Hierarchically Structured CNT@Co-N-CNF Interlayers for Enhanced Lithium Polysulfide Confinement in Lithium-Sulfur Batteries

Hierarchically Structured CNT@Co-N-CNF Interlayers for Enhanced Lithium Polysulfide Confinement in Lithium-Sulfur Batteries | Authorea try { document.documentElement.classList.add('js'); } catch (e) { } var _gaq = _gaq || []; _gaq.push(['_setAccount', 'G-8VDV14Y67G']); _gaq.push(['_trackPageview']); (function() { var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true; ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s); })(); Skip to main content Preprints Collections Wiley Open Research IET Open Research Ecological Society of Japan All Collections About About Authorea FAQs Contact Us Quick Search anywhere Search for preprint articles, keywords, etc. Search Search ADVANCED SEARCH SCROLL This is a preprint and has not been peer reviewed. Data may be preliminary. 8 September 2025 V1 Latest version Share on Hierarchically Structured CNT@Co-N-CNF Interlayers for Enhanced Lithium Polysulfide Confinement in Lithium-Sulfur Batteries Authors : Seoye Shin , Dae Kyom Kim , Jeong Jun Park , San Moon , Je-Nam Lee , Jong Hyeok Park , Sang-Gil Woo , and Jungdon Suk 0000-0002-3974-2920 [email protected] Authors Info & Affiliations https://doi.org/10.22541/au.175735026.69439136/v1 163 views 77 downloads Contents Abstract Information & Authors Metrics & Citations View Options References Figures Tables Media Share Abstract Lithium-sulfur batteries (LSBs) are considered promising candidates for high-energy-density storage systems. However, challenges such as the polysulfide shuttle effect and limited cycling stability hinder their commercialization. This study introduces a hierarchically structured interlayer, CNT @Co-N-CNF (CCNC), fabricated through a novel process that combines electrospinning with ZIF-67-derived carbonization. This interlayer uniquely integrates physical and chemical confinement mechanisms for lithium polysulfides (LiPSs) by leveraging a conductive carbon nanotube (CNT) network, nitrogen (N)-doping, and embedded cobalt species. Designed to enhance sulfur utilization and effectively suppress LiPS migration, the 50-CCNC interlayer demonstrates an initial discharge capacity of 1137.4 mAh g⁻1, along with excellent cycling stability in coin cell configurations. Furthermore, its practical potential is validated in a pouch stack cell configuration, achieving an initial capacity of 1059.7 mAh g⁻1 and retaining 99.54% of its capacity after 40 cycles. These findings underscore the interlayer’s effectiveness in addressing key challenges for large-scale LSB applications and represent a significant step toward the commercialization of high-energy-density LSB technology. 1. Introduction Global reliance on fossil fuels dominates energy consumption, but their long-term use is unsustainable due to severe environmental consequences, particularly climate change and environmental degradation [1] . This has accelerated the shift toward renewable energy sources, which are essential for meeting global energy demands while minimizing environmental impact. A major challenge in this transition is the development of advanced energy storage systems capable of efficiently harnessing and distributing renewable energy. Among current technologies, lithium-ion batteries (LIBs) have become the most widely used energy storage solutions, especially in electric vehicles (EVs) and portable electronic devices, due to their relatively high energy density and long cycle life. However, despite their prevalence, current LIBs—providing an energy density in the range of 250–300 Wh kg⁻ 1 —are inadequate for next-generation applications, such as long-range EVs and grid-scale renewable energy storage [2] . Lithium-sulfur batteries (LSBs) have garnered significant attention as a promising alternative to LIBs due to their higher theoretical energy density (~2600 Wh kg⁻¹) and specific capacity (1675 mAh g⁻¹) [3] . These attributes make LSBs particularly appealing for applications requiring higher energy storage capacities [4] . However, despite their potential, several intrinsic challenges hinder the commercialization of LSBs. These include sulfur’s poor electrical conductivity, significant volume expansion (~80%) during cycling, and instability of the solid-electrolyte interphase (SEI) [5] . Most critically, the polysulfide shuttle effect, which arises from the dissolution and migration of lithium polysulfides (LiPSs) during battery cycling, remains a major obstacle to the practical deployment of LSBs [6] . This shuttle effect leads to continuous loss of active sulfur material, low coulombic efficiency, and rapid capacity fading, as LiPSs migrate to the anode and undergo parasitic reactions [7] . Moreover, the dissolution-precipitation mechanism of LiPSs degrades the cathode structure, further worsening battery performance during extended cycling [8] . To address these challenges, various strategies have been proposed, including developing conductive host materials that encapsulate sulfur, designing functional separators to trap LiPSs, and introducing interlayers between the cathode and separator to act as barriers to LiPS migration [9] . Among these approaches, interlayers have emerged as one of the most effective and scalable solutions for mitigating the shuttle effect [10] . By serving as both physical barriers and electrochemical mediators, interlayers can prevent LiPS diffusion, facilitate sulfur reutilization, and significantly enhance the electrochemical performance and cycling stability of LSBs [11],[12] . For an interlayer to be effective, it must meet several design criteria: (1) high affinity for electrolytes to ensure uniform ion transport, (2) efficient lithium-ion diffusion and high ionic conductivity, (3) the ability to chemically and physically adsorb LiPSs to prevent their migration to the anode, (4) mechanical flexibility to accommodate volume changes during cycling, (5) high electrical conductivity to function as an upper current collector, and (6) robust structural stability to withstand prolonged cycling [13] . Among the various materials investigated for interlayer fabrication, including polymers [14] , heteroatoms [15] , and metal-organic frameworks (MOFs) [16] , carbon-based materials such as carbon fibers [17] , carbon nanofibers (CNFs) [18] , and carbon nanotubes (CNTs) [19] have been particularly favored due to their excellent electrical conductivity, chemical stability, and large surface areas [20] . Despite these advantages, traditional carbon materials face significant limitations when used independently. The smooth surfaces of carbon fibers provide minimal chemical interaction with LiPSs, reducing their ability to trap polysulfides effectively and resulting in suboptimal performance in LSBs. To address these shortcomings, researchers have explored functionalizing carbon materials with heteroatoms, inorganic metal compounds, or incorporating MOFs to enhance their ability to trap LiPSs and improve overall electrochemical performance [21] . In this context, MOFs have attracted considerable attention due to their versatile chemistry, tunable pore sizes, and exceptionally high surface areas, making them ideal candidates for enhancing LiPS trapping in LSBs [22] . MOFs, composed of metal centers coordinated by organic linkers, offer a highly porous framework with customizable pore size distribution and active sites for LiPS adsorption. One particularly promising MOF is zeolitic imidazolate framework-67 (ZIF-67), which consists of cobalt ions (Co²⁺) and N-containing organic linkers (2-methylimidazole) [23] . ZIF-67 has demonstrated remarkable potential in capturing LiPSs due to the strong affinity of its Co metal centers for polysulfides and its tunable structure, which facilitates both physical and chemical adsorption [24], [25] . Furthermore, when subjected to heat treatment under