Enhanced Kinetics of Lithium-Ion Charge Storage on Si Anode through Ultrasmall Magnesium Nitride Nanoparticles toward...

Silicon, known for its high Li⁺ storage capacity, low redox potential, abundant reserves, and low cost, is regarded as a promising anode material for all-solid-state lithium-ion batteries (ASSLBs). Nevertheless, its practical application is hindered by severe volume expansion and sluggish reaction kinetics. Herein, Si@Mg₃N₂ composites are synthesized via a vacuum evaporation method, wherein ultrasmall Mg₃N₂ nanoparticles with an average size of 9 nm are uniformly coated onto the surface of commercial silicon microsheets. During the initial lithiation process, these Mg₃N₂ nanoparticles undergo an in situ phase transformation, forming a Li-Mg-Si alloy, Li-Mg alloy, and Li₃N irreversibly. The resulting Li-rich substances with the mixed ionic/electronic conductive function effectively mitigate the substantial volume expansion associated with the Li-Si alloying reaction (reducing it from 210% to 38.6%), thereby enhancing electrode kinetics and mechanical stability. As a result, the Si@Mg₃N₂ composite anode delivers a reversible capacity of 2619 mAh g^-1 at 0.1 A g^-1 and maintains a discharge capacity of 1460 mAh g^-1 even at a high rate of 5 A g^-1 in half-cell configurations. Furthermore, ASSLBs incorporating the Si@Mg₃N₂ anode exhibit excellent rate capability (50.8 mAh g^-1 at 40 C) and robust cycling stability (61.6% capacity retention after 1000 cycles).