A Thin‐Layer, Li⁺ Compensation, Moisture‐Tolerant Interfacial Modification of Cu Substrate Toward the Anode‐Less, Energy/Power Dense Li Metallic Batteries

Abstract The unregulated metallic deposition and continuous cracking of the fragile solid electrolyte interphase are considered the critical barriers that compromise the cyclability of lithium metal batteries (LMB), especially under low N/P ratio (<3) pairing modes. Herein, an ultra‐thin (5 µm), lightweight (0.25 mg cm⁻²), and moisture‐proof interfacial layer composed of the high‐entropy alloys (denoted as HEAs) and interweaved carbon nanotubes (CNTs) scaffold is constructed to modify the current collector, moreover, the thermally‐induced Li₂₂Si₅ alloy blended with the hydrophobic ethylene‐vinyl acetate copolymer (EVA) is infiltrated into the scaffold pores as the moisture‐proof cation reservoir. The HEA@CNT/Li₂₂Si₅@EVA interfacial layer not only maximizes the Li‐utilization degree with minimal voltage divergence in symmetric cells but also compensates for irreversible Li depletion in the pouch‐format anode‐less models. As the HEA@CNT/Li₂₂Si₅@EVA‐Cu substrate paired with the LiNi_0.8Mn_0.1Co_0.1O₂ cathode in a 200 mAh prototype, the phase evolution of oxide cathode and efficient Li utilization at the anode substrate can be real‐time monitored by the transmission‐mode operando X‐ray diffraction. This interfacial layer strategy affords multifunctionality to enable the LMB prototyping without excessive Li abuse. Consequently, cycling endurance and the balanced energy densities (420.1 Wh kg⁻¹) are obtained on the whole cell.