To characterize the microstructural features of the prepared MoO3/T-CNF composite aerogels, SEM was employed to observe different samples. As shown in Fig. 2, compared to the smooth surface of pure T-CNF aerogel (Figure S1), significant changes in the pore structure and surface roughness were observed in the MoO3/T-CNF composite aerogels with varying ratios of MoO3 and T-CNF. As shown in Fig. 2a-c, when the proportion of MoO3 increases and the proportion of T-CNF decreases, the porosity of the aerogel increases and the surface becomes rougher. This is attributed to the uniform spatial structure formed by the increased MoO3 nanosheets and T-CNF, which prevents excessive accumulation caused by T-CNF. However, when there is an excessive amount of MoO3 nanosheets, the enrichment of MoO3 in the aerogel may result in reduced porosity and blockage of the porous structure, as shown in Fig. 2d. Furthermore, as observed in Figure S2, the volume change of the prepared aerogel material is minimal before (a) and after (b) annealing. This intuitively proves that carbonization does not cause the material collapse.

Furthermore, in Fig. 3a, infrared spectroscopy analysis of MoO3 nanosheets and MoO3/T-CNF-3 aerogel reveals that stretching vibration peaks of the C-O-C bonds in the cellulose pyranose ring (1042 cm− 1) and the stretching vibration peaks of Mo-O-Mo in MoO3 (889 cm− 1) can be simultaneously detected in the infrared spectrum of MoO3/T-CNF-3 aerogel, indicating the successful composite of MoO3 and T-CNF[39]. To delve deeper into the pore structure characteristics of the prepared material, we began by assessing its specific surface area using nitrogen adsorption-desorption testing. As shown in Fig. 3b, compared to the pure T-CNF (105.50 m2/g) aerogel, the MoO3/T-CNF-3 aerogel exhibits a significantly higher specific surface area of 297.54 m2/g. This is attributed to the increased intermolecular interactions upon the introduction of MoO3, which effectively prevents the aggregation of nanoscale fiber materials. The linear T-CNF nanowires and planar MoO3 nanosheets form a cross-linked structure, greatly enhancing the surface area and mechanical strength. In contrast, pure T-CNF shows a limited specific surface area because of the clustering of nanowires.

To further confirm the successful formation of the composite of MoO3 and T-CNF, we conducted X-ray diffraction (XRD) analysis on MoO3/T-CNF-1, MoO3/T-CNF-2, MoO3/T-CNF-3, MoO3/T-CNF-4, MoO3, and T-CNF, and the results are plotted in Fig. 4. The analysis revealed distinct MoO3 characteristic peaks at 12.8°, 23.4°, 25.7°, 27.4°, and 39.0° in the prepared composite aerogels, with the peak intensities gradually increasing with the increased amount of MoO3 doping. Additionally, the broad peak around 22.8° signifies the successful integration of MoO3 and T-CNF within the MoO3/T-CNF aerogel.

Furthermore, X-ray photoelectron spectroscopy (XPS) was employed to determine the elemental composition of the composite aerogel films and analyze the composite of MoO3 nanosheets and T-CNF in the MoO3/T-CNF-3 aerogel (Fig. 5). It is well known that cellulose is composed of a series of glucuronic acid units, which are connected through dehydration at the 1st and 4th positions, resulting in the presence of C-O and O-C-O bonds in the cellulose monomer. However, the appearance of a new C = O bond in the characteristic peak of C1s in Fig. 5b indicates the selective formation of numerous C6 carboxylic acid groups on the surface of nanocellulose through TEMPO-mediated oxidation [118]. As shown in Fig. 5a, characteristic peaks of Mo are observed in the MoO3/T-CNF-3 aerogel, and further confirmation of the successful preparation of the MoO3/T-CNF composite aerogel is obtained through fitting analysis of the characteristic peaks of O1s (Fig. 5c) and Mo3d (Fig. 5d), which is consistent with the XRD and FTIR analyses mentioned above.

To investigate the electrochemical performance of the prepared materials, a series of tests were conducted. As shown in Fig. 6a, cyclic voltammetry (CV) measurements were performed on the cathode materials of T-CNF and MoO3/T-CNF aerogels. The CV curves of T-CNF, MoO3/T-CNF-1, MoO3/T-CNF-2, MoO3/T-CNF-3, and MoO3/T-CNF-4 electrode materials after three cycles (Fig. 6a) exhibit distinct oxidation-reduction peaks, indicating the redox reactions and transformations between elemental sulfur, polysulfides, and lithium sulfides. Notably, the integrated area of the CV curve for MoO3/T-CNF-3 is greater than that of the other materials, demonstrating the superior energy storage performance of the MoO3/T-CNF-3 composite aerogel among these electrode materials.

