Solid Polