Ultra‐Stable Breathing Anode for Li‐Free All‐Solid‐State Battery Based on Li Concentration Gradient in Magnesium Particles

Abstract The alloying behavior of Li‐alloy‐forming metals in the anode of all‐solid‐state batteries (ASSBs) critically affects the viscoplastic flow and deposition of Li, determining cell performance. Herein, an ultra‐stable breathing Mg anode for Li‐free ASSBs is reported with changes in the inter‐particle distance of the Mg particles during operation. It is proposed that this unique Li deposition between Mg particles is derived from the Li concentration gradient (LCG) from the surface to the core of the Mg particle, creating a driving force that attracts Li toward the low‐concentration side and Li accumulation followed by deposition on the Mg surface. Based on a comparative study of Li‐alloy‐forming metals with different alloying and diffusion kinetics, this study ascribes the LCG to the slow alloying kinetics of Mg with Li and slow Li diffusion through the Mg–Li alloys. Interfacial stability is secured by accommodating Li deposits uniformly inside the anode. A full cell with a LiNi 0.8 Mn 0.1 Co 0.1 O 2 cathode exhibits ultrahigh stability and reversibility with Coulombic efficiency over 99.9% for 1000 cycles at 30 °C.