Self-Assembled-Monolayer-Induced Polyaniline-Grafted Silicon Nanoparticles for Highly Stable Lithium-Ion Battery Anodes.

Silicon possesses a high gravimetric capacity (4200 mAh g^-1), which makes it an attractive lithium-ion battery anode material. However, its application is hindered by the substantial volumetric change (∼300%) that occurs during the lithium-ion insertion/extraction process, leading to mechanical disintegration and rapid capacity fading. Here, we have rationally designed a novel configuration that chemically bonds polyaniline (PANI) to the surface of silicon (Si) nanoparticles, which preserves the mechanical integrity of the electrode and enhances its electrochemical performance. This process is accomplished by first functionalizing Si nanoparticles with self-assembled monolayers (SAMs), then chemically bonding PANI to these SAM-grafted surfaces. With optimum PANI coating, the PANI-Si anode presented an initial specific capacity of 798 mAh g^-1 at a current density of 0.5 A g^-1 and also achieved an initial Coulombic efficiency of 76%. The PANI-Si anode maintained a reversible discharge capacity of 510 mAh g^-1 after 2000 cycles significantly outperforming the pristine Si electrode, which exhibited over 92% capacity loss after 300 cycles. The electrode also reached 100% Coulombic efficiency by the sixth cycle and maintained this perfect efficiency over 2000 cycles. Electrochemical impedance spectroscopy (EIS) analysis revealed that the PANI-Si electrode exhibited lower interface and diffusion impedances, which enhanced both electron transfer and lithium-ion migration. Overall, our study demonstrated that PANI coatings effectively improved the mechanical stress tolerance and structural integrity of silicon while also boosting its electrical conductivity.