Currently, lithium-ion batteries (LiBs) are used for large-scale applications due to their high energy density (150–200 Wh/kg) and high theoretical capacity [1,2]. However, there are limitations when using LiBs for large-capacity energy storage devices such as electric vehicles (EVs) and energy storage systems (ESSs) due to the low energy density and low theoretical capacity of their graphene-based electrodes [3,4]. Among the various nextgeneration batteries, lithium-sulfur (Li–S) batteries may be advantageous due to their high theoretical capacity (1675 mAh/g) and high energy density (about 2600 Wh/kg) [5]. Additionally, sulfur is not only non-toxic and ecofriendly but also abundant, making it possible to manufacture competitive batteries for a low price [6]. However, Li– S batteries still have several limitations that need to be addressed before commercialization [7–9]. First, sulfur has low electrical conductivity. To overcome this issue, highly conductive materials should be synthesized [10]. The energy density of the electrode will be reduced as the conductive materials increase due to the lower proportion of sulfur [11]. Second, Li–S batteries experience significant volume changes during the charging and discharging process. The oxidation-reduction reaction from S8 to lithium polysulfide (Li₂S_x, 4  x  8) leads to continuous volume expansion and contraction during cycling, with an expansion of up to 80% and subsequent contraction during the oxidation reaction [12]. The volume changes create stress within the electrode, which leads to the loss of contact between sulfur and the conductive material, reducing the battery capacity [13,14]. Third, polysulfides easily dissolve in the electrolyte and migrate from the anode to the cathode, which is known as the shuttle phenomenon. This phenomenon can cause a significant loss of the active material, extreme self-discharge, and deterioration of cycle characteristics [3,14].

To address these challenges, researchers have introduced high-conductivity materials such as porous carbon [15,16], carbon nanotubes (CNT) [17], carbon nanofibers (CNF) [18], and graphene-based materials [19] to Li–S batteries. Among them, porous carbon has been particularly effective in improving sulfur conductivity and trapping a large amount of sulfur due to its high specific surface area and pore volume, thereby reducing polysulfide elution [20,21]. Polymer and biomass materials such as SBA (Santa Barbara Amorphous) [22], PVdF (Polyvinylidene Fluoride) [23], banana peels [22], corn cobs [23], bamboo [24], and beans [25] have been used to produce porous carbon. Jun Zhang et al. [26] synthesized the biomass-derived activated carbon with a 3D connected architecture for Li–S batteries. The synthesized electrode shows a high specific capacity of 750 mAh/g at 0.2 C-rate after 100 cycles. Qinghuiqiang Xiao et al. [26] synthesized hierarchical porous carbon and used it as a sulfur host. The synthesized electrode delivered a high initial capacity of 1258 mAh/g at 0.2 C-rate and outstanding cyclic stability. Kenaf is a biomass with a fast growth rate and a high abundance, and it may be a sustainable natural precursor due to its low density, large surface area, and rich porous structure [27,28]. Moreover, the kenaf tree is also very helpful for the global environment because it absorbs nine times more carbon dioxide than pine trees while growing. Coating the surface of the S@KPC composite with polar materials can also effectively adsorb the polysulfides. This can be done with various types of polar materials such as polymers, carbides, and metal oxides. Among them, polyvinylpyrrolidone (PVP) has been used in various industries due to its low toxicity, biocompatibility, adhesive properties, film formation ability, and complex compound formation ability [29]. Guangyuan Zheng’s research team modified the surface of CNF (carbon nanofiber) by adding PVP [30]. At this time, PVP minimized dissolution in the electrolyte by inducing an interaction between non-polar carbon and polar lithium sulfide.

