Controlled Synthesis of Porous Carbon Nanostructures with Tunable Closed Mesopores via a Silica-Assisted Coassembly Strategy

Open AccessCCS ChemistryRESEARCH ARTICLE1 May 2021Controlled Synthesis of Porous Carbon Nanostructures with Tunable Closed Mesopores via a Silica-Assisted Coassembly Strategy Binbin Guo†, Chen Li†, Haoran Wu†, Jiahang Chen, Jiulin Wang, Hao Wei and Yiyong Mai Guo† School Chemistry Chemical Engineering, Frontiers Science Center for Transformative Molecules, Shanghai Key Laboratory Electrical Insulation Thermal Ageing, Jiao Tong University, 200240 Electronic Information †B. Guo, C. Li, H. Wu contributed equally to this work.Google Scholar More articles by author , Li† Wu† Google Wang *Corresponding authors: E-mail Address: [email protected] https://doi.org/10.31635/ccschem.020.202000400 SectionsSupplemental MaterialAboutAbstractPDF ToolsAdd favoritesTrack Citations ShareFacebookTwitterLinked InEmail Controllable fabrication mesoporous carbon nanoparticles (MCNs) tunable pore structures is great interest, due the remarkable effect structure on electrochemical performance materials. However, it has remained major challenge. Here, we demonstrate controlled synthesis MCNs closed silica-assisted coassembly strategy, which employs polystyrene-block-poly(ethylene oxide) diblock copolymers as soft template, phenolic resol tetraethyl orthosilicate silica precursors, respectively. Through simply varying sequential cross-linking precursors or copolymer composition, novel alluring spherical, hollow-hoop-structured, yolk-shell-like mesopores are tunably prepared. In particular, serving cathode materials lithium–sulfur batteries, resultant silica-hybridized exceptional hollow-hoop moderate sulfur-loading content 46 wt % exhibit top-level performance. This study opens an avenue construction particles pores provides clues geometry porous batteries. Download figure PowerPoint Introduction Discrete have attracted tremendous interest in energy storage conversion applications, including secondary batteries supercapacitors, their high specific surface areas (SSAs), electrical conductivity, flexible processing into electrode materials.1–4 Serving materials, plays vital role determining since can seriously affect mass charge transport during charge–discharge process.5–7 Much effort been devoted MCNs, primarily includes hard- soft-template methods.8–11 Although both these approaches own merits, strategy shows predominant advantages different architectures easy removal template. Predominantly, method based self-assembly block (BCPs) may produce shapes sizes, example, polymer composition conditions.12–17 Nevertheless, utilization BCP series various well-defined rarely explored difficulties finding appropriate parameters among large number affecting factors. Rechargeable (Li–S) proven be promising next-generation devices theoretical density, low cost, environmental friendliness.18–25 practical application Li–S still impeded three problems: (1) inherent poor electron conductivity sulfur its final discharge products (i.e., polysulfides), (2) shuttling polysulfide intermediates, (3) volume expansion around 80% upon lithiation. These problems result severe self-discharge, coulombic efficiency, rapid decline capacity cycling.26,27 Heretofore, host carbons,28,29 nanotubes,30,31 hollow spheres,32,33 fibers,34,35 graphene,36,37 so forth designed improve strategies mainly focus enhancement physical adsorption polysulfides carbonaceous insufficient inhibit leakage active species weak interaction between species.38,39 contrast, effective limiting loss species. Meanwhile, introduction some polar moieties such hybridization SiO2, contribute species.40,41 our knowledge, combination not yet investigated. As well, cathodes unexplored.42–48 protocol, employing (PS-b-PEO) (TEOS) respectively (Figure 1). Unprecedented