Fabrication of porous nanonetwork-structured carbons from well

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Applications of Polymer, Composite, and Coating Materials

Fabrication of porous nanonetwork-structured carbons from well-defined cylindrical molecular bottlebrushes Xidong Lin, Guojun Xie, Shaohong Liu, Michael R. Martinez, Zelin Wang, He Lou, Ruowen Fu, Dingcai Wu, and Krzysztof Matyjaszewski ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.9b04502 • Publication Date (Web): 25 Apr 2019 Downloaded from http://pubs.acs.org on April 25, 2019

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ACS Applied Materials & Interfaces

Fabrication

of

porous

nanonetwork-structured

carbons from well-defined cylindrical molecular bottlebrushes Xidong Lin,†,§ Guojun Xie,‡,§ Shaohong Liu,† Michael R. Martinez,‡ Zelin Wang,† He Lou,† Ruowen Fu,† Dingcai Wu*,† and Krzysztof Matyjaszewski*,‡ §

These authors contributed equally to this work.

†

Materials Science Institute, PCFM Lab and GDHPRC Lab, School of Chemistry, Sun Yat-sen

University, Guangzhou 510275, P. R. China. ‡

Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United

States. *E-mail: [email protected] (D.W.); [email protected] (K.M.).

KEYWORDS

atom

transfer

radical

polymerization;

molecular

bottlebrush;

porous

nanonetwork-structured carbon; lithium-sulfur battery

ABSTRACT Atom transfer radical polymerization (ATRP) was utilized to prepare well-defined cylindrical molecular bottlebrushes which were employed as building blocks and transformed into porous nanonetwork-structured carbons (PNSCs) via hypercrosslinking chemistry and shape-regulated carbonization. The as-prepared PNSCs exhibited a unique nanomorphology-

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tunable characteristic with simply varying carbonization conditions. Due to their threedimensional network nanomorphologies with well-developed hierarchical porous structures and conductive carbon framework, the PNSCs demonstrated excellent electrochemical performances in lithium-sulfur batteries.

INTRODUCTION Porous materials are a class of materials which have received growing interest in both fundamental academic research and commercial applications.1-6 Recently, porous nanonetworkstructured carbons (PNSCs), which integrate hierarchical micro- and meso-/macroporosity, have achieved considerable attention as a new class of highly tunable and porous material. 7-10 Their large pore volume, high surface area, good conductivity, tunable composition and fast mass transport have enabled PNSCs to be employed in various applications, including adsorption, 11-12 catalysis13-14 and energy storage.15-17 For example, PNSCs have been utilized as cathode scaffolds in lithium-sulfur (Li-S) batteries which mitigated deleterious insulation of sulfur and shuttling dissoluble polysulfides.18-21 Typically, the microporosity of PNSCs improves encapsulation of sulfur and polysulfide intermediates, while the interconnected meso/macroporous skeleton serves as rapid and accessible channels for ion/electron transportation. Consequently, this synergy in structural hierarchy of PNSCs contributes to the effectively enhanced stability, discharge capacity and rate performance of Li-S battery. The performance and application of PNSCs are dictated by the structural parameters of its polymeric precursor. Recent reports of PNSCs have expanded the structure of precursory network units to include solid/hollow nanospheres11,15,22 and core/yolk-shell structured nanospheres.23-24 Fabrication of PNSCs involves synthesis of a precursor with well-defined


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construction, followed by carbonization of the precursor into the ultimate product. Generally, the architecture of the precursor will have the greatest impact on the nanomorphology of the network, and carbonization of the material is required to form highly conductive PNSCs. The structure of a precursor will typically dictate the nanomorphology of the PNSCs product; for example, nanospherical precursors form PNSCs with nanospherical morphologies, and nanofibrous precursors yield PNSCs with nanofiber morphologies. Previously, we reported a class of PNSCs which applied polystyrene-grafted carbon nanotubes as building blocks. 25 Such PNSCs demonstrated good supercapacitance performance due to their well-orchestrated porous network. However, their network units’ structure, mostly depended on the heterogeneous fibroid substrates, hardly could be further tailored or customized under molecular level. This presents a unique challenge, as precursors are often prepared using tedious synthetic methods with few opportunities for tunability. Herein, we report an efficient method to fabricate carbonization-induced PNSCs with tunable nanomorphologies based on Friedel-Crafts hypercrosslinking and shape-regulated carbonization. The key to this strategy is the implementation of molecular bottlebrushes as building blocks. Bottlebrushes have tuneable polymeric backbone and side chain lengths and can adopt cylindrical conformations.26 The extended structure and cylindrical conformation of poylmer brushes makes them especially attractive in the fabrication of hierarchically porous networks. 30

27-

As illustrated in Figure 1 and S1, atom transfer radical polymerization (ATRP) was utilized

to prepare the poly[2-(2-bromoisobutyryloxy)ethyl methacrylate-graft-polystyrene] (PBiBEM-gPS) building blocks.31-33 The PS side chains were then hypercrosslinked to frabricate porous nanonetwork-structured polymers (PNSPs) with polymeric microporous nanowires as network units. Finally, a library of PNSCs with different nanomorphologies, including nanowires,


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nanorods and nanoparticles, were facilely obtained via shape-regulated carbonization of the PNSPs precursors. We envision that this method would allow for facile fabrication and manipulation of nanomorphology-tunable PNSCs. PNSCs fabricated using this route differ from materials prepared through the conventional oneto-one (precursor-to-carbon) strategy, as the same precursor could be used to create multiple networks of different nanomorphologies by utilizing selective carbonization of the same precursor. Moreover, such PNSCs have a 3D interconnected hierarchical porous structure which minimizes ion transportation distances from bulk electrolytes, and could form long-range pathways with high conductivity. In addition, PNSCs are composed of very tiny network units (ca. 20 nm in diameter) which allow for high exposure of active sites. Given the benefits of the well-developed hierarchical porous nanonetwork structure with unique nanowire network units, PNSCs exhibited good lithium sulfur battery performance.