an inert atmosphere, ZIF-67 catalyzes the growth of CNTs, enhancing both the conductivity and surface area of the resulting material [26], [27] . However, previous studies using ZIF-67-based materials in LSBs have often produced suboptimal results. Limitations included poor control over the hierarchical structure and insufficient conductivity, leading to high internal resistance and reduced active surface area. Additionally, the direct interaction between ZIF-67 and the sulfur cathode often resulted in an unstable interface, diminishing long-term cycling performance. These factors compromised the material’s ability to fully confine LiPSs, resulting in degraded electrochemical performance. To address these shortcomings, electrospinning has emerged as an effective method for fabricating interlayers with superior properties. Electrospinning is a versatile technique that produces continuous, ultrafine fibers with high surface-area-to-volume ratios and tunable porosity [28] , making it ideal for creating carbon nanofiber-based structures. This process enables uniform fiber formation and precise control over fiber diameters, resulting in lightweight, flexible mats with excellent mechanical strength [29] , which is crucial for accommodating the volumetric expansion during sulfur cycling in LSBs. Moreover, electrospinning offers significant flexibility in material integration, allowing various dopants, metal precursors, and nanomaterials, such as MOFs, to be incorporated directly into the fiber matrix [30] . This facilitates chemical bonding between CNFs and functional materials, creating multifunctional interlayers. During subsequent carbonization, embedded materials undergo chemical transformations that activate their properties. For example, metal precursors introduced during electrospinning can transform into metal nanoparticles or carbon structures during carbonization, significantly enhancing the interlayer’s structural integrity, surface area, and conductive network [31] . Simultaneously, nitrogen (N)-containing precursors can be integrated into the fibers to introduce N functionalities, which improve the chemical affinity for LiPSs, further enhancing the interlayer’s ability to confine them. This synergy of materials allows for the design of interlayers that not only serve as physical barriers but also improve electrochemical performance through enhanced conductivity and polysulfide immobilization. This study presents a novel interlayer design that integrates CNFs and ZIF-67-derived materials to address the challenges associated with the polysulfide shuttle effect in LSBs. The CNT@Co-N-CNF (CCNC) interlayer was fabricated using an innovative approach that combines electrospinning and ZIF-67-derived carbonization. Briefly, the interlayer was synthesized by electrospinning a polyacrylonitrile (PAN) solution containing a Co precursor, followed by the in-situ growth of ZIF-67 particles on the fiber surface. Subsequent carbonization at 800 °C under an argon atmosphere resulted in an interconnected CNF structure decorated with Co/CNTs. Throughout this process, optimal synthesis conditions, such as the concentration of the Co precursor, were carefully investigated to achieve the ideal interlayer composition. The resulting CCNC interlayer exhibited enhanced LiPS adsorption through the synergistic contributions of N-doping, cobalt species, and the increased surface area provided by the CNTs. This interlayer design, developed under optimized synthesis conditions, effectively addresses the critical challenges of sulfur utilization and LiPS migration, marking a significant advancement in improving the electrochemical performance and cycling stability of LSBs. 2. Results and Discussions 2.1 Structural, Morphological, and Surface Chemistry Characterization The fabrication process of the CCNC interlayer is schematically illustrated in Figure 1a. This study introduces an innovative approach to interlayer design by integrating metal-organic framework (MOF) chemistry into the electrospinning process, resulting in a flexible, free-standing interlayer with a hierarchical structure. Initially, a Co-infused mat (Co-mat) was synthesized using a one-step electrospinning technique with a PAN and N,N-Dimethylformamide (DMF) solution containing Co(NO₃)₂·6H₂O as the Co precursor [32] . By adjusting the concentration of the Co precursor to 25%, 50%, and 75% by weight, precise control over the final composition of the interlayer was achieved, which is crucial for optimizing its performance. After electrospinning, the Co-mat was immersed in a 2-methylimidazole solution to facilitate the in-situ growth of ZIF-67 on the fiber surfaces (denoted as %-ZCP, where % indicates the weight percentage of the Co precursor). This step introduces a key innovation, integrating MOF chemistry directly with electrospinning to create a hierarchical structure on the fiber surfaces. The direct growth of ZIF-67 serves multiple purposes: it provides additional catalytic sites, promotes uniform distribution of Co species, and acts as a scaffold for carbonization. The carbonization process, conducted at 800 °C under an argon atmosphere, transforms the ZIF-Co-PAN fibers (designated as %-ZCP) into CNT@Co-N-CNF (designated as %-CCNC). During this transformation, the embedded ZIF-67 catalyzes the formation CNTs on the fibers, using the PAN-derived CNFs as the carbon source. In this mechanism, the Co particles function as catalysts, promoting the decomposition of carbon precursors from the pyrolysis of CNFs and facilitating the nucleation and growth of CNTs directly on the fiber surfaces. Carbon atoms dissolve into the Co nanoparticles and subsequently precipitate out to form tubular carbon structures, creating the integrated CNT network. Unlike conventional chemical vapor deposition (CVD) methods that require an external carbon source, this process utilizes the intrinsic pyrolysis of CNFs to generate a reducing environment, thus driving the simultaneous carbonization and CNT growth [33] . This unique approach not only simplifies the fabrication process but also results in a flexible and porous architecture that outperforms conventional interlayer designs [34] . The CCNC interlayer exhibits superior mechanical flexibility compared to traditional CNFs ( Figure S1 ), which is essential for accommodating volume changes during battery cycling. By employing this innovative combination of materials and processing techniques, the resulting interlayer features a unique hierarchical structure, abundant catalytic sites, and an integrated CNT network. These characteristics are expected to enhance sulfur utilization and suppress polysulfide migration, ultimately improving the electrochemical performance of LSBs. The subsequent analysis provides a detailed examination of the interlayer’s morphology and surface characteristics to further elucidate its structure-performance relationship. Figure. 