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 (TLi+) 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.