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

Abstract

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