Subsequently, galvanostatic charge-discharge (GCD) tests were conducted on the cathode materials of T-CNF and MoO3/T-CNF aerogels at rate ranging from 0.1C to 2C, and the results are shown in Fig. 6(b-f). It can be observed that the voltage drop of the charge-discharge curves for MoO3/T-CNF-3 is relatively small, indicating longer discharge time and absence of significant polarization, demonstrating strong reaction kinetics. Due to the stable porous structure of MoO3/T-CNF-3 and effective anchoring of polysulfides at high current density, even at a rate of 2C, the discharge plateau remains distinct and stable. In addition to the GCD test at low rate, the test at high rate is also a characterization method to prove its excellent electrochemical performance. Therefore, as shown in Figure S3, galvanostatic charge-discharge tests (GCD) from 0.1C to 5C were performed on T-CNF (Figure S3a) and MoO3/T-CNF-3 (Figure S3b) aerogel electrode materials. When the rate is greater than 2C, the discharge time of MoO3/T-CNF-3 aerogel electrode material was still significantly better than that of T-CNF material, which proves the excellent electrochemical performance of MoO3/T-CNF-3 aerogel electrode material.

In Fig. 7a, the rate performance test of T-CNF and MoO3/T-CNF aerogel electrode materials at ranging from 0.1C to 2C demonstrates the superior reversible discharge specific capacity of the prepared MoO3/T-CNF-3 material, indicating its improved performance. At a rate of 0.1C, the reversible discharge specific capacity of MoO3/T-CNF-3 (1721.8 mA h/g) is significantly higher than that of T-CNF (776.7 mA h g− 1), MoO3/T-CNF-1 (1007.2 mA h g− 1), MoO3/T-CNF-2 (1222.8 mA h g− 1), and MoO3/T-CNF-4 (1188.1 mA h g− 1). Furthermore, for each electrode material, the reversible discharge specific capacity decreases as the current density increases, which is attributed to insufficient reaction at the electrode-electrolyte interface under high current density. Upon returning to a rate of 0.1C, the reversible discharge specific capacity of the electrode material recovers to its original level. This excellent performance is mainly attributed to the porous aerogel material's high adsorption efficiency, facilitating rapid lithium-ion transport and effective anchoring of polysulfides, thereby enhancing the kinetics of the redox reactions.

Furthermore, in Fig. 7b, the rate performance of T-CNF and MoO3/T-CNF-3 aerogel electrode materials at higher current densities were tested. The reversible discharge specific capacity variation is similar to that shown in Fig. 8a, confirming the excellent stability of the MoO3/T-CNF-3 aerogel electrode material.

Electrochemical impedance tests were carried out to analyze the conductivity of T-CNF and MoO3/T-CNF composite electrode materials, the result was shown in Fig. 8a. In the high-frequency region, the intercept on the real axis represents the internal resistance (Rs) of the battery. From the graph, the internal resistances of T-CNF, MoO3/T-CNF-1, MoO3/T-CNF-2, MoO3/T-CNF-3, and MoO3/T-CNF-4 aerogel cathodes are determined to be 2.2 Ω, 5.9 Ω, 7.6 Ω, 3.1 Ω, and 2.9 Ω, respectively. Among which, the MoO3/T-CNF-4 aerogel cathode displays the lowest internal resistance due to increased incorporation of MoO3. This reduction decreases the ohmic resistance of the cathode material and enhances electronic conductivity.

In the mid-frequency range, the semicircle illustrates the rate of charge transfer at the electrode-electrolyte interface, which correlates with the charge transfer resistance (Rct). Among the T-CNF, MoO3/T-CNF-1, MoO3/T-CNF-2, MoO3/T-CNF-3, and MoO3/T-CNF-4 aerogel cathodes, the MoO3/T-CNF-3 aerogel cathode shows the lowest charge transfer resistance. While Rs value of the MoO3/T-CNF-3 aerogel cathode isn’t the lowest, its superior ion transport structure and uniform coating contribute to a favorable pathway for rapid charge transfer at the electrode interface. This is also due to the high specific surface area and enhanced wetting effect of the MoO3/T-CNF-3 aerogel cathode.

In the low-frequency region, the corresponding diagonal line reflects the diffusion process of lithium ions within the electrode, corresponding to the Warburg impedance (Wo). The consistent coating structure of MoO3 in the MoO3/T-CNF-3 aerogel significantly enhances the speed of charge transfer at the interface and the diffusion pathway of ions.

Cycle performance of T-CNF and MoO3/T-CNF composite electrode material was shown in Fig. 8b. The discharge specific capacities of T-CNF, MoO3/T-CNF-1, MoO3/T-CNF-2, MoO3/T-CNF-3, and MoO3/T-CNF-4 aerogel cathodes at 0.1 C are 776.6, 1060, 1277.9, 1511.6, and 1116.8 mA h g− 1, respectively. Following 200 cycles, the MoO3/T-CNF-3 aerogel cathode continues to sustain a capacity of 1282.4 mA h g− 1, with a coulombic efficiency of 99.6%. In contrast, the pure C-CNF aerogel exhibits a capacity of only 17.1 mA h g− 1 after 200 cycles, significantly lower than that of the MoO3/T-CNF-3 aerogel. This indicates that the combination strategy of spatial structure and strong adsorption sites effectively enhances the cycling stability of lithium-sulfur batteries.