RESULTS AND DISCUSSION ATRP affords excellent control over polymer chain growth, enabling the precise design of PBiBEM-g-PS molecular bottlebrushes with well-defined architecture. 34-35 Consequently, the molecular bottlebrush building blocks dictate the nanomorphology of the nanowire network. The PBiBEM polymer backbone macroinitiators were synthetized in two steps. 2-(Trimethylsilyloxy) ethyl methacrylate (HEMA-TMS) was first polymerized via ATRP, and then one-pot deprotection and functionalization with 2-bromoisobutyryl bromide yielded the fully functionalized PBiBEM backbones. Styrene (S) was then grafted from the functionalized backbones by ATRP to yield PBiBEM-g-PS molecular bottlebrushes. This robust and simple technique allowed for the synthesis of two PBiBEM-g-PS molecular bottlebrushes with well-


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defined construction, i.e., PBiBEM372-g-PS210 and PBiBEM1860-g-PS220. The brushes had similar lengths of PS side chains but different backbone lengths to highlight the impact of backbone length on the tunability and morphology of the final carbonized network. The degree of polymerization (DP) of all samples was calculated by the initial monomer to initiator feed ratio ([M]o/[I]o) multiplied by the monomer conversion determined by proton nuclear magnetic resonance (1H NMR), Figure S2 and Table S1-2. Gel permeation chromatography (GPC) traces of PBiBEM372-g-PS210 and PBiBEM1860-g-PS220 highlighted narrow dispersities (Đ) of 1.07 and 1.33 with monomodal molecular weight distributions, indicating polymerizations were wellcontrolled (Figure S3 and Table S1-2). The bottlebrushes were utilized as building blocks for fabrication of the PNSPs, which were hypercrosslinked using a Friedel-Crafts reaction by virtue of anhydrous aluminum chloride (AlCl3), as the strong Lewis acid catalyst, and carbon tetrachloride (CCl 4) as both the solvent and crosslinker.36 During this process (Figure S4), -CCl2- bridges were formed between neighbor phenyl rings, and subsequently transformed into -CO- groups via in-situ hydrolysis as the reaction progressing.35 This resulted in both inter- and intrabrush hypercrosslinking between PS side chains. It should be noted that inter- and intramolecular crosslinking bridges influenced the structural integrity and microstructure of the networks. The presence of intrabrush -COcrosslinks enhanced the rigidity of the soft bottlebrushes and guaranteed the internal micropores remained well-defined after removal of solvent. Meanwhile, the interbrush -CO- crosslinking bridges led to the formation of meso-/macropores by covalent interconnection of nanowire network units in all directions.25,37 Scanning electron microscopy (SEM) images of PNSP 1860 and PNSP372, prepared from respective PBiBEM372-g-PS210 and PBiBEM1860-g-PS220 homogeneous network units, exhibited stable 3D continuous of different nanomorphologies (Figure 2). As the


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backbone DP was increased, the topology of network units shifted from nanospheres (Figure 2a) to nanowires (Figure 2b), indicating the molecular structure significantly influenced the nanostructure of the PNSPs. The presence of meso-/macropores was attributed to both dense and sparse hypercrosslinked aggregation of precursory bottlebrush building blocks. This resulted in an average diameter of 25 nm for the PNSP 1860 network unit. The porosity of PNSP1860 was then evaluated. N2 adsorption-desorption isotherms showed an increase in nitrogen uptake at low relative pressures as well as further increase in adsorption at higher pressures with no observable plateau (Figure 3a). The strong uptake at both low and high pressures indicated well-defined micro and meso-/macroporosity, respectively. 35 The BrunauerEmmett-Teller surface area (SBET) of the entire sample was determined to be 268 m 2 g-1, with meso-/macropore (Sext) and micropore (Smic) surface areas of 162 m2 g-1 and 106 m2 g-1 , respectively. The density functional theory (DFT) pore size distribution curve in Figure 3b indicated PNSP1860 had hierarchal porosity, with micropores of 1.4 nm in size and a distribution of meso/macropores from 8 to 137 nm, with a maximum of 34 nm. Thermogravimetric analysis (TGA) measurement was performed to estimate the carbonization of PNSP1860. According to the Figure S5, the majority of mass loss was attributed to decomposition of polymeric skeletons before 500 °C. At temperatures above 500 °C, carbonaceous matter underwent a combination of graphitization/densification and heteroatoms (e.g. hydrogen and oxygen) and loosely bonded carbon atoms were further eliminated. 38 The carbonization yield was found to be 44% by TGA, indicating highly thermal stability of PNSP1860 during carbonization. Subsequently, crude PNSP1860 was annealed under nitrogen atmosphere, denoted as PNSC1860. The nanoarchitectures of PNSC1860 samples were tunable through carbonization temperatures and times (Table 1). For the same carbonization time (3 h),


