Ultrafine Ti3C2 MXene Nanodots-Interspersed Nanosheet for High

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Ultrafine TiC MXene Nanodots-Interspersed Nanosheet for High-Energy-Density Lithium-Sulfur Batteries Zhubing Xiao, Zhonglin Li, Pengyue Li, Xueping Meng, and Ruihu Wang ACS Nano, Just Accepted Manuscript • DOI: 10.1021/acsnano.9b00177 • Publication Date (Web): 13 Mar 2019 Downloaded from http://pubs.acs.org on March 13, 2019

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Ultrafine Ti3C2 MXene Nanodots-Interspersed Nanosheet for High-Energy-Density Lithium-Sulfur Batteries Zhubing Xiao†, ‡, Zhonglin Li†, ‡, Pengyue Li†, Xueping Meng†, and Ruihu Wang*† †

State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the

Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, China. E-mail: [email protected] ‡

University of Chinese Academy of Sciences, Beijing, 100049, China.

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ABSTRACT The nanostructured carbon materials have been extensively used for encapsulating sulfur and improving cyclic stability of lithium-sulfur (Li-S) batteries, but high carbon content and low packing density greatly limit their volumetric energy density. Herein, we present MXene-based Ti3C2Tx (Tx stands for the surface terminations) nanodots-interspersed Ti3C2Tx nanosheet (TCD-TCS) to accomplish spatial immobilization and conversion of high-loaded sulfur species. Rich surface polar sites in TCD-TCS enhance structural integrity of the resultant electrode, while the absence of the carbon-based materials and conductive additives results in high tap density of the cathode materials. The TCD-TCS/S electrode exhibits an almost theoretical discharge capacity at a medium sulfur loading of 1.8 mg cm-2. Notably, ultrahigh volumetric capacity (1957 mAh cm-3) and high areal capacity (13.7 mAh cm-2) are synchronously achieved at a high sulfur loading of 13.8 mg cm-2. The mechanism study of sulfur evolution during discharge process highlights the importance of the integration of MXene-based nanodots and nanosheets in Li-S batteries. This proposed methodology holds great promises for the development of various high-performance energy storage materials.

KEYWORDS: lithium-sulfur batteries, functional motif, shuttle effect, volumetric capacity, areal capacity

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The ever-growing demand for portable electronic devices, electric vehicles and large-scale smart grids has driven rapid development of energy-storage technologies. Lithium-sulfur (Li-S) batteries have been considered as one of promising next-generation energy storage systems because of conspicuous advantages of the cathode material sulfur, such as high theoretical specific capacity, abundant natural reserve, low cost and environmental benignity.1,2 However, there are still several challenges that need to be addressed for commercial application, including the insulating nature of sulfur and its solid discharge products, the dissolution and shuttle effect of soluble lithium polysulfide (LiPS) intermediates, and large volume variation of the active materials during charge/discharge cycles. These disadvantages greatly limit their practical applications.3-5 Considerable efforts have been devoted to overcoming the aforementioned challenges. One of successful techniques is to employ conductive carbonaceous materials as sulfur hosts for constructing advanced sulfur composite cathodes.6-16 However, owing to weak interactions between low polar carbon and high polar LiPS, both physical sequestration and chemical adsorption provided by carbon-based materials are not strong enough to alleviate the capacity fading over a long lifespan, especially for high sulfur loading cell. Moreover, the poor affinity of carbon-based materials and LiPS also prevents efficient interfacial charge transfer and slows down reaction kinetics of sulfur species.17 Recently, a variety of polar materials, such as transition metal oxides, carbides and sulfides, have been employed as the additives of carbon hosts for improving trapping ability of LiPS and/or exerting positive catalytic

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effects on the conversion of LiPS,18-25 which promotes the springing up of sulfur cathodes with high specific capacities and cyclic performance. Some problems have been encountered in these carbon-based hybrid materials. The hybridation of these polar additives with conductive carbon materials inevitably forms heterogeneous grain boundary and interfaces, thus increasing internal charge-transfer resistance.26,27 The weak surface affinity among different type of host materials is also apt to trigger detachment of the additives from the surface of carbon materials, resulting in structural collapse and catastrophic capacity decay after extended cycling.24 Most importantly, these additives are hybridized with excess low-tap-density carbon materials, which greatly compromise the volumetric energy density, an important metrics in advanced energy storage systems with the imposed constraints by device volume and chip area. Therefore, engineering one type of sulfur host materials with high conductivity and rich exposed active sites are highly desirable for achieving high areal and volumetric capacities. MXene is one types of emerging two-dimensional (2-D) layered materials in the field of energy storage, which exhibits high conductivity, outstanding hydrophilicity and excellent chemical/mechanical stability.28-31 Their surfaces are terminated with rich polar groups, such as -OH, O and F, which could provide strong chemical interactions for LiPS trapping. Recently, some layered MXene-based materials, such as Ti2CTx or Ti3C2Tx (Tx stands for the surface terminations) have been used as the additives of sulfur hosts in Li-S batteries, resulting in dramatically improved cyclability and stability.32,33 In comparison with 2-D layered materials, MXene-based

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nanodots possess special physical and chemical properties due to their quantum confinement and edge effects.34-36 Ultrasmall size of the nanodots could allow for the exposure of more surface terminations for effective trapping of LiPS in the cathode region. However, one of the deficiencies of the nanodots is that their self-aggregation and coalescence during charge/discharge cycles, their discrete distribution is also unfavorable for their global electron transport. One of feasible solutions is the integration of MXene-based nanodots on the surface of nanosheets, which can greatly strengthen their independent physiochemical performance. In such a well-designed MXenen-based architecture, the close connection between nanodots and nanosheets could greatly decrease their interfacial resistance, thus expediting global electron transport and electrochemical reaction kinetics. High density of surface polar sites can not only minimize the dissolution and shuttle effect of LiPS, but also mediate sulfur infiltration and deposition of solid discharge products, thus enabling high sulfur utilization even at high current densities and high sulfur loading. Most importantly, the MXene-based composite is preferable for forming a closely-packed structure after sulfur infiltration to acquire high volumetric capacity. Despite these promises for high-performance Li-S batteries, to the best of our knowledge, only Ti3C2Tx nanodots have been reported for multicolor cellular imaging,34 the integration of MXene-based nanodots and nanosheets have not been reported hitherto. As a proof-of-concept study, herein, we choose typical layered Ti3C2Tx as a precursor, and provide one type of MXene-based conductive materials, Ti3C2Tx nanodots-interspersed Ti3C2Tx nanosheet (TCD-TCS). The use of TCD-TCS as a

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sulfur host greatly boosts the overall performance of sulfur cathodes in the absence of the carbon-based materials and conductive additives. An almost theoretical discharge behavior is achieved in medium areal sulfur loading (ASL), while high areal/volumetric capacities are synchronously achieved at high ASL of 13.8 mg cm-2. The deliberate construction of TCD-TCS/S offers an in-depth insight into the engineering of sulfur host materials towards high-performance Li-S batteries.

