Layer-by-Layer Assembled Architecture of Polyelectrolyte Multilayers

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Layer-by-Layer Assembled Architecture of Polyelectrolyte Multilayers and Graphene Sheets on Hollow Carbon Spheres/ Sulfur Composite for High-Performance Lithium-Sulfur Batteries Feng Wu, Jian Li, Yuefeng Su, Jing Wang, Wen Yang, Ning Li, Lai Chen, Shi Chen, Renjie Chen, and Liying Bao Nano Lett., Just Accepted Manuscript • DOI: 10.1021/acs.nanolett.6b01981 • Publication Date (Web): 01 Aug 2016 Downloaded from http://pubs.acs.org on August 3, 2016

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Layer-by-Layer Assembled Architecture of Polyelectrolyte Multilayers and Graphene Sheets on Hollow Carbon Spheres/Sulfur Composite for HighPerformance Lithium-Sulfur Batteries Feng Wu,†,§ Jian Li,† Yuefeng Su,*,†,§ Jing Wang,†,§ Wen Yang,*,‡ Ning Li,† Lai Chen,† Shi Chen,†,§ Renjie Chen,†,§ and Liying Bao†,§ †

School of Material Science and Engineering, Beijing Institute of Technology, Beijing 100081, China.

‡

Beijing Key Laboratory of Photoelectronic/Electrophotonic Conversion Materials, School of Chemistry, Beijing Institute of Technology, Beijing 100081, China. §

Collaborative Innovation Center of Electric Vehicles in Beijing, Beijing 100081, China.

ABSTRACT: In the present work, polyelectrolyte multilayers (PEMs) and graphene sheets are applied to sequentially coat on the surface of hollow carbon spheres/sulfur composite by a flexible layer-by-layer (LBL) self-assembly strategy. Owing to the strong electrostatic interactions between the opposite charged materials, the coating agents are very stable and the

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coating procedure is high efficient. The LBL film shows prominent impact on the stability of the cathode by acting as not only a basic physical barrier, and more importantly, an ionpermselective film to block the polysulfides anions by coulombic repulsion. Furthermore, the graphene sheets can help to stabilize the polyelectrolytes film and greatly reduce the inner resistance of the electrode by changing the transport of the electrons from a “point-to-point” mode to a more effective “plane-to-point’’ mode. Based on the synergistic effect of the PEMs and graphene sheets, the fabricated composite electrode exhibits very stable cycling stability for over 200 cycles at 1 A g-1, along with a high average coulombic efficiency of 99%. With the advantages of rapid and controllable fabrication of the LBL coating film, the multifunctional architecture developed in this study should inspire the design of other lithium-sulfur cathodes with unique physical and chemical properties.

KEYWORDS: Lithium-sulfur batteries, layer-by-layer, polyelectrolyte, graphene, coating

Compared with conventional intercalation lithium-ion batteries, lithium-sulfur (Li-S) batteries are capable of providing a significantly higher energy density of 2600 Wh kg-1 when calculated on the basis of the lithium anode and the sulfur cathode. Furthermore, sulfur has the advantages of natural abundance and environmental tolerance. These qualities make Li-S batteries ones of the most promising power sources to meet the demands for long-range electric vehicles and large-scale energy-storage systems.1-6 However, some inherent problems still hinder the practical application of Li-S batteries, such as the poor conductivity of elemental sulfur and its solid reduction products (Li2S2/Li2S), huge volume change during cycling process and the so called polysulfides shuttle effect. Specifically, the shuttle reaction caused by the repeated