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the carbon product obtained from 600 °C, PNSC 1860-600-3, adopted a wire-like morphology (Figure S6a), while increaing the temperature to 800 °C, PNSC1860-800-3, showed continuous and small nanoparticle network units, ca. 18 nm in diameter (Figure S6b). However, by altering the carbonization time, the nanowire network morphology could be further modified. For instance, increasing the carbonization time from 0.5 h to 3 h at 800 °C allowed for tunability of nanoarchitecture from well-defined carbon nanowires (PNSC 1860-800-0.5, Figure 2c,d) into nanorod (PNSC1860-800-1, Figure S6c) and nanospheres (PNSC1860-800-3, Figure S6b). The tunability of nanoscale architecture in these products could be ascribed to skeleton shrinkage and anisotropic surface tension triggering the separation of longer units from nanowire through nanorods into nanospheres to minimize surface energy during carbonization. In contrast, PNSC372-800-3 still consisted of spherical network units after carbonization (Figure S6d). The graphitic microcrystalline structure of PNSC 1860-800-0.5 was confirmed by Raman shifts at 1350 cm-1 (D-band) and 1600 cm-1 (G-band) (Figure S7). This facile carbonization process could improve porosity by elimination of heteroatoms and carbon-containing compounds during pyrolysis. The SBET of PNSC1860-800-0.5 notably increased to 616 m2 g-1, and its Smic and Sext were measured to be 493 and 123 m2 g-1, respectively. Comparison of DFT pore size distributions between PNSP1860 and PNSC1860-800-0.5 indicated that the carbonization treatment fabricated plentiful new tiny mircopores (< 1 nm) while other pore sizes decreased by varying amounts. It should be noted that PNSC1860-800-0.5 could serve as a promising cathode host in Li-S batteries. The hierachally porous 3D interdigitated conductive nanonetwork could enhance the performance of a Li-S battery by allowing for increased diffusion of ions within the network‘s conductive framework while preventing dissolution of polysulfides from the framework (Figure


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4). The cathodic [email protected] composite was prepared via impregnation of PNSC 1860800-0.5 with ~70 wt% sulfur (Figure S8). The galvanostatic charge-discharge curve of [email protected] exhibited a two-step discharging procedure within a voltage window of 1.7 to 2.8 V along with two discharge plateaus which corresponded to the reduction of sulfur (Figure S9).39-41 Furthermore, the rate capability of the [email protected] composite was evaluated at various current densities (Figure 5a). With successively increasing the current rate from 0.5, 1, 2, 3, 4 and 5 C, the [email protected] composite still exhibited stable capacities of 776, 696, 646, 605, 580 and 562 mAh g-1, respectively, and the capacitance retention ratios were calculated up to 72.4%. When the current rate switched back to 0.2 C, the capacity was mostly recovered, indicative of high stability. This rate performance is obviously superior to that of PS-based PNSCs with nanosphere network units, e.g. 414 mAh g-1 at 2 C for PCA-90010H5R/S.11 Long-term cycling tests were employed to estimate the stability of the S@PNSC 1860-800-0.5 cathode. The capacity was maintained at 604 mAh g-1 at a current density of 1 C even after 150 cycles with capacity retention ratio of 71.0% (Figure 5b). The specific capacitance of [email protected] was 505 mAh g-1 at 2 C after 200 cycles (Figure S10), much higher than that of activated carbon (S@AC, 172 mAh g-1). Furthermore, at a higher rate of 5 C, the [email protected] composite still demonstrated stable cycling stability after 300 cycles (Figure 5c). Both Coulombic efficiencies were very close to 100% during the cycling processes. Remarkably, these electrochemical performances of S@PNSC 1860-800-0.5 were comparable or even superior to those of many reported sulfur host materials (Table S3), including long-term cycle stabilities of S@UHCS-900 (~580 mAh g-1)42, S/HPC (562 mAh g-1)43 and BMC-1/S-50 (550 mAh g-1)44 for 100 cycles at 1 C, and rate performances of G/S (~350 mAh g-1 at 5 C)45, G-


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NBCL/S (480 mAh g-1 at 3 C)46 and EFG-S (480 mAh g-1 at 4 C)47. These results indicated the well-developed micropores could effectively encapsulate sulfur and retard the dissolution of polysulfides, while the interconnected interstitial nanonetworks ensure fast-ionic transportation during a charge-discharge process.

CONCLUSIONS In summary, a highly effective approach to design and fabricate PNSCs from well-defined cylindrical molecular bottlebrushes was reported. Bottlebrushes of highly tunable architecture were prepared via ATRP, hypercrosslinked, and carbonized into PNSCs. The PNSCs also displayed tunable nanomorphologies based upon carbonization process, allowing for transformation into nanowires, nanorods, or nanoparticles. This presented a unique opportunity to fabricate porous graphitic materials from both synthetic and processing areas of focus. PNSCs performed well as electrode materials for Li-S batteries, which could be attributed to the network’s hierarchal porosity encouraging fast ionic transport while limiting dissolution of polysulfides during charge transport. We hope that our findings will influence future work in the area of high-performance porous materials and will lead to applications and innovations in fields ranging from energy to environment.