In this study, the kenaf stem was utilized as a micro/mesoporous carbon source. Despite kenaf’s many advantages, little research has been conducted so far to manufacture it into porous carbon and apply it to lithium-sulfur batteries. After activation and carbonation, kenaf porous carbon (KPC) can be used to inhibit polysulfide dissolution and electron channels. To further constrain the dissolution of polysulfides into the electrolyte, a PVP layer was coated on the surface of the S@KPC composite to form a PVP-coated S@KPC composite, as shown in Fig. 1. A double barrier containing PVP coating and KPC ensures that most polysulfides are adsorbed, resulting in excellent electrochemical performance in Li–S batteries. Moreover, the PVP coating layer has a rich oxygenated group, high bonding strength with Li_xS, and a hydrophobic group to hold polysulfide in the carbon matrix. The resultant composite displays a high specific capacity (1228 mAh/g at 0.3 C-rate (PVP-coated S@KPC 1–4)) and good cycling life with a reversible capacity of 632 mAh/g after 100 cycles at 0.3 C-rate.

The synthesis of porous carbon with a high specific surface area and large pore volume is required to enhance the electrochemical performance of Li–S batteries. Thus, by adjusting the NaOH ratio in KC, porous carbon with a high specific surface area and large pore volume was created in this study. The KC was obtained from kenaf stem, and the NaOH activator (1:3, 1:4, and 1:5) was added to the KC to synthesize micro/mesoporous KPC. The specific surface area and pore distribution were analyzed according to nitrogen adsorption-desorption curves, as shown in Fig. 2. KC has a low specific surface area of 195.41 m²/g and a low pore volume of 0.09 cm³/g, as shown in Fig. 2a. The specific surface areas of KPC-3, KPC-4, and KPC-5 after activation were 1365.0, 1936.6, and 2472.7 m²/g, respectively. The degree of volume occupancy according to the diameter of the pores in the porous carbon was analyzed through the BJH method. Fig. 2b&c show the pore distribution in the micro/mesoporous range. The KC, KPC-3, KPC-4, and KPC-5 have micro/mesopores ranging from 0.4 to 10 nm. The maximum volume diameter of the pore is about 2 to 3 nm. Among them, KPC-5 has a high specific surface area (2472.7 m²/g) and a large pore volume (1.40 cm³/g) compared to the other materials. The specific surface area, pore volume, and average pore size were calculated by the BET and BJH methods, as shown in Table 1. These results indicate that the NaOH activation process is suitable for producing porous carbon with high specific surface areas by creating pores in carbide. In addition, the surface area improved as the NaOH activator ratio increased. The volume characteristics of the pores generated by this process are very important in determining the sulfur content of the active material [31,32]. As can be seen from the results of Fig. 2 and Table 1, the KPC-5 sample was considered to have the most suitable pore characteristics for sulfur loading. Therefore, the subsequent experiments and analysis were conducted with only the KPC-5 sample, and KPC-5 was subsequently marked as KPC to simplify the name of the specimen.

The inner shape and PVP coating layer of KPC (KPC-5) and PVP-coated S@KPC 1–4 were analyzed through HR-TEM. EDS was used to analyze the contents and distribution of carbon, sulfur, oxygen, and nitrogen. Fig. 3a–c shows that KPC (KPC-5) had similar results to typical TEM images of porous carbons with micro/mesoporous structures [33]. It was confirmed through EDS analysis that carbon atoms were uniformly distributed at 98.40 at.% on the surface of KPC. However, nitrogen and oxygen were not found in KPC (KPC-5). Fig. 4 shows the HR-TEM and EDS elemental mapping images of PVP-coated S@KPC 1–4. The coating layer of several tens of nanometers cannot be clearly observed in low magnification HR-TEM images, as shown in Fig. 4a. Still, the coating layer (marked red line) can be observed in the high magnification HR-TEM analysis, as shown in Fig. 4b–d. However, the coating layers were observed unevenly because of dissolution and dispersion of the PVP due to the use of ethanol during TEM sampling and agglomeration caused by heat from HRTEM light during HR-TEM analysis, as shown in Fig. 4b–d. The coating layer is analyzed through EDS elemen-tal mapping in low magnification HR-TEM, as shown in Fig. 4e. The outside of the particle is evenly surrounded by carbon, nitrogen, and oxygen, which are constituent elements of PVP (a bright line on the edge of the particle), and also sulfur is evenly distributed and loaded inside the particle. These results show that the PVP was successfully coated on the S@KPC composite. The thickness of the PVP coating layer on the surface of S@KPC according to the PVP weight ratio was analyzed by EDS line file, and the results are shown in Fig. S1. The TEM measurements show that the PVP coating thicknesses for S@KPC 1-3, S@KPC 1–4, and S@KPC 1–5 are approximately 39 nm, 67 nm, and 83 nm, respectively. It is assumed that S@KPC 1–4 and S@KPC 1–5 have an appropriate thickness of PVP layer.

