Enabling a Stable and Kinetically Enhanced Interface for Silicon Anodes via in Situ Formation of F/P-Doped Li_xSi_yO_z...

Silicon (Si) is regarded as the most promising anode material for advanced lithium ion batteries due to its high theoretical specific capacity. However, its severe volume expansion during cycling and insufficient intrinsic ionic/electronic conductivity hinder its practical application. To address these challenges, a novel two-step synthesis strategy is developed to fabricate a F/P-doped Si@Li_xSi_yO_z@C composite (denoted as P-Si). Firstly, the F/P-doped Li₂SiO₃ and Li₂Si₂O₅ phases are in situ constructed on the Si surfaces via solid phase reacting with lithium difluorophosphate (LiPO₂F₂). Subsequently, carbon dioxide is converted into a homogeneous carbon coating layer through the ball milling process. Electrochemical measurements reveal that the multiphase interface significantly enhances the lithium ion transport capability and kinetic property of the P-Si anode. Simultaneously, Chemical analysis and structural characterization demonstrate that F and P doping promotes the formation of a stable SEI with high Young's modulus, which contributes to improved interfacial integrity. Furthermore, theoretical calculations confirm that the constructed coating not only facilitates lithium ion diffusion but also promotes lithium ion adsorption onto the Si surface, thereby accelerating the alloying reaction. Owing to these synergistic effects, the full cell assembled with the prelithiated P-Si anode and LiFePO₄ cathode exhibits a capacity retention rate of 87.1% after 200 cycles at 1 C. This facile strategy offers a promising approach for developing high performance Si-based anodes.