Conversion of LiPSs Accelerated by Pt‐Doped Biomass‐Derived Hyphae Carbon Nanobelts as Self‐Supporting Hosts for Long‐Lifespan Li–S Batteries

Rechargeable Li–S batteries (LSBs) are emerging as an important alternative to lithium‐ion batteries (LIBs), owing to their high energy densities and low cost; yet sluggish redox kinetics of LiPSs results in inferior cycle life. Herein, we prepared multifunctional self‐supporting hyphae carbon nanobelt (HCNB) as hosts by carbonization of hyphae balls of Rhizopus, which could increase the S loading of the cathode without sacrificing reaction kinetics. Trace platinum (Pt) nanoparticles were introduced into HCNBs (PtHCNBs) by ion‐beam sputtering deposition. Based on the X‐ray photoelectron spectroscopy analyses, the introduced trace Pt regulated the local electronic states of heteroatoms in HCNBs. Electrochemical kinetics investigation combined with operando Raman measurements revealed the accelerated reaction mechanics of sulfur species. Benefiting from the synergistic catalytic effect and the unique structures, the as‐prepared PtHCNB/MWNCT/S cathodes delivered a stable capacity retention of 77% for 400 cycles at 0.5 C with a sulfur loading of 4.6 mg cm−2. More importantly, remarkable cycling performance was achieved with an high areal S loading of 7.6 mg cm−2. This finding offers a new strategy to prolong the cycle life of LSBs.

incorporating catalysts in these hosts can further accelerate the conversion kinetics of LiPSs.
In this study, we designed a self-supporting multifunctional sulfur host material of Pt-doped HCNBs/multi-walled carbon nanotube (denoted as PtHCNB/MWNCT).The self-supporting multifunctional HCNBs containing trace N, O, and P heteroatoms were prepared by carbonizing hyphae balls of Rhizopus, and they exhibited good mechanical stability to prevent the structural collapse caused by volume expansion during the charge/discharge process, possessed abundant adsorption sites for anchoring LiPSs to inhibit the shuttling effect, and facilitated rapid ionic diffusion at high S loadings.The PtHCNB composite was prepared by ion-beam sputtering deposition.Inlaying platinum (Pt) nanoparticles (NPs) as a model catalyst on HCNBs modulated the local electronic states of O, P, and N heteroatoms in HCNBs through chemical bonds based on the X-ray photoelectron spectroscopy (XPS) analysis, which could lead to more active sites and accelerate the redox kinetics of LiPSs by synergistic catalytic effects.In addition, the introduction of multi-walled carbon nanotubes (MWCNTs) improved the cathode conductivity.A LSB stability enhancement mechanism was demonstrated based on operando Raman measurements and electrochemical kinetics investigations regarding the polysulfide conversion pathway and precipitation/dissolution behaviors of Li 2 S on the PtHCNB host.The asprepared self-supporting PtHCNB/MWNCT/S cathode exhibited stable cycling performance with a capacity retention of 77% for over 400 cycles at 0.5 C at a high sulfur loading of 4.6 mg cm À2 .Moreover, with this unique electrode structure, a high areal specific capacity of 9.8 mAh cm À2 was achieved at 0.1 C, outperforming reported sulfur hosts materials based on metal oxides/sulfides/nitrides and carbon. [20,21]