The crystal structure of the synthesized materials was analyzed through XRD, as shown in Fig. 5a, and Fig. S2. The XRD peaks of KC in Fig. 5a correspond to the (002) and (100) planes of the hexagonal graphite structure, and broad peaks (marked “arrow”) around 23o and 44o indicate the existence of a typical amorphous carbon structure [15,16]. After activation, the graphite (002) peak of KPC (KPC-5) is much broader than KC, indicating an increased average interlayer distance and decreased number of stacked layers. The tendency for the (002) peak to disappear becomes stronger with an increasing activator ratio (see Fig. S2). The above result indicates the indiscriminate stacking structure of carbon layers due to carbon consumption by oxygen and Na penetration between the graphitic carbon layers [34]. In the XRD pattern of pure sulfur, several sharp diffraction peaks corresponding to orthorhombic sulfur (S8) are located at 15.5o, 23.3o, 26.1o, 28.1o, and 28.9o [35]. S@KPC, which was synthesized to have sulfur in the pores of KPC, showed a similar pattern to KC. KPC and sulfur were mixed by a physical method and then heat-treated at 155^oC to melt the sulfur and diffuse it into the pores, and heat-treated again at 200^oC to remove sulfur that may have existed on the surface. As a result, no peaks were found at the same position as the elemental sulfur peaks. PVP-coated from that, all the KC, KPC, and S@KPC samples show two typical Raman peaks at around 1343 and 1581 cm^–1, which correspond to disordered carbon (D band) and graphitic carbon (G band) structures, respectively (Fig. 5b) [36,37]. The intensity ratio of D band to G band (I_D/I_G) for KC, KPC, and PVP-coated S@KPC 1–4 is 0.83, 0.91, and 0.89, respectively. The above results indicate the more defective nature of KPC compared to KC, ascribed to the highly porous structure and abundant element doping. The slight changes in the positions of the D (1343 cm^–1 to 1363 cm^–1) and G (1581 cm^–1 to 1595 cm^–1) bands that were observed in the spectrum of the composite are related to the interaction of sulfur with carbon during the heat treatment process.

The FT-IR spectra of the PVP, S@KPC, and PVP-coated S@KPC 1–4 composite are displayed in Fig. 5c. It is clear that the band at 1652 cm^–1 in the case of pure PVP is related to the C=O stretching mode in the pyrrolidone ring. The CH2 absorption band’s C–H asymmetric stretching is seen at 2955 cm^–1. The stretching vibration of O–H is correlated with a strong band at 3498 cm^–1. The vibrations of the C–C stretching mode are responsible for the band at 896 cm^–1. The vibrations of the C–N are represented by the peaks at 1018 cm^–1 and 1291 cm^–1. CH2 bending is visible at the peak at 1450 cm^–1 [38,39]. Sulfur is inert in the infrared, which is why the FT-IR spectra of the S@KPC composite show very few signals. In the case of PVPcoated S@KPC 1–4 composite, the escalation of new peaks after PVP coating strongly confirms the presence of the PVP layer around the S@KPC composite. Moreover, the distinct absorption bands at 1661 cm^–1 and 1471 cm^–1 can be ascribed to the fundamental stretching vibrations of the C=O and C–N bonds in the pyrrole ring, respectively. The broad bands at 1200 and 1040 cm^–1 are associated with the C–N stretching and C–H deformation vibrations, respectively [40]. All these results show that the PVP was successfully coated on the surface of S@KPC and improved the electrochemical performance of the Li-S batteries. It