Interface engineering is an effective approach to solving the difficult Li-dendrite issues in lithium–metal batteries, and yet a robust large-capacity Li anode (≥20 mA h cm⁻²) working at an ultrahigh rate density (≥20 mA cm⁻²) is still rarely achieved. Herein, an integrated Li–metal-based anode with a top-down composition gradient (Li₂O–LiOH–Li₃Sb/Li) is constructed through a thermal-induced reaction of molten Li with polyantimonic acid (PAA). Unexpectedly, the lattice-water-containing PAA is found in favor of a mild but homogeneous lithiation reaction, whilst accompanied by a spontaneous phase separation between the resulting Li₂O, LiOH, and Li₃Sb components due to their significant interfacial energy discrepancy. The consequent Li₂O-enriched top layer affording a high Young's modulus (>10 GPa) and electron-shielding ability can effectually suppress the Li-dendrite growth, while the underlying LiOH–Li₃Sb interphase as ionic-channels homogenize Li⁺-flux distribution, in turn enabling dendrite-free Li deposition in a lithiophilic Li₃Sb/Li bottom layer. With this free-standing integrated electrode, large-areal-capacity symmetrical cells (25 mA h cm⁻²) can maintain over 1280 h Li plating/stripping cycles at an ultrahigh-current-density of 50 mA cm⁻², and the full-cells paired with high-capacity LiCoO₂ (3.5 mA h cm⁻²) exhibit improved cycling stability under a practical low N/P ratio (1.33). Importantly, this robust integrated anode also showcases decent compatibility with gel-polymer/Li₇La₃Zr₂O₁₂ solid-state electrolytes, signifying the application potential in safe Li–metal batteries.