EXPERIMENTAL SECTION Materials. Styrene (S, 99%, Aldrich) and (2-trimetylsiloxy)ethyl methacrylate (HEMA-TMS, Scientific Polymer Products) were passed through a basic alumina plug to remove inhibitor before use. Ethyl 2-bromoisobutyrate (EBiB, 98%, Acros), cuprous bromide (CuBr, 99.999%, Aldrich),


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N,N,N′,N′′,N′′-pentamethyldiethylenetriamine (PMDETA, 99%, Aldrich), cupric bromide (CuBr2, 98%, Acros), α-bromoisobutyryl bromide (BiBBr, 98%, Aldrich), 2,5-di-tertbutylphenol (DTBP, 99%, Aldrich), potassium fluoride (KF, 99%, Aldrich), tetrahydrofuran (THF, HPLC, Aldrich), 1 M tetrabutylammonium fluoride solution (TBAF, Aldrich), trifluoroacetic acid (TFA, ≥98%, Aldrich), 4,4′-dinonyl-2,2′-bipyridyne (dNbpy, 97%, Aldrich), triethylamine (TEA, ≥99%, Aldrich), anhydrous aluminum chloride (AlCl 3, Aladdin), carbon tetrachloride (CCl4, ≥99.5%, Aladdin), activated carbon (YP50, Kuraray) and these agents were used as received.

Materials characterization. The conversion of the sample polymerization was measured in CDCl 3 by 1H NMR spectroscopy by virtue of Bruker Advance 300 MHz NMR. Molecular weights (Mn) and dispersities (Đ) were measured by GPC relative to calibration by linear PS and poly(methyl methacrylate) standards. Characterization by GPC was conducted using THF as an eluent at a flow rate of 1 mL min−1 at 35 °C using a Waters 515 pump with a Waters 2414 refractive index detector and PSS columns (SDV 500, 103, 105 Å). The nanomorphology of the samples was observed by a Hitachi S-4800 SEM. N2 adsorption was measured via Micromeritics ASAP2020 analyzer at 77 K. TGA was evaluated by PerkinElmer PE Pyris1 TGA thermogravimetric analyzer. Raman spectra were acquired using a Renishaw in Via Laser Micro-Raman Spectrometer with 514 nm laser excitation.

Synthesis of poly(2-bromoisobutyryloxyethyloxy methacrylate) (PBiBEM) Backbone Macroinitiator.


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The procedure used to prepare PBiBEM372 is outlined below. Preparation of PBiBEM1860 was conducted using the same procedure with variations in stoichiometry outlined in Table S1. This procedure was slightly modified from previously reported methods used to prepare PBiBEM macroinitiators.31,36,48 CuBr2 (4.5 mg, 0.0202 mmol), dNbpy (0.150 g, 0.368 mmol), HEMATMS (20.0 mL, 91.9 mmol), EBiB (17.9 mg, 0.0919 mmol), anisole (5.0 mL), and a magnetic stir bar were loaded into a 50 mL Schlenk flask. The mixture stirred at room temperature until the solution appeared homogeneous. Three rounds of freeze-pump-thaw were used to degass the solution. The flask was refilled with nitrogen on the final cycle, and CuBr (23.4 mg, 0.164 mmol) was rapidly put into the flask under positive nitrogen pressure. The flask was thawed to room temperature, and then lowered into an oil bath (40 °C) to begin polymerization. Polymerization progress was tracked by 1H NMR spectroscopy and was stopped once conversion reached 37.2%. The DP was calculated to be 372 by DP = [M] o/[I]o*(conv.). The concentrated mixture was diluted with dichloromethane and residual catalyst was removed through a neutral alumina plug. The mixture was then concentrated by rotary evaporation in a 250 mL round bottom flask for use in the next step without further purification. The product from the last step (10.4 g, 51.5 mmol HEMA-TMS) along with DTBP (1.06 g, 5.14 mmol), KF (3.65 g, 61.8 mmol), and a magnetic stir bar were loaded into a 250 mL roundbottom flask. The flask was sealed and degassed by three rounds of evacuation under vacuum and refill with nitrogen. Then, under positive nitrogen pressure, dry THF (150 mL) was added to dissolve the solid mixture. The flask was stirred at room temperature until it appeared visibly homogenous. The flask was lowered an ice bath, where a tetrabutylammonium fluoride stock solution in THF (0.51 mL, 1.0 M in THF, 0.51 mmol) was added, followed by BiBBr (7.6 mL, 62 mmol). Both reagents were injected dropwise with fast stirring. The reaction mixture came to


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room temperature to stir for a total reaction time of 24 h. After completion, salt precipitates removed by filtration through a cotton filter before dropwise precipitation into a methanol/water (70/30) mixture to remove residual salts. The crude product was re-dissolved in dichloromethane and precipitated an additional three times in hexanes. The purified product was filtered from hexanes and dried overnight at ambient temperature under vacuum. The molecular weight and dispersity of purified PBiBEM372 macroinitiator were measured relative to linear PMMA standards by THF GPC: Mn,GPC = 47,300, and Đ = 1.16.

