Electrolyte Engineering for 5 V Lithium Metal Batteries

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.