Electrolyte Engineering for 5 V Lithium Metal Batteries.

Abstract

Lithium-metal batteries employing lithium-rich manganese-based oxide (LRMO) cathodes offer great potential for achieving gravimetric energy densities exceeding 750 Wh kg^-1. However, their practical deployment is hindered by severe electrolyte decomposition and rapid capacity fade, particularly under high-voltage conditions. Herein, N-methyltrifluoroacetamide (NMTFA) as a novel electrolyte additive is introduced, in combination with lithium difluoro(oxalato)borate (LiDFOB), to modulate the electrolyte solvation structure and enhance interfacial stability. Endowed with lone pair electrons and an N-H bond, NMTFA acts as an electron donor capable of scavenging oxygen radicals released from the LRMO cathode, thereby mitigating electrolyte degradation and suppressing gas evolution. Additionally, hydrogen-bonding interactions between NMTFA and the primary solvent, along with the incorporation of DFOB^- anions into the primary solvation sheath, weaken Li⁺-solvent interactions, promoting the formation of a nitrogen-/boron-rich interphase that facilitates faster Li⁺ desolvation and improves electrode stability. As a result, the Li||LRMO full cell delivers exceptional cycling stability, retaining over 70% of its initial capacity after 800 cycles at a cut-off voltage of 4.8 V and over 80% retention after 300 cycles at 5.0 V. This study provides critical insights into the rational design of advanced electrolytes for high-voltage lithium-metal batteries.