Figure 1. Schematic diagram for the preparation of TCD-TCS and TCD-TCS/S.

RESULTS AND DISCUSSION The route for preparing TCD-TCS is schematically illustrated in Figure 1 (see details in Supporting information). Bulk Ti3C2Tx was initially obtained by selectively etching the aluminium layer in the Ti3AlC2 precursor using aqueous HF acid. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images (Figure S1) reveal good etching result of Ti3AlC2, which is further confirmed by the disappearance of typical Ti3AlC2 diffraction peaks in the X-ray di raction (XRD) pattern of as-prepared Ti3C2Tx (Figure S2). The hydrothermal treatment of

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as-prepared Ti3C2Tx using sodium alginate (SA) at 100 oC for 2 h gave rise to TCD-TCS. The evolution process of TCD-TCS was investigated through tailoring reaction temperature from 60 oC to 80 oC and 100 oC (Figure 2), the corresponding products are labeled as TC-60, TC-80 and TC-100, respectively. When hydrothermal treatment was performed at relatively low temperature of 60 oC, abundant Ti3C2Tx nanoribbons and small amount of nanoflakes are simultaneously formed, they are adhered on the voile-like corrugated nanosheets (Figure 2a and Figure S3). The rise of reaction temperature to 80 oC gave rise to varisized nanodots, which are adhered on the corrugated nanosheets (Figure 2b and Figure S4). Of much interest is that the TCD-TCS nanostructure is generated at 100 oC. Ultrafine nanodots are uniformly interspersed on the nanosheets (Figure 2c, d). The high-resolution TEM image clearly shows interplanar spacing of 0.24 nm corresponding to (103) crystal plane (Figure S5a),37 which is identical with that in TC-80 (Figure S4b), indicating that hydrothermal treatment has no obvious effect on intrinsic structure of Ti3C2Tx. The particle size distribution shows that the lateral size of TCD is in the range from 1.0 to 6.0 nm with an average size around 2.5 nm (Figure S6). To the best of our knowledge, such small size of nanodots in MXene has not been reported to date. The TCD-TCS structure integrates the advantages of high planar conductivity of 2D nanosheets and high density of polar active sites of nanodots, which could exert significant role in trapping LiPS and monitoring deposition of solid charge/discharge products. To get better insight into the evolution of TCD-TCS, the reaction time at 100 oC was elongated. As shown in Figure S5b, high density of ultrafine nanodots are

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uniformly interspersed on the nanosheets in 4 h, but some crevices at the edge of nanosheets are clearly detected (denoted by purple arrows), indicative of further hydrothermal scissoring of TCS by SA. The total split of the Ti3C2Tx nanosheets into variegated nanofragments occurs in 6 h (Figure S5c), further cutting of the nanofragments is observed in 8 h (Figure S5d). Notwithstanding, these nanofragments are clearly interspersed with ultrafine nanodots, suggesting intimate linkage between TCD and TCS, which is probably attributed that affluent surface terminations (-OH and O etc.) on Ti3C2Tx surface result in strong interparticle interactions between the TCD and TCS. This structural integrity is not only favorable for facilitating charge conduction in the TCD-TCS backbone, but also contributes to minimizing the irreversible loss of LiPS during cycling, thus enabling high utilization of active materials even at a high current density The above observations clearly show that SA has exerted pivotal influences on the formation and microstructure of obtained products during hydrothermal treatment of as-prepared Ti3C2Tx. It is known that SA is a linear polysaccharide with carboxyl/hydroxy groups in the -D-mannuronate and -L-guluronate units.38 These groups could serve as the reaction initiators to offer powerful impetus for exfoliation and scission of as-prepared Ti3C2Tx. The strong coordination between carboxyl groups of long SA chains and edge Ti atoms of the Ti3C2Tx surface as well as extensive hydrogen bonds between Ti3C2Tx and SA could weaken the Ti-C bonds of Ti3C2Tx and the van der Waals force between the adjacent nanosheets, thus leading to exfoliation of outermost layer and synchronous cleavage of Ti-C bonds in TCS

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(Figure S7). On the basis of these facts, a SA-mediated ecto-entad bond-scission mechanism has been proposed. As schematically illustrated in Figure S8, the Ti-O bonds on the surface of the outermost layer are in a line arrangement on the Ti lattice due to its ABCABC ordering stacking,28 and strong chemical interactions between the Ti sites of Ti3C2Tx and the O sites of SA trigger the cleavage of underlying C-Ti bonds. Once the rupture appears, the exposed Ti-OH/Ti-O/C-O edge sites are dramatically augmented and energetically promote subsequent cleavage of more C-Ti bonds, thus rendering complete rupture of the Ti3C2Tx nanosheets to form lateral size-shrunken nanoflakes and nanoribbons. The presence of these defects makes the lateral TCS vulnerable,39 the nanoflakes and nanoribbons terminated by the mixed Ti-OH/Ti-O/C-O active sites could be further laniated with the increment of temperature, generating smaller nanoflakes and nanodots at 80 oC (Figure 2b). Further increasing reaction temperature to 100 oC, a great deal of Ti3C2Tx nanoflakes turn into nanodots, which leads to the formation of the TCD-TCS nanostructure (Figure 2d). The elongation of reaction time at 100 oC results in excessive cutting of TCS into the Ti3C2Tx nanofragments containing interspersed nanodots (Figure S5). Notably, rich accessible surface terminations enable them to possess strong coupling effect with nanodots to form a structural integrity for TC-60, TC-80 and TC-100. Nitrogen absorption/desorption measurements show that Brunauer-Emmett-Teller surface area and pore volume of TC-100 are 138 m2 g-1 and 0.21 cm3 g-1, respectively, which are higher than with those of TC-60 (114 m2 g-1, 0.15 cm3 g-1) and TC-80 (125 m2 g-1, 0.18 cm3 g-1). The pore size distributions exhibit that they mainly consist of

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mesopores (~ 3 nm). The large surface area and abundant mesopores are apt to entrap the LiPS intermediates and facilitate the ion transfer. The tap densities of TC-60, TC-80 and TC-100 are as high as 2.88, 2.82 and 2.98 g cm-3, respectively. Their electrical conductivities, which were measured by the four-probe method on pressed pellets, are as high as 1380 ± 50, 1359 ± 50 and 1320 ± 50 S cm-1, respectively. The high tap density and high conductivity hold great potentials to assemble electrodes with high volumetric capacity.