spherical (denoted MCN-cs), (MCN-hh), (MCN-ys) obtained tunably. Mechanism reveals that structural control governed determine packing parameter formed aggregates particles. The along endow excellent capability preventing effect. Particularly, MCN-hh unique possesses SSA 857 m2/g, 0.55 cm3/g, 8.3 %. material battery, loading MCN-hh/S) exhibits remarkably (e.g., 1350–1080 mAh/g within 100 cycles at 0.1 C) outstanding cycling stability (0.07% average decay rate per cycle). superior those most reported carbon/S cathodes, even much higher loading. Figure 1 | guided synthetic routes toward (A: only formaldehyde was added; B: TEOS were added simultaneously; C: 5 min prior addition formaldehyde). Experimental Methods compositions condition A: PS-b-PEO (10 mg) first dissolved tetrahydrofuran (THF; 4 mL), then 20 mL deionized water dropwise mixture generate micellar aggregation under stirring. After resorcinol (100 ammonia (200 ?L) h, (140 introduced mixture. stirring 30 °C 24 h. THF (4 Afterward, (180 simultaneously added. Finally, above. min, 140 ?L For all procedures mentioned above, resulting composites washed times dried vacuum 60 carbonization 800 2 h N2 atmosphere furnace. heating °C/min. Results Discussion PSn-b-PEO114 (the subscripts n 114 denote degrees polymerization PS PEO blocks, respectively) synthesized living atomic transfer radical (see Supporting “Experimental Section”). Nuclear magnetic resonance (NMR) gel permeation chromatography (GPC) measurements prove successful lengths ( Figures S1 S2).49,50 illustrated Route 1, PS79-b-PEO114 micelles quick (20 mL) solution (2.5 mg/mL). Then, suitable amounts mixed solution. Next, sequences followed process, there situations: (A) obtain MCN sample without hybridation 1A), (B) 1B), (C) 1C), allowed hydrolysis partial TEOS. formaldehyde, polycondensation reaction occurred rapidly system, forming framework accompanied processes (C), hydrolyzed (tetrahydroxysilane) could cross-linked skeleton.51,52 purified centrifugation converted atmosphere. During carbonization, templates also removed, leaving (MCN-ctrl, MCN-cs, MCN-hh). another route 2), utilizing PS158-b-PEO114 longer block, following procedure similar 1B. morphology characterized scanning microscopy (SEM) transmission (TEM). SEM images reveal morphologies narrow size distributions S3). Furthermore, high-magnification indicate possess smooth surfaces any observable (insets S3), suggesting internalized sealed spheres. TEM show presence MCN-ctrl MCN-cs (Figures 2a 2b), while no obvious difference particle diameters (200–300 nm) (?9 nm). Compared MCN-ys do multiple interior, whereas they solid “yolk” encapsulated “shell” 2c). yolks 210 ± 42 nm 25 nm, Most interestingly, 2d many mean diameter 8 align parallel spheres 2d). To interior MCN-hh, sliced, cross sections imaged 2e). 2e1 side view sliced 2e2 represents geometrical model. It clear “hollow hoops” nearly each other, uniform distance ca. two neighboring hoops. 2e3 clearly embedding hoops periphery Based images, model 2e4. Notably, evident outer “shells” peripheries, seal mesopores. MCNs. (a) MCN-ctrl, (b) (c) MCN-ys, (d) MCN-hh. thicknesses t ¯ ) shells given corresponding images. (e) [(1) view, tilt (4) view. sectional specimen prepared slicing embedded epoxy ultramicrotome]. (f) Element mapping MCN-hh: (f1) STEM image, (f2) C element, (f3) O (f4) Si (f5) HADDF image C, O, element. distribution particles, element analyses performed field-emission (FETEM). elements uniformly distributed spheres, atoms exist dominantly peripheral shell S4), indicating majority tetrahydroxysilane molecules polycondensation. reason S5) 2f), throughout whole matrix hybrid confirmed X-ray photoelectron spectroscopy (XPS) spectra, Si4+ signals attributed SiO2 seen 100.1 150.5 eV 3a). contents determined thermogravimetric analysis (TGA; 3b S6) listed Table 1. 