was calculated through the BJH method that the pore volume of the porous carbon synthesized from Kenaf was 1.40 cm³/g. Theoretically, 1 g of porous carbon with a pore volume of 1.40 cm³/g can be loaded with up to about 2.90 g of sulfur, and the weight of sulfur in the composite is about 74 wt%. The temperature-dependent mass change of S@KPC obtained through TGA is shown in Fig. 5d and Fig. S3. Pure sulfur loses weight starting at 156^oC and completely vaporizes at 243^oC. In the case of sulfur present in the pores, the weight loss starts at higher temperatures due to the strong physical adsorption of KPC, and the vaporization rate also slows down. Accordingly, the temperature at which sulfur was completely vaporized in S@KPC increased to 348^oC, and the sulfur content in the pores was measured to be 68 wt%. Compared to the theoretically calculated content, there is a difference of about 6 wt%, which is the 0.03 cm³/g of sulfur content contained in the pores. This volume can be expected to correspond to a very small size pore distribution due to the presence of sulfur. In Fig. 5d, the weight reduction of the PVP-coated sample starts at a slightly higher temperature than that of S@KPC, and the vaporization rate also slows down. This result is because the S@KPC particle has a stronger adsorption capacity for sulfur. After all, a single layer of carbon, nitrogen, and oxygen is wrapped around the S@KPC particle due to the PVP coating. As a result, the sulfur contents of PVP-coated S@KPC 1–3, PVP-coated S@KPC 1–4, and PVP-coated S@KPC 1–5 were 60, 56, and 52 wt%, respectively. Also, at 349^oC, the second weight loss by PVP starts, as shown in Fig. 5d. The TGA result of pure PVP are shown in Fig. S3, which is in good agreement with that of second weight loss, as shown in Fig. 5d. Residual sulfur reacts with PVP and starts to lose weight at a temperature slightly lower than that of PVP. Finally, at 452^oC, the weight reduction rates of PVP-coated S@KPC 1–3, PVP-coated S@KPC 1–4, and PVPcoated S@KPC 1–5 were 64, 63, and 60 wt%, respectively. The weights corresponding to PVP are expected to be 4, 7, and 8 wt%. The PVP-coated S@KPC composites have higher sulfur loading, ensuring the excellent electrochemical performance of the lithium-sulfur batteries.

Fig. 6 shows the FE-SEM images for analyzing the particle shapes of the synthesized KC, KPC (KPC-5), S@KPC, and PVP-coated S@KPC 1–4 composites. Amorphous carbon was obtained by carbonizing the kenaf stem at 800^oC for 3 h, as shown in Fig. 6a. The KC has a particle size of several tens of micrometers and has large pores of about 20 μm. The pores were created by the heating of organic matter by carbonization. After carbonization, the kenaf stem still maintains its cell shape due to its cellulose, hemicellulose, and lignin content. Thermal decomposition at 600 to 800^oC is an important process for synthesizing char, which is a material made by carbonizing cellulose, coconut shells, lignite, and phenolic resin [41]. KC was synthesized into KPC (KPC-5) by performing chemical activation using NaOH as shown in Fig. 6b. The EDS elemental mapping shown in Fig. 6c&d reveals the uniform distributions of C, O, and S, suggesting the homogeneous distribution of sulfur on the S@KPC and PVP-coated S@KPC 1–4 composites and that carbon is dispersed around the sulfur. These results demonstrate that the PVP-coated S@KPC 1–4 nanostructure effectively accommo-dates the sulfur inside the micro/mesoporous carbon.

