Achieving a higher lithium density in anodes surpassing that of pure metallic lithium for high-energy-density batteries†

Abstract

The low-density, high-porosity lithium (Li) plating layer at the anode is one of the principal determinants of the overall volumetric expansion in rechargeable high-energy-density Li metal batteries, which accounts for a significant cause of battery performance degradation. In this study, we elucidated Li densification at the anode through the formation of a high-Li-density solid solution with tailed components and a dense Li deposit structure, representing an alternative concept for the low-expansion Li metal anode. Specifically, we revealed that a Li–Ag solid solution with a Li/Ag atomic ratio ranging from 12/1 to 18/1 demonstrated a significantly higher volumetric Li density, referring to the volumetric Li storage capability, compared to bulk metallic Li. A Li metal anode with a specific-thickness Ag upper layer could be elaborately designed to produce such a high-Li-density Li–Ag solid solution after intake of active Li from Li-containing cathodes during the battery charging process, suppressing the overall volume change of the cell. Impressively, a 50 μm-thick Li/Ag anode demonstrated minimal volume expansion of only 11% after 50 cycles at 1 mA cm⁻² and 4 mA h cm⁻². This is significantly lower than the expansion observed in its counterpart with pure Li, which exceeded 220%. Remarkably, an Ah-class Li metal pouch cell (∼421 W h kg⁻¹), assembled with the ultrathin Li/Ag anode (40 μm) and the LiNi_0.6Co_0.2Mn_0.2O₂ (NCM622, 4.1 mA h cm⁻²) cathode, demonstrated a lifespan exceeding 320 cycles under harsh conditions with a low negative/positive capacity (N/P) ratio of 1.95 and an electrolyte/capacity (E/C) ratio of 1.71 g A h⁻¹.