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oxidation/reduction of the soluble polysulfides is the main reason for the low coulombic efficiency and poor cycling stability of the electrode.7-11 Therefore, prevention of the polysulfides shuttle is extremely necessary for the practical application of Li-S batteries. Tremendous efforts have been devoted to address the challenges mentioned above. For example, a variety of carbonaceous materials, such as porous carbon,12-14 carbon nanofiber,15,16 hollow carbon spheres17,18 and graphene,19-22 have been widely applied as conductive scaffolds for sulfur confining. The fabricated C/S composites display both enhanced rate capability and cycling stability, however, a single carbon scaffold is insufficient for long-term polysulfides immobilization due to the open pore structure of the carbon matrix. Thus, additional coating strategies are necessary to enhance its confine ability for polysulfides. Polymer materials have been widely studied to confine sulfur or C/S composites.23-26 By acting as physical barriers or chemical adsorbents, these materials can maintain the active-sulfur and polysulfides within the composites matrixes, thus increase the stability of the electrodes. While the chemical adsorption abilities of some polymer materials to polysulfides are relatively weak,23 and the as-coated polymer shells may lead to lower electronic conductivity of the electrodes.3,27 Therefore, a specific coating of materials with various functional groups that can strongly interact with polysulfides would be a possible way to enhance the stability of the sulfur cathodes. Polyelectrolytes equipped with massive ionic groups28-30 can be potentially used as protective materials for prevention of polysulfides migration.31-33 With a simple but flexible layer-by-layer (LBL) self-assembly technology,34,35 the polyelectrolyte multilayers (PEMs) can be fabricated by strong electrostatic interactions and closely adhere on the target substrate. While the stability of the polyelectrolytes film may be influenced by the huge electrode expansion during electrochemical cycling32 and the electrolyte environment with high salt concentration36,37, it is


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necessary to additionally introduce other charged materials like functionalized graphene or CNTs38,39 into the LBL system. As these flexible functional carbon materials may stabilize the polyelectrolytes film and import new conduction property to the overall structure, thus we are motivated to explore the possibility of fabricating Li-S electrode configuration that combines the advantages of polyelectrolyte multilayers and carbon materials with different functionalities.

Figure 1. Schematic illustration of the structure and functions of the PEMs and functionalized GS coating film. (a) The configuration of the LBL assembled polyethylene imine (PEI), polystryrene sulfonate (PSS) and GS on HCSs/S composite. (b) Functions of GS on facilitating the electrons transport with a plane-to-point conduction mode, stabilizing the polyelectrolyte multilayers and accommodating the volume expansion. (c) Function of PEMs on confining Sn2anions within the carbon matrix by electrostatic repulsion of the high-density negatively charged SO3- groups on PSS.


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In the present work, a novel coating system composed of polyelectrolyte multilayers and functionalized graphene sheets (GS) were successfully fabricated on the surface of hollow carbon spheres/sulfur (HCSs/S) composite particles to elevate the ability of polysulfides immobilization and facilitate the electronic connections of the electrode (see details in Supporting Information). As introduced in Figure 1, the attached hydroxylated graphene sheets with conductive and flexible network on the outmost layer can provide rapid electrochemical transport, stabilize the polyelectrolyte multilayers and accommodate the volume expansion of the sulfur cathode (shown in Figure 1b). While as for the internal PEMs ([PEI/PSS]4-PEI) assembled by consecutive electrostatic coating of the opposite charged polyelectrolytes, they can act as an ion-permselective film to suppress the migration of the polysulfide anions (Sn2-) by electrostatic repulsive forces (Figure 1c). The total LBL thin film is believed to be stable in the electrolyte environment and robust enough to endure the long-term cycling process. Therefore, with this novel architecture, the fabricated sulfur cathode is expected to display significant improvements on both the cycling stability and rate capability over bare HCSs/S composite without LBL protection layers. Figure 2 illustrates the morphologic change from the HCSs to the final LBL film coated HCSs/S composite (denoted as HCSs/S-LBL). As illustrated in the transmission electron microscopy (TEM) image of Figure 2a, the HCSs, which were used as basic sulfur hosts here, have homogeneous diameters of around 200 nm and highly porous carbon shells (inset in Figure 2a). HCSs in the scanning electron microscopy (SEM) image of Figure S1 (Supporting Information) show a large compressive deformation due to the high vacuum testing environment.40 However, with the introduction of sulfur in this hollow structure by a meltdiffusion strategy, the shrinkage of the carbon spheres disappears as shown in Figure 2b and