1 (a) Schematic illustration of the synthesis process of CCNC interlayer. (b-i) SEM image: (b) PAN, (c) 25-ZCP, (d) 50-ZCP, (e) 75-ZCP, (f) CNF, (g) 25-CCNC, (h) 50-CCNC, and (i) 75-CCNC. (j-n) TEM image and EDS mapping: (j-k) 50-ZCP and (l-n) 50-CCNC. The fiber morphology was examined using scanning electron microscopy (SEM) to understand the structural evolution before ( Figure 1b–e ) and after ( Figure 1f–i ) thermal treatment across different Co precursor concentrations. As the Co precursor percentage increased, the fiber thickness also increased, likely due to enhanced ZIF-67 formation on the fiber surfaces, which contributed to a more substantial initial structure. After carbonization, a significant reduction in fiber thickness was observed, primarily due to the decomposition and pyrolysis of the PAN matrix. This process eliminates non-carbon elements (e.g., nitrogen, hydrogen) and releases volatile compounds, condensing the fibers into carbon nanofibers (CNFs) ( Table S1 ) [35] . SEM images revealed that the crystal-like structures of ZIF-67 were present only in the 50-ZCP and 75-ZCP samples before carbonization ( Figure 1d and e ). This observation suggests that a minimum concentration of Co precursor is necessary to facilitate ZIF-67 nucleation and growth on the fiber surfaces. In the 25% Co precursor sample ( Figure 1c ), the Co ion concentration was likely too low to generate sufficient nucleation sites, leading to the absence of ZIF-67 crystal growth on the fiber surfaces. In contrast, the 75-ZCP sample ( Figure 1e ) exhibited a high concentration of Co precursor that promoted extensive nucleation, resulting in a densely packed arrangement of ZIF-67 crystals. This excessive nucleation likely caused aggregation, diminishing the distinctiveness of the crystals and creating a less-defined morphology due to overlapping and closely packed growth. Conversely, the 50-ZCP sample ( Figure 1d ) achieved an optimal balance in precursor concentration. The moderate Co precursor amount provided enough nucleation sites for ZIF-67 growth without inducing aggregation, resulting in well-defined, evenly distributed crystals on the fiber surfaces. This uniform distribution is essential for creating a hierarchical structure that facilitates subsequent carbonization and CNT growth processes. Upon carbonization, the PAN fibers underwent pyrolysis, transforming into CNFs. This process eliminated non-carbon elements such as nitrogen and hydrogen, resulting in the densification and stabilization of the carbon structure. In the 25-ZCP sample, the absence of ZIF-67 structures and an inadequate amount of Co catalyst inhibited CNT growth on the fiber surfaces, as shown in Figure 1g . Consequently, the resulting CNFs were smooth and lacked the hierarchical architecture characteristic of CNTs. In contrast, the 50-ZCP sample exhibited an optimal concentration of ZIF-67, which functioned as a catalyst for CNT formation during carbonization. This facilitated the growth of long, uniformly distributed CNTs on the fiber surfaces, as illustrated in Figure 1h . The even distribution of ZIF-67 created a balanced nucleation environment that promoted consistent CNT growth along the CNFs. Meanwhile, the 75-CCNC sample displayed a densely packed network of CNTs ( Figure 1i ) due to excessive ZIF-67 growth prior to carbonization. The excessive ZIF-67 not only increased the number of nucleation sites but also led to aggregation, resulting in closely packed CNTs that may affect the interlayer’s porosity and lithium-ion transport pathways. All fiber samples, regardless of their initial precursor concentration, maintained a uniform distribution at a larger scale ( Figure S2 ). The final carbonized interlayers exhibited a thickness of approximately 40 μm, as confirmed by cross-sectional imaging ( Figure S3 ). This uniform thickness is crucial for ensuring consistent ion transport and stable electrochemical performance in LSBs, as it facilitates homogeneous current distribution and optimal ion diffusion pathways during battery operation. Further characterization of the 50-ZCP and 50-CCNC samples was conducted using transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS) mapping before and after carbonization ( Figure 1j–n ). The TEM image of the 50-ZCP sample ( Figure 1j ) and the corresponding elemental mapping ( Figure 1k ) revealed particles embedded on the carbon fiber surfaces, originating from the Co precursor. During carbonization, these Co particles acted as catalysts for CNT growth, facilitating the decomposition of the carbon precursor and subsequent nucleation of CNTs directly on the fibers. The observed CNT growth mechanism typically results in Co particles being located at the tips or within the core of the CNTs. In this study, nanosized Co particles were found at the tips of the CNTs ( Figure 1m ), indicative of their catalytic role. The strong electron scattering caused by the high atomic number of Co compared to carbon atoms appeared as dark spots in the TEM images. This phenomenon was more pronounced in the 75-CCNC sample, where TEM and EDS mapping ( Figure S9 ) displayed aggregated Co particles around the densely packed CNTs. This aggregation suggests that excessive Co precursor and ZIF-67 growth led to clustered Co particles, which may influence the structural integrity and electrical conductivity of the interlayer. Elemental mapping of both the 50-ZCP and 50-CCNC samples ( Figure 1k and n ) confirmed a relatively even distribution of Co throughout the fibers, indicating the successful incorporation of Co into the fiber matrix. Furthermore, EDS mapping across all samples ( Figure S4–S9 ) consistently showed a uniform elemental distribution, signifying the homogeneity of the synthesis process and the effective formation of the hierarchical interlayer structure. This uniform distribution of Co and carbon elements is essential for ensuring consistent catalytic activity and conductive pathways throughout the interlayer, thereby enhancing the overall electrochemical performance of LSBs. The crystalline structures of CNF, 25-CCNC, 50-CCNC, and 75-CCNC were analyzed using X-ray diffraction (XRD), as shown in Figure 2a. A broad peak at 26° was observed, corresponding to the (002) lattice plane of carbon, indicating the graphitic nature of the CNFs [36] . Sharper carbon peaks indicate a higher degree of graphitization, associated with more ordered carbon structures. Among the CCNC samples, the level of graphitization increased with higher concentrations of Co, likely due to Co’s catalytic effect during carbonization, which promotes the rearrangement of carbon atoms into more ordered graphitic structures by lowering the energy barrier for carbon atom realignment [37] . In the XRD patterns of 50-CCNC and 75-CCNC, additional diffraction peaks appeared around 44°, 51°, and 76°, corresponding to the (111), (200), and (220) lattice planes of metallic Co (JCPDS No. 04-004-8491) [38] . The presence of these peaks indicates the successful incorporation of metallic Co within the carbon matrix. In contrast, 25-CCNC did not exhibit any Co diffraction peaks, likely due to the absence of ZIF-67-derived CNTs in this sample, which play a crucial role in facilitating the retention and transformation of Co during the carbonization process. Raman spectra for CNF, 25-CCNC, 50-CCNC, and 75-CCNC are shown in Figure 2b , illustrating the structural evolution of the carbon matrix with increasing Co concentration. Two characteristic peaks are evident: the D-band at 1357 cm⁻¹, associated with defects and disorder in the carbon lattice, and the G-band at 1575 cm⁻¹, indicating graphitic sp²-hybridized carbon structures [39] . The intensity ratio of the D-band to the G-band (I D /I G ) reveals insights into the degree of graphitization and defect density within the carbon materials. As the Co concentration increases, the I D /I G ratio decreases, signifying a higher degree of graphitization. This trend can be attributed to the catalytic role of Co during carbonization, where Co reduces the energy barrier for carbon atom rearrangement, facilitating the transformation of amorphous carbon into a more ordered graphitic structure [40] . The catalytic effect is more pronounced at higher Co concentrations, leading to fewer defects and a more ordered carbon structure, thereby reducing the I D /I G ratio [41] . In addition to the D- and G-bands, a small peak near 670 cm⁻¹ is observed in the Raman spectra of Co-containing samples. The enlarged Raman spectrum of 50-CCNC ( Figure S10 ) displays four additional peaks at 470, 517, 615, and 676 cm⁻¹, corresponding to the E g , F­ 1 2g, F­ 2 2g , and A­ 1g modes of the Co₃O₄ crystalline phase, respectively [42],[43] . The presence of these peaks indicates the formation of Co oxide, which originates from the thermal decomposition of the Co precursor, Co(NO₃)₂·6H₂O, during