Preparation and Characterization of HCNBs
The preparation process of multifunctional self-supporting PtHCNB/S composites is illustrated in Figure 1a.Hyphae of Rhizopus were cultured by inoculation in a solid potato dextrose agar (PDA) medium and amplification in a liquid Sabouraud dextrose broth medium for 2 days to obtain hyphae balls of Rhizopus.The hyphae balls are 5 cm in diameter (Figure 1b) and exhibit 3D cross-linked networks composed of organic hyphae (Figure 1d).Subsequently, self-supporting HCNBs were prepared by freeze-drying (Figure 1c) and carbonizing (Figure 1e).Finally, self-supporting PtHCNBs were obtained by ion-beam sputtering deposition.Crystal structures of the as-prepared samples were characterized by X-ray diffraction (XRD), as shown in Figure S1, Supporting Information.Both HCNBs and PtHCNBs show two broad peaks at 23.6°and 43.0°, indicating the amorphous properties of the biomass carbon species. [22]In addition, no peaks related to Pt NPs were observed in the XRD pattern of PtHCNBs due to the good dispersion and/or a low content of Pt NPs.
Morphologies and microstructures were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM).As shown in Figure 2a-c, the as-prepared PtHCNBs are composed of dense and cross-linked carbon nanobelts with 3-5 lm in width.The TEM image shown in Figure 2d presents that the surface of the carbon nanobelts is smooth without cracks.In addition, they are transparent owing to the ultrathin thickness.In high-resolution TEM image (HRTEM, Figure 2e), the dark spots distributed on the carbon nanobelt originate from Pt NPs with a size of approximately 2 nm.The halo feature of selected area electron diffraction (SAED) patterns (Figure 2f) confirms the amorphous nature of PtHCNBs, which is consistent with the XRD results.The high-angle annular dark fieldscanning transmission electron microscopy (HAADF-STEM) image and the corresponding elemental mappings of the nanobelt are shown in Figure 2g.Signals from C, O, N, P, and Pt are uniformly distributed on the carbon nanobelt surface, confirming the existence of O, N, and P heteroatoms in HCNBs, which can play a crucial role in catalyzing the conversion of LiPSs.The atomic contents of C, O, N, P, and Pt are 76.9 at%, 16.3 at%, 5.13 at%, 1.07 at%, and 0.6 at%, respectively, as shown in Figure S2, Supporting Information, indicating that the incorporation of heteroatoms would give rise to abundant active sites to anchor LiPSs.In addition, the biomass carbon nanobelts are tightly connected into a continuous conductive network for the rapid ion/electron transport in electrochemical reactions, and the porous structure can host a large amount of active S 8 and accommodate the cathode volume change during cell cycling.

Electrochemical performance of PtHCNB/MWCNT/S cathodes
Multi-walled carbon nanotubess were incorporated into HCNB/S and PtHCNB/S composites (denoted as HCNB/MWCNT/S and PtHCNB/ MWCNT/S) after HCNBs and PtHCNBs were mixed with S, respectively.The sulfur content in the PtHCNB/MWCNT/S composite is calculated to be 49.3% by the thermogravimetric analysis (TGA) curve in N 2 atmosphere (Figure S3, Supporting Information).For comparison, the TGA curve of the HCNB/MWCNT/S composite with the same loading is also shown in Figure S3, Supporting Information, and the sulfur content is 46.7%.Rate performance of PtHCNB/MWCNT/S cathodes was investigated at different current densities and a high S loading of 4.6 mg cm À2 , as shown in Figure 3a.Specific discharge capacities for PtHCNB/MWCNT/S cathodes are 1389, 1204, 951, 779, and 635 mAh g À1 at 0.1 C, 0.2 C, 0.5 C, 1 C, and 2 C, respectively, which are much higher than those for HCNB/MWCNT/S cathodes, and the capacity reaches 1363 mAh g À1 when the C-rate is switched to 0.1 C, manifesting remarkable reversibility.It is noteworthy that the two discharge plateaus for PtHCNB/MWCNT/S cathodes are maintained even at 2 C (Figure S4, Supporting Information), indicating PtHCNBs can effectively promote the reaction kinetics and improve the sulfur utilization under high S-loading conditions.It should be pointed out that the rate performance of PtHCNB/MWCNT/S cathodes is superior to other cathodes with similar S loadings (Table S1, Supporting Information), highlighting the advantages of PtHCNB/MWCNT/S cathodes due to the introduced trace Pt.
Cycling performance of the PtHCNB/MWCNT/S cathode was evaluated in comparison with the HCNB/MWCNT/S cathode.As shown in Figure 3b, the initial discharge capacity (1416 mAh g À1 / 6.43 mAh cm À2 ) of PtHCNB/MWCN cathodes exceeds that of HCNB/MWCNT/S cathodes (1159 mAh g À1 /5.26 mAh cm À2 ) at 0.1 C.After 200 cycles, the specific capacity of PtHCNB/MWCNT/S cathodes is 1132 mAh g À1 , corresponding to a capacity retention of approximately 80%, whereas that of HCNB/MWCNT/S cathodes is 735 mAh g À1 with a capacity retention of 63%, revealing that the introduction of Pt catalysts can further alleviate the performance degradation caused by the high S loadings on the basis of HCNB materials.
To further exhibit the stability of the PtHCNB/MWCNT/S cathode, extended cycling performance was evaluated at a high C-rate of 0.5 C.