X-ray photoelectronic spectroscopy (XPS) was used to examine the impact of micro/mesoporous carbon on electrochemical performance. Fig. 7a shows the full XPS spectrum of KPC, S@KPC, and PVP-coated S@KPC 1–4 composites. The main two distinct peaks of C 1s and O 1s are shown in the KPC sample. The C 1s and O 1s were derived from the kenaf stem carbonization process. Extra S 2s and S 2p peaks are observed in the S@KPC and PVP coated S@KPC 1–4 composite after sulfur loading. In the case of PVP coated S@KPC 1– 4, a nitrogen peak (N 1s) was generated due to the polyvinylpyrrolidone coating, and the intensity of oxygen increased while that of sulfur decreased accordingly. The bonding states of carbon, oxygen, sulfur, and nitrogen present in the PVP-coated S@KPC 1–4 composite are shown in Fig. 7b–e. The spectrum of C 1s of PVP-coated S@KPC composite was divided into four individual peaks according to C–C/C=C (284.7 eV), C–O/C=C (286.0 eV), O–C=O (287.1 eV), and C=O/C=N (288.1 eV), as shown in Fig. 7b [42,43]. As seen in Fig. 7c, the O 1s is obtained from the physicochemical adsorption of oxygen during the production process. As seen in Fig. 7d, the S 2p XPS spectra were examined to identify the sulfur molecules' chemical state and distinguish between the different forms of sulfur in Li–S batteries. Due to the spin-orbital coupling effect at 163.6 eV and 164.9 eV, the S 2p spectra of the PVP-coated S@KPC composite are limited to the distinctive sulfur splitting of the S 2p signal into two components, S 2p3/2 and S 2p1/2, which is consistent with S8 molecules [44,45]. The high-resolution N 1s peaks were divided into two peaks C–N (399.8 eV) and graphitic N (400.9 eV), as shown in Fig. 7e [46]. The above results confirm that the N atoms are successfully doped and chemically combined with S@KPC after PVP coating. More active sites can be created by the acquired Natoms in the composite than by the non-doped carbons, and stronger chemical adsorption was produced by the combined effects of the double activation of carbon atoms. Furthermore, it is known that C–N and graphitic N are more active in creating S–Li–N interactions utilizing N lone-pair electrons [25]. The strong interactions alleviate the dissolution of lithium polysulfides into the electrolyte and enhance the redeposition process during the charge-discharge process. The resulting charge delocalization in the PVP-coated S@KPC composite will deliver high conductivity and good electrochemical performance.

An additional experiment was conducted to evaluate the lithium polysulfide adsorption ability of the PVP coating layer of S@KPC. For clear analysis by XPS, a new sample was prepared by coating only PVP on a KPC (weight ratio 1:4) containing no sulfur. Lithium polysulfide solution (Li₂S₆) was prepared by dispersing S (5 mol) and Li₂S (1 mol) in DOL/DME (1:1 vol.%) and stirring on a hot plate at 60^oC for 24 h. The powder for the lithium polysulfide adsorption experiments was obtained by mixing 15 mg of PVP-coated KPC and 35 mL of a lithium polysulfide solution (Li₂S₆), maintaining the mixture for 48 hours, and drying it in an oven. Fig. 8a shows the XPS spectrum of the KPC and PVP-coated KPC after adsorbing the Li₂S₆. This result is similar to that of Fig. 7a. In other words, a new peak of nitrogen appeared, and the intensity of oxygen increased. Thus, the PVP has been coated on the KPC surface successfully. Fig. 8b–f shows the high-resolution XPS spectrum of C 1s, O 1s, S 2p, N 1s, and Li 1s of PVP-coated KPC. The XPS peaks (C 1s, O 1s, and N 1s) after adsorption of polysulfides were similar to the XPS peaks before adsorption of polysulfides (Fig. 7b, c and e). In comparison with before polysulfide adsorption, an obvious new peak at 533.2eV is detected in the O 1 s XPS spectrum after interacting with polysulfide solution (Fig. 8c), agreeing with the Li–O bond [47]. Fig. 8d shows the highresolution S 2p spectrum shows the two major fitting peaks with binding energies around 163.1 and 164.5 eV, ascribing to S 2p_1/2 and S 2p_3/2, correspondingly, a result of the spin-orbital coupling effect [48]. Precisely, the peak at 165.7 eV is attributed to be related to the metal-sulfur bonds, while the peak at 164.5 eV is attributed to sulfide-ion (S2-) in a low coordination state at the surface [49]. Meanwhile, the broad peak at 168.5 eV agrees with the Sat. (S-O(-SOx)), signifying the presence of -SOx species based on the surface oxidation. Likewise, the Li₂S peak was formed with a higher intensity with PVP-coated KPC, which could indicate more efficient lithium polysulfide conversion into lithium sulfides in contrast to the other samples. The Li 1s XPS spectra show richer Li–O (55.9 eV) and Li–S (55.6 eV) peaks [50], representing the chemical bonds formed between the Li₂S₆ and the PVP-coated KPC, as shown in F ig. 8f. Therefore, oxygen and lithium bond to lithium and oxygen at 529.8 (Fig. 8c), and 55.9 eV (Fig. 8f), respectively. These XPS spectral variations further indicate the chemical linking between the PVP-coated KPC and sulfur species. Thus, the PVP coating applied in this study contributes to suppressing the dissolution of lithium polysulfide.