Synthesis

of

poly(2-bromoisobutyryloxyethyloxy

methacrylate)-graft-polystyrene)

(PBiBEM-g-PS). The general procedure used to prepare polystyrene bottlebrushes was outlined below for PBiBEM372-g-PS210. Stoichiometric ratios of other samples were outlined in Table S2. The procedure used to prepare PS bottlebrushes was also slightly modified from previously reported literature.36 A 50 mL Schlenk adapted flask was charged with PBiBEM372 (0.0146 g, 0.0523 mmol) polymer macroinitiator, CuBr2 (1 mg, 0.043 mmol), styrene (15.00 mL, 13.6 g, 131 mmol), PMDETA (45.3 mg, 0.261 mmol), anisole (1.7 mL), and a magnetic stir bar. The mixture was allowed to briefly stir until it was visibly homogeneous. The solution was then frozen under liquid nitrogen and degassed by three cycles of freeze-pump-thaw. On the last cycle, nitrogen refilled the flask under high flow. CuBr (36.8 mg, 0.257 mmol) was rapidly put into the flask under positive nitrogen pressure. The flask was quickly re-sealed and further degassed by five rounds of evacuation under vacuum and refill with nitrogen. The frozen mixture was allowed to thaw to room temperature before immersion in an oil bath (60 °C) to start polymerization. Polymerization progress was tracked by 1H NMR spectroscopy and was stopped once conversion


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reached 8.3 % by opening the flask to air. Catalyst was removed from the crude product by passing the solution through a neutral alumina plug before dropwise precipitation into methanol. The sample was isolated through vacuum filtration as a white powder. The product was further dried under vacuum at ambient temperature overnight. The molecular weight and dispersity of the sample relative to linear PS standards was determined by THF GPC to be 767,000 and 1.07, respectively.

Synthesis of porous nanonetwork-structured polymers (PNSPs). Typically, anhydrous AlCl3 (1.00 g) was dispersed in CCl4 (10 mL) at 75 oC for 30 min under magnetic stirring with reflux condenser. Subsequently, the PBiBEM-g-PS solution (0.1 g in 10 mL of CCl4) was rapidly added to the AlCl3 mixture under fast stirring at the same temperature for 24 h. Hydrochloric acid solution (HCl, 1 M, 50 mL) was employed to stop the reaction, followed by stirring at 75 oC for 30 min. The PNSPs was obtained via filtering, washing with acetone, 1 M HCl and deion water at least three times, and drying under vacuum.

Synthesis of porous nanonetwork-structured carbons (PNSCs). PNSPs were carbonized at selective carbonization temperature/time at a rate of 5 oC min-1 in a furnace under high purity N2 flow to yield PNSCs samples. The carbonization temperatures were within a range of 600 to 800 °C with carbonization times among 0.5-3 h. The carbonized PNSCs were termed PNSC-x-y, where x and y correspond to the specific carbonization temperature and time, respectively.

Lithium sulfur (Li-S) battery tests.


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Sulfur and PNSC1860-800-0.5 (7:3 by weight) were thoroughly mixed and sealed in the autoclave at 155 ℃ for 20 h, leading to S@PNSC 1860-800-0.5 composites. The working electrodes were fabricated by mixing S@PNSC 1860-800-0.5, (poly(vinylidene difluoride), PVDF) binder, and carbon black (Super P) at a weight ratio of 7:1:2 in N-methyl-2-pyrrolidinone (NMP). Subsequently, the mixture was cast onto a carbon coated Al foil substrate and dried under vacuum at 55 °C for 12 h. 1 M lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) (50 v/v% of 1,3-dioxalane (DOL) and dimethyl ether (DME)) with 1 wt% LiNO 3 additive was utilized as the electrolyte. Cells were assembled inside of an Ar-filled glovebox. The galvanostatic charge/discharge tests conducted within a voltage window of 1.7 to 2.8 V with varying current densities using a LAND CT2001A battery tester. The long-term cycling tests were evaluated after preforming at 0.2 C for the first three cycles.

ASSOCIATED CONTENT Supporting Information Experimental procedures and supplementary figures. (PDF) Reaction condition and illustration, 1H NMR spectrum, GPC traces, TGA curves, SEM images, Raman spectrum, discharge-charge curves, cycling stability curves, comparation of electrochemical properties.

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] (D.W.)


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*E-mail: [email protected] (K.M.). ACKNOWLEDGMENTS The authors would like to acknowledge funding through the National Science Foundation (DMR 1501324), National Program for Support of Top-notch Young Professionals, National Natural Science Foundation of China (U1601206, 51872336, and 51422307), National Key Basic Research Program of China (2014CB932402), Fundamental Research Funds for the Central Universities (18lgzd10), and Leading Scientific, Technical and Innovation Talents of Guangdong Special Support Program (2017TX04C248). Notes The authors declare no competing financial interest. REFERENCES 1. Cheng, C.; Jiang, G.; Simon, G. P.; Liu, J. Z.; Li, D. Low-Voltage Electrostatic Modulation of Ion Diffusion through Layered Graphene-Based Nanoporous Membranes. Nat. Nanotechnol. 2018, 13, 685-690. 2. Tang, C.; Zhong, L.; Zhang, B.; Wang, H.; Zhang, Q. 3D Mesoporous Van Der Waals Heterostructures for Trifunctional Energy Electrocatalysis. Adv. Mater. 2018, 30, 1705110. 3. Wu, D.; Xu, F.; Sun, B.; Fu, R.; He, H.; Matyjaszewski, K. Design and Preparation of Porous Polymers. Chem. Rev. 2012, 112, 3959-4015. 4. Xu, F.; Wu, D.; Fu, R.; Wei, B. Design and Preparation of Porous Carbons from Conjugated Polymer Precursors. Mater. Today 2017, 20, 629-656. 5. Yang, S.; Feng, X.; Zhi, L.; Cao, Q.; Maier, J.; Müllen, K. Nanographene-Constructed Hollow Carbon Spheres and their Favorable Electroactivity with Respect to Lithium Storage. Adv. Mater. 2010, 22, 838-842. 6. Zheng, X.; Luo, J.; Lv, W.; Wang, D.; Yang, Q. Two-Dimensional Porous Carbon: Synthesis and Ion-Transport Properties. Adv. Mater. 2015, 27, 5388-5395.


