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

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 LiFePO₄ 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.