Enhanced electrochemical performance of micro-Si@SiOx anode with (Si3N4 + SiC+C) triple-phase protective coating for lithium-ion batteries

Micro-Si anodes offer high volumetric energy density and low-cost advantages; however, their significant volumetric expansion during Li + insertion/extraction and poor ion/electron transport properties severely hinder commercialization. This study designed a Si/C composite anode material (WM-30C-N) with a three-phase coating structure through a one-step wet milling combined with heat treatment. Using micro-Si as a raw material, a Si@SiO 2 core-shell structure was in situ constructed via mechanochemical wet water milling, with bitumen introduced as a carbon source for surface coating. Following treatment at 1300 °C under a nitrogen atmosphere, the inner SiO 2 layer undergoes a “valence-neutralization reaction” with the Si core to form an intermediate Si@SiO x layer. The exposed Si at the interface reacts in situ to form SiC and Si 3 N 4 through the control of the carbon content in the bitumen, ultimately resulting in a multiphase composite material, Si@SiO x @(Si 3 N 4 + SiC+C). Structural characterization and electrochemical performance evaluation verify that the designed synergistic architecture integrates the merits of all constituent phases. The rigid network constructed by Si 3 N 4 and SiC efficiently alleviates the volume expansion of inner Si and inhibits electrode structural pulverization. The amorphous carbon layer coupled with nitrogen doping builds uninterrupted conductive networks and abundant electroactive sites, which decreases charge transfer resistance and mitigates intrinsic internal stress. The interlayer in-situ generated SiO x (0 < x ≤ 2) endows the composite with both favorable lithium storage activity and structural ductility, accelerating Li + diffusion kinetics. By further regulating the surface nitridation process and structural cycling stability through a gradient in bitumen content, the optimized WM-30C-N exhibited relatively good overall performance, with an initial coulombic efficiency (ICE) of 81.3%. After 350 cycles, the capacity reached 645.9 mA h/g, with a capacity retention rate of 71.2%, and the capacity loss per cycle was only 0.09% (0.2C). This study employed a gradient ceramic‑carbon composite coating strategy to balance the capacity and stability of Si anodes, providing a potential pathway for the commercial application of Si-based anodes in high-performance lithium-ion batteries.