Figure 2. TEM images of (a) TC-60, (b) TC-80. (c) SEM and (d) TEM images of TC-100 with hydrothermal treatment for 2 h. (e) Li 1s spectra of TC-100 and TC-100-Li2S6. (f) pH-dependent Zeta potential for TC-60, TC-80 and TC-100 with a concentration of 1.5 mg mL-1 in water. (g) Zeta potential of TC-60, TC-80 and TC-100 in water, LiNO3 and Li2SO4 solution at pH = 7. (h) Ti 2p XPS spectra of TC-100 and TC-100-Li2S6. (i) CV curves of symmetrical cells for TC-60, TC-80, TC-100 and CNTs electrodes in the electrolytes with 0.5 M Li2S6.

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It is well known that the surface chemistry of sulfur host materials has important effects on the LiPS adsorptivity and distribution of solid sulfur species during electrochemical cycling. The surface compositions and functional groups of as-prepared TC-60, TC-80 and TC-100 were investigated using the Fourier transformed infrared (FTIR) spectroscopy. As shown in Figure S10, TC-60, TC-80 and TC-100 show the identical stretching vibrations, which includes the characteristic peaks of -OH at 3432 and 1562 cm-1, C=O at 1586 cm-1, C-F at 1115 cm-1, C-O at 1025 cm-1, C-Ti-C at 2953 cm-1 and Ti-O at 685 cm-1.36 With the increment of reaction temperature, the C-Ti-C stretching vibrations gradually weaken, while the peaks of -OH, C=O and Ti-O are dramatically intensified, indicative of more exposed edge sites in TC-100, which serves as effective LiPS-trapping active sites. These observations are consistent with SA-mediated bond-scission mechanism proposed above. The entrapment behavior of these host materials toward LiPS was probed using visualized adsorption test by adding the same amount of TC-60, TC-80 and TC-100 into the Li2S6 solution (15 mM) in DOL/DME. For comparison, commercial carbon nanotubes (CNTs), which are one of the common carbonaceous materials for sulfur hosts and conductive additives in Li-S batteries, were also investigated. As expected, CNTs only slightly decolor blank Li2S6 solution, while TC-100 substantially de-colors the Li2S6 solution, light brown solutions are observed after the addition of TC-60 and TC-80 (Figure S11). These results indicate the strongest adsorption ability of TC-100 toward Li2S6, which could be ascribed to the presence of high density of exposed active sites in TCD-TCS.

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To further probe superior LiPS adsorptivity of TCD-TCS, XPS studies of pristine Li2S6 and TC-100/Li2S6 retrieved from the adsorption test were performed. Li 1s XPS spectrum of pristine Li2S6 exhibits typical Li-S peak at 55.7 eV (Figure 2e). Upon contact with TC-100, the peak is downshifted by 0.5 eV, indicative of a strong chemical interaction that originates from electron transfer from the TC-100 surface to Li ions. This is highlighted by the emergence of Li-O characteristic peak at 56.9 eV (Figure 2e). Moreover, strong lithiophilicity of TC-100 is further evidenced by the zeta potential ( ) measurements. As shown in Figure 2f, TC-60, TC-80 and TC-100 show the electronegative behavior at neutral, basic and even weak acidic conditions, but the values of TC-100 are more negative than those in TC-80 and TC-60 in wide pH range of 2-12. The point of zero charge (PZC) for TC-100 is measured to be at 2.5, which is much lower than that of TC-80 (2.9) and TC-60 (3.5). These prominent surface charge behaviors strongly confirm improved concentration of the surface active sites in the TCD-TCS structure, which is substantially favorable for the entrapment of positively charged Li+ in LiPS. To further verify this statement, measurements were conducted in neutral lithium salt solutions of LiNO3 and Li2SO4 (0.1 mM). As shown in Figure 2g, their

values are reduced to some extent when

compared with their counterparts, amenable to strong chemical interactions between host materials and Li+ ions. Furthermore, the

values of TC-100 in the LiNO3 and

Li2SO4 solutions are steeply reduced to -26 and -21 mV, respectively. The reduced values (

) of 57 and 52 mV are greatly higher than those in TC-60 and TC-80,

further indicating the strongest lithiophilicity of TC-100. In addition, TC-100

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possesses strong binding capability towards other alkali metal cations (Figure S12). Lithium bond theory has been proposed in Li-S batteries to interpret chemical interactions between LiPS and carbon-based host materials that contain heteroatoms, such as oxygen and nitrogen,40 which suppress the shuttle effect of LiPS and facilitates the redox kinetics. In our case, strong lithiophilicity of the Ti3C2Tx hosts, especially for TC-100, mainly originates from their high density of electronegative active termination sites, which are propitious to form a strongly coupled interface for maintaining active materials in the cathode region. Notably, strong Ti-S interaction is also indicated by the binding energy peak at 455.8 eV in the Ti 2p XPS spectrum of TC-100/Li2S6 (Figure 2h),32 revealing the sulfiphilicity of TC-100. This amphipathic LiPS-anchoring behavior favors smooth charge transfer between host materials and LiPS, thus accelerating redox reactions of LiPS, which is adequately verified by the symmetrical cells measurement (see details in Supporting information).20 It could be clearly observed that the current density, corresponding to the redox current of Li2S6, significantly increases in TC-100 when compared with that of TC-60, TC-80 and nonpolar CNTs (Figure 2i), revealing the fastest reaction kinetics between TC-100 and LiPS. This is further highlighted by the EIS plots of symmetrical cells. As shown in Figure S13, the semicircle in the Nyquist plot of TC-100 corresponds to charge transfer, it greatly shrinks in comparison with that of TC-60, TC-80 and CNTs, which indicates that the charge transfer at the interface of TC-100 and LiPS is much faster than other electrodes, further demonstrating the favorable electrochemical kinetics in TC-100/S. Considering that the symmetrical cells are free of metallic Li, the

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decreased interfacial resistance is probably attributed to enhanced interfacial affinities between TC-100 and LiPS as well as rapid charge transport in the redox reactions. All these results collectively verify strong chemisorption capability of TC-100 toward LiPS and high electrochemical activity of sulfur species.

