Semi-Carbonized Dual-Polymer Coating Enables Stable Silicon Anodes via Artificial SEI for High-Performance Lithium-Ion Batteries

Silicon anodes hold great promise for high-energy lithium-ion batteries but suffer from severe volume expansion and unstable solid electrolyte interphase (SEI) formation. To address these challenges, this study develops a thermally crosslinked dual-polymer (KH550/sodium alginate) coating strategy. The 350 °C-pyrolyzed coating forms a semi-carbonized artificial SEI on the surface of Si particles that effectively suppresses side reactions and accommodates volume changes. Comparing with uncarbonized polymer coating, the denser semi-carbonized one demonstrates its unique effect in matching Li⁺ diffusion kinetics between the interface and bulk silicon, retaining the structural integrity of Si particles during lithiation. The resulting Si anode exhibits minimal volume expansion (8%), 82.5% initial Coulombic efficiency, 948 mAh g⁻¹ after 500 cycles at 2 A g⁻¹, thereby developing a new gate on enhancing electrochemical performance by pre-constructing semi-carbonized polymer coating around Si particles.