Fabricating three-dimensional (3D) composite lithium anodes via thermal infusion effectively addresses uncontrollable Li deposition and large volume changes. However, potential risks due to the long wetting time and high melting point remain a critical yet unconsidered issue. Herein, we report a stable 3D composite Li anode by infusing molten Li into a 3D scaffold within 3 s at 220 °C. The key-enabling technique is the growth of a lithiophilic Mg-Al double oxide (LDO) nanosheet array layer on the scaffold. The in-situ formed lithiophilic alloy, combined with the capillary forces from the nanosheet arrays, enabled the transient infiltration of molten Li. In addition, the formed high ionic-conductivity Li phase can help construct a robust solid electrolyte interphase (SEI), stabilize the Li anode/electrolyte interface, and guide uniform Li deposition. The 3D composite anode exhibited a long cycling life of 1,000 h under a current density of 1 mA·cm⁻² and over 1,600 h under a current density of 2 mA·cm⁻² with a high areal capacity of 4 mAh·cm⁻² in Li/Li symmetric cells. The 3D composite anodes paired with high areal capacity LiFePO₄ (LFP) and S cathodes demonstrate its practical application feasibility.