## 2 Results and Discussion
Our observations indicated that with an increase in the content of free carbon, there was a corresponding gradual rise in the G peak's intensity. The \(\rm I_{D}/I_{G}\) values for CF-25, CF-50, CF-75, and CF-100 were 1.22, 1.80, 1.11, and 1.03, respectively. In addition, the Raman spectrum of pure SiOC with an \(\rm I_{D}/I_{G}\) value of 1.24 is provided in Figure S2. This indicated that Fe could catalyze the conversion of free carbon to graphite carbon in CF, and with increasing free carbon content, the level of induced graphitization was higher. Moreover, a 2D peak attributed to CNTs was observed around 2700 cm\({}^{-1}\). This suggested that Fe catalyzed the development of CNTs from the carbon source during the pyrolysis process of the precursor, which is consistent with the TEM results. Further, an analysis of the specific surface area and pore size distribution curves for the CF series samples was conducted, as illustrated in Figure 2e,f, and the particular data are detailed in Table S1. The CF ceramic materials demonstrated type IV isotherms accompanied by H3-type hysteresis loops, which are indicative of their mesoporous characteristics. As the free carbon content in the ceramics increased, there was an initial rise followed by a subsequent decline in the specific surface area, pore volume, and pore size of the CF materials. This trend was attributed to the introduction of FeAC, which altered the dense cross-linked structure of the precursor, while the decomposition of DVB during pyrolysis increased the release of organic small molecules. However, excessive DVB led to a reduction in specific surface area and pore volume, which might be related to the growth of CNTs in the pores. Notably, CF-75 exhibited a larger specific surface area and mesoporous structure, which makes it promising for offering increased electrochemical activity and accommodating more lithium ions. The atomic structure in the CF material was further analyzed using XPS spectroscopy. Figure S3 shows the XPS full spectra of the CF ceramic materials, where characteristic peaks for C 1s, Si 2s, Si 2p, and O 1s are observable. However, Fe characteristic peaks were not identified, which might be attributed to the low 1% Fe content in the precursor and the encapsulation of metal particles by graphite carbon during CNT growth. Therefore, we focused on the electronic environment of Si 2p and C 1s. Figure 3a-d displays the C 1s fitting spectrum of the CF ceramic materials, which shows five distinct peaks corresponding to C-O, C=O, C-C, C=C, and C-Si bonds, located at 288.8 eV, 286.9 eV, 284.8 eV, 284.3 eV, and 283.1 eV, respectively. With the increase in DVB content, the proportion of C-Si bonds gradually increased, which was due to the rearrangement of more vinyl and phenyl groups with Si atoms during pyrolysis. Additionally, C=C bonds arose from graphitized carbon and CNTs. Furthermore, the composition of different structural units in the CF ceramic materials was analyzed using the Si 2p fitting spectrum shown in Figure 3e-h. Four fitted peaks were located at 104.0 eV, 103.1 eV, 102.1 eV, and 101.2 eV, corresponding to the four structural units of SiO\({}_{4}\), SiO\({}_{3}\)C, SiO\({}_{2}\)C\({}_{2}\), and SiOC\({}_{3}\), respectively [39]. It was observed that the proportion of SiO\({}_{4}\) gradually decreased with increasing DVB content, while the combined proportion of SiO\({}_{3}\)C and SiO\({}_{2}\)C\({}_{2}\) increased, with the CF-75 sample showing the highest proportion. This result is consistent with the C 1s fitting spectrum, and the specific proportions are listed in Table S2. Therefore, it could be confirmed that a higher DVB content promoted the formation of SiO\({}_{x}\)C\({}_{y}\) tetrahedral units within the ceramics. However, an excessive amount of DVB led to a dominant reaction between free carbon atoms, resulting in more free carbon. Under Fe catalysis, this carbon transformed into CNTs, thereby reducing the bonding with Si.