The charge-discharge performance of the pure sulfur, S@KPC, PVP-coated S@KPC 1–4, PVP-coated S@KPC 1–3, and PVP-coated S@KPC 1–5 electrodes is shown in Fig. 9a–c, and Fig. S4a&b. The prepared electrodes show two flat regions in the discharge curve. The plateau at about 2.3 V indicates a reduction in the linear structure of lithium polysulfide (Li₂S_x, 4  x  8) [45]. The plateau at 2.1 V corresponds to the formation of lower monomeric polysulfide (Li₂S_x, x  2). The charge-discharge behaviors of the synthesized electrodes are identical to those of pure sulfur electrodes. At a 0.3 C-rate, the electrodes (pure S, S@KPC, and PVP-coated S@KPC 1–4) show initial capacities of 506, 1289, and 1228 mAh/g and retained capacities of 239, 466, and 632 mAh/g after 100 cycles, as shown in Fig. 9d. The pure sulfur electrode shows a low capacity and capacity retention rate (44%) due to low conductivity, volume expansion during charging-discharging, and the formation of lithium polysulfides. The S@KPC electrode's initial discharge capacity increased by more than twice that of pure sulfur due to the high conductivity of the synthesized KPC. The PVP-coated materials are rich in polar C=O bonds and polysulfide adsorbed by strong chemical adsorption. Fig. S6 shows the capacity retention of S@KPC and PVP-coated S@KPC electrodes. The PVP-coated S@KPC sample exhibits slightly improved capacity retention and higher initial Coulombic efficiency compared to S@KPC, indicating enhanced polysulfide confinement and interfacial stability. This suggests that while KPC provides the primary confinement, PVP contributes to early-cycle stabilization and reduced active material loss. The PVP-coated S@KPC 1–4 electrode displays the best cycling stability and higher specific capacities than the other electrodes. However, the PVP-coated S@KPC electrode exhibited a slight decrease in specific capacity in several cycles due to the formation of the SEI layer. The PVP-coated S@KPC 1–4 electrode displays good stability after 100 cycles and an excellent capacity retention rate (51.5%). By contrast, the pure S, S@KPC, PVP-coated S@KPC 1–3, and PVP-coated S@KPC 1–5 electrodes display lower specific capacities as well as inferior cycling stabilities during the discharge-charge process. Excellent specific capacity, high coulomb efficiency, and good capacitance retention are demonstrated by the PVP-coated S@KPC 1–4 electrode, demonstrating the carbon’s micro/mesoporous structure’s role in suppressing LiPSs. The PVP-coated S@KPC electrodes show better electrochemical performance due to the carbon’s micro/mesoporous struc-ture, which enhances electron transport, ion diffusion, and conversion kinetics. These findings highlight the crucial roles that S@KPC coated in PVP plays in efficiently reducing dead sulfur and the shuttle effect in order to achieve high-efficiency sulfur utilization. The Fig. 9e shows the coulombic efficiency of the prepared electrodes. The effects of the carbon’s micro- and mesoporous structure on the charge transfer resistance and ion diffusion rate were examined using the electrochemical impedance (EIS) and appropriate equivalent circuit designs. As illustrated in Fig. 9f, the PVP-coated S@KPC 1–4 cathode shows a faster charge transfer and sulfur conversion than those of pure S (220.5 Ω), S@KPC (180.4 Ω), PVP coated S@KPC 1–3 (150.2 Ω), and PVP coated S@KPC 1–5 (110.6 Ω) at a high frequency. The lower high-frequency intercept observed for the