carbonization. Interestingly, while XRD reveals the peaks associated with metallic Co, Raman spectroscopy detects the characteristic signals of Co oxide. This discrepancy arises from the different sensitivities of XRD and Raman spectroscopy; XRD detects the crystalline bulk structure, indicating metallic Co, while Raman spectroscopy is sensitive to surface vibrational modes, revealing the presence of Co₃O₄ [44] , [45] . This suggests that a surface oxide layer forms on the metallic Co particles during carbonization due to the tendency of Co to undergo surface oxidation. Therefore, the coexistence of metallic Co (detected by XRD) and a surface oxide layer (observed in Raman) is confirmed within the sample. The ZIF-67 structure not only facilitates CNT growth but also plays a crucial role in reducing Co ions to metallic Co by creating a localized reducing environment. In the absence of sufficient ZIF-67 to catalyze CNT formation, the carbonization environment becomes less favorable for reducing Co ions, leading to their oxidation and the formation of Co₃O₄ instead of metallic Co. In samples like 50-CCNC, which contain adequate ZIF-67, metallic Co is effectively stabilized due to the local reducing environment established during carbonization. The coexistence of metallic Co and a surface oxide layer, confirmed by both XRD and Raman spectroscopy, underscores the critical role of ZIF-67-derived CNTs in controlling the chemical environment during synthesis. This unique environment not only ensures the stabilization of Co in its metallic form but also promotes the formation of a surface oxide layer that enhances interactions with LiPSs. Therefore, the 50-CCNC structure, with its optimal incorporation of ZIF-67-derived CNTs, emerges as the most effective design for improving LSB performance. The surface chemistry of the synthesized samples was thoroughly investigated using X-ray photoelectron spectroscopy (XPS). The elemental survey spectra of CNF, 25-CCNC, 50-CCNC, and 75-CCNC ( Figure 2c ) confirmed the presence of carbon (C), nitrogen (N), and oxygen (O) atoms across all samples. Notably, cobalt (Co) was detected exclusively in the CCNC samples, indicating the successful incorporation of the Co precursor during synthesis. XPS quantification ( Table S2 ) provided insights into the surface composition, revealing a clear increase in the relative atomic concentration of Co with the rise in Co precursor percentage. Specifically, the atomic percentage of Co progressively increased from 25-CCNC to 75-CCNC, confirming that the surface concentration of Co is directly related to the initial amount of Co precursor used during synthesis. This trend is consistent with the enhanced growth of Co-based structures on the fiber surface, contributing to the distinct surface characteristics of each sample. For a more detailed analysis, high-resolution XPS spectra for C 1s, N 1s, Co 2p, and O 1s were obtained for both 50-ZCP and 50-CCNC ( Figure 2d–i ). The high-resolution C 1s spectrum of 50-ZCP ( Figure 2d ) consists of three subpeaks, including the C–N peak at 283.8 eV and the C–C/C–H peak at 282.75 eV, corresponding to contributions from the ZIF-67 particles and the PAN matrix, respectively. This distribution indicates that the ZIF-67 retains its chemical integrity during the initial stages of synthesis. However, in the 50-CCNC sample, the C 1s spectrum ( Figure 2g ) displayed four peaks, including a new C=N peak at 285.05 eV post-carbonization. This new peak, alongside the existing C=N and C–N peaks at 285.55 eV, confirms successful N-doping into the carbon matrix [33],[46] . N-doping plays a crucial role in enhancing the surface properties of carbon materials by introducing chemical functional groups that can interact with LiPSs, thereby improving polysulfide confinement. The high-resolution N 1s spectra of both 50-ZCP and 50-CCNC ( Figure 2e and h ) reveled multiple N species, including pyridinic N (binding energies at 396.8 and 398.8 eV) and pyrrolic N (397.8 and 401.1 eV) [47],[48] . Notably, the intensity of pyrrolic N increased after carbonization. These N species are significant because pyridinic N and pyrrolic N introduce defect sites on the carbon surface that serve as active centers for the chemical binding of LiPSs [49] . Furthermore, the presence of N species contributes to the overall polarity of the carbon matrix, enhancing its chemical affinity for polar LiPS molecules. This enhanced interaction between the interlayer and LiPSs restricts polysulfide migration, thereby increasing sulfur utilization. Additionally, the emergence of a graphitic N peak at 403.8 eV in 50-CCNC indicates the formation of graphitic N during carbonization. Graphitic N is known to enhance the electrical conductivity of the carbon framework, facilitating improved charge transfer during battery operation [50],[51] . Therefore, N-doping in 50-CCNC serves a dual purpose: it introduces surface defects that act as trapping sites for LiPSs and increases the electronic conductivity of the interlayer, supporting higher electrochemical performance. Notably, similar N species were observed in the N 1s spectrum of CNF ( Figure S11 ), indicating that the N-doping in 50-CCNC largely originates from the CNF precursor [52] . The incorporation of pyridinic, pyrrolic, and graphitic nitrogen into the carbon structure of 50-CCNC contributes to the multifunctional nature of the interlayer. These N functionalities enhance the conductivity of the carbon network and provide active sites for the adsorption of LiPSs, effectively mitigating the shuttle effect. This dual role is crucial for improving the overall electrochemical performance and cycling stability of LSBs. The high-resolution Co 2p spectra of 50-ZCP and 50-CCNC ( Figure 2f and i ) reveal distinct peaks corresponding to Co 2p₁/₂ and Co 2p₃/₂. Deconvolution of these spectra indicates the presence of Co²⁺, Co³⁺, and satellite peaks. The Co²⁺ species primarily originate from the Co precursor, Co(NO₃)₂·6H₂O, while both Co²⁺ and Co³⁺ are primarily contributed by the ZIF-67 structure. In the case of 50-CCNC, the spectra show additional subpeaks, confirming the formation of metallic Co derived from the decomposition of ZIF-67 during carbonization. Furthermore, the Co²⁺ and Co³⁺ peaks in 50-CCNC are attributed to the combined contributions of the decomposed ZIF-67 and heat-treated Co(NO₃)₂·6H₂O [53],[54] . The thermal decomposition of Co(NO₃)₂·6H₂O at temperatures exceeding 473 K results in the formation of Co oxides, specifically Co₂O₃ and Co₃O₄ [55] . The combination of N-doping and various Co species in 50-CCNC is pivotal for enhancing the material’s interaction with sulfur redox reactions. The introduction of these Co species increases the polar surface area of the carbon substrate, facilitating more effective chemical adsorption of LiPSs. This is particularly evident when comparing the XPS spectra of 50-ZCP and 50-CCNC. In 50-ZCP, the detected bonds are associated with PAN, ZIF-67, and Co(NO₃)₂·6H₂O. After carbonization, 50-CCNC exhibits bonds corresponding to CNF, Co₂O₃, and Co₃O₄. Additionally, 25-CCNC and 75-CCNC display similar high-resolution XPS spectra ( Figure S12 and S13 ). However, 25-CCNC lacks the C=N bond in the C 1s spectrum and the metallic Co peak in the Co 2p spectrum due to the absence of ZIF-67 particles on its surface [33] . This absence further emphasizes the critical role of ZIF-67-derived structures in shaping the surface chemistry and electrochemical properties of the interlayers. Furthermore, Brunauer-Emmett-Teller (BET) analysis is essential for understanding the surface area and porosity of interlayers in LSBs [20],[21] . For an interlayer like 50-CCNC, a high surface area and optimized pore size are crucial for enhancing sulfur utilization, facilitating lithium-ion diffusion, and trapping LiPSs [9] . These properties help mitigate the shuttle effect, extend battery cycle