In situ cryomilling-engineered silicon nitride coating for ultradurable silicon anodes in lithium-ion batteries

Silicon anodes offer very high theoretical capacity, but their low ionic conductivity and the development of an unstable solid electrolyte interphase (SEI) lead to fast capacity loss and restricted rate performance. In this work, we present a novel surface engineering approach using liquid nitrogen-assisted cryomilling to form an ultrathin silicon nitride (Si N) layer in situ on nano‑silicon particles. The resulting Si@Si-N composite has a dual-phase coating composed of electrochemically inert Si 3 N 4 and active, non-stoichiometric SiN x . These phases synergistically stabilize the electrode/electrolyte interface and enhance Li-ion transport. TEM, XPS, and EDS analysis confirm the formation of a uniform amorphous Si N layer. Electrochemical tests show outstanding performance: after 500 cycles at 1 A g −1 , the Si@Si-N anode delivers a high reversible capacity of 1152 mAh g −1 , with an initial coulombic efficiency of 82.8 %. In rate capability tests, it delivers 759 mAh g −1 at 5 A g −1 and recovers 98.49 % of its capacity when the current returns to 0.2 A g −1 . GITT and EIS analyses reveal significantly improved Li + diffusion kinetics, which can be attributed to the formation of a highly conductive Li 3 N-rich interphase during lithiation, along with the mechanically robust Si 3 N 4 framework that collectively mitigate SEI degradation. This work provides a scalable, cost-effective strategy for stabilizing silicon anodes, representing a significant advancement toward their commercial use in high-energy-density lithium-ion batteries.