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Figure S2. As sulfur particles were dispersed into the robust carbon shell, the volume expansion of active sulfur during cycling can be well restrained, thus reduced the inner pressure to the further coated LBL film. No discernible sulfur particles are found outside the carbon shell, suggests the uniform dispersion of sulfur inside the carbon spheres. This is also consistent with the XRD patterns as observed in Figure S3. The unique coating architecture of the polyelectrolyte multilayers and graphene sheets on the HCSs/S composite can be clearly identified by TEM (Figure 2c and d) and SEM images (Figure S4). The PEMs coated HCSs/S composite (denoted as HCSs/S-PEMs) of Figure 2c shows obvious interface between the carbon shell and the attached [PEI/PSS]4-PEI multilayers.37 The total thickness of the nine polymer layers is estimated to be 5 nm, corresponding to a thickness of 0.6 nm for each layer, as is identical with the value reported in literature.41 Meanwhile, it is worth noting that the film thickness can be freely tailored within nano-scale by just changing the number of assembled layers (shown in Figure S5). Figure 2d displays that large numbers of the HCSs/S-PEMs particles are thoroughly wrapped by crumpled micro-sized graphene sheets. The bridging graphene sheets with high conductivity and large surface area are supposed to offer high efficient electronic connections for the scattered HCSs/S particles. The robust and convenient building process of this unique architecture by electrostatic reaction was revealed by digital images in Figure S6. It is believed that with the protection of the carbon shell, the PEMs and the graphene sheets, the HCSs/S-LBL composite is expected to be much stabilized when used as a cathode material for Li-S batteries. To further confirm the successful layer-by-layer depositing of the charged polyelectrolytes and functionalized graphene sheets (as shown in the schematic of Figure 2e), surface zeta potentials of the composites were measured after each coating layers (Figure 2f). After first PEI layer was


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coated, the zeta potential of the negative charged HCSs/S composite surface changed from -30 to +10 mV. Then the zeta potentials exhibit typical zigzag dependence of the subsequent adsorbed negatively/positively charged polyelectrolytes and hydroxylated graphene sheets, which is strong evidence of the formation of consecutive LBL film on the HCSs/S composite.37

Figure 2. Evidence of the successful depositing of PEMs and GS on the HCSs/S composite. (a) TEM images of the HCSs composite (inset: magnified view of the porous shell). (b) SEM image of the HCSs/S composite. (c) TEM images of the HCSs/S-PEMs composite (inset: magnified view of the black rectangle area). (d) TEM image of the HCSs/S-LBL composite. (e) Schematic of the electrostatic assembled HCSs/S-LBL configuration. (f) Zeta potentials of the bare HCSs/S, after adsorption of subsequent polyelectrolytes of PEI/PSS and GS.


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As the sulfur loading level is a key factor to determine the energy density in practical applications, the thermogravimetric analysis (TGA) have been carried out in Figure 3a. Based on the sulfur weight loss stage at 180-280 °C, the sulfur contents of the HCSs/S、HCSs/S-PEMs and HCSs/S-LBL composites were 69、67 and 65 wt%, respectively, which is very close to the elemental analysis (EA) results (Table S1, Supporting Information). Note that the total weight of the LBL film takes up 5.8 wt% of the composite (corresponding to 4.6 wt% of the electrode), which is less than the commonly used coating materials.42-44 Moreover, the derivative thermogravimetric (DTG) curves (Figure 3b) shows that the temperature with maximum sulfur loss rate of the HCSs/S composite, which is 248 °C, increased to 257 and 263 °C for the HCSs/S-PEMs composite and the HCSs/S-LBL composite, respectively. This result suggests that the tightly adsorbed PEMs and graphene sheets can enhance the thermal stability of the HCSs/S core composite45 and this unique architecture can possibly play an important role in enhancing the safety and stability of the batteries that operating at a high temperature environment. To evaluate the blocking ability and stability of the self-assembled LBL film to the polysulfides, an erosion test was conducted by soaking the as-synthesized HCSs/S-LBL and HCSs/S composites in 5 mM Li2S4 catholyte solutions, respectively. As the dissolved Li2S4 can possibly penetrate the carbon shell and react with sulfur to form long chain polysulfides over time (in the form of Li+ and Sn2-, n=5-8), so the UV-vis spectroscopy as a powerful tool to differ different types of polysulfides,46 can thus evaluate the erosion degree of the sulfur contained composites. The UV-vis spectra of Figure 3c shows that the reflect index at 513 nm of the Li2S4 solution was only slightly decreased after soaking the HCSs/S-LBL composite for 24 hours. However, this value of the solution after soaking the HCSs/S composite was much decreased from 51.2% to 19.5%, indicating that large amount of long chain polysulfides were formed by


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the reaction of Li2S4 with sulfur within the HCSs. This comparison suggests that the LBL protection layers were efficient in cutting off the movement of the Sn2- anions through the carbon shell.