life, and improve overall electrochemical performance. In this study, BET was conducted to assess the surface area and pore size distribution of the CNF and the 50-CCNC interlayer. The results reveal that the 50-CCNC interlayer has a BET surface area of 13.84 m² g⁻¹, slightly larger than the 13.53 m² g⁻¹ of CNF. Although this increase in surface area is modest, it signifies an enhancement in the number and accessibility of active sites for LiPS adsorption within the 50-CCNC interlayer, particularly due to its improved pore structure [56],[57] . his slight increase in surface area indicates the successful growth of CNTs on the carbon fibers, resulting in a more porous and interconnected structure. Furthermore, the pore size distribution plays a crucial role in the performance of the interlayer. According to the IUPAC classification, the isotherm of 50-CCNC exhibits a type IV curve with an H3 hysteresis loop in the higher relative pressure range (P/P₀ = 0.5–1.0) [58] , indicating a mesoporous structure. Mesoporosity is particularly important for an interlayer in LSBs as it allows for efficient electrolyte infiltration and ion transport [59],[60] . It also provides sufficient space for the capture and retention of LiPSs, preventing their diffusion to the lithium anode and mitigating the shuttle effect. The pronounced hysteresis loop observed in the 50-CCNC interlayer compared to CNF indicates the presence of additional mesopores ( Figure S14a ). This finding is further supported by the pore size distribution curve ( Figure S14b ), which shows a broader range and greater concentration of mesopores in the 50-CCNC. The total pore volume of 50-CCNC is 0.055 cm³ g⁻¹, nearly twice that of CNF, which has a total pore volume of 0.029 cm³ g⁻¹ ( Table S3 ). This significant increase in pore volume enhances the interlayer’s capacity to trap LiPSs, providing ample space for their adsorption and reducing their migration through the separator. The increased surface area, combined with higher mesoporosity and pore volume in 50-CCNC, signifies its effectiveness as an interlayer in improving the electrochemical performance of LSBs. By offering a more extensive network of active sites for LiPS adsorption and enhancing ion transport pathways, the 50-CCNC interlayer is expected to facilitate better sulfur utilization, mitigate the shuttle effect, and extend the battery’s cycle life. Figure. 2 (a) XRD patterns, (b) Raman spectra, and (c) XPS elemental survey spectrum of CNF, 25-CCNC, 50-CCNC, and 75CCNC. High-resolution spectra of (d, g) C 1s, (e, h) N1s, and (f, i) Co2p of 50-ZCP and 50-CCNC. 2.2 Electrochemical Performance and Rate Capability The electrochemical performance of LSBs was systematically studied using a bare sulfur electrode paired with CNF, 25-CCNC, 50-CCNC, and 75-CCNC interlayers placed between the cathode and separator. The primary function of the CCNC interlayers is to effectively trap LiPSs generated during the cycling of the sulfur cathode, which is expected to be more efficient than the unmodified CNF interlayer ( Figure 3a ). Cyclic voltammetry (CV) measurements were conducted within a potential window of 1.8–2.6 V at a scan rate of 0.1 mV s⁻¹ ( Figure 3b ) to evaluate the redox behavior and kinetics of the interlayers. All LSBs exhibited two pairs of distinct peaks corresponding to the reduction and oxidation processes of sulfur. The reduction peaks at approximately 2.3 V and 2.05 V correspond to the stepwise conversion of elemental sulfur (S₈) into high-order LiPSs (Li₂Sₓ, 4 ≤ x ≤ 8) and eventually into low-order Li₂S₂ and Li₂S. Conversely, the oxidation peaks near 2.3 V and 2.4 V represent the reversible conversion of Li₂S back to elemental sulfur during the charging phase. Notably, the LSBs with 50-CCNC and 75-CCNC interlayers displayed sharper and more distinct peaks compared to those with 25-CCNC and CNF interlayers, indicating enhanced redox kinetics and more efficient sulfur utilization. The sharper peaks suggest more effective trapping of LiPSs and a facilitated sulfur redox reaction [61] , implying that the interlayer composition and structure play crucial roles in stabilizing the intermediate polysulfides and promoting faster electrochemical reactions. Furthermore, the CV curves of 50-CCNC and 75-CCNC exhibited stable peak positions and intensities over five consecutive cycles at a scan rate of 0.1 mV s⁻¹ ( Figure S15) , highlighting the superior electrochemical stability of these interlayers. This stability indicates that they can maintain their structure and functionality during prolonged cycling, which is essential for the practical application of LSBs. While 50-CCNC and 75-CCNC demonstrated superior performance in terms of redox kinetics and cycle stability, all interlayers maintained consistent CV profiles over five cycles, indicating robust structural integrity and reliable performance during repeated cycling. To further investigate lithium-ion diffusion kinetics, CV was conducted at various scan rates ranging from 0.1 to 0.5 mV s⁻¹ ( Figure S16) . The lithium-ion diffusion coefficients (\(D_{\text{Li}}\) ) were estimated using the Randles-Sevick equation [62] : \(I_{\text{peak}}=\ 2.69\ \times\ 10^{5}\ n^{1.5\ }\text{A\ }D_{\text{Li}}^{0.5}\ v^{0.5}\ C_{\text{Li}}\) . (1) In this equation, the slope of the linear fit between the peak current ( I peak ) and square root of the scan rate (v 1/2 ) is proportional to the square root of the lithium-ion diffusion coefficient [63] . The linear fitting of the peak current density (A g -1 ) versus the square root of the scan rate (v 1/2 s -1/2 ) for cathodic peaks A and B, as well as anodic peak C, is presented in Figure S17 , with specific slope values detailed in Table S4 . Among all the samples, 50-CCNC exhibited the highest slope values for all peaks, demonstrating a significant enhancement in lithium-ion diffusion compared with the other interlayers. This improved diffusion is attributed to the synergistic effect of the hierarchical porous structure and the conductive network of CNTs within the 50-CCNC, which promotes rapid ion transport and efficient LiPS adsorption [64] . The presence of CNTs creates interconnected conductive pathways, reducing the internal resistance and facilitating faster kinetics of lithium-ion migration. Further analysis of the galvanostatic charge-discharge profiles was conducted to assess the electrochemical performance of the interlayers. Figure 3c displays the charge-discharge curves of LSBs with and without interlayers (CNF, 25-CCNC, 50-CCNC, and 75-CCNC) at a formation rate of 0.1 C (1.0 C = 1675 mAh g⁻¹) within a voltage range of 1.8–2.6 V. All cells exhibit the characteristic double-plateau discharge pattern, indicative of the multistep reduction process of sulfur [6] . The first plateau at approximately 2.3 V corresponds to the reduction of solid sulfur (S₈) into high-order soluble LiPSs (Li₂Sₓ, where 4 ≤ x ≤ 8), while the second plateau near 2.1 V represents further reduction to low-order, insoluble species such as Li₂S₂ and Li₂S [65] . Notably, the 50-CCNC interlayer achieved the highest specific capacity of 1137.4 mAh g⁻¹ at 0.1 C, highlighting its superior performance in sulfur utilization. Moreover, the length of the 2.3 V plateau, associated with the formation of high-order polysulfides, remained consistent across all samples at approximately 380 mAh/g. However, a significant variation was observed in the length of the 2.1 V plateau, which corresponds to the generation of low-order polysulfides. This variation suggests that a portion of the dissolved high-order polysulfides was captured by the interlayer and continued to participate in the discharge reaction, remaining adsorbed onto the interlayer. The charge-discharge profiles of the 50-CCNC interlayer at varying C-rates (0.1 C to 2.0 C) are shown in Figure S18b . Even at a high C-rate of 2.0 C, the LSBs containing the 50-CCNC interlayer