Spatially Confined Ni3Se4/C Architecture via Continuous Selenization: Dual-Role Carbon Matrix Enables Ultrahigh-Rate Lithium Storage and Reveals Sodium-Ion Transport Limitations

Nickel selenides' structural diversity offers promising avenues for advanced battery anodes, yet their practical implementation faces persistent challenges of structural instability and sluggish kinetics. Addressing these limitations, we pioneer a spatially confined architecture through template-directed hydrothermal synthesis: ~48 nm Ni ₃ Se ₄ nanoparticles uniformly encapsulated within conductive carbon nanoplates. Time-dependent XRD analysis confirms continuous selenization-driven phase evolution, while XPS/TGA verify the composite (30.6 wt% carbon) comprises Ni ²⁺ , Se ₂ ^2- and Se ^2- species. This dual-role design - where carbon simultaneously serves as electron highway and volume-change buffer - enables breakthrough lithium storage performance: 586.2 mAh g ^-1 after 100 cycles (0.2 A g ^-1 ) with exceptional 375.5 mAh g ^-1 retention at ultrahigh 5 A g ^-1 . Electrochemical analysis demonstrates carbon spacers reduce charge-transfer resistance by >40% versus bare counterparts. The strategically engineered interface provides critical insights for stabilizing conversion-type anodes, though sodium storage remains challenging (167.9 mAh g ^-1 after 100 cycles), highlighting fundamental differences in ion storage mechanisms that guide future material design.