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As displayed in Figure 3c, the PtHCNB/MWCNT/S cathodes deliver a higher initial capacity of 870 mAh g À1 and maintain a capacity retention of 77% at 0.5 C after 500 cycles compared with HCNB/MWCNT/ S cathodes (713 mAh g À1 and 62%).These results confirm that the diffusion of LiPSs can be effectively inhibited and the utilization of active materials is significantly increased under high S-loading conditions.
The key to commercializing LSBs is to increase the areal S loading to achieve high energy densities.To further reveal the application potential, PtHCNB/MWCNT/S cathodes with a higher S loading of 7.6 mg cm À2 were evaluated.As shown in Figure 3d, PtHCNB/ MWCNT/S cathodes achieve a high initial areal capacity of 9.8 mAh cm À2 (1289 mAh g À1 ) at 0.1 C.After 100 cycles, a capacity of 7.22 mAh cm À2 (953.1 mAh g À1 ) is still maintained, far exceeds the practical requirement of 4 mAh cm À2 for commercial LIBs. [23]The Coulombic efficiency remains as high as 98%-99%.In contrast, HCNB/MWCNT/S cathodes have an areal capacity of 5.7 mAh cm À2 after 60 cycles at the same S loading.More importantly, when the S loading is increased to 15 mg cm À2 , the PtHCNB/MWCNT/S cathodes deliver an initial capacity of 649 mAh g À1 at 0.1 C and maintain approximately 543 mAh g À1 after 70 cycles, revealing a remarkable cycling stability (Figure S5, Supporting Information).
Li-S batteries usually operate in lean electrolytes.Therefore, PtHCNB/MWCNT/S cathodes with a S loading of 4.6 mg cm À2 were assembled at a relatively low E/S ratio of 5 lL mg À1 , and the corresponding performance is shown in Figure S6, Supporting Information.PtHCNB/MWCNT/S cathodes deliver the initial discharge specific capacity of 781 mAh g À1 at 0.1 C and still have a high capacity of 593.4 mAh g À1 after 50 cycles, which is highly competitive with conventional lithium-ion batteries.The S loading and E/S ratio affect the electrochemical performance of LSBs.As the S loading increases, the high utilization of S is remained, although the cycle life and discharge capacity fall slightly due to an increase in resistance caused by the insulating sulfur.Nonetheless, all the cathodes maintain an excellent electrochemical stability.As the E/S ratio decreases, the cycle life and discharge capacity decrease.Figure 3e   PtHCNB/MWCNT/S cathodes are superior to those reported [19,[24][25][26][27][28][29]40] in the cycle number (100 cycles), initial capacity (1289 mAh g À1 ), and areal capacity (9.8 mAh cm À2 ).

