## 5 Mechanism for Lithium-Ion Storage in Si-Based Anode Materials  
### Intercalation/De-Intercalation Process  
Regarding the lithium storage mechanism of SiOC, scientists have approached various angles of exploration. The intercalation and de-intercalation processes of lithium-ions  
Figure 10: **(a)** The oxygen-rich SiCNO ceramic demonstrates a higher reversible capacity compared to the nitrogen-rich counterpart. **(b)** First charge/discharge cycles for SiCNO anodes prepared from nitrogen-rich (N/O = 61) and nitrogen-deficient (N/O = 0) specimens. Copied with permission from Elsevier [20].  
are key to the electrochemical performance of polymer-derived ceramic anode materials. During intercalation, lithium-ions first diffuse through the electrolyte to the anode surface and then enter the material's crystal lattice or amorphous structure (Figure 11). [PERSON] [1] suggested that by comparing the capacity differentials of anode materials containing only Si, C, or O elements, the Si-O-C glass phase was confirmed to be the primary source of its reversible capacity. During intercalation, lithium-ions react with silicon, carbon, and oxygen elements in the material to form compounds such as Li\({}_{x}\)Si, Li\({}_{x}\)C, and Li\({}_{x}\)O, which constitute the basis for lithium-ion storage and release. The main lithium-intercalation platform of C/Si-O-C anode material corresponds to the interaction of the same lithium-ions in Si-O-C glass. The Si-O-C glass phase may have different lithium intercalation mechanisms.  
During de-intercalation, lithium-ions are released from the material's crystal lattice or amorphous structure and re-enter the electrolyte. [PERSON] [13] noted that the structural evolution of different silicon units in SiOC ceramics during lithium-ion intercalation and de-intercalation significantly affects the reversibility of lithium-ions. Specifically, the silicon units in the Si-O-C glass phase undergo significant structural changes during lithium-ion intercalation and de-intercalation, directly impacting the material's electrochemical performance and cycling stability [26].  
[PERSON] et al. [61] used NMR for the first time to track the changes of Li before and after cycling in SiOC, demonstrating that SiOC contains three active sites where Li is stored: graphite interlayer or edge, SiOC phase, and micropores. After comparing the intensities of the three peaks, it was concluded that the graphite interlayer or edge is the main lithium storage active site in SiOC.  
Figure 11: (**a**) Atomic configuration evolution within the SiOC matrix during lithiation reveals that the percolating carbon network backbone provides structural stabilization. Full lithiation induces a maximum cell volume expansion of 22%. (**b**) Local structural reorganization accompanying lithiation (depicted in (**a**)) involves: Si–O bond elongation and fracture, geometric distortion of Si–C–C–Si clusters, bond rearrangement within carbon rings. Atomic species are denoted: Si (purple), O (red), C (gray), Li (green). Copied with permission from American Chemical Society [62].  
Additionally, [PERSON] and colleagues [19] used molecular dynamics simulations to study the lithium-ion intercalation and de-intercalation processes in porous silicon embedded in a ceramic matrix. They found that the diffusion and reaction behavior of lithium-ions in the porous structure significantly affects the material's electrochemical performance. These studies indicate that optimizing the material's microstructure and chemical composition is key to improving the electrochemical performance of polymer-derived ceramic anode materials. Moreover, free carbon is also important in lithium storage and the other roles of free carbon will be specifically discussed in Section 6.