Breaking the molecular symmetricity of sulfonimide anions for high-performance lithium metal batteries under extreme cycling conditions

Abstract

Lithium metal batteries operating under extreme conditions are limited by the sluggish desolvation process and poor stability of the electrode–electrolyte interphase. However, rational interphase design is hindered by the ill-defined understanding of interphasial chemistry at the molecular level. Here we design and synthesize a series of sulfoximide salts, lithium bis(trifluoromethanesulfinyl)imide (LiBSTFSI) and lithium (trifluoromethanesulfinyl)(trifluoromethanesulfonyl)imide (LiSTFSI), that possess distinctive oxidizability. Their molecular structure and interphasial chemistry were correlated. An anionic electro-polymerization was induced by the asymmetric LiSTFSI to establish a bilayer catholde–electrolyte interphase (CEI) with LiF dominated inner covered by negative-charged inorganic polymers. LiSTFSI-derived CEI enables superior mechanical stability and accelerated Li⁺ desolvation that contribute to the stable cycling and superior energy and power densities under ultra-high rate and ultra-low temperature conditions. Industrial pouch cells of 474 Wh kg⁻¹ achieved extreme power density of 5,080 W kg⁻¹ at 30 °C and exceptional low-temperature energy and power densities at −20 °C (382 Wh kg⁻¹, 3,590 W kg⁻¹) and −40 °C (321 Wh kg⁻¹, 1,517 W kg⁻¹).