Simple and Effective Gas-Phase Doping for Lithium Metal Protection in Lithium Metal Batteries

Abstract

Elemental lithium metal has received a great attention as an ideal high-energy-density negative electrode material for lithium batteries, owing to the highest theoretical specific capacity (3860 mAh g-1) and the lowest negative electrochemical potential (-3.040V vs. standard hydrogen electrode). While these latent merits have been significantly plagued by the catastrophic safety issues of lithium metal anodes, which are tied to chronic problems such as (1) lithium dendritic growth and (2) the high reactivity of metallic lithium in electrolyte, recent intense demands for rechargeable batteries with higher energy density has made lithium metal come into the spotlight again. Moreover, various next-generation batteries including lithium-sulfur (Li-S) and lithium-oxygen (Li-O2) systems with exceptionally high energy density heavily rely on the stable cycling of lithium metal electrode. Thus, the utilization of lithium metal anode in rechargeable system is pivotal not only for the further development of lithium ‘ion’ batteries employing high energy lithium metal anode, but also for the realization of the next-generation battery chemistries. Herein, we propose a facile and cost-effective approach to stabilize lithium metal anode using gas phase doping to the electrolyte. We find that the use of gaseous sulfur dioxide as an electrolyte additive is particularly effective for enhancing the chemical/electrochemical stability of the lithium metal surface among various gas additives. The surface analyses reveal that the reduction of sulfur dioxide gas occurs on the lithium metal and produces a thin layer of inorganic Li-S-O compounds, which aids in the development of artificially uniform SEI layers. It also leads to the homogeneous supply of lithium ions to the lithium electrode throughout the uniform SEI layer. Furthermore, the applicability of sulfur dioxide-induced protection layer is examined in several electrolyte systems including acetonitrile based electrolytes which are highly reactive with lithium metal, confirming the simple and effective gas doping strategy to stabilize lithium metal electrode for various types of lithium batteries. This finding of the enhancement of lithium metal stability using sulfur dioxide gas also suggests the underlying reason for the remarkably long calendar life and high efficiency of lithium-sulfur dioxide primary batteries that have been developed in 1970s. This revisit demonstrates that stable and homogeneous protection layers on the lithium metal induced by sulfur dioxide additives efficiently suppress the selective growth of lithium and provides with a detailed mechanistic study using the combined experimental and computational investigations.