Bis(fluorosulfonyl)imide- and allyl-functionalized electrolyte additive as an interface stabilizer for Li-metal batteries

Abstract

Lithium (Li) metal anodes have emerged as an appealing advanced electrode material, however, there are numerous limitations because of its unstable chemical and electrochemical reactivities and dendritic Li formation. Here, dually functionalized electrolyte additives using bis(fluorosulfonyl)imide- and allyl-functional groups are designed, and their electrochemical properties are investigated. The electrochemical reduction of allyldimethylpropylammonium bis(fluorosulfonyl)imide (ANP-F) and diallyldimethylammonium bis(fluorosulfonyl)imide (ANA-F) additives results in the formation of an inorganic–organic combined solid electrolyte interphase (SEI) layer on the Li metal surface, which is responsible for the prolonged cycling of the cells. Even after 1100 h, the Li/Li symmetric cells with ANP- and ANA-F additives exhibit stable cycling, and further in- and ex-situ analyses show that electrolyte decomposition and dendritic Li formation on the Li metal surface are suppressed. The cells cycled with 2.0 ANP- and 2.0 ANA-F show an average coulombic efficiency (CE) of 97.7 % and 94.1 %, respectively, as compared to that of the standard electrolyte of 91.3 %. As a result, the 2.0 ANP- and 2.0 ANA-F provide stable cycling retention of Li metal/LFP cells because the bi-functionalized SEI layer produced by the electrochemical reduction of the ANP- and ANA-F additives prevents parasitic reactions at the Li metal interfaces.