Lithium diffusion-controlled Li-Al alloy negative electrode for all-solid-state battery

Metal alloy negative electrodes are promising candidates for lithium all-solid-state batteries due to their high specific capacity and low cost. However, chemo-mechanical degradation and atomic transport limitations in the solid state remain unresolved challenges. Herein, we demonstrate a lithium-aluminum alloy negative electrode design (Li_xAl₁, x = molar ratio of lithium to aluminum) based on a comprehensive understanding of the underlying diffusion mechanisms within the lithium-poor α (0 ≤ x ≤ 0.05) and lithium-rich β phases (0.95 ≤ x ≤ 1). The lithium-aluminum alloy negative electrodes with a higher lithium to aluminum ratio facilitate lithium migration through the β-LiAl phases, which serve as highly lithium-conductive channels with a lithium diffusion coefficient that is ten orders of magnitude higher than that of the α phase. In addition, a bulk dense negative electrode and an intimate negative electrode-electrolyte interface is demonstrated in the cross-sections of the lithium-aluminum alloy negative electrodes. Consequently, a high-rate capability of 7 mA cm^-2 is attained in LiNi_0.8Co_0.1Mn_0.1O₂-based full-cell operation. The optimal cell configuration of Li_0.5Al₁ | |LiNi_0.8Co_0.1Mn_0.1O₂ shows stable lithium reversibility during 2000 cycles with a capacity retention of 83% at 4 mA cm^-2 with a LiNi_0.8Co_0.1Mn_0.1O₂ loading of 5 mAh cm^-2.