Anions with a Dipole: Toward High Transport Numbers in Solid Polymer Electrolytes

Solid-state lithium metal (Li°) batteries (SSLMBs) are believed to be the most promising technology to satisfy the high energy demand, meet the safety requirements, and overcome the limitations ascribed to currently used Li-ion batteries. Solid polymer electrolytes (SPEs) arise as the best candidates mainly due to their easy manufacturing, flexibility, and cost compared to their inorganic counterparts. However, conventional lithium bis­(trifluoromethanesulfonyl)­imide and poly­(ethylene oxide)-based SPEs suffer from a low lithium-ion transference number (T_Li⁺) and poor Li° electrode compatibility as demonstrated by the compromised cyclability of these electrolytes in SSLMBs. Herein, we report the performance of SPEs comprising a newly designed N-ethyl-N-methyl-functionalized sulfonimide lithium salt, with wide electrochemical stability, decreased anionic diffusivity, sufficient Li-ion conductivity, and superior compatibility with the Li° electrode.