Figure 3. (a) TGA and (b) DTG curves of the HCSs/S, HCSs/S-PEMs and HCSs/S-LBL composites. (c) UV-vis spectra of 5mM pristine Li2S4 solution and solutions after soaking the HCSs/S-LBL and HCSs/S composites. The observation of the high resolution TEM images of the soaked composites is quite consistent with the UV-vis result. As shown in Figure 4a, sulfur was still full filled in the HCSs matrix after the soaking process, and the PEMs and graphene sheets wrapped structure was well preserved as well, indicating that the LBL film was stable in the electrolyte environment. In


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contrast, considerable amount of sulfur was eroded by the catholyte solution and plenty of vacancies were left in the HCSs/S composite after soaking (Figure 4b), which was resulted from the poor protection ability of the porous carbon shell. The superior blocking ability of the PEMs and functionalized graphene sheets could be attributed to two reasons: (1) by through strong electrostatic interactions, the LBL multilayers are tightly adsorbed on the HCSs/S surface and can prevent the polysulfides from escaping by acting as physical barriers; and (2) the LBL film with abundant of negatively charged SO3- groups from the PEMs and hydroxyl groups from the graphene sheets will display great electrostatic repulsive forces to the Sn2- anions as an ionpermselective film.9,41

Figure 4. High resolution TEM images of the (a) HCSs/S-LBL and (b) HCSs/S composites after soaking in the Li2S4 solutions. In order to comprehensively explore the electrochemical advantages of the self-assembly treatment, cathodes of the HCSs/S-LBL and the bare HCSs/S composites were both assembled and evaluated in coin cells with lithium foil as the anode. Figure 5a and b show the initial cyclic voltammogram (CV) curves of the two types of electrodes for the first five cycles with a scan rate of 0.1 mV s-1. As presented in Figure 5a, no additional peak, other than the typical four


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reduction/oxidation peaks of the sulfur cathode, is observed of the HCSs/S-LBL composite, indicating that the LBL film is stable in the tested voltage range. This composite shows good reactive reversibility and cycling stability, as all the redox peaks remain sharp and constant upon cycling. In contrast, the CV plots of the HCSs/S composite (Figure 5b) show much broader redox peaks, and the two oxidation peaks are overlapped and shift to higher voltage of around 2.5 V due to its high polarization and inner resistance. Moreover, the high anodic current between 2.5 to 3 V implies the occurrence of a serious shuttle reaction in this unprotected C/S structure.47 The CV results reveal that the coated PEMs and graphene sheets play an important role in both reducing the inner resistance and stabilizing the soluble polysulfides within the carbon matrix simultaneously. The galvanostatic discharge/charge performance of the HCSs/S-LBL composite electrode under different current densities is illustrated in Figure S7. When cycled at 0.5, 1 and 1.5 A g-1, initial discharge capacities of 1017, 850 and 790 mAh g-1 could be obtained, indicating high utilizations of the active material. As both the self-assembled PEMs and graphene sheets showed strong capability to suppress the diffusion of polysulfides, and the continuous and high surface area graphene network contributed to large electronic transport channels, stable reversible capacity of 575 mAh g-1 and average coulombic efficiency of as high as 99% were successfully achieved for the HCSs/S-LBL composite after 200 cycles at 1 A g-1 (as shown in Figure 5c). Overcharge phenomenon of the electrode was almost fully inhibited. The SEM and TEM images of the cycled HCSs/S-LBL composite show that the PEMs and graphene sheets were well preserved on the HCSs/S composite (Figure S8 and Figure S9). As the unprotected polyelectrolytes film could be partially decomposed when simply soaked in the electrolyte (Figure S10), and accordingly the cycle performance of the HCSs/S-PEMs composite showed


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the gradual failure of the polyelectrolytes film on polysulfides confining (Figure S11). After comparing the two different electrodes behaviors of the HCSs/S-LBL and HCSs/S-PEMs composites, it can be concluded that the flexible graphene sheets could play an important role in helping the PEMs to against the electrode expansion and the high concentration electrolyte environment. The bare HCSs/S electrode showed the poorest performance with very low initial capacities and long electrochemical cycles to be fully active, indicating the high inner resistance that caused by the inconvenient electrons transport pass ways within the scattered HCSs/S particles. It also showed very weak ability in trapping polysulfides as the serious shuttle reaction during cycling could be clearly evidenced by the high overcharge capacity and low coulombic efficiency of only 90% in the 200th cycle.


