Dual ion regulation enables High-Coulombic-efficiency lithium metal batteries

Abstract

Lithium (Li) metal batteries are ideal alternatives for pursuing high-energy-density batteries. Nevertheless, their subpar cycling capabilities and safety problems remain a significant concern because of the insufficient reversibility of Li plating/stripping processes. Herein, potassium trifluoromethanesulfonate (KOTf) is proposed as an electrolyte additive to achieve high Coulombic efficiency during cycling, which could be assigned to the synergistic regulation effect of anions and cations in KOTf. On the one hand, the OTf- helps form an anion-rich solvation structure, which could be preferentially reduced to obtain a robust and conductive inorganic-rich SEI film to stabilize the lithium metal anode. On the other hand, the existence of K+ induces the generation of K+-rich positive charge shielding layer, further hindering the growth of Li dendrite. The KOTf-assisted Li||Cu cell shows a high Coulombic efficiency (CE) of 99.7 % and an extremely long-cycle life of 700 cycles with an average CE of 99.01 % under 0.5 mA cm−2 and 0.5 mAh cm−2. The excellent lithium metal stripping/plating efficiency is mainly due to the OTf--derived inorganic-rich SEI and the electrostatic shielding effect of K+. This work emphasizes the important role of salts’ anions and cations in determining the CE of LMBs and provides an effective strategy to improve the cycling performance of LMBs.