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7. Wang, D.; Li, F.; Liu, M.; Lu, G.; Cheng, H. 3D Aperiodic Hierarchical Porous Graphitic Carbon Material for High-Rate Electrochemical Capacitive Energy Storage. Angew. Chem. Int. Ed. 2008, 47, 373-376. 8. Liu, T.; Zhang, F.; Song, Y.; Li, Y. Revitalizing Carbon Supercapacitor Electrodes with Hierarchical Porous Structures. J. Mater. Chem. A 2017, 5, 17705-17733. 9. Dutta, S.; Bhaumik, A.; Wu, K. Hierarchically Porous Carbon Derived from Polymers and Biomass: Effect of Interconnected Pores On Energy Applications. Energ. Environ. Sci. 2014, 7, 3574-3592. 10. Lin, X.; Liang, Y.; Lu, Z.; Lou, H.; Zhang, X.; Liu, S.; Zheng, B.; Liu, R.; Fu, R.; Wu, D. Mechanochemistry: A Green, Activation-Free and Top-Down Strategy to High-Surface-Area Carbon Materials. ACS Sustain. Chem. Eng. 2017, 5, 8535-8540. 11. Xu, F.; Xu, J.; Xu, H.; Lu, Y.; Yang, H.; Tang, Z.; Lu, Z.; Fu, R.; Wu, D. Fabrication of Novel Powdery Carbon Aerogels with High Surface Areas for Superior Energy Storage. Energy Storage Mater. 2017, 7, 8-16. 12. Wu, D.; Li, Z.; Zhong, M.; Kowalewski, T.; Matyjaszewski, K. Templated Synthesis of Nitrogen-Enriched Nanoporous Carbon Materials from Porogenic Organic Precursors Prepared by ATRP. Angew. Chem. Int. Edit. 2014, 53, 3957-3960. 13. Liang, H.; Zhuang, X.; Brüller, S.; Feng, X.; Müllen, K. Hierarchically Porous Carbons with Optimized Nitrogen Doping as Highly Active Electrocatalysts for Oxygen Reduction. Nat. Commun. 2014, 5, 4973. 14. Zhang, J.; Zhao, Z.; Xia, Z.; Dai, L. A Metal-Free Bifunctional Electrocatalyst for Oxygen Reduction and Oxygen Evolution Reactions. Nat. Nanotechnol. 2015, 10, 444-452. 15. Liang, Y.; Liang, F.; Zhong, H.; Li, Z.; Fu, R.; Wu, D. An Advanced Carbonaceous Porous Network for High-Performance Organic Electrolyte Supercapacitors. J. Mater. Chem. A 2013, 1, 7000-7005. 16. Yan, Y.; Yin, Y.; Guo, Y.; Wan, L. A Sandwich-Like Hierarchically Porous Carbon/Graphene Composite as a High-Performance Anode Material for Sodium-Ion Batteries. Adv. Energy Mater. 2014, 4, 1301584. 17. Xu, J.; Tan, Z.; Zeng, W.; Chen, G.; Wu, S.; Zhao, Y.; Ni, K.; Tao, Z.; Ikram, M.; Ji, H.; Zhu, Y. A Hierarchical Carbon Derived from Sponge-Templated Activation of Graphene Oxide for High-Performance Supercapacitor Electrodes. Adv. Mater. 2016, 28, 5222-5228.