Figure 3. (a-c) Top-view SEM images and corresponding elemental mapping, (d) TEM image, (e) particle size distribution, (f) SAED, (g, h) side-view SEM images and (i) side-view TEM image for TC-100/S. In view of these structural and chemical superiorities, TC-100 was then applied as a sulfur host material. After 67.6% sulfur was infiltrated into TC-100 by traditional melt-diffusion method (Figure S14), sharp and strong diffraction peaks in the XRD pattern of TC-100/S manifest that the incorporated sulfur is crystalline with typical Fddd orthorhombic structure (Figure S15). The morphology of TC-100/S is depicted in Figure 3. Similar to pristine TC-100 (Figure 2d), the nanodots are uniformly interspersed on the TCS surface, there are no distinguishable large sulfur particles or

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agglomerates as revealed by the element mapping (Figure 3a-d). The particle size distribution shows the size of the nanodots is in the range of 4-12 nm with an average size around 9 nm (Figure 3e), which is nearly five times higher than that of pristine TCD (Figure 2d), implying that TCD is covered with sulfur. Moreover, there are divergent lattice fringes with interplanar spacings of 0.24 and 0.34 nm, which are assignable to (103) and (026) diffraction peaks of Ti3C2Tx and sulfur,37,41 respectively (Figure 3f), reconfirming that sulfur is effectively adhered on the surface of TCD and TCS. Revealingly, the sulfur layer in TC-100/S has large contact area with TC-100, short diffusion distance of the electrons/Li ions and better electrolyte wetting, which greatly weakens the insulating nature of solid sulfur species and facilitates the electrochemical reaction of sulfur species.42 More importantly, the closely-packed structure of TC-100/S could be visualized in the side-view SEM and TEM images (Figure 3g-i), which is ascribed to strong surface interactions between TC-100 and sulfur resulting from ample exposed polar sites in TCD-TCS, as confirmed by FTIR results (Figure S10). The thermogravimetric analysis of TC-100/S also reveals strong host-guest surface interactions as verified by its much delayed sulfur evaporation temperature (Figure S14), which contributes to the immobilization of active materials during charge/discharge processes. For comparison, TC-60 and TC-80 were also used as sulfur hosts, the morphologies of the TC-60/S and TC-80/S composites are provided in Figure S16a, b and S17a, b, which are comparable with those in pristine TC-60 (Figure 2a, S3) and TC-80 (Figure 2b, S4), respectively. Corresponding element mappings (Figure S16c and S17c) reveal that sulfur is uniformly distributed

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on the surface of TC-60 and TC-80.

Figure 4. (a) Voltage profile and (b) rate performance of the TC-60/S, TC-80/S and TC-100/S electrodes with ASL of 1.8 mg cm-2. (c) Cycling performance of TC-100/S at 2 C with ASL of 1.8 mg cm-2. Cycling performance of electrodes with ASL of (d) 9.2 and (e) 13.8 mg cm-2 at 0.05 C. (f) Side-view SEM image of TC-100/S after 400 cycles in the discharge state. (g) Side-view, (h) top-view SEM images and (i) TEM image for TC-100/S after 400 cycles in the charge state. The electrochemical performance of TC-100/S, TC-80/S and TC-60/S was evaluated by pairing them with metallic lithium foils. The electrodes with a medium ASL of 1.8 mg cm-2 were examined to gain accurate reaction mechanism and kinetics that impose on sulfur utilization and cycling stability. Impressively, the TC-100/S electrode exhibits an ultrahigh initial discharge capacity of 1609 mAh g-1 at current density of 0.05 C (Figure 4a) after the extraction of capacity contribution from Ti3C2Tx (Figure S18, Table S1),43 which is about 96.1% of the theoretical capacity of sulfur and is much superior to that of TC-60/S (1360 mAh g-1) and TC-80/S (1345 16


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mAh g-1). Moreover, the high-potential plateau at 2.40-2.09 V provides a discharge capacity of 405 mAh g-1 (QH), and the low-potential plateau at 2.09 V together with subsequent tailing slope (2.09-1.50 V) delivers a specific capacity of 1204 mAh g-1 (QL) for the TC-100 electrode, the QL/QH ratio of 2.97 is close to the theoretical value of 3:1. The TC-100/S electrode also presents the lowest voltage hysteresis ( V) in the galvanostatic charge-discharge profiles, which suggests facile electrochemical redox reaction and low resistance. The EIS of TC-100/S also possesses the lowest charge transfer resistance. As shown in Figure S19, the TC-100/S electrode shows a much depressed semicircle in high frequency region followed by an almost vertical line in low frequency region, indicating faster electron/ion transfer kinetics in the TC-100/S electrode, echoing the galvanostatic charge-discharge results (Figure 4a). The promoted sulfur electrochemistry is further proved by the cyclic voltammetry curves (Figure S20). The TC-100/S electrode exhibits higher cathodic peak positions and lower anodic peak position than TC-60/S and TC-80/S, moreover, the peak intensities of TC-100/S are also enhanced. These results indicate the polarization decrement and kinetic acceleration for LiPS redox in the TC-100/S electrode. It should be mentioned that lithium (de)-insertion behavior in TC-60, TC-80 and TC-100 could not be observed in the CV curves owing to the overlapping by the redox peaks of sulfur species.32,33 The rate performance of the TC-60/S, TC-80/S and TC-100/S electrodes was also evaluated by increasing the current densities from 0.05 to 3 C per 5 cycles. As shown in Figure 4b, the TC-100/S electrode achieves superior rate performance over

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TC-60/S and TC-80/S. When cycled at medium rates of 1 C, 2 C and 3 C, the TC-100/S electrode delivers high discharge capacities of 1081, 950 and 882 mAh g-1, respectively. When the current density is abruptly shifted back to 0.2 C, it restores to original specific capacity of 1377 mAh g-1, suggesting fast redox kinetics of sulfur species and high reversible electrochemistry of the TC-100/S electrode. The TC-100/S electrode also possesses prominent cycling stability (Figure 4c). The initial specific capacity of 1058 mA h g-1 is decreased to 815 mAh g-1 after 400 cycles at 2 C, the capacity fading rate is as low as 0.057 % per cycle and the average Coulombic efficiency is over 98.5 %. High sulfur utilization and excellent cycling stability are attributed to the synergetic effect between the TCD and TCS, in which the amphipathic interaction of the TCD-TCS host toward LiPS tightly confines active sulfur species in the cathode region and effectively suppresses the shuttle effect of LiPS. This is further verified by the comparison of rate performance between TC-100/S and the Ti3C2Tx/S electrodes (Figure S21). The discharge capacities of TC-100/S are much higher than those of the Ti3C2Tx/S electrode at various currents, indicative of overwhelming superiority of the attached TCD on the surface of TCS. Meantime, the closely-packed layered structure could effectively buffer volume variation of the sulfur cathode through elastic shrinkage/expansion in the third dimension, which is beneficial for structural integrity and electrode stability. High sulfur-loading electrodes have been extensively explored in consideration of the requirements for commercialization, but most of them are based on freestanding carbon/sulfur or alternately arranged carbon/sulfur layer cathodes. The

