiO2. J. Mater. Chem. A 2014, 2, 14339−14343. (49) He, H.; Frost, R. L.; Bostrom, T.; Yuan, P.; Duong, L.; Yang, D.; Xi, Y.; Kloprogge, J. T. Changes in the Morphology of Organoclays with HDTMA+ Surfactant Loading. Appl. Clay Sci. 2006, 31, 262−271. (50) He, H.; Frost, R. L.; Zhu, J. X. Infrared Study of HDTMA+ Intercalated Montmorillonite. Spectrochim. Acta, Part A 2004, 60, 2853−2859. (51) Wei, Q.; An, Q.; Chen, D.; Mai, L.; Chen, S.; Zhao, Y.; Hercule, K. M.; Xu, L.; Khan, A. M.; Zhang, Q. One-Pot Synthesized Bicontinuous Hierarchical Li3V2(PO4)3/C Mesoporous Nanowires for High-Rate and Ultralong-Life Lithium-ion Batteries. Nano Lett. 2014, 14, 1042−1048. (52) Harrison, K. L.; Manthiram, A. Microwave-Assisted Solvothermal Synthesis and Characterization of Various Polymorphs of LiVOPO4. Chem. Mater. 2013, 25, 1751−1760. (53) Pramanik, M.; Tsujimoto, Y.; Malgras, V.; Dou, S. X.; Kim, J. H.; Yamauchi, Y. Mesoporous Iron Phosphonate Electrodes with Crystalline Frameworks for Lithium-Ion Batteries. Chem. Mater. 2015, 27, 1082−1089. (54) Augustyn, V.; Come, J.; Lowe, M. A.; Kim, J. W.; Taberna, P. L.; Tolbert, S. H.; Abruna, H. D.; Simon, P.; Dunn, B. High-Rate Electrochemical Energy Storage Through Li+ Intercalation Pseudocapacitance. Nat. Mater. 2013, 12, 518−522. (55) Brezesinski, T.; Wang, J.; Polleux, J.; Dunn, B.; Tolbert, S. H. Templated Nanocrystal-Based Porous TiO2 Films for Next-Generation Electrochemical Capacitors. J. Am. Chem. Soc. 2009, 131, 1802−1809. (56) Li, X.; Meng, X.; Liu, J.; Geng, D.; Zhang, Y.; Banis, M. N.; Li, Y.; Yang, J.; Li, R.; Sun, X.; Cai, M.; Verbrugge, M. W. Tin Oxide with Controlled Morphology and Crystallinity by Atomic Layer Deposition Onto Graphene Nanosheets for Enhanced Lithium Storage. Adv. Funct. Mater. 2012, 22, 1647−1654. (57) Kim, H.; Cho, M.-Y.; Kim, M.-H.; Park, K.-Y.; Gwon, H.; Lee, Y.; Roh, K. C.; Kang, K. A Novel High-Energy Hybrid Supercapacitor with an Anatase TiO2-Reduced Graphene Oxide Anode and an Activated Carbon Cathode. Adv. Energy Mater. 2013, 3, 1500−1506. (58) Leng, K.; Zhang, F.; Zhang, L.; Zhang, T.; Wu, Y.; Lu, Y.; Huang, Y.; Chen, Y. Graphene-Based Li-Ion Hybrid Supercapacitors with Ultrahigh Performance. Nano Res. 2013, 6, 581−592. (59) Wang, Y.; Hong, Z.; Wei, M.; Xia, Y. Layered H2Ti6O13Nanowires: A New Promising Pseudocapacitive Material in NonAqueous Electrolyte. Adv. Funct. Mater. 2012, 22, 5185−5193. 2468
DOI: 10.1021/acsnano.6b07668 ACS Nano 2017, 11, 2459−2469
Article
ACS Nano (60) Aravindan, V.; Chuiling, W.; Madhavi, S. High Power LithiumIon Hybrid Electrochemical Capacitors Using Spinel LiCrTiO4 as Insertion Electrode. J. Mater. Chem. 2012, 22, 16026−16031. (61) Sathiya, M.; Prakash, A. S.; Ramesha, K.; Tarascon, J. M.; Shukla, A. K. V2O5-Anchored Carbon Nanotubes for Enhanced Electrochemical Energy Storage. J. Am. Chem. Soc. 2011, 133, 16291− 16299.
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