Post-Densified conformal coating of a Pyrogallol/Polyethyleneimine complex as a durable Electrolyte-Blocking organic layer for High-Capacity anode materials

The strategic implementation of artificial solid electrolyte interphases (SEI) as conformal coating layers on Si-based anode materials has emerged as a key approach to suppressing SEI formation and enhancing long-term stability of Li-ion batteries (LIBs). These layers are designed to be compact enough to block electrolyte penetration yet sufficiently thin to allow efficient Li-ion diffusion. However, most studies have predominantly focused on smooth-surfaced bare Si particles, overlooking the challenges posed by Si/C composites, which are more commonly used in industry and characterized by their rough textures with surface inertness. To bridge this gap, in this work, we have developed a highly robust conformal coating process for Si/C composites using a pyrogallol and polyethyleneimine (PG/PEI) complex. This approach introduces an initially thick and swollen PG/PEI layer, followed by thermal annealing to densify and thin the layer, eventually ensuring complete surface coverage while achieving a minimal thickness less than 10 nm. This technique not only imparts surface conformity on rough Si/C composite particles but also supports the sustained performance of LIBs. Finally, this method, validated in a full-cell operation that aligns with industry standards, achieves an initial capacity of 6.3 mAh at a high loading of 6.02 mg cm⁻². Specifically, it operates under extremely lean electrolyte conditions of 2.05 μL mAh⁻¹ and maintains performance over 500 cycles, even tested under constant current-constant voltage (CC-CV) mode to affirm the effectiveness of our coating strategy.