High‐Stability Dual Janus Li‐Alloy Anode via Single‐Step Surface Solution Etching

Abstract Alloying Li with electrochemically‐inert elements represents a compelling scalable solution to mitigate rampant dendrite proliferation and parasitic side reactions. However, current approaches predominantly involve melting excess Li with inert elements to yield dense Li‐rich alloys, which fail to address long‐term cycling degradation for their similar electrochemical behaviors to metallic Li. Here, a single‐step surface solution etching strategy through selective Li removal is proposed to engineer a compositional and structural dual‐Janus lithium‐silver alloy (DJ‐LiAg) anode, featuring a Li‐free porous LiAg surface architecture and a Li‐rich dense LiAg‐Li bottom reservoir. Symmetric cells using such a DJ‐LiAg anode demonstrate unprecedented cycling stability over 4000 h, far exceeding the bare Li (≈760 h) as well as monolithic LiAg‐Li (m‐LiAg) alloys (≈980 h). Full cells paired with high‐loading LiFePO ₄ cathodes (2 mAh cm ⁻² ) and DJ‐LiAg anode retain 85.9% capacity after 500 cycles at 2 C, outperforming pristine m‐LiAg (23.4%). This strategy demonstrates universal applicability across various Li‐based alloy systems and enables precise control of the Janus‐surface thickness, facilitating N/P ratio tuning for commercialization. By integrating roll‐to‐roll compatibility with etching efficiency, the work establishes a scalable paradigm for high‐performance lithium alloy design which bridges the gap between high energy density, interfacial stability, and industrial feasibility.