Covalently Bonded Conductive Polymer Coating Si Nanoparticles for Anodes of Lithium-Ion Batteries

Silicon anodes offer ultrahigh theoretical capacity but suffer from drastic volume changes and unstable solid-electrolyte interphases (SEIs), leading to rapid capacity fading. Here, we construct a covalently encapsulated Si anode by embedding Si nanoparticles into a formic-acid-doped PEDOT:PSS gel matrix reinforced with uniformly dispersed carbon nanotubes. At the interface, surface Si–OH groups react with PEDOT:PSS to form strong covalent bonds, providing multipoint anchoring and enhanced mechanical/electronic coupling, while the gel-like PEDOT:PSS/CNT framework builds a continuous, conductive and compliant network that buffers Si volume fluctuations and preserves electrode integrity. The Si–P-5 composite electrode still retains a capacity of over 1200 mAh g–1 after 150 cycles at a current density of 1 A g–1, and exhibits excellent rate capability, with overall electrochemical performance markedly superior to that of conventional silicon electrodes based on carboxymethyl cellulose and poly(acrylic acid). Scanning electron microscope reveals limited thickness swelling and suppressed cracking, and X-ray photoelectron spectroscopy confirms that the SEI composition and effective thickness remain nearly unchanged upon extended cycling, indicating a structurally stable SEI formed on the encapsulation layer. This work offers a general strategy to reconcile high capacity with durable cycling in Si-based lithium-ion batteries via covalent polymer-Si interfaces and gel-type conductive scaffolds.