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Figure 5. Electrochemical performances of the HCSs/S-LBL and HCSs/S composites. (a) CV curves of the HCSs/S-LBL composite. (b) CV curves of the HCSs/S composite with severe shuttle phenomenon. (c) Prolonged cycle performance and coulombic efficiency of the HCSs/SLBL and HCSs/S electrodes cycled at 1 A g-1. (d) Rate capabilities of the HCSs/S-LBL and HCSs/S composites (0.5 A g-1 increased for every 10 cycles). (e) Discharge/charge voltage profiles of the HCSs/S-LBL electrode under different current densities. The HCSs/S-LBL and HCSs/S composites were also subjected to cycling at increasing current densities to evaluate their robustness. As shown in Figure 5d, after firstly cycled at a low current density of 0.5 A g-1, the electrode performance of the HCSs/S-LBL composite was barely influenced when the current density was increasingly switched to higher levels, which is a result of the plane-to-point conduction network that imported by the graphene sheets. Much higher reversible discharge capacities of 832, 754, 722 and 698 mAh g-1 than its counterpart were obtained at higher current densities of 1, 2, 3 and 4 A g-1, respectively. The superior conduction ability of this electrode was also evidenced by the corresponding relatively constant voltage plateaus as presented in Figure 5e. A further electrochemical impedance spectroscopy (EIS) measurement shows that the ultrathin LBL coating film can greatly reduce the charge transfer resistance (Figure S12). This advantage caused by the multifunctional PEMs and graphene sheets is consistent with the conclusions mentioned above. It should be noted that the multi-function LBL film cannot be simply alternated by a mixture of the film components. The synergistic effect of the PEMs and graphene film can only be valid when the polyelectrolytes and the graphene sheets have been organized in a layer by layer order, as disturbance of their building structure will also destroy their specific functionalities. The significant improvement in electrochemical performance of the LBL film protected HCSs/S


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composite can be possibly attributed to the following reasons: (1) the PEMs with high density of ionized SO3- groups can act as a blocking shield to confine the Sn2- anions within the hollow carbon, therefore alleviating the loss of active sulfur; (2) the movement of Li+ ions through the thin LBL film may be accelerated by the negatively charged SO3- groups from the PEMs and the hydroxyl groups from the graphene sheets. Meanwhile, the influence of the NH3+ groups may be very slight due to the low charge density of PEI layer as revealed by its lower zeta potential; (3) the stability of the polyelectrolytes film can be maintained by the inward HCSs and the outward graphene sheets that help to against the pressure of sulfur expansion; (4) the attached graphene sheets with large surface area can provide excellent electrical contact with the HCSs/S particles to form a high efficient “plane-to-point’’ conduction mode; (5) the synergistic effect of the flexible HCSs shell, PEMs and graphene sheets can accommodate the volume change of the electrode and maintain its compatibility. In conclusion, flexible multifunctional polyelectrolytes and graphene layers have been successfully fabricated on the HCSs/S composite by a LBL self-assembly method. The LBL film is robust enough in the electrolyte environment under long-term cycling process. The HCSs/S composite with the LBL protective film exhibits significant improvements in thermal stability, reactive reversibility, cycling stability and rapid conduction ability over the bare HCSs/S composite. Owing to the synergistic effect of the polyelectrolytes and graphene sheets, the HCSs/S-LBL composite displays a stable reversible capacity for over 200 cycles at 1 A g-1 with very high coulombic efficiencies. As the thickness, composition, permeability, and surface chemistry of the LBL film architectures can be freely tailored by appropriate choice of the charged materials, a further exploration of the novel LBL structures with unique physical and


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chemical properties, should inspire in developing the desired cycle-stable and high-rate Li-S batteries as well as other promising energy storage devices.