XPS Studies Elucidating the Adsorption Capability and the Type of Chemical Bonding in PtHCNBs
It is well known that local atomic environments can modulate the electrocatalytic performance of catalysts.To gain insight into the introduced trace Pt regulating the surface electronic states of PtHCNBs, the chemical bonding in PtHCNBs was analyzed by XPS.For a comparison, XPS spectrum of HCNBs is also presented in Figure 4a.Compared with XPS spectra shown in Figure 4a, a new peak at 530.7 eV appears in O 1s spectrum of PtHCNBs, which can be assigned to Pt-O bonds (Figure 4b). [30]In addition, for the N 1s XPS spectrum, the contents of pyrrolic-N and pyridinic-N increase while that of graphite-N decreases in after introducing the Pt.This is likely because interactions between Pt and graphitic-N result in a conversion of graphitic-N to pyrrolic-N and pyridinic-N.It has been reported that pyrrolic-N and pyridine-N are beneficial to improve the electrochemical performance of LSBs. [31]n particular, pyrrolic-N is more effective than pyridinic-N for enhancing charge transfer and adsorption of LiPSs due to its low carrier scattering and high donor capacity. [10,32]Each pyrrolic-N atom can provide a pair of lone electrons in the aromatic ring of carbon, providing a binding site for the positively charged Li + in LiPSs, thus forming Li 2 S n -N bonds and preventing the dissolution and shuttling effects of Li 2 S n .Moreover, the content of P-O bond at 134.2 eV becomes higher, which is conducive to binding LiPSs (see below).XPS analyses concluded that the local electronic states of O, N, and P heteroatoms are significantly modulated after the introduction of Pt, which can effectively increase the active sites in PtHCNBs and accelerate the redox kinetics of LiPSs.After adsorbing Li 2 S 6 , the high-resolution XPS spectra of O, N, and P atoms exhibit a significant change compared to those before adsorption.As shown in Figure 4c,d, two new peaks at approximately 530.0 eV (Li-O) and 531.5 eV (Li-CO 2 À ) appear in the O 1s spectrum, [33] due to the interaction between Li 2 S 6 and oxygen species on the surfaces of PtHCNBs and HCNBs.Noting that the contents of Li-O and Li-CO 2 À bonds in PtHCNBs are much higher than those in HCNBs (Figure 4e), indicating that the PtHCNBs has a stronger LiPSs adsorption than that of HCNBs.In addition, the pyrrolic-N content in both samples decreases, but the pyrrolic-N decrease in PtHCNBs is Energy Environ.Mater.2024, 7, e12623 significantly more than that in HCNBs (Figure 4f), indicating that PtHCNBs possesses a stronger ability to anchor LiPSs. [34]Furthermore, the relative intensity for the peak of P-O/P-Li bonds increases substantially, whereas that of the P-O bond decreases (Figure 4g), which confirms the formation of the P-Li bond owing to the interaction between the Li atoms in Li 2 S 6 and the P atoms.Moreover, changes in the corresponding content of Li-O, Li-N, and Li-P bonds in the Li 1s spectrum and S-O and S-S bonds in the S 2p spectrum after adsorption further prove the stronger adsorption of PtHCNBs toward LiPSs (Figures S7 and S9a,b, Supporting Information).In addition, as shown in Figure S8, Supporting Information, the Pt 4f spectrum of PtHCNBs can be divided into four characteristic peaks before and after the adsorption.
Two peaks located at 71.3 and 74.7 eV correspond to metal Pt 0 , and the other two peaks at 72.2 and 75.9 eV are attributed to Pt-O bonds. [35,36]After adsorption, the relative intensity of the peaks related to the Pt-O bond increases significantly (Figure S9c, Supporting Information) due to the formation of Pt-S bonds after the strong interaction between Pt atoms and S atoms in Li 2 S 6 . [37]The Pt-O/S peaks have a 0.2 eV shift toward negative binding energies, indicating electron transfer from negative LiPSs to positive Pt, which also demonstrates the strong chemical interactions between LiPSs and Pt.These results further prove that the introduced trace Pt is beneficial to adsorb LiPSs.In addition, it is noteworthy that Pt regulates the local electronic states of N, O, and P heteroatoms, which is conducive to promoting the ability to anchor LiPSs and the catalytic ability to boost LiPSs conversions.