maintained more distinct discharge plateaus compared to those with the CNF interlayer ( Figure S18a ). This observation indicates robust electrochemical performance and efficient sulfur utilization under high current densities. The hierarchical structure of the 50-CCNC, featuring an extensive surface area and an integrated conductive CNT network, plays a crucial role in stabilizing the redox reactions of sulfur, minimizing polarization, and enhancing reaction kinetics. The rate capability of the LSBs was assessed across different C-rates, ranging from 0.1 C to 2.0 C, over every five cycles ( Figure 3d ). Among all tested interlayers, the 50-CCNC interlayer exhibited the highest initial discharge capacity of 1137.4 mAh g⁻¹ at 0.1 C, maintaining excellent rate capabilities of 855.1, 729.8, 640.2, and 537.1 mAh g⁻¹ at 0.2, 0.5, 1.0, and 2.0 C, respectively. The introduction of the CCNC interlayers significantly enhanced the rate capability of the LSBs compared to the bare sulfur electrode, indicating a significant improvement in sulfur redox kinetics and LiPS trapping. The superior rate performance of the CCNC interlayers, particularly the 50-CCNC, can be attributed to several key factors. Firstly, the unique hierarchical structure of the 50-CCNC, comprising a network of uniformly distributed CNTs and embedded Co species (including Co oxides and metallic Co), provides an interconnected conductive framework. This framework facilitates rapid electron and ion transport, reducing internal resistance and polarization within the cell. The combination of CNTs and Co species enhances overall electrical conductivity and catalytic activity, effectively promoting sulfur redox reactions and ensuring high sulfur utilization across various C-rates. Conversely, although the 75-CCNC interlayer contains grown CNTs and Co species, its aggregated morphology, as seen in the SEM image ( Figure 1i ), results in less effective ion transport pathways. The excessive growth of ZIF-67 in the 75-CCNC sample leads to the dense packing and aggregation of CNTs, compromising the interlayer’s porosity and impeding efficient ion diffusion. This aggregation diminishes the interlayer’s ability to effectively trap LiPSs and facilitate the rapid charge-transfer processes necessary for high-rate performance, resulting in relatively sluggish rate capability compared to the 50-CCNC. The exceptional rate performance of the 50-CCNC interlayer is further enhanced by its diverse Co species, including Co oxides and metallic Co, which catalyze sulfur redox reactions, improving reaction kinetics and reducing the overpotential associated with sulfur conversion processes. The N-doping within the carbon matrix provides additional polar sites for LiPS adsorption, thereby mitigating the polysulfide shuttle effect. Furthermore, the synergistic integration of CNTs increases the surface area, providing ample active sites for sulfur redox reactions and LiPS adsorption, thus sustaining high-capacity retention even under high current densities. Collectively, the optimized architecture of the 50-CCNC interlayer—including its enhanced surface area, conductive CNT network, diverse Co species, and N-doping—contributes to its outstanding capacity retention, stability at various rates, and high initial discharge capacity. This synergy underscores the critical importance of the interlayer’s structure and composition in achieving superior electrochemical performance in LSBs. Building on the superior rate performance demonstrated by the 50-CCNC interlayer, the cycling stability of the LSBs was evaluated to further validate the long-term benefits of this interlayer design. Cells were assembled with and without interlayers—specifically, CNF, 25-CCNC, 50-CCNC, and 75-CCNC—and subjected to 400 charge-discharge cycles at a rate of 0.5 C ( Figure 3e ). The results indicate that the LSBs incorporating the 50-CCNC interlayer achieved the highest specific discharge capacity, decreasing from an initial 893.0 mAh g⁻¹ to 762.9 mAh g⁻¹ after 400 cycles. This performance significantly outperformed that of the LSBs with the CNF interlayer, where the discharge capacity dropped from 658.1 mAh g⁻¹ to 570.6 mAh g⁻¹ over the same period. Furthermore, the capacity retention rates for all interlayers remained relatively high throughout the cycling test, with the CNF interlayer retaining 86.7% of its initial capacity, 25-CCNC at 82.4%, 50-CCNC at 85.4%, and 75-CCNC at 82.1%. Among these, the 50-CCNC interlayer exhibited exceptional capacity retention of 85.4%, along with a near-perfect coulombic efficiency of 99.9%. To further assess the interlayer’s performance, additional cycling tests were conducted at a higher current density, with a discharge rate of 2.0 C and a charge rate of 1.0 C ( Figure 3f ). Under these more stringent conditions, the LSB equipped with the 50-CCNC interlayer delivered an initial discharge capacity of 711.3 mAh g⁻¹, which decreased to 607.1 mAh g⁻¹ after 400 cycles, corresponding to an excellent capacity retention rate of 85.3%. Furthermore, this cell maintained an exceptional coulombic efficiency of 100.0% throughout the 400 cycles, indicating highly reversible electrochemical reactions and minimal side reactions. In contrast, the LSB with the CNF interlayer exhibited a significantly lower initial discharge capacity of 438.2 mAh g⁻¹, underscoring the substantial improvements in electrochemical performance provided by the 50-CCNC interlayer. The superior cycling stability and high-rate performance of the 50-CCNC interlayer can be attributed to the synergistic effects of its unique structural and chemical components. The presence of metallic and ionic Co species plays a crucial role in catalyzing sulfur redox reactions, promoting more efficient sulfur conversion and enhancing reaction kinetics. Meanwhile, various nitrogen species (e.g., pyridinic, pyrrolic, and graphitic N) introduce additional active sites for the chemical adsorption of LiPSs, reducing their dissolution into the electrolyte and minimizing the shuttle effect. Additionally, the uniformly distributed CNTs within the 50-CCNC interlayer provide a highly conductive network that significantly enhances both electron and ion transport, reduces internal resistance, and stabilizes the electrode structure during repeated cycling. This robust conductive framework mitigates mechanical stress and structural degradation, contributing to the long-term stability and durability of the LSBs. Collectively, these features enable the 50-CCNC interlayer to achieve high capacity retention, superior rate performance, and excellent coulombic efficiency, significantly enhancing the overall performance and cycling stability of LSBs. Figure. 3 (a) Illustration of the performance of CNF and CCNC interlayers within LSBs. (b) Comparison of CV curves at a scan rate of 0.1 mV s⁻¹ for bare sulfur, CNF, 25-CCNC, 50-CCNC, and 75-CCNC. (c) Galvanostatic charge-discharge profiles at 0.1 C. (d) Rate capabilities of each interlayer. (e) Cycle performance at 0.5 C, and (f) at 2 C discharge rates. 