PVP-coated S@KPC 1–3 sample compared to the S@KPC is attributed to the improved interfacial contact and enhanced ionic conductivity introduced by the PVP coating. PVP is known to be a polar polymer with oxygen- and nitrogen-containing functional groups that can interact with both Li-ions and the surface of the carbon host [51]. This interac#on likely facilitates btter electrolyte we%ng and Li⁺ ion transport at the electrode/electrolyte interface. As a result, the interfacial resistance (reflected in the high-frequency intercept on the Nyquist plot) is reduced. Furthermore, the PVP coating can suppress the formation of resistive interfacial layers by mitigating the polysulfide shuttle effect and promoting more stable electrode-electrolyte interfaces over cycling, which also contributes to the lower resistance observed. Fig. S5 shows the enlarged EIS spectrum of the prepared electrodes. The cathode also displays a lower charge transfer resistance (R_ct) of 100.5 Ω and internal electrical resistance R1 of 10.1 Ω. The redox interactions between the carbon's micro/mesoporous structure and LiPSs on the cathode surface are responsible for the new interface indicated by the internal electrical resistance R1 of 10.1 Ω appearing at the intermediate frequency.

Compared with recently reported Li-S battery electrode materials, the micro/mesoporous carbon derived from the kenaf stems significantly improved cycling performance, as shown in Table 2. The probable details are below. First, the micro/mesoporous structure is consistently dispersed throughout the carbon, and these micro/mesopores deliver an incessant pathway for electron transport. Secondly, the PVP-coated carbon material shows a higher surface area than the KPC to decrease the volume changes. Moreover, the hydrophobic group of PVP generated oxygenated groups to improve the lifespan of the lithium-sulfur batteries through chemical bonding with Li_xS (0 ≤ x ≤ 2). Thus, excellent electrochemical performance was obtained.

In this study, kenaf micro/mesoporous carbon (KPC) was prepared through the carbonization of a kenaf stem and NaOH activation. The specific surface area and pore volume characteristics of the KPC (KPC-5) were 2472.7 m²/g and 1.40 cm³/g, respectively. The sulfur was loaded in the micro/mesoporous carbon through the melt-diffusion method. The KPC imparts conductivity to the non-conductive material of sulfur, so the charge transfer resistance (R_ct) decreased from 220.5 Ω (pure S) to 180.4 Ω (S@KPC). As a result, the initial discharge capacity was improved from 506 mAh/g to 1289 mAh/g. To improve the electrochemical properties of S@KPC, polyvinylpyrrolidone (PVP) was coated on the surface of S@KPC with a thickness of 39 to 83 nm, depending on the PVP ratio with S@KPC. The R_ct of the PVP-coated S@KPC 1–4 electrode (100.5 Ω) was significantly lower than that of the pure sulfur electrode (220.5 Ω). In addition, the initial discharge capacity of PVP-coated S@KPC 1–4 was 1228 mAh/g at 0.3 C, and the capacity retention was 52% after 100 cycles. This result indicates that the micro/mesoporous carbon physically adsorbs polysulfide to its carbon matrix. Moreover, the hydrophobic group of PVP generated oxygenated groups to improve the lifespan of the lithium-sulfur batteries through chemical bonding with Li_xS (0 ≤ x ≤ 2). This work suggests a costeffective and eco-friendly strategy for the development of carbon-sulfur composites for high-performance Li-S batteries.