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excessive use of low-tap-density carbon hosts or conductive additives in these scenarios usually generates loose electrode structures with oversize thickness.40 The imbalance between cathode thickness and active materials loading enables the reported electrodes to possess high areal energy densities yet accompanied with poor volumetric performance. On the other hand, the notorious shuttle effect of LiPS and irregular deposition of solid charge/discharge products will become more intractable when sulfur loading is considerably increased, which are mainly ascribed to weak interactions between carbon-based materials and sulfur species as well as kinetically sluggish conversion between solid charge/discharge products (S8/Li2S). Considering the advantages of TC-100 in terms of high tap density, high electrical conductivity, rich exposed active sites and facilitated redox kinetics of sulfur species, TC-100/S could serve as one type of electrodes without extra conductive additives to synchronously achieve high areal/volumetric capacities. Therefore, the TC-100/S electrodes with ultrahigh ASL of 9.2 and 13.8 mg cm-2 were further fabricated using traditional slurry-coating technique. Both of them show typical two-plateau discharge profiles (Figure S22). The electrode with ASL of 9.2 mg cm-2 initially delivers high areal capacity of 9.5 mAh cm-2 and ultrahigh volumetric capacity of 1827 mAh cm-3 at current rate of 0.05 C. The values are slightly decreased to 7.6 mAh cm-2 and 1462 mAh cm-3, respectively, after 100 cycles (Figure 4d). Even higher areal/volumetric capacities up to 13.7 mAh cm-2/1957 mAh cm-3 are achieved when ASL is further increased to 13.8 mg cm-2, despite slight capacity deterioration to certain extent (Figure 4e). It should be mentioned that the areal capacities in these electrodes are

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comparable with reported state-of-the-art carbon-based slurry-coating electrodes, and ultrahigh volumetric capacities are rare in high-energy-density Li-S batteries (Table S2).6-15,43,45-48 All these results have demonstrated the appealing superiorities for the TC-100/S to replace conventional carbon-based cathode materials in Li-S batteries, which provides approaches for synchronous gain in high areal and volumetric capacities. To better understand the appealing superiorities of the TC-100/S electrode in Li-S batteries, post-morterm morphological characterizations were performed after extracting the cathode composites from the cycled cell. SEM and TEM images for the TC-100/S electrode with ASL of 1.8 mg cm-2 after 400 cycles are shown in Figure 4f-i and Figure S23. In discharge state, SEM images show the cycled TC-100/S electrode maintains the closely-packed structure (denoted by dashed yellow lines) with uniform surface coverage by active materials, there are no detectable large sulfur particles. TEM image further confirms the rich coverage of Li2S on TC-100 surface, the particles size of the nanodots is greatly enhanced in comparison with those of fresh TC-100/S composite owing to sulfur coverage (Figure 3d), indicating the interspersed TCD plays vital roles in retarding the dissolution of LiPS and guiding the deposition of discharge products. The structural maintenance and rich surface coverage of active materials (denoted by yellow arrows) are also detected in charge state (Figure 4g-i). The elemental mappings collected from SEM further indicate the uniform distribution of sulfur (Figure S24). These observations vividly confirm that TCD-TCS is able to effectively anchor sulfur species and modulate the deposition of

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solid sulfur/Li2S on the surface of TCD-TCS, which further supports the advantages of TCD-TCS in boosting the reaction kinetics and prolonging the battery lifespan.

Figure 5. Schematic illustration for the evolution of active materials during discharge process for (a) conventional C/S and (b) TC-100/S cathodes. Benefiting from high conductivity, high density of polar trapping sites and closely-packed structure, the theoretical limit of discharge capacity is almost realized in TC-100/S. This behavior is further validated by the ex-situ XPS measurement. As shown in Figure S25, the depth of discharge (DoD) of 70% (about 1.8 V) shows two sets of binding energy doublet peaks at 161.9/162.8 and 159.8/160.7 eV, which are assigned to short-chain Li2Sx and final discharge product Li2S, respectively.42 While the peaks of short-chain Li2Sx almost diminish at DoD of 100%. These observations

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show that Li2S is major solid product after discharging to 1.5 V and sulfur could be thoroughly reduced. As schematically illustrated in Figure 5, the multistep discharge behavior of Li-S battery could be roughly divided into two processes, which correspond to high and low voltage plateaus, respectively.2,42 When elemental sulfur is gradually reduced to soluble LiPS in the discharge process, relatively weak carbon-sulfur interactions in the conventional carbon-based cathode materials could not effectively suppress the dissolution of LiPS into the electrolytes and subsequent migration to anode region. Moreover, high sulfur loading fails to guarantee sufficient electrical contact between all of sulfur and the carbon substrate, sulfur in the core domain is incapable of participating in the electrochemical reaction, which causes incomplete utilization of element sulfur (process 1 in Figure 5a). After liquid phase reduction of long-chain LiPS to short-chain species, they are further reduced into insoluble Li2S2 and Li2S, the insulating nature of these solid reduction products and arbitrary deposition of Li2S could block intimate contact of Li2S2 with the electrode and/or electrolyte, which results in incomplete reduction of Li2S2, thus hindering continuous electrochemical transformation between element sulfur and Li2S (process 2 in Figure 5a). In sharp contrast, the uniform distribution of high density of TCD on TCS make the accumulation depth of active materials above TCD lower than those in TCS, which is favorable for the penetration of the electrolyte and the electron/ion transfer in TCD-TCS (process 1 in Figure 5b). As the lithiation progress, strong LiPS-trapping ability and high conductivity of TCD-TCS could effectively suppress the shuttle effect of soluble LiPS and ensure high utilization of sulfur. Most

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importantly, the advantages of TCD-TCS promise smooth transformation of liquid-to-solid reduction from short-chain LiPS to Li2S2 and Li2S, contributing to nucleation of solid Li2S and orderly growth on the local surface of TCD-TCS, which finally endows the TC-100/S cathode with an almost theoretical capacity of sulfur (process 2 in Figure 5b). The spatial immobilization-conversion mechanism of sulfur species on TCD-TCS in the discharge process, in turn, could energetically promote charge process, as verified by post-morterm morphological characterizations (Figure 4g-i). These results have forcefully validated that high-conductive TCD-TCS supports are promising sulfur host materials in the development of high-performance Li-S batteries.