2.3 Surface Morphology of Cycled Lithium Anodes The surface morphology of the lithium metal anode in cycled LSBs, both with and without an interlayer, was investigated using SEM to observe the effects of interlayers on mitigating LiPS shuttling and reducing surface degradation of lithium metal. The SEM images of lithium metal anodes paired with CNF and 50-CCNC interlayers after 25 cycles at 0.5 C are presented in Figure 4a–f . The SEM analysis clearly demonstrates the protective effects of the CCNC interlayer. In LSBs without an interlayer, the lithium anode surface exhibited a rough, cracked morphology ( Figure 4a ), indicative of severe degradation. The cross-sectional SEM image ( Figure 4d ) revealed a thick, porous oxidation layer formed due to continuous side reactions initiated by the shuttle effect, in which dissolved LiPSs migrate between the electrodes. This process of repeated dissolution and redeposition of LiPSs, along with the accumulation of Li₂S and Li 2 S 2 , leads to irregular lithium deposition and the formation of a thick, porous byproduct layer [66],[67] . Interactions between LiPSs and electrolyte additives further exacerbate this degradation, resulting in increased surface roughness and reduced cycling efficiency. In contrast, the introduction of interlayers such as CNF or 50-CCNC significantly mitigated these adverse effects, with the 50-CCNC interlayer demonstrating superior performance. The lithium anode paired with the 50-CCNC interlayer exhibited a much smoother and more uniform surface ( Figure 4c ) compared to that of the CNF interlayer ( Figure 4b ). This smoother morphology indicates that the 50-CCNC interlayer effectively prevents LiPS shuttling, thereby reducing undesirable side reactions and surface corrosion. The cross-sectional SEM image of the lithium anode with the 50-CCNC interlayer ( Figure 4f ) further highlights its protective role, displaying a thinner and more intact oxidation layer compared to both the bare sulfur cell ( Figure 4d ) and the CNF interlayer ( Figure 4e ). This observation underscores the ability of the 50-CCNC interlayer to suppress the formation of thick oxidation layers, effectively preserving the integrity of the lithium metal surface during extended cycling. Additional SEM analysis of the interlayers after 25 cycles at 0.5 C ( Figure S19 ) confirmed the advantageous behavior of Li₂S deposition in the presence of the 50-CCNC interlayer. The fibrous texture of the 50-CCNC interlayer was well-preserved, showing a uniform Li₂S coating on its surface. Notably, the CNTs remained visible even after prolonged cycling, indicating the interlayer’s capacity for continued LiPS capture and suppression of lithium dendrite growth. This preserved structure implies that the 50-CCNC not only facilitates uniform and consistent lithium deposition but also provides an extended active surface for ongoing LiPS adsorption, thus enhancing the cycling stability and performance of the LSBs. Figure. 4 Surface and cross-section SEM images of lithium metal after 25 cycles at 0.5 C for (a, d) without an interlayer (bare sulfur), (b, e) CNF, and (c, f) 50-CCNC. 2.4 Interfacial Resistance and Polysulfide Trapping To evaluate interfacial resistance and the corresponding LiPS trapping capability, the conductivities of the CNF and 50-CCNC interlayers were analyzed using four-point probe measurements ( Table S5 ). The CNF interlayer exhibited a resistance of 135.5 Ω, while the 50-CCNC interlayer showed a significantly lower resistance of 71.8 Ω. This difference translates to calculated conductivities of 0.39 S cm⁻¹ for CNF and 0.68 S cm⁻¹ for 50-CCNC, indicating the enhanced conductivity of the 50-CCNC interlayer. This improvement is primarily due to the growth of CNTs, which form a highly conductive network within the interlayer, facilitating faster charge transport [68] . To gain deeper insights into the charge-transfer kinetics introduced by the interlayers, electrochemical impedance spectroscopy (EIS) was performed on LSBs with three configurations: without an interlayer (bare sulfur), with a CNF interlayer, and with a 50-CCNC interlayer. EIS effectively discerns charge-transfer kinetics by measuring cell impedance across a range of frequencies, differentiating between resistive and capacitive elements associated with electrochemical processes [69] . When an interlayer such as 50-CCNC is introduced, it is expected to reduce charge-transfer resistance and improve lithium-ion diffusion by providing additional conductive pathways and catalytic sites for electrochemical reactions. This improvement is primarily attributed to the CNT network and the catalytic activity of Co species, which are known to lower internal resistance. A smaller semicircle in the high-frequency region and a steeper slope in the low-frequency region of the Nyquist plot typically indicate enhanced charge-transfer and ion diffusion kinetics, respectively [34],[70] . Nyquist plots were obtained for both fresh and cycled cells, and the data were analyzed using an equivalent circuit model ( Figure S20a ). This model includes elements that represent cell and electrolyte resistance (R cell ), as well as components related to ion diffusion and charge transfer at the anode and cathode interfaces (Z w , R an , CPE an , R­ ca , and CPE ca ) [71] . The cell and electrolyte resistance (R cell ) were found to be similar for fresh ( Figure S20b ) and cycled cells ( Figure S20c ) across the bare sulfur, CNF, and 50-CCNC interlayer configurations. This consistency suggests that the interlayers do not impede lithium-ion transport. To further investigate diffusional resistance, the slope of the Warburg region in the Nyquist plot was analyzed, where a steeper slope indicates faster lithium-ion diffusion [72],[73] . While the slopes of freshly assembled cells were comparable, after 10 cycles, the 50-CCNC interlayer exhibited the steepest slope, indicating superior lithium-ion diffusion during cycling. This enhancement can be attributed to the increased surface area and conductive pathways provided by the uniformly distributed CNTs. Additionally, the charge-transfer resistance at the cathode (R ca ) in the fresh LSB with the 50-CCNC interlayer was significantly reduced to 3.129 Ω, compared to 14.33 Ω for the bare sulfur cell and 13.17 Ω for the CNF interlayer. This substantial reduction in R ca results directly from the increased surface area and enhanced electron conductivity imparted by the CNTs in the 50-CCNC interlayer. Overall, the 50-CCNC interlayer exhibited the lowest total resistance among the tested samples, confirming its superior charge-transfer properties. Detailed values for the interfacial resistance components, fitted using the equivalent circuit model, are presented in Table S6 . To further investigate the polysulfide-trapping capability of the interlayers, H-type permeation cells were assembled to visually assess the diffusion behavior of LiPSs. In this setup, the right compartment was filled with pure DME/DOL, while the left compartment contained 0.1 M Li₂S₆ in DME/DOL ( Figure 5 ). Three different configurations were tested: a separator alone, a CNF interlayer with a separator, and a 50-CCNC interlayer with a separator, each placed between the two compartments to separate the solutions. In the cells with only a separator or a CNF interlayer, the right compartment exhibited a distinct color change, turning orangish brown after 10 h, indicating significant polysulfide migration. This result highlights the inability of both the separator and the CNF interlayer to effectively inhibit the polysulfide shuttle effect. In contrast, the cell incorporating the 50-CCNC interlayer showed a much subtler color change, shifting to a light yellow after 10 h, demonstrating its ability to significantly restrict LiPS diffusion. The enhanced polysulfide confinement can be attributed to the structural and chemical properties of the 50-CCNC interlayer, including its higher surface area, the presence of CNTs, and various Co species, which serve as active sites for both chemical adsorption and physical trapping of LiPSs [74],[75] . These observations suggest that the 50-CCNC interlayer provides a more effective physical and chemical barrier against LiPS migration, thereby reducing the shuttle effect. This enhanced polysulfide trapping not only protects the lithium anode but also improves the overall cycling stability of LSBs by minimizing side reactions and preserving electrode integrity. Figure. 