Impact of Li–Mg Alloy Anodes on Performance of Sulfide‐Based All Solid‐State‐Batteries

Lithium–magnesium (Li–Mg) alloys have emerged as promising alternatives to pure Li‐metal anodes in sulfide‐based all‐solid‐state batteries (SSBs). Here, we synthesized Li (100‐ x ) Mg x alloys ( x = 0.5–10 at%) and performed a systematic investigation on their structural, mechanical, and interfacial properties, focusing on establishing their correlations with electrochemical performance. The alloys form homogeneous single‐phase body‐centered cubic solid solutions, where increasing Mg content progressively refines grain size and enhances stiffness and hardness while reducing creep. Symmetric cell tests showed enhanced critical current density (∼1.8 mA/cm 2 ), widen cumulative areal capacity window, and stable cycle life at x ∼ 1.5 at%. Unlike the large microvoids (∼3 μm) observed at pure Li/solid‐electrolyte interface, the x = 1.5 at% alloy exhibited only isolated nanovoids, as evidenced by plasma‐focused ion beam scanning electron microscopy analysis. Room‐temperature (RT) SSB cell testing using LiNi 0.6 Mn 0.2 Co 0.2 O 2 cathodes further demonstrated the advantages of optimizing Mg content in alloy anodes. The x = 1 at% alloy achieved the highest capacity retention (93.1% after 300 cycles), superior high‐rate performance, and lowest R Total growth (37.1%). The Li (100– x ) Mg x alloys with 0.5–1.5 at% Mg exhibit optimal chemo‐mechanical interfacial stability and electrochemical performance, highlighting their promise as viable alternative anodes for next‐generation SSBs.