16

Page 17 of 24 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


18. Tang, C.; Li, B.; Zhang, Q.; Zhu, L.; Wang, H.; Shi, J.; Wei, F. CaO-Templated Growth of Hierarchical Porous Graphene for High-Power Lithium-Sulfur Battery Applications. Adv. Funct. Mater. 2016, 26, 577-585. 19. Shi, J.; Tang, C.; Huang, J.; Zhu, W.; Zhang, Q. Effective Exposure of Nitrogen Heteroatoms in 3D Porous Graphene Framework for Oxygen Reduction Reaction and Lithium-Sulfur Batteries. J. Energy Chem. 2018, 27, 167-175. 20. Ni, L.; Zhao, G.; Yang, G.; Niu, G.; Chen, M.; Diao, G. Dual Core-Shell-Structured S@C@MnO2 Nanocomposite for Highly Stable Lithium-Sulfur Batteries. ACS Appl. Mater. Interfaces 2017, 9, 34793-34803. 21. Peng, H.; Huang, J.; Zhao, M.; Zhang, Q.; Cheng, X.; Liu, X.; Qian, W.; Wei, F. Nanoarchitectured Graphene/CNT@Porous Carbon with Extraordinary Electrical Conductivity and Interconnected Micro/Mesopores for Lithium- Sulfur Batteries. Adv. Funct. Mater. 2014, 24, 2772-2781. 22. Wu, D.; Hui, C.; Dong, H.; Pietrasik, J.; Ryu, H.; Li, Z.; Zhong, M.; He, H.; Kim, E.; Jaroniec, M.; Kowalewski, T.; Matyjaszewski, K. Nanoporous Polystyrene and Carbon Materials with Core-Shell Nanosphere-Interconnected Network Structure. Macromolecules 2011, 44, 5846-5849. 23. Liu, H.; Li, Z.; Liang, Y.; Fu, R.; Wu, D. Facile Synthesis of MnO Multi-Core@NitrogenDoped Carbon Shell Nanoparticles for High Performance Lithium-Ion Battery Anodes. Carbon 2015, 84, 419-425. 24. Lin, Y.; Xiong, K.; Lu, Z.; Liu, S.; Zhang, Z.; Lu, Y.; Fu, R.; Wu, D. Functional Nanonetwork-Structured Polymers and Carbons with Silver Nanoparticle Yolks for Antibacterial Application. Chem. Commun. 2017, 53, 9777-9780. 25. Liang, Y.; Chen, L.; Zhuang, D.; Liu, H.; Fu, R.; Zhang, M.; Wu, D.; Matyjaszewski, K. Fabrication and Nanostructure Control of Super-Hierarchical Carbon Materials from Heterogeneous Bottlebrushes. Chem. Sci. 2017, 8, 2101-2106. 26. Paturej, J.; Sheiko, S. S.; Panyukov, S.; Rubinstein, M. Molecular Structure of Bottlebrush Polymers in Melts. Sci. Adv. 2016, 2, e160147811. 27. Xu, Y.; Wang, T.; He, Z.; Zhong, A.; Yu, W.; Shi, B.; Huang, K. Synthesis of Triphenylphosphine-Based Microporous Organic Nanotube Framework Supported Pd Catalysts with Excellent Catalytic Activity. Polym. Chem. 2016, 7, 7408-7415.


17


Page 18 of 24

28. Xu, Y.; Wang, T.; He, Z.; Zhong, A.; Huang, K. Carboxyl-Containing Microporous Organic Nanotube Networks as a Platform for Pd Catalysts. RSC Adv. 2016, 6, 39933-39939. 29. Xie, G.; Krys, P.; Tilton, R. D.; Matyjaszewski, K. Heterografted Molecular Brushes as Stabilizers for Water-in-Oil Emulsions. Macromolecules 2017, 50, 2942-2950. 30. Altay, E.; Nykypanchuk, D.; Rzayev, J. Mesoporous Polymer Frameworks From End Reactive Bottlebrush Copolymers. ACS Nano 2017, 11, 8207-8214. 31. Xie, G.; Ding, H.; Daniel, W. F. M.; Wang, Z.; Pietrasik, J.; Sheiko, S. S.; Matyjaszewski, K. Preparation of Titania Nanoparticles with Tunable Anisotropy and Branched Structures from Core-Shell Molecular Bottlebrushes. Polymer 2016, 98, 481-486. 32. Wang, J. S.; Matyjaszewski, K. Controlled Living Radical Polymerization-Atom-Transfer Radical Polymerization in the Presence of Transition-Metal Complexes. J. Am. Chem. Soc. 1995, 117, 5614-5615. 33. Matyjaszewski, K. Atom Transfer Radical Polymerization (ATRP): Current Status and Future Perspectives. Macromolecules 2012, 45, 4015-4039. 34. Pang, X.; He, Y.; Jung, J.; Lin, Z. 1D Nanocrystals with Precisely Controlled Dimensions, Compositions, and Architectures. Science 2016, 353, 1268-1272. 35. Wu, D.; Nese, A.; Pietrasik, J.; Liang, Y.; He, H.; Kruk, M.; Huang, L.; Kowalewski, T.; Matyjaszewski, K. Preparation of Polymeric Nanoscale Networks from Cylindrical Molecular Bottlebrushes. Acs Nano 2012, 6, 6208-6214. 36. Xie, G.; Lin, X.; Martinez, M. R.; Wang, Z.; Lou, H.; Fu, R.; Wu, D.; Matyjaszewski, K. Fabrication of Porous Functional Nanonetwork-Structured Polymers with Enhanced Adsorption Performance from Well-Defined Molecular Brush Building Blocks. Chem. Mater. 2018, 30, 8624-8629. 37. Zou, C.; Wu, D.; Li, M.; Zeng, Q.; Xu, F.; Huang, Z.; Fu, R. Template-Free Fabrication of Hierarchical Porous Carbon by Constructing Carbonyl Crosslinking Bridges Between Polystyrene Chains. J. Mater. Chem. 2010, 20, 731-735. 38. Yuan, Y.; Cabasso, I.; Liu, H. Surface Morphology of Nanostructured Polymer-Based Activated Carbons. J. Phys. Chem. B 2008, 112, 14364-14372. 39. Xu, F.; Tang, Z.; Huang, S.; Chen, L.; Liang, Y.; Mai, W.; Zhong, H.; Fu, R.; Wu, D. Facile Synthesis of Ultrahigh-Surface-Area Hollow Carbon Nanospheres for Enhanced Adsorption and Energy Storage. Nat. Commun. 2015, 6, 7221.


