Enhanced Electrode/Electrolyte Interphases in Fluorinated Orthoformate Electrolytes for Stable High-Voltage Lithium Metal Batteries

Abstract

Rechargeable lithium (Li) metal batteries (LMBs) have been revived in recent years because of the ever-increasing demand for high-energy-density batteries. 1,2 However, significant challenges, such as low Columbic efficiency (CE), pulverization and large volume expansion related to the Li metal anode still limit the large-scale application of these batteries. 3 Here, we report an approach to improve the Li CE and minimize the Li pulverization and volume expansion by using fluorinated orthoformate in electrolytes. 4 Tris(2,2,2-trifluoroethyl) orthoformate (TFEO) functions as an efficient diluent in electrolytes based on lithium bis(fluorosulfonyl)imide (LiFSI) and 1,2-dimethoxyethane (DME) and formulates highly concentrated LiFSI-DME clusters that are dispersed among the TFEO diluent. Such localized high-concentration electrolytes demonstrate superior electrochemical properties when used in LMBs with a high voltage LiNi0.8Mn0.1Co0.1O2 (NMC811) cathode. The mechanisms behind the long cycle life of Li||NMC811 cells under practical conditions are mainly the formation of highly effective solid electrolyte interphase and cathode electrolyte interphase, which are monolithic and prevent continuous electrode/electrolyte side reactions. This work provides guidance for further development of electrolytes for high-energy-density LMBs. The details will be discussed during the presentation.References1 J.-G. Zhang, W. Xu, W. A. Henderson, Lithium Metal Anodes and Rechargeable Lithium Metal Batteries. XV, 194 (Springer International Publishing, 2017).2 J. Liu, et al. Pathways for practical high-energy long-cycling lithium metal batteries. Nature Energy 4, 180-186 (2019).3 C. Niu, et al. High-energy lithium metal pouch cells with limited anode swelling and long stable cycles. Nature Energy 4, 551-559 (2019).4 X. Cao, et al. Monolithic solid–electrolyte interphases formed in fluorinated orthoformate-based electrolytes minimize Li depletion and pulverization. Nature Energy 4, 796-805 (2019).