Achieving a higher lithium density in anode 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 account for a significant cause of battery performance degradation. In this study, we elucidated the Li densification at the anode through the formation of a high-Li-density solid solution with tailed components and dense Li deposit structure, representing an alternative concept for the low-expansion Li metal anode. Specifically, we revealed 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 the Li-containing cathodes during the battery charge 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 mAh cm−2. This is significantly lower than the expansion observed in its counterpart with pure Li, which exceeded 220%. Remarkably, Ah-class Li metal pouch cell (~421 Wh kg−1), assembled with the ultrathin Li/Ag anode (40 μm) and LiNi0.6Co0.2Mn0.2O2 (NCM622, 4.1 mAh 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 electrolyte/capacity (E/C) ratio of 1.71 g Ah−1.