18

Page 19 of 24 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


40. 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-EnergyDensity Lithium-Sulfur Batteries. Nat. Commun. 2017, 8, 482. 41. Yu, M.; Wang, Z.; Wang, Y.; Dong, Y.; Qiu, J. Freestanding Flexible Li 2S Paper Electrode with High Mass and Capacity Loading for High-Energy Li-S Batteries. Adv. Energy Mater. 2017, 7, 1700018. 42. Hao, G.; Tang, C.; Zhang, E.; Zhai, P.; Yin, J.; Zhu, W.; Zhang, Q.; Kaskel, S. Thermal Exfoliation of Layered Metal-Organic Frameworks into Ultrahydrophilic Graphene Stacks and their Applications in Li-S Batteries. Adv. Mater. 2017, 29, 1702829. 43. Xu, G.; Ding, B.; Nie, P.; Shen, L.; Dou, H.; Zhang, X. Hierarchically Porous Carbon Encapsulating Sulfur as a Superior Cathode Material for High Performance Lithium-Sulfur Batteries. ACS Appl. Mater. Interfaces 2014, 6, 194-199. 44. He, G.; Ji, X.; Nazar, L. High "C" Rate Li-S Cathodes: Sulfur Imbibed Bimodal Porous Carbons. Energ. Environ. Sci. 2011, 4, 2878-2883. 45. Fei, L.; Li, X.; Bi, W.; Zhuo, Z.; Wei, W.; Sun, L.; Lu, W.; Wu, X.; Xie, K.; Wu, C.; Chan, H. L. W.; Wang, Y. Graphene/Sulfur Hybrid Nanosheets From a Space-Confined "Sauna" Reaction for High-Performance Lithium-Sulfur Batteries. Adv. Mater. 2015, 27, 5936-5942. 46. Yuan, S.; Bao, J. L.; Wang, L.; Xia, Y.; Truhlar, D. G.; Wang, Y. Graphene-Supported Nitrogen and Boron Rich Carbon Layer for Improved Performance of Lithium-Sulfur Batteries Due to Enhanced Chemisorption of Lithium Polysulfides. Adv. Energy Mater. 2016, 6, 1501733. 47. Wang, Z.; Dong, Y.; Li, H.; Zhao, Z.; Wu, H. B.; Hao, C.; Liu, S.; Qiu, J.; Lou, X. W. D. Enhancing Lithium-Sulphur Battery Performance by Strongly Binding the Discharge Products on Amino-Functionalized Reduced Graphene Oxide. Nat. Commun. 2014, 5, 5002. 48. Yuan, R.; Kopec, M.; Xie, G.; Gottlieb, E.; Mohin, J. W.; Wang, Z.; Lamson, M.; Kowalewski, T.; Matyjaszewski, K. Mesoporous Nitrogen-Doped Carbons from Pan-Based Molecular Bottlebrushes. Polymer 2017, 126, 352-359.


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Page 20 of 24

Figure 1. Schematic illustration of preparation procedures for PNSCs with well-defined cylindrical

molecular

bottlebrushes

as

building

blocks,

including

Friedel-Crafts

hypercrosslinking reaction and shape-regulated carbonization. The nanowire morphology of the network units of PNSPs can be transformed into morphologies of (a) nanosphere, (b) nanorod and (c) nanowire for PNSCs, depending on carbonization conditions.


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Figure 2. SEM images of (a) PNSP372, (b) PNSP1860 and (c, d) PNSC1860-800-0.5.


21

600

a

0.9 PNSC1860-800-0.5

dV/dlogD/g (cm3 g-1 STP)

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

Quantity Adsorbed (cm3 g-1 STP)


PNSP1860

400

200

Page 22 of 24

b

PNSC1860-800-0.5 PNSP1860

0.6

0.3

0.0

0 0.0

0.2 0.4 0.6 0.8 Relative Pressure (P/P0)

1.0

1

10 Pore Diameter (nm)

100

Figure 3. (a) N2 adsorption-desorption isotherms and (b) DFT pore size distributions curves of PNSP1860 and PNSC1860-800-0.5.

Figure 4. Illustrative model of PNSCs with a well-developed network structure for rapid electron/ion transportation.


22

c

1600

1600

0.2 C

1200

0.5 C

800

1C

2C

0.2 C

3C

4C

5C

400 0 10

20 Cycle Number

30

40

100

1200 1C

800

50

400 0

0 0

50

Cycle Number

100

1200

150

100

800

5C

50

400 0

0 0

100

Cycle Number

200

Coulombic Efficiency (%)

0

Coulombic Efficiency (%)

b

Specific Capacity (mAh g-1)

a


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 23 of 24

300

Figure 5. (a) Rate performance of [email protected] at various current densities of 0.2-5 C. Long-term cycle stability and Coulombic efficiency of S@PNSC 1860-800-0.5 at (b) 1 C and (c) 5 C.


23


Page 24 of 24

Table 1. Summary of the nanoarchitectures of PNSCs obtained from different building blocks and carbonization temperatures and times. Carbonization

Carbonization

temperature (oC)

time (h)

PBiBEM372-g-PS210

800

3

Nanosphere

PNSC1860-600-3

PBiBEM1860-g-PS220

600

3

Nanowire

PNSC1860-800-3

PBiBEM1860-g-PS220

800

3

Nanosphere

PNSC1860-800-1

PBiBEM1860-g-PS220

800

1

Nanorod

PNSC1860-800-0.5

PBiBEM1860-g-PS220

800

0.5

Nanowire

Sample

Building block

PNSC372-800-3

Nanoarchitecture

Table of Contents


24

Fabrication of porous nanonetwork-structured carbons from well

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