BiDirectional Catalytic Behaviors of Li 2 S Deposition and Oxidation
To elucidate the synergistic catalytic effect, LiPSs conversion reactions were investigated.Symmetric cells were assembled using the same working and counter electrodes in Li 2 S 6containing electrolytes, and the corresponding cyclic voltammetry (CV) curves are shown in Figure S10, Supporting Information.The symmetric cell assembled with PtHCNB/MWCNT electrodes achieves a higher redox current density than that of HCNB/MWCNT electrodes, demonstrating a faster LiPSs conversion.More importantly, the CV curve of the PtHCNB/MWCNT symmetric cell consists of four different redox peaks at a fast scan rate of 10 mV s À1 .Peaks a and b represent the reduction of Li 2 S 6 to Li 2 S on the working electrode, and peaks c and d correspond to the oxidation of Li 2 S to Li 2 S 6 . [38]These peaks cannot be observed in HCNB/MWCNT symmetric cells, confirming that the reversible conversion of LiPSs on PtHCNB/MWCNT can be remained even at high scan rates.
The reversible precipitation-decomposition behavior of Li 2 S is another important indicator to assess the electrocatalytic capability of the electrode materials in LSBs.Nucleation and dissociation of Li 2 S in Li 2 S 8 -containing electrolytes were studied using potentiostatic intermittent titration technique (PITT). [39]The assembled cells were potentiostatically discharged from 2.25 to 2.05 V at 50.0 mV intervals (Figure 5a,c).High-order LiPSs are reduced to low-order LiPSs at high titration potentials above 2.05 V, and the appearance of a broadening peak at 2.05 V represents the Li 2 S precipitation from LiPSs.For the potentials above 2.05 V, the current intensity for the PtHCNB/MWCNT electrode is substantially lower than that for the HCNB/MWCNT electrode after the initial discharge, indicating that the liquid-liquid conversion of LiPSs on the PtHCNB/MWCNT electrode is slow.However, the nucleation peak of Li 2 S is significantly earlier (0.32 9 10 4 s) for PtHCNB/ MWCNT compared with HCNB/MWCNT electrodes (1.37 9 10 4 s), revealing that the redox kinetics of the liquid-solid conversion is fast on PtHCNB/MWCNT electrodes (Figure 5e).The observed difference Energy Environ.Mater.2024, 7, e12623 6 of 10 in the two conversion stages implies Pt is a selective catalyst, which is in line with Hua et al., 44.The nucleation/dissociation capacity of Li 2 S can be calculated by integrating the current density with time at the voltage of peak currents. [40]The nucleation capacities on HCNB/ MWCNT and PtHCNB/MWCNT cathodes are 385 and 561 mAh g À1 (Figure 5g), respectively.Li 2 S dissociation was investigated by potentiostatically charging the cells from 2.2 to 2.5 V at 100.0 mV intervals (Figure 5b,d).As shown in Figure 5f, the Li 2 S dissociation for the PtHCNB/MWCNT electrode occurs at 0.095 9 10 4 s, which is much faster than that for the HCNB/MWCNT cathode (0.15 9 10 4 s), and the PtHCNB/MWCNT cathode shows a high dissociation capacity of 588 mAh g À1 (Figure 5g).This implies that PtHCNB/ MWCNT cathodes can achieve excellent bidirectional Li 2 S redox kinetics.These results strongly demonstrate that the multifunctional self-supporting PtHCNB/MWCNT electrode is conducive to the bidirectional reactions of Li 2 S with the introduction of Pt catalysts and, simultaneously, can promote the rapid conversion from higher order LiPSs to Li 2 S.
To understand the detailed effect of the Pt catalyst on Li 2 S nucleation, we performed a dimensionless analysis of the current-time curves based on the Scharifker-Hills model (Figure S11a, Supporting Information). [41]he nucleation rates of 2D progressive nucleation (2DP) and 2D instantaneous deposition (2DI) are controlled by the crystal phase, while the nucleation rates of 3D progressive nucleation (3DP) and 3D instantaneous deposition (3DI) are mainly determined by ion diffusion, which could greatly improve the nucleation rate of Li 2 S. As shown in Figure S11b,c, Supporting Information, for HCNB/MWCNT electrodes, the nucleation of Li 2 S exhibits a 2DP mode.Distinctly, the Li 2 S nucleation of PtHCNB/MWCNT electrodes shows a 3DI mode, indicating that its Li 2 S nucleation is not affected by the crystal plane, and it is easier to nucleate and grow, which further demonstrates that the addition of the Pt catalyst not only increases the adsorption of polysulfides, but also improves the redox reaction kinetics, and promotes the deposition of Li 2 S.