5 Image of lithium polysulfide diffusion test over 10 hours using a commercial PP separator, CNF, and 50-CCNC. 2.5 Pouch Stack Cell Performance To further validate the practical applicability of the 50-CCNC interlayer, its performance was evaluated in a stack cell configuration within a Li-S pouch cell exceeding 1 Ah ( Figure 6a ). Stack cell applications are particularly crucial for commercial battery technology because they represent scalable architectures with multiple electrode layers, closely resembling the real-world battery packs used in electric vehicles and portable electronics. Stack cell applications are particularly crucial for commercial battery technology because they represent scalable architectures with multiple electrode layers, closely resembling the real-world battery packs used in electric vehicles and portable electronics. Testing the 50-CCNC interlayer in a pouch-stack cell format introduces a novel and challenging evaluation, as it assesses the effectiveness of the interlayer under high sulfur loading and more demanding conditions for polysulfide trapping. Success in this configuration signifies the potential of the interlayer for integration into high-energy-density, commercially viable Li-S batteries. The galvanostatic charge-discharge performance of the pouch stack cell with the 50-CCNC interlayer was investigated at 0.1 C (1.0 C = 1000 mAh) within a voltage range of 1.7–2.8 V ( Figure 6b ). During the initial cycling, the pouch cell exhibited high discharge capacities of 1140.7 mAh and 1106.8 mAh in the first and second cycles, respectively. These capacities are higher than the theoretical capacity of sulfur, indicating an initial activation process in which excess LiPSs are trapped and stored within the porous structure of the 50-CCNC interlayer. The higher-than-expected capacity is attributed to the ability of the interlayer to effectively confine LiPSs, thus enhancing sulfur utilization and contributing extra capacity from the trapped LiPS electrochemical reactions. These results demonstrate that the 50-CCNC interlayer not only promotes sulfur utilization, but also mitigates the polysulfide shuttle effect, even under the more demanding conditions of a stack cell configuration. To further assess the cycling performance, the Li-S pouch stack cell was cycled for 40 cycles at 0.1 C ( Figure 6c ). The discharge capacity decreased from 1059.7 mAh in the first cycle to 1054.8 mAh by the 40th cycle, resulting in a capacity retention of 99.54%. It also exhibited a high Coulombic efficiency of 95.86% even after 40 cycles. These results indicate that the 50-CCNC interlayer contributes to improved cycling stability and polysulfide trapping in a high-loading stack-cell environment, although challenges related to long-term capacity retention remain. The successful implementation of the 50-CCNC interlayer in a stacked-cell pouch configuration highlights its potential for real-world applications. The novelty of this study lies in the demonstration of the capability of the interlayer to handle the complexities of multilayer electrode stacking, which is critical for the advancement of commercially viable LSBs. Although the interlayer shows promising initial capacity and cycling stability, the observed capacity fading suggests areas for further optimization, especially under the high-loading conditions typical of stack-cell configurations. This study lays the foundation for future research on interlayer design for large-scale, high-energy-density LSBs. To benchmark the long-term stability of our cell relative to recently reported Li-S batteries that employ interlayers, we collected the data summarized in Table S7. Whereas most studies rely on sulfur-carbon composite cathodes, our design employs a simple Sulfur : Super-P : PVDF blend. Despite this minimalist configuration, the cell retains 893 mAhg -1 after 400 cycles at 0.5 C (1.3~1.4 mg/cm 2 ). Many recent Li-S studies assess cells at 0.3 C or lower for fewer than 300 cycles, and the limited reports that test at 0.5 C rarely extended to 400 cycles and generally retain below 700 mAhg -1 . In our work, the cell delivers 893 mAhg -1 after 400 cycles at 0.5 C, indicating that the 50-CCNC interlayer effectively mitigates polysulfide shuttling and maintains electrode integrity without a sulfur-carbon host structure. Figure. 6 (a) Digital Image of the Lithium-Sulfur Pouch Stack Cell. (b) Galvanostatic Charge-Discharge Profiles at 0.1C for the First and Second Cycles. (c) Cycling Performance at 0.1C 40 cycles. 3. Conclusion This study introduced a novel CNT@Co-N-CNF (50-CCNC) interlayer, created through the innovative integration of electrospinning and ZIF-67-derived carbonization. The hierarchical structure of the interlayer, featuring uniformly distributed CNTs, N-doping, and embedded Co species, effectively mitigated the polysulfide shuttle effect in LSBs. This multifunctional design enhanced sulfur utilization and improved cycling stability, outperforming conventional interlayers. Furthermore, the successful demonstration of the 50-CCNC interlayer in a pouch stack cell configuration marked a critical advancement toward practical, large-scale LSB applications. These findings highlighted the significant potential of the 50-CCNC interlayer for developing high-energy-density LSBs, providing a promising path toward commercialization. Future research will focus on optimizing the interlayer’s properties to maximize long-term cycling stability, paving the way for advanced LSB technologies. Supporting Information Supplementary information is available for this paper at https://doi.org/. Supporting information contains the methods, supplementary figures, supplementary discussions, and supplementary references. Acknowledgements This research was supported by National Research Council of Science & Technology (NST) grant by the Korea Government (MSIT) (No. GTL24011-000), and Korea Research Institute of Chemical Technology (KRICT), Republic of Korea Conflict of Interest All authors must declare financial/commercial conflicts of interest. If the authors have no conflicts of interest, this should be stated. References [1] J. B. Goodenough, Y. Kim, Chemistry of materials 2010 , 22 , 587.[2] K. Liu, Y. Liu, D. Lin, A. Pei, Y. Cui, Science advances 2018 , 4 , eaas9820.[3] W. Kang, N. Deng, J. Ju, Q. Li, D. Wu, X. Ma, L. Li, M. 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Information & Authors Information Version history V1 Version 1 08 September 2025 Copyright This work is licensed under a Non Exclusive No Reuse License. Keywords carbon nanofiber interlayers lithium-sulfur batteries polysulfide suppression stack cell pouch Authors Affiliations Seoye Shin Korea Research Institute of Chemical Technology View all articles by this author Dae Kyom Kim Korea Research Institute of Chemical Technology View all articles by this author Jeong Jun Park Korea Research Institute of Chemical Technology View all articles by this author San Moon Korea Research Institute of Chemical Technology View all articles by this author Je-Nam Lee Korea Electronic Technologies Institute View all articles by this author Jong Hyeok Park Yonsei University View all articles by this author Sang-Gil Woo Korea Electronic Technologies Institute View all articles by this author Jungdon Suk 0000-0002-3974-2920 [email protected] Korea Research Institute of Chemical Technology View all articles by this author Metrics & Citations Metrics Article Usage 163 views 77 downloads .FvxKWukQNSOunydq8rnd { width: 100px; } Citations Download citation Seoye Shin, Dae Kyom Kim, Jeong Jun Park, et al. Hierarchically Structured CNT@Co-N-CNF Interlayers for Enhanced Lithium Polysulfide Confinement in Lithium-Sulfur Batteries. Authorea . 08 September 2025. DOI: https://doi.org/10.22541/au.175735026.69439136/v1 If you have the appropriate software installed, you can download article citation data to the citation manager of your choice. Simply select your manager software from the list below and click Download. For more information or tips please see 'Downloading to a citation manager' in the Help menu . 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