ASSOCIATED CONTENT Supporting Information Experimental details, SEM images of HCSs, HCSs/S and HCSs/S-LBL composite, XRD patterns of sulfur contained materials, digital images of fabrication process, TEM images of HCSs/S coated by different thicknesses of PEMs, rate capability of HCSs/S-LBL electrode, SEM and TEM images of cycled HCSs/S-LBL composite, TEM image of HCSs/S-PEMs composite after soaking in electrolyte, cycle performance of HCSs/S-PEMs composite, EIS plots of HCSs/S and HCSs/S-LBL composites, results of elemental composition by EA. This material is available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Authors *(Y.S.) E-mail: [email protected] *(W.Y.) E-mail: [email protected] Author Contributions F.W. and J.L. contributed equally to this work. Notes The authors declare no competing financial interest.


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ACKNOWLEDGMENT This work was funded by the Chinese National 973 Program (2015CB251100), National Natural Science Foundation of China (51472032, 51202083), Program for New Century Excellent Talents in University (NCET-13–0044), the Special Fund of Beijing Co-construction Project and BIT Scientific and Technological Innovation Project (2013CX01003). ABBREVIATIONS PEMs, polyelectrolyte multilayers; LBL, layer by layer; Li-S, lithium-sulfur; GS, graphene sheets; PEI, polyethylene imine; PSS, polystryrene sulfonate; HCSs, hollow carbon spheres. REFERENCES (1) Manthiram, A.; Fu, Y.; Su, Y.-S. Acc. Chem. Res. 2013, 46, 1125-1134. (2) Liang, X.; Hart, C.; Pang, Q.; Garsuch, A.; Weiss, T.; Nazar, L. F. Nat. Commun. 2015, 6, 5682. (3) Yin, Y. X.; Xin, S.; Guo, Y. G.; Wan, L. J. Angew. Chem. Int. Ed. 2013, 52, 13186-13200. (4) Wang, J.; He, Y.-S.; Yang, J. Adv. Mater. 2015, 27, 569-575. (5) Scrosati, B.; Hassoun, J.; Sun, Y.-K. Energy Environ. Sci. 2011, 4, 3287-3295. (6) Xu, R.; Lu, J.; Amine, K. Adv. Energy Mater. 2015, 5, 1500408. (7) Suo, L.; Hu, Y. S.; Li, H.; Armand, M.; Chen, L. Nat. Commun. 2013, 4, 1481. (8) Ai, G.; Dai, Y.; Ye, Y.; Mao, W.; Wang, Z.; Zhao, H.; Chen, Y.; Zhu, J.; Fu, Y.; Battaglia, V.; Guo, J.; Srinivasan, V.; Liu, G. Nano Energy 2015, 16, 28-37.


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(9) Huang, J.-Q.; Zhang, Q.; Peng, H.-J.; Liu, X.-Y.; Qian, W.-Z.; Wei, F. Energy Environ. Sci. 2014, 7, 347-353. (10) Ding, Y.; Zhao, Y.; Yu, G. Nano Lett. 2015, 15, 4108-4113. (11) Yu, X.; Pan, H.; Zhou, Y.; Northrup, P.; Xiao, J.; Bak, S.; Liu, M.; Nam, K.-W.; Qu, D.; Liu, J.; Wu, T.; Yang, X.-Q. Adv. Energy Mater. 2015, 5, 1500072. (12) Ji, X.; Lee, K. T.; Nazar, L. F. Nat. Mater. 2009, 8, 500-506. (13) Zhang, B.; Qin, X.; Li, G. R.; Gao, X. P. Energy Environ. Sci. 2010, 3, 1531-1537. (14) Weng, W.; Pol, V. G.; Amine, K. Adv. Mater. 2013, 25, 1608-1615. (15) Zheng, G.; Yang, Y.; Cha, J. J.; Hong, S. S.; Cui, Y. Nano Lett. 2011, 11, 4462-4467. (16) Zheng, G.; Zhang, Q.; Cha, J. J.; Yang, Y.; Li, W.; Seh, Z. W.; Cui, Y. Nano Lett. 2013, 13, 1265-1270. (17) Zhang, C.; Wu, H. B.; Yuan, C.; Guo, Z.; Lou, X. W. Angew. Chem. 2012, 124, 97309733. (18) Jayaprakash, N.; Shen, J.; Moganty, S. S.; Corona, A.; Archer, L. A. Angew. Chem. 2011, 123, 6026-6030. (19) Song, J.; Yu, Z.; Gordin, M. L.; Wang, D. Nano Lett. 2016, 16, 864-870. (20) Wang, X.; Gao, Y.; Wang, J.; Wang, Z.; Chen, L. Nano Energy 2015, 12, 810-815. (21) Zhao, M.-Q.; Liu, X.-F.; Zhang, Q.; Tian, G.-L.; Huang, J.-Q.; Zhu, W.; Wei, F. ACS Nano 2012, 6, 10759-10769.