CONCLUSIONS We developed a SA-mediated ecto-entad bond-scission method to in situ fabricate MXene-based TCD-TCS nanoarchitecture. Sulfur could be tightly adhered on the surface of TCD-TCS, forming a closely-packed structure. The uniform interspersion of high density of ultrafine TCD on the TCS surface greatly decreases their interfacial resistance and promotes the redox kinetics of sulfur species, enabling high sulfur utilization even at high current densities and high sulfur loading. The electrochemical performance is greatly superior to those in the traditional carbon-based cathode materials. The synchronous gain in high areal capacity and ultrahigh volumetric capacity is realized using the MXene-based materials. The areal and volumetric capacities can compete with the state-of-the-art those in Li-S batteries. This study offers an instructive material engineering strategy to improve overall performance of

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Li-S batteries, which could be extended to various energy storage and conversion systems, such as lithium-ion batteries, supercapacitors and electrochemical catalysis.

EXPERIMENTAL SECTION Synthesis of TCD-TCS (TC-100). Commercial Ti3AlC2 powder (2 g) was immersed in 32% HF (50 mL) and vigorously stirred under Ar bubbling at 50 oC for 48 h. The resultant powder was rinsed with deionized water until pH value of the solution reached 7. The powder was retrieved by centrifugation at 4000 rpm for 5 min, and the supernatant was discarded. The wet sediments were dried under vacuum at 80 oC for 24 h. In a N2-protected environment, the etched Ti3C2Tx powder was then dispersed in 30 mL deionized water/SA hydrosol (2g L-1), followed by alternant stirring and sonication for 2 h. The resultant mixture was transferred into 50 mL Teflon-lined stainless steel autoclave, and heated at 100 oC for appropriate time, respectively. After hydrothermal treatment, the supernatant was collected through centrifugating at 1000 rpm for 10 min, and the sediment was discarded. Then the obtained supernatant was retrieved by centrifugation at 5000 rpm for 5 min, and the supernatant was discarded. The TCD-TCS are obtained after washed using a copious of deionized water and ethanol, followed by freeze drying for 24 h. As a control experiment, other products obtained under various conditions, such as the hydrothermal temperature and time, were synthesized in the same way. The resulting materials were denoted accordingly as TC-60, TC-80, TC-100, and so on. Synthesis of TC-100/S composite. The as-prepared TC-100 (300 mg) was ground with sulfur (700 mg, 99.999%, Sigma-Aldrich). The mixture was transferred in a glass

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vial in horizontal tube furnace and heated at 160 oC under nitrogen atmosphere with internal pressure of 110 KPa for 12 h, and further heated at 200 oC for 3 h. After cooling to room temperature, the TC-100/S composite was obtained, the final mass fraction of sulfur in the composite was determined by TGA. As a comparison, the CNTs-S composite was prepared through following the same procedures.

ASSOCIATED CONTENT Supporting Information Available: Additional SEM, TEM, XPS, EDX, TGA, and electrochemical performance is available free of charge on the ACS Publications website.

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] The authors declare no competing financial interest.

ACKNOWLEDGMENTS The authors acknowledge the National Natural Science Foundation of China (21601191, 21673241 and 21471151), the Natural Science Foundation of Fujian Province (2018J01030) and the Strategic Priority Research Program of the Chinese Academy of Sciences (XDB20000000).

REFERENCES (1) Bruce, P. G.; Freunberger, S. A.; Hardwick, L. J.; Tarascon, J. Li-O2 and Li-S Batteries with High Energy Storage. Nat. Mater. 2012, 11, 19 29. (2) Deng, D.; Xue, F.; Bai, C.; Lei, J.; Yuan, R.; Zheng, M.; Dong, Q. Enhanced

25


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

Adsorptions to Polysulfides on Graphene-Supported BN Nanosheets with Excellent Li-S Battery Performance in a Wide Temperature Range. ACS Nano 2018, 12, 11120 11129. (3) Zhang, G.; Peng, H.; Zhao, C.; Chen, X.; Zhao, L.; Li, P.; Huang, J.; Zhang, Q. The Radical Pathway Based on a Lithium-Metal-Compatible High Dielectric Electrolyte for Lithium-Sulfur Batteries. Angew. Chem. Int. Ed. 2018, 57, 16732 16736. (4) Shi, H.; Lv, W.; Zhang, C.; Wang, D.; Ling, G.; He, Y.; Kang, F.; Yang, Q. Functional Carbons Remedy the Shuttling of Polysulfides in Lithium-Sulfur Batteries: Confining, Trapping, Blocking, and Breaking up. Adv. Funct. Mater. 2018, 28, 1800508. (5) Peng, H.; Huang, J.; Cheng, X.; Zhang, Q. A Quinonoid-Imine-Enriched Nanostructured Polymer Mediator for Lithium-Sulfur Batteries. Adv. Energy Mater. 2017, 7, 1700260. (6) Li, C.; Shi, J.; Zhu, L.; Zhao, Y.; Lu, J.; Xu, L. Titanium Nitride Hollow Nanospheres with Strong Lithium Polysulfide Chemisorption as Sulfur Hosts for Advanced Lithium-Sulfur Batteries. Nano Res. 2018, 11, 4302 4312. (7) Zhang, J.; Huang, M.; Xi, B.; Mi, K.; Yuan, A.; Xiong, S. Systematic Study of Effect on Enhancing Specific Capacity and Electrochemical Behaviors of Lithium-Sulfur Batteries. Adv. Energy. Mater. 2018, 8, 1701330. (8) Gueon, D.; Hwang, J. T.; Yang, S. B.; Cho, E.; Sohn, K.; Yang, D. K.; Moon, H. K. Spherical Macroporous Carbon Nanotube Particles with Ultrahigh Sulfur Loading

