Lithium Diffusion-Controlled Li-Al Alloy Anode for All-Solid-State Battery

Metal alloy anodes are promising candidates for Lithium (Li) all-solid-state batteries due to their high specific capacity and low cost. However, chemo-mechanical degradation and diffusion-limited operation remain unresolved challenges. Herein, we demonstrated Li-Al alloy anode design (Li_xAl₁, x = molar ratio of Li to Al) based on a comprehensive study of underlying diffusion mechanism within the Li-poor α (0 ≤ x ≤ 0.05) and Li-rich β phases (0.95 ≤ x ≤ 1). The Li-Al alloy anodes with a higher Li ratio facilitate Li⁺ migration through the β-LiAl phases, which serve as highly Li-conductive channels with ten orders of magnitude higher Li⁺ diffusivity compared to the α phase. In addition, a bulk dense anode and intimate anode-electrolyte interface were clearly demonstrated in the cross-sections of the Li-Al alloy anodes. Consequently, a remarkably high critical current density of 7 mA cm^-2 was attained in LiNi_0.8Co_0.1Mn_0.1 (NCM811)-based full-cell operation. The optimal cell configuration of Li_0.5Al₁ | NCM showed extremely stable Li reversibility during 2000 cycles with a capacity retention of 83% at 4 mA cm^-2 with a high loading of 5 mAh cm^-2.