### Si-Based Polymer-Derived Ceramics  
Si-based polymer-derived ceramics is a new category of advanced ceramics produced via pyrolysis of organosilicon polymers which has been developed in the early 1960s. Owing to structural and functional superiorities as well as their ability for being shaped by various processing techniques, people gradually pay more attention to the progress of polymer--derived ceramics. The number of publications resulting from a search with the key word \"polymer derived ceramic\" from 1 January 2000 to 10 May 2025 is shown in Figure 2. The most known classes of PDCs are in the binary systems Si\({}_{3}\)N\({}_{4}\), SiC, BN, and AlN, ternary systems SiCN, SiCO, and BCN as well as in the quaternary systems SiCNO, SiBCN, SiBCO, SiAlCN, and SiAlCO. In recent years, several pentanary systems of PDCs (e.g., SiHfBCN, SiHfCNO) have been reported as well [18; 26].  
Polymer derived Si-based ceramics exhibit several beneficial properties for application as anode materials in lithium-ion batteries. They are chemically inert with respect to battery components and are lightweight materials. In addition, they are able to minimize the agglomeration of lithium ions. Importantly, the chemical and physical properties of the PDCs can be tailored via tuning the molecular structure of starting polymers and/or controlling the thermal treatment parameters. The preparation of silicon-based polymer-derived ceramics (PDCs) typically involves three steps: (1) synthesis of Si-containing preceramic polymers; (2) shaping and crosslinking (100-400 \({}^{\circ}\)C); (3) polymer-to-ceramic transformation (400-1400 \({}^{\circ}\)C). After polymer-to-ceramic conversion, the PDCs are generally amorphous (Figure 3) [18]. Upon annealing at higher temperatures (\(\geq\)1400 \({}^{\circ}\)C), they will transform into (poly)crystalline ceramics [27]. Two typical polymer-derived ceramics are silicon oxycarbide (SiOC) and silicon carbonitride (SiCN), both of which possess unique microstructures not commonly found in other ceramic materials. SiC is typically amorphous, with Si atoms tetrahedrally coordinated by O and C atoms. The microstructure of amorphous SiCN ceramics is primarily influenced by the molecular structures of the preceramic polymers. The key difference between amorphous SiCN ceramics is whether there are Si-C/N mixed bonds (the presence of SiCxNy units) in the ceramic matrix or  
Figure 1: A schematic representation of the different reaction mechanisms observed in electrode materials for lithium batteries. Black circles: voids in the crystal structure, blue circles: metal, yellow circles: lithium. Copied with permission from the Royal Society of Chemistry [25].  
not (27). Due to their physical-chemical and functional properties and their capabilities of being shaped using lots of processing ways, PDCs have the broad application potential in the field of lithium-ion batteries. However, PDCs remain far from practical applications due to persistent challenges such as low initial coulombic efficiency and an incompletely understood lithium storage mechanism. To address this knowledge gap, this review systematically examines recent advances in SiOC, SiCN, SiBCN and SiOCN for lithium-ion battery applications, with a focus on their synthesis protocols, structural characteristics, and electrochemical performance. Furthermore, we elucidate the lithium storage mechanisms in PDCs, highlighting the critical role of free carbon phases in enhancing their electrochemical behavior.  
Figure 3: The process of converting polymers into ceramics. Copied with permission from Elsevier (26).  
Figure 2: Number of publications resulting from a search with the key word “polymer derived ceramic”, from 2000 up to 10 May 2025 (data from Web of Science).