8.9%, 8.3%, 7.6%, further supported elemental (Table Raman spectra samples bands 1345 1585 cm?1, D G disordered graphitized carbons, 3c S7). intensity ratio (about 1) suggests degree graphitization beneficial conductivity. adsorption–desorption carried out SSAs volumes 3d S8–S10). calculated Brunauer–Emmett–Teller method, Barrett–Joyner–Halenda employed distribution. results micropores samples, possibly generated matrices precursors. MCN-crtl (?770 m2/g) (?0.50 cm3/g). presents m2/g larger lower 523 smaller 0.38 cm3/g 1), apparent structure.53 3 Various characterizations XPS survey spectrum, TGA curve, nitrogen inset curve). Structural Parameters Resulting Sample (m2/g) Average Pore Diameter (nm) Volume (cm3/g) Content (wt %) 771 10 0.51 82.0 0 763 9 0.50 75.0 8.9% 74.2 8.3% 74.0 7.6% considered composite copolymer, TEOS, understand formation mechanism shapes, tracked process before carbonization. after (Route (approaching diameter) S11). Subsequently, adsorb hydrophilic coronae hydrogen-bonding interaction, drive association form compound (LCMs; S12).49 Then situation A, absorbed domains stabilized LCMs, PS-b-PEO/resol S13), is, precursor MCN-ctrl. B, cocross-link matrix,51,52 producing PS-b-PEO/resol/silica namely MCN-cs. case LCMs probably induced transformation hoop-like follow-up cocross-linking resorcinol, together,51,52 yielding identified contrast substance S14), hoop template formation. should noted here highly difficult systems difficulty parameters.50 never found before. study, PS-b-PEO, resulted associated thus providing opportunity generation above-discussed cases, believe residual resols solution, subsequent generates shells, internal On other side, vesicles 130 wall thickness 16 S15). adsorbed cavities vesicles. vesicle cavities, generating MCN-ys. pyrolysis, resol/silica inside cavity yolk. experiments absent copolymers, nonporous nanospheres rather than validating engineering Since candidates impregnation sulfur. efficiently alleviate process. addition, known strong through binding charged Si-O groups polysulphide anions, energies Li2S, Li2S2, Li2S4, Li2S6 ?11.78, ?9.51, ?11.60, ?10.67 eV, respectively, nonpolar hosts.41 Therefore, contributes enhancing polysulfides, effect.40,54,55 verify abilities compared adding mg electrolyte solutions (1 mM). No change color observed period experiment 4a). sharp colorless standing proving distinct samples. enhance mechanical strength prevent them from smashing cycling.54 worth mentioning close optimum values (10–15 %54), would reduce skeleton, unfavorable photographs treated blank control, (b–d) Characterizations MCN-hh/S Nitrogen isotherm schematic diagram images: (d1) (d2) (d3) S (d4) prepare MCNS filled melt-diffusion protocol56 “Experiment encapsulation conducted temperature 155 °C. At turns liquid penetrate walls mesopores.56 largest chose evaluating Three representative MCN-hh/S), had 35, 46, (determined analysis), evaluation. filling detected analysis, revealed significant decreases instance, decreased sharply (857 reduced 4b). Moreover, appeared curve (inset almost full micrographs retained original 4c). Elemental 4d), confirming Button cells assembled evaluate MCNs/S First, cyclic voltammetry (CV) curves recorded scan 0.5 mV/s potential window 1.5–2.9 V. S16 displays cathodic peaks (?2.0 ?2.3 V), S8 long-chain reduction short-chain sulfides (Li2S2/Li2S), characteristic peak (?2.45 V) reverse oxidation anodic scan. battery testing (areal mg/cm2) exhibited best initial ?910 532 500 S17). 35 858 670 mAh/g, 470 400 cycles, comparison, therefore near next evaluations 2). tested (<30 comparison Comparison Battery Performance Cathodes Different Structures (Areal Sulfur Loading Is 1.2 Initial Capability (mAh/g) Finial Cycles Rate MCN-ctrl/S 43% 1015 895 0.1–2 767 433 1046–517 MCN-cs/S 47% 1280 935 909 1137–554 46% 1350 1080 1003 656