26


Page 26 of 33

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

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for Lithium-Sulfur Battery Cathodes. ACS Nano 2018, 12, 226 233. (9) Wu, X.; Xie, H.; Deng, Q.; Wang, H.; Sheng, H.; Yin, Y.; Zhou, W.; Li, R.; Guo, Y. Three-Dimensional Carbon Nanotubes Forest/Carbon Cloth as an Efficient Electrode for Lithium-Polysulfide Batteries. ACS Appl. Mater. Interfaces 2017, 9, 1553 1561. (10) Li, M.; Zhang, Y.; Hassan, F.; Ahn, W.; Wang, X.; Liu, W.; Jiang, G.; Chen. Z. Compact High Volumetric and Areal Capacity Lithium Sulfur Batteries through Rock Salt Induced Nano-Architectured Sulfur Hosts. J. Mater. Chem. A 2017, 5, 21435 21441. (11) Sun, L.; Li, M.; Jiang, Y.; Kong, W.; Jiang, K.; Wang, J.; Fan, S. Sulfur Nanocrystals Confined in Carbon Nanotube Network as a Binder-Free Electrode for High-Performance Lithium Sulfur Batteries. Nano Lett. 2014, 14, 4044 4049. (12) Pei, F.; Lin, L.; Ou, D.; Zheng, Z.; Mo, S.; Fang, X.; Zheng, N. Self-Supporting Sulfur Cathodes Enabled by Two-Dimensional Carbon Yolk-Shell Nanosheets for High-Energy-Density Lithium-Sulfur Batteries. Nat. Commun. 2017, 8, 482. (13) Fang, R.; Liang, C.; Xia, Y.; Xiao, Z.; Huang, H.; Gan, Y.; Zhang, J.; Tao, X.; Zhang, W. Supercritical CO2 Mediated Incorporation of Sulfur into Carbon Matrix as Cathode Materials Towards High-Performance Lithium-Sulfur Batteries. J. Mater. Chem. A 2018, 6, 212 222. (14) Medenbach, L.; Escher, I.; Kçwitsch, N.; Armbrgster, M.; Zedler, L.; Dietzek, B.; Adelhelm, P. Sulfur Spillover on Carbon Materials and Possible Impacts on Metal-Sulfur Batteries. Angew. Chem. Int. Ed. 2018, 57, 13666 13670.

27


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

Page 28 of 33

(15) Yuan, Z.; Peng, H.; Huang, J.; Liu, X.; Wang, D.; Cheng, X.; Zhang, Q. Hierarchical Free-Standing Carbon-Nanotube Paper Electrodes with Ultrahigh Sulfur-Loading for Lithium-Sulfur Batteries. Adv. Funct. Mater. 2014, 24, 6105 6112. (16) Yun, J. H.; Kim, J. H.; Kim, D. K.; Lee, H, W. Suppressing Polysulfide Dissolution

via

Cohesive

Forces

by

Interwoven

Carbon

Nanofibers

for

High-Areal-Capacity Lithium-Sulfur Batteries. Nano Lett. 2018, 18, 475 481. (17) Peng, H.; Zhang, Q. Designing Host Materials for Sulfur Cathodes: from Physical Confinement to Surface Chemistry. Angew. Chem. Int. Ed. 2015, 54, 11018 11020. (18) Ma, L.; Zhang, W.; Wang, L.; Hu, Y.; Zhu, G.; Wang, Y.; Chen, R.; Chen, T.; Tie, Z.; Liu, J.; Jin, Z. Strong Capillarity, Chemisorption, and Electrocatalytic Capability

of

Crisscrossed

Nanostraws

Enabled

Flexible,

High-Rate,

and

Long-Cycling Lithium-Sulfur Batteries. ACS Nano 2018, 12, 4868 4876. (19) Liang, X.; Nazar, L. F. In Situ Reactive Assembly of Scalable Core-Shell Sulfur-MnO2 Composite Cathodes. ACS Nano 2016, 10, 4192 4198. (20) Yuan, Z.; Peng, H.; Hou, T.; Huang, J.; Chen, C.; Wang, D.; Cheng, X.; Wei, F.; Zhang, Q. Powering Lithium-Sulfur Battery Performance by Propelling Polysulfide Redox at Sulfiphilic Hosts. Nano Lett. 2016, 16, 519 527. (21) Song, Y.; Zhao, W.; Kong, L.; Zhang, L.; Zhu, X.; Shao, Y.; Ding, F.; Zhang, Q.; Sun, J.; Liu, Z. Synchronous Immobilization and Conversion of Polysulfides on a VO2-VN Binary Host Targeting High Sulfur Load Li-S Batteries. Energy Environ. Sci. 2018, 11, 2620 2630.

28


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

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(22) Chen, T.; Zhang, Z.; Cheng, B.; Chen, R.; Hu, Y.; Ma, L.; Zhu, G.; Liu, J.; Jin, Z. Self-Templated Formation of Interlaced Carbon Nanotubes Threaded Hollow Co3S4 Nanoboxes for High-Rate and Heat-Resistant Lithium-Sulfur Batteries. J. Am. Chem. Soc. 2017, 139, 12710 12715. (23) Tao, X.; Wang, J.; Liu, C.; Wang, H.; Yao, H.; Zheng, G.; Seh, Z. W.; Cai, Q.; Li, W.; Zhou, G.; Zu, C.; Cui, Y. Balancing Surface Adsorption and Diffusion of Lithium-Polysulfides on Nonconductive Oxides for Lithium-Sulfur Battery Design. Nat. Commun. 2016, 7, 11203. (24) Zhou, F.; Li, Z.; Luo, X.; Wu, T.; Jiang, B.; Lu, L.; Yao, H.; Antonietti, M.; Yu, S. Low Cost Metal Carbide Nanocrystals as Binding and Electrocatalytic Sites for High Performance Li-S Batteries. Nano Lett. 2018, 18, 1035 1043. (25) Tang, W.; Chen, Z.; Tian, B.; Lee, H. W.; Zhao, X.; Fan, X.; Fan, Y.; Leng, K.; Peng, H.; Kim, M. H.; Li, M.; Lin, M.; Su, J.; Chen, J.; Jeong, H. Y.; Yin, S.; Zhang, Q.; Zhou, W.; Loh, K. P.; Zheng, G. W. In Situ Observation and Electrochemical Study of Encapsulated Sulfur Nanoparticles by MoS2 Flakes. J. Am. Chem. Soc. 2017, 139, 10133 10141. (26) Bi, C.; Wang, Q.; Shao, Y.; Yuan, Y.; Xiao, Z.; Huang, J. Non-Wetting Surface-Driven High-Aspect-Ratio Crystalline Grain Growth for Efficient Hybrid Perovskite Solar Cells. Nat. Commun. 2015, 6, 7747. (27) Ma, E.; Zhu, T. Towards Strength-Ductility Synergy through the Design of Heterogeneous Nanostructures in Metals. Mater. Today 2017, 20, 323 331. (28) Anasori, B.; Lukatskaya, M. R.; Gogotsi, Y. 2D Metal Carbides and Nitrides