Redox Reaction Kinetics of Sulfur Species
The redox kinetics of the two cathodes were investigated to manifest the role of synergistic catalytic effects in conversions of sulfur species.Figure 6a shows the galvanostatic charge/discharge (GCD) curves of PtHCNB/ MWCNT/S and HCNB/MWCNT/S cathodes for the first cycle at 0.1 C with a sulfur loading of 4.6 mg cm À2 .Notably, the PtHCNB/ MWCNT/S cathode presents a lower polarization (205 mV) than that for the HCNB/ MWCNT/S cathode (210 mV), which implies the reversible conversion reactions of LiPSs are promoted on PtHCNB/MWCNT cathodes. [42]A transient plateau appears at ~2.3 V owing to the conversion of S 8 to Li 2 S 4 , and the discharge capacity contributed by this plateau is denoted as Q H .A long plateau at ~2.1 V corresponds to the conversion of Li 2 S 4 to Li 2 S, and the discharge capacity provided by this plateau is denoted as Q L .Theoretically, the ratio of Q L to Q H in LSBs is ~3. [43]A higher Q L /Q H ratio demonstrates a more efficient conversion reaction of LiPSs.As presented in Figure 6b, Q H , Q L , and Q L /Q H for the PtHCNB/MWCNT/S cathodes are 363 mAh g À1 , 1053 mAh g À1 , and 2.9, respectively, which are significantly higher than those for HCNB/MWCNT/S cathodes (280.3 mAh g À1 , 797.3 mAh g À1 , 2.8).The high discharge capacities and Q L /Q H for PtHCNB/MWCNT/S cathodes manifest that the PtHCNB/MWCNT hosts can chemically adsorb LiPSs near their surfaces and effectively improve the conversion rate of liquid-solid phases.
To further evaluate the redox reaction kinetics of the PtHCNB/ MWCNT host, CV measurements of PtHCNB/MWCNT/S cathodes were conducted (Figure 6c).During discharging, two reduction peaks Figure 5. PITT curves of a, c) a discharge process from 2.25 to 2.05 V and b, d) a charge process from 2.2 to 2.5 V. Current response in the PITT test at the constant potentials of e) 2.05 V in the discharge process and f) 2.4 V in the charge process.g) Specific capacities of Li 2 S nucleation and dissociation.
Energy Environ.Mater.2024, 7, e12623 (Peak I and Peak II) in CV curves represent the reduction of S 8 to Li 2 S 4 and then to Li 2 S. For charging, the oxidation peak (Peak III) is attributed to the conversion from Li 2 S to Li 2 S n and finally to S 8 .Compared with HCNB/MWCNT, PtHCNB/MWCNT cathodes have a smaller overpotential with a significantly positive shift for Peak II and negative shift for Peak III (Figure S12a, Supporting Information), indicating that the coexistence of heteroatoms leads to synergistic catalytic effects after the introduction of the trace Pt catalyst. [44]Figure S12b, Supporting Information, displays that the Peak I position for PtHCNB/MWCNT/S cathodes shows a negative shift compared with HCNB/MWCNT/S cathodes, indicating the conversion of S 8 to Li 2 S 4 is slow, attributed to the incorporation of the Pt.In other words, the introduced trace Pt results in a slow conversion of Li 2 S 8 to Li 2 S 4 but accelerates the reduction of Li 2 S 4 to Li 2 S. Additionally, the oxidation peak shifts to lower voltages (Figure S12c, Supporting Information), suggesting the bonding of Pt with Li 2 S weakens Li-S bonds in the Li 2 S and boosts the oxidation reaction of Li 2 S to S 8 .
Tafel slopes are critical to assess the reaction kinetics and catalytic activity. [45]Figure 6e shows the Tafel slopes for the two cathodes.For the reduction process of S 8 to Li 2 S 4 , the Tafel slopes for HCNB/MWCNT/S and PtHCNB/MWCNT/S cathodes are 124 and 144 mV dec À1 (Figure S13a, Supporting Information), respectively, indicating that the PtHCNB/MWCNT/S cathodes have a slower conversion of S 8 to Li 2 S 4 compared with HCNB/MWCNT/S.For the Li 2 S 4 to Li 2 S reduction process (Figure 6d), the Tafel slope of PtHCNB/MWCNT cathodes (47 mV dec À1 ) is smaller than that of HCNB/ MWCNT/S cathodes (64 mV dec À1 ), which is because the synergistic catalytic effect of Pt, O, N, and P heteroatoms in the PtHCNB/ MWCNT host can effectively accelerate the Li 2 S 4 to Li 2 S conversion.During the oxidation process, the PtHCNB/MWCNT/S cathode presents a smaller Tafel slope of 279 mV dec À1 (Figure S13b, Supporting Information), indicating its fast reaction kinetics for Li 2 S to S 8 .The PtHCNB/MWCNT/S cathode clearly demonstrates its bidirectional catalytic effect on enhancing the conversion between S 8 and Li 2 S owing to the synergistic catalytic effect of Pt, O, N, and P heteroatoms.
To monitor the sulfur redox reactions in real time and provide detailed insights into the polysulfide conversion pathway and the precipitation/dissolution behaviors of Li 2 S on PtHCNB/MWCNT host, operando Raman spectroscopy was employed.PtHCNB/MWCNT/S electrodes were assembled into an operando Raman cell and the corresponding operando Raman spectra were tested using laser with a wavelength of 488 nm, as shown in Figure 6f.During the discharging process, the Raman peaks from S 8 were first detected at 80, 146, 213, and 466 cm À1 at the open-circuit voltage (OCV).And then, three new peaks at 398, 446, and 503 cm À1 can be clearly observed at 2.26 V, corresponding to the formation of Li 2 S n . [46]hen the voltage dropped to the second plateau (~2.1 V), the intensities of the three peaks began to decrease significantly.When it reached 1.7 V, operando Raman signals of the three peaks completely vanished, which is consistent with Zhao et al. [39] For comparison, the operando Raman spectra of HCNB/MWCNT/S cathodes are also shown in Figure S14, Supporting Information).The three peaks at 398, 446, and 503 cm À1 appeared at 2.28 V.These signals were clearly observed at 1.7 V.For the charge process in PtHCNB/MWCNT cathodes, Li 2 S is rapidly and completely converted to soluble Li 2 S n due to the incorporation of the Pt catalyst, and S 8 could be detected when the cathodes were charged to 2.5 V.The conversion was completed at 2.8 V for PtHCNB/MWCNT cathodes.However, weak signals from Li 2 S n were remained at 2.8 V for HCNB/MWCNT/S cathodes.Compared with HCNB/MWCNT cathodes, it is concluded that i) S 8 is strongly adsorbed on the PtHCNB/ MWCNT/S cathode, which results in slower conversion from S 8 to Li 2 S 4 and then rapider conversion from Li 2 S 4 to Li 2 S due to the selective catalysis of Pt [44,47] ; ii) the oxidation reaction of sulfur in the PtHCNB/ MWCNT/S cathode is accelerated due to the existence of the Pt catalyst.These findings are in perfect agreement with the Tafel and XPS analyses.

