Examining the Electrochemical Properties of Hybrid Aqueous/Ionic Liquid Solid Polymer Electrolytes through the Lens of Composition-Function Relationships

Solid polymer electrolytes (SPEs) have the potential to meet evolving Li-ion battery demands, but for these electrolytes to satisfy growing power and energy density requirements, both transport properties and electrochemical stability must be improved. Unfortunately, improvement in one of these properties often comes at the expense of the other. To this end, a hybrid aqueous/ionic liquid SPE (HAILSPE) which incorporates triethylsulfonium-TFSI (S-2,S-2,S-2) or N-methyl-N-propylpyrrolidinium-TFSI (Pyr(1,3)) ionic liquid (IL) alongside H2O and LiTFSI salt to simultaneously improve transport and electrochemical stability is studied. This work focuses on the impact of HAILSPE composition on electrochemical performance. Analysis shows that an increase in LiTFSI content results in decreased ionic mobility, while increasing IL and water content can offset its impact. pfg-NMR results reveal that preferential lithium-ion transport is present in HAILSPE systems. Higher IL concentrations are correlated with an increased degree of passivation against H2O reduction. Compared to the Pyr(1,3) systems, the S-2,S-2,S-2 systems exhibit a stronger degree of passivation due to the formation of a multicomponent interphase layer, including LiF, Li2CO3, Li2S, and Li3N. The results herein demonstrate the superior electrochemical stability of the S-2,S-2,S-2 systems compared to Pyr(1,3) and provide a path toward further enhancement of HAILSPE performance via composition optimization.

Automated summary

To meet the increasing demands of Li-ion batteries, solid polymer electrolytes (SPEs) need to improve both transport properties and electrochemical stability. This study investigates a hybrid aqueous/ionic liquid SPE (HAILSPE) that can simultaneously enhance transport and electrochemical stability. The results demonstrate that the composition of HAILSPE can greatly impact its electrochemical performance.