Effect of LiFSI Concentrations To Form Thickness- and Modulus-Controlled SEI Layers on Lithium Metal Anodes

Abstract

Improving the cyclic stability of lithium metal anodes is of particular importance for developing high-energydensity batteries. In this work, a remarkable finding shows that the control of lithium bis(fluorosulfonyl)imide (LiFSI) concentrations in electrolytes significantly alters the thickness and modulus of the related SEI layers, leading to varied cycling performances of Li metal anodes. In an electrolyte containing 2 M LiFSI, an SEI layer of ∼70 nm that is obviously thicker than those obtained in other concentrations is observed through in situ atomic force microscopy (AFM). In addition to the decomposition of FSI − anions that generates rigid lithium fluoride (LiF) as an SEI component, the modulus of this thick SEI layer with a high LiF content could be significantly strengthened to 10.7 GPa. Such a huge variation in SEI modulus, much higher than the threshold value of Li dendrite penetration, provides excellent performances of Li metal anodes with Coulombic efficiency higher than 99%. Our approach demonstrates that the FSI − anions with appropriate concentration can significantly alter the SEI quality, establishing a meaningful guideline for designing electrolyte formulation for stable lithium metal batteries.

High‐Power Lithium Metal Batteries Enabled by High‐Concentration Acetonitrile‐Based Electrolytes with Vinylene Carbonate Additive

“…It is demonstrated that the formation of LiF has to be based on the co‐adsorption of Li + –FSI − pair on Li surface. [ 32 ] This reaction is more probable at higher concentration of LiFSI since the coordinated Li + –solvent aggregates and FSI − anions are less elongated due to the limited solvent molecules. Consistently, the highest intensity of LiF is observed for [LiFSI]:[AN]:[VC] = 0.78:1:0.09.…”

Bisalt ether electrolytes: a pathway towards lithium metal batteries with Ni-rich cathodes

“…The lower reduction potential of DME relative to the anions generally prevents solvent decomposition reactions on the bare metal electrode. 55,65 Viscosity of the bisalt electrolyte relative to the single salt variant may also play a role in slowing degradation as well. Molecules and fragments experience drag due to interaction with the surface and could provide a lingering screening effect.…”

Advances in sodium secondary batteries utilizing ionic liquid electrolytes

“…Thus, for the development of negative electrodes, exploring compatible electrolytes is indispensable. The performance and safety of a battery are highly dependent on SEI layer properties 399 which are sensitive to parameters such as the salt concentration of the electrolyte, 400 temperature, 160,401 and the binder used. 402 Investigating the physical and chemical properties of SEI layers is very important for understanding the degradation mechanisms in batteries.…”