Conclusions
In summary, a biomass-derived multifunctional self-supporting electrode through chemical bonds were successfully prepared by freezedrying and carbonizing hyphae balls of Rhizopus.The self-supporting PtHCNB thin film is an ideal current collector with excellent electronic/ ionic conductivity and provides sufficient constraint for high sulfur loadings.More importantly, the incorporation of trace Pt NPs significantly regulates the local electronic states of O, N, and P heteroatoms, which gives rise to a synergistic catalytic effect on LiPSs conversions.The as-prepared cathodes effectively catalyze the conversion of LiPSs and accelerate the redox kinetics of sulfur species, which leads to the enhancement in battery performance of LSBs under high sulfur loadings.The mechanism was investigated using XPS and operando Raman analyses.Assembled full LSBs achieved a high areal capacity of 9.8 mAh cm À2 at 0.1 C, and the capacity of 7.3 mAh cm À2 was maintained after 60 cycles, exhibiting the excellent cycling stability.This finding provides a new sulfur host material design strategy with synergistic catalytic effects from heteroatoms to accelerate the redox reaction kinetics of sulfur species and enhance the cycle life of LSBs.

Experimental Section
Culture of hyphae balls of Rhizopus: Hyphae balls of Rhizopus were cultivated through a biological inoculation and amplification process.Rhizopus was inoculated into a solid potato dextrose agar medium (PDA solid medium) and cultured for 48 h in an incubator with the constant temperature of 28 °C.The cultured Rhizopus hyphae was inoculated into a liquid Sabouraud dextrose broth medium (SDB liquid medium) and transferred to a shaker at 28 °C with 130 r min À1 for 24 h.Subsequently, the rotation speed was increased to 155 r min À1 for 24 h.The preparation method of the culture medium is shown in Table S2, Supporting Information.
Synthesis of HCNBs: Hyphae balls of Rhizopus were soaked in absolute ethanol and washed to neutral by deionized water.The washed hyphae balls of Rhizopus were freeze-dried for 2 days.The HCNBs with self-supporting structures were obtained by annealing the freeze-dried hyphae balls at 800 °C for 2 h under N 2 .
Synthesis of PtHCNBs and PtHCNB/MWNCT/S: The PtHCNBs were obtained by spraying Pt onto the surface of HCNBs using a sputter coater.The direct growth of Pt nanoparticles on HCNB materials were carried out by sputtering the corresponding Pt target by argon ions with an energy of 0.8 keV and an ion beam current density of 0.15 mA cm À2 at a residual atmosphere pressure that was no higher than 10 À2 Pa.The growth time for Pt was 30 s.To prepare the PtHCNB/MWNCT/S cathode, commercial sulfur was dissolved in a carbon disulfide solution (CS 2 ), and PtHCNBs were placed in CS 2 and heated at 45 °C until the CS 2 disappeared completely.The PtHCNB/S was sealed in a stainlesssteel container and heated to 155 °C for 12 h, and a MWNCT solution was filtered into the PtHCNB/S to obtain PtHCNB/MWNCT/S cathodes.The areal mass loading of sulfur was approximately 4.6-15 mg cm À2 .The HCNB/MWNCT/S cathodes were prepared by the same process.
Assembly of symmetric cells: Symmetric cells were assembled in the absence of S. The host material was used as the electrode.The electrolyte was 80 lL of 0.5 M Li 2 S 6 and 1 M LiTFSI with 0.2 wt% LiNO 3 as an additive in DOL/DME (v/ v = 1/1).