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(22) Qiu, Y.; Li, W.; Zhao, W.; Li, G.; Hou, Y.; Liu, M.; Zhou, L.; Ye, F.; Li, H.; Wei, Z.; Yang, S.; Duan, W.; Ye, Y.; Guo, J.; Zhang, Y. Nano Lett. 2014, 14, 4821-4827. (23) Li, W.; Zhang, Q.; Zheng, G.; Seh, Z. W.; Yao, H.; Cui, Y. Nano Lett. 2013, 13, 55345540. (24) Seh, Z. W.; Wang, H.; Hsu, P.-C.; Zhang, Q.; Li, W.; Zheng, G.; Yao, H.; Cui, Y. Energy Environ. Sci. 2014, 7, 672-676. (25) Seh, Z. W.; Zhang, Q.; Li, W.; Zheng, G.; Yao, H.; Cui, Y. Chem. Sci. 2013, 4, 3673-3677. (26) Li, W.; Zheng, G.; Yang, Y.; Seh, Z. W.; Liu, N.; Cui, Y. Proc. Natl. Acad. Sci. USA 2013, 110, 7148-7153. (27) Zhou, J.; Li, R.; Fan, X.; Chen, Y.; Han, R.; Li, W.; Zheng, J.; Wang, B.; Li, X. Energy Environ. Sci. 2014, 7, 2715-2724. (28) Kim, B.-S.; Park, S. W.; Hammond, P. T. ACS Nano, 2008, 2, 386-392. (29) Wilson, J. T.; Cui, W.; Kozlovskaya, V.; Kharlampieva, E.; Pan, D.; Qu, Z.; Krishnamurthy, V. R.; Mets, J.; Kumar, V.; Wen, J.; Song, Y.; Tsukruk, V. V.; Chaikof, E. L. J. Am. Chem. Soc. 2011, 133, 7054-7064. (30) Tang, Z.; Wang, Y.; Podsiadlo, P.; Kotov, N. A. Adv. Mater. 2006, 18, 3203-3224. (31) Bucur, C. B.; Muldoon, J.; Lita, A. Energy Environ. Sci. 2016, 9, 992-998. (32) Osada, N.; Bucur, C. B.; Aso, H.; Muldoon, J. Energy Environ. Sci. 2016, 9, 1668-1673.


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(46) Patel, M. U. M.; Demir-Cakan, R.; Morcrette, M.; Tarascon, J.-M.; Gaberscek, M.; Dominko, R. ChemSusChem 2013, 6, 1177-1181. (47) Xiao, L.; Cao, Y.; Xiao, J.; Schwenzer, B.; Engelhard, M. H.; Saraf, L. V.; Nie, Z.; Exarhos, G. J.; Liu, J. Adv. Mater. 2012, 24, 1176-1181.


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Figure 1. Schematic illustration of the structure and functions of the PEMs and functionalized GS coating film. 104x116mm (300 x 300 DPI)


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Figure 2. Evidence of the successful depositing of PEMs and GS on the HCSs/S composite. 105x141mm (300 x 300 DPI)


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Figure 3. TGA, DTG and UV-vis spectra results. 159x261mm (300 x 300 DPI)


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Figure 4. High resolution TEM images of the soaked composites. 169x83mm (300 x 300 DPI)


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Figure 5. Electrochemical performances of the HCSs/S-LBL and HCSs/S composites. 294x339mm (300 x 300 DPI)


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TOC Graphic 101x69mm (300 x 300 DPI)


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Layer-by-Layer Assembled Architecture of Polyelectrolyte Multilayers

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