29


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

(MXenes) for Energy Storage. Nat. Rev. Mater. 2017, 2, 16098. (29) Xia, Y.; Mathis, T. S.; Zhao, M.; Anasori, B.; Dang, A.; Zhou, Z.; Cho, H.; Gogotsi, Y.; Yang, S. Thickness-Independent Capacitance of Vertically Aligned Liquid-Crystalline MXenes. Nature 2018, 557, 409 412. (30) Dong, Y.; Wu, Z.; Zheng, S.; Wang, X.; Qin, J.; Wang, S.; Shi, X.; Bao, X. Ti3C2 MXene-Derived Sodium/Potassium Titanate Nanoribbons for High-Performance Sodium/Potassium Ion Batteries with Enhanced Capacities. ACS Nano 2017, 11, 4792 4800. (31) Lian, P.; Dong, Y.; Wu, Z.; Zheng, S.; Wang, X.; Wang, S.; Sun, C.; Qin, J.; Shi, X.; Bao, X. Alkalized Ti3C2 MXene Nanoribbons with Expanded Interlayer Spacing for High-Capacity Sodium and Potassium Ion Batteries. Nano Energy 2017, 40, 1 8. (32) Liang, X.; Rangom, Y.; Kwok, C. Y.; Pang, Q.; Nazar, L. F. Interwoven MXene Nanosheet/Carbon-Nanotube Composites as Li-S Cathode Hosts. Adv. Mater. 2017, 29, 1603040. (33) Dong, Y.; Zheng, S.; Qin, J.; Zhao, X.; Shi, H.; Wang, X.; Chen, J.; Wu, Z. All-MXene-Based Integrated Electrode Constructed by Ti3C2 Nanoribbon Framework Host and Nanosheet Interlayer for High-Energy-Density Li-S Batteries. ACS Nano 2018, 12, 2381 2388. (34) Medintz, I. L.; Uyeda, H. T.; Goldman, E. R.; Mattoussi, H. Quantum Dot Bioconjugates for Imaging, Labelling and Sensing. Nat. Mater. 2005, 4, 435 446. (35) Pan, D.; Zhang, J.; Li, Z.; Wu, M. Hydrothermal Route for Cutting Graphene Sheets into Blue-Luminescent Graphene Quantum Dots. Adv. Mater. 2010, 22, 734

30


Page 30 of 33

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

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738. (36) Xue, Q.; Zhang, H.; Zhu, M.; Pei, Z.; Li, H.; Wang, Z.; Huang, Y.; Deng, Q.; Zhou, J.; Du, S.; Huang, Q.; Zhi, C. Photoluminescent Ti3C2 MXene Quantum Dots for Multicolor Cellular Imaging. Adv. Mater. 2017, 29, 1604847. (37) 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. (38) Zong, L.; Li, M.; Li, C. Bioinspired Coupling of Inorganic Layered Nanomaterials with Marine Polysaccharides for Efficient Aqueous Exfoliation and Smart Actuating Hybrids. Adv. Mater. 2017, 29, 1604691. (39) Li, J.; Liu, Y.; Shu, Q.; Liang, J.; Zhang, F.; Chen, X.; Deng, X.; Swihart, M. T.; Tan, K-J. One-Pot Hydrothermal Synthesis of Carbon Dots with Efficient Up and Down-Converted Photoluminescence for the Sensitive Detection of Morin in a Dual-Readout Assay. Langmuir 2017, 33, 1043 1050. (40) Hou, T.; Xu, W.; Chen, X.; Peng, H.; Huang, J.; Zhang, Q. Lithium Bond Chemistry in Lithium-Sulfur Batteries. Angew. Chem. Int. Ed. 2017, 56, 8178 8182. (41) Li, G.; Sun, J.; Hou, W.; Jiang, S.; Huang, Y.; Geng, J. Three-Dimensional Porous Carbon Composites Containing High Sulfur Nanoparticle Content for High-Performance Lithium-Sulfur Batteries. Nat. Commun. 2016, 7, 10601. (42) Chen, H.; Wang, C.; Dong, W.; Lu, W.; Du, Z.; Chen, L. Monodispersed Sulfur Nanoparticles for Lithium-Sulfur Batteries with Theoretical Performance. Nano Lett.

31


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2015, 15, 798 802. (43) Cheng, Z.; Xiao, Z.; Pan, H.; Wang, S.; Wang, R. Elastic Sandwich-Type rGO-VS2/S Composites with High Tap Density: Structural and Chemical Cooperativity Enabling Lithium-Sulfur Batteries with High Energy Density. Adv. Energy Mater. 2018, 7, 1702337. (44) Lochala, J.; Liu, D.; Wu, B.; Robinson, C.; Xiao, J. Research Progress Toward the Practical Applications of Lithium-Sulfur Batteries. ACS Appl. Mater. Interfaces 2017, 9, 24407 24421. (45) Zhang, H.; Zhao, W.; Zou, M.; Wang, Y.; Chen, Y.; Xu, L.; Wu, H.; Cao, A. 3D Mutually

Embedded

MOF@carbon

Nanotube

Hybrid

Networks

for

High-Performance Lithium-Sulfur Batteries. Adv. Energy Mater. 2018, 8, 1800013. (46) Xiao, Z.; Yang, Z.; Zhou, L.; Zhang, L.; Wang, R. Highly Conductive Porous Transition Metal Dichalcogenides via Water Steam Etching for High-Performance Lithium-Sulfur Batteries. ACS Appl. Mater. Interfaces 2017, 9, 18845 18855. (47) Zhou, T.; Lv, W.; Li, J.; Zhou, G.; Zhao, Y.; Fan, S.; Liu, B.; Li, B.; Kang, F.; Yang,

Q.

Twinborn

TiO2-TiN

Trapping-Diffusion-Conversion

of

Heterostructures Polysulfides

Enabling

Towards

Smooth

Ultralong

Life

Lithium-Sulfur Batteries. Energy Environ. Sci. 2017, 10, 1694 1703. (48) Wang, L.; Yang, Z.; Nie, H.; Gu, C.; Hua, W.; Xu, X.; Chen, X.; Chen, Y.; Huang, S. A Lightweight Multifunctional Interlayer of Sulfur-Nitrogen Dual-Doped Graphene for Ultrafast, Long-Life Lithium-Sulfur Batteries. J. Mater. Chem. A 2016, 4, 15343 15352.

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