Potentiostatic intermittent titration technique test:
The Li 2 S 8 (0.5 M) solution was prepared by mixing Li 2 S and S 8 in a tetraglyme solvent with a molar ratio of 1:7.HCNBs and PtHCNs were used as a cathode, and Li metal was used as an anode.A total quantity of 50 lL of the electrolyte containing Li 2 S 8 was dropped onto the cathode side and 20 lL of the routine electrolyte was dropped onto the anode side.Finally, the assembled cells were potentiostatically discharged from 2.25 to 2.05 V at intervals of 50.0 mV, followed by charging from 2.2 to 2.5 V at intervals of 100.0 mV.
In operando spectroscopy: The operando Raman cell with a quartz window and a hole on the stainless steel were assembled with PtHCNB/MWCNT/S cathodes, lithium anodes, and porous polypropylene (Celgard 2400) separators.The cathodes (sulfur loading: 4.6 mg cm À2 ) were tested at a rate of 0.1 C, using the laser line of 488 nm.Each spectrum was acquired for 20 s.
Electrochemical measurements: The electrolyte was 1 M LiTFSI and 2.0 wt% LiNO 3 in a mixture of DOL/DME (v/v = 1:1).CR2025 coin cells were assembled with lithium anodes and porous polypropylene (Celgard 2400) separators in an Ar-filled glovebox.The E/S ratio of all cells is 20 lL mg À1 .GCD was tested on a LANCT battery test system with a voltage window of 1.7-2.8V. CV measurement was performed by a VMP3 multichannel electrochemical workstation (BioLogic, France) at a voltage range of 1.7-2.8V with a scan rate of 0.1 mV s À1 .
shows a Radar chart comparing PtHCNB/MWCNT/S with cathodes reported recently (2021-2022) based on LSB parameters as follows: a) number of cycles, b) initial capacity, c) sulfur loading, d) areal capacity, and e) rate performance.

Figure 1 .
Figure 1.a) Schematic illustration of the preparation process of PtHCNB/S composites.b) Digital photo of a hyphae ball in a liquid medium.c) Rhizopus hyphae slice after freeze-drying.d) Microscopic morphology (magnification by 200 times) of c).e) Rhizopus hyphae slice after carbonization.

Figure 2 .
Figure 2. a-c) SEM images of PtHCNBs at different magnifications.d) TEM image, e) HRTEM image, and f) SAED pattern of PtHCNB.g) HAADF-STEM image and the corresponding elemental mapping images of the PtHCNB.

Figure 3 .
Figure 3. a) Rate performance of HCNB/MWCNT and PtHCNB/MWCNT cathodes at different rates.Cycling performances of HCNB/MWCNT and PtHCNB/ MWCNT cathodes b) at 0.1 C and c) at 0.5 C. d) Cycling performance of HCNB/MWCNT and PtHCNB/MWCNT cathodes with a sulfur loading of 7.6 mg cm À2 at 0.1 C. e) Radar chart comparing the performance of the PtHCNB/MWCNT/S cathode with previously reported cathodes.

Figure 6 .
Figure 6.a) GCD profiles with a sulfur loading of 4.6 mg cm À2 at 0.1 C. b) Values of Q H , Q L , and Q L / Q H obtained from a). c) CV curves of different cathodes at 0.1 mV s À1 .d) Tafel slopes corresponding to the reduction of Li 2 S 4 to Li 2 S. e) Comparison of Tafel slope values for different cathodes.f) Operando Raman spectra of PtHCNB/MWCNT/S cathodes during the first cycle at 0.1 C.