Anomalous Si-based composite anode design by densification and coating strategies for practical applications in Li-ion batteries

Si-based Li-ion battery (LIB) anode materials often possess porous structures to accommodate the intrinsic volumetric expansion of Si upon cycling. However, the porous structure may cause poor initial coulombic efficiency (ICE), inadequate cycle life due to the continuous generation of a solid-electrolyte interface, and incompatibility with calendaring processes. To overcome these issues, we designed an optimized Si/C (P–Si/C) composite anode consisting of Si nanoparticles, graphite, and pitch, with a highly densified structure, suppressing Si expansion and enabling compatibility with the calendaring process. To further enhance the cycle life, the surface of the P–Si/C composite was modified by chemical vapor deposition using CH4 gas (C–Si/C). The P–Si/C anode exhibited a high ICE of 88.0% with a rapid surge up to 99.0% after only the 4th cycle. The C–Si/C anode presented an improved capacity retention of 49.5% after the 39th cycle, compared with 46.0% for the P–Si/C anode after the 31st cycle, while maintaining the same ICE. Moreover, anodes prepared with 8 wt% P–Si/C or C–Si/C and 92 wt% graphite (m-P-Si/C and m-C-Si/C, respectively) showed higher capacity retentions compared with pure Si/C anodes. The m-C-Si/C anode exhibited a higher capacity retention of 80.1% after the 40th cycle, compared with 71.2% for the m-P-Si/C anode. The m-C-Si/C anode also displayed an extremely low expansion rate and the majority of the expansion was elastically recovered. This C–Si/C composite provided a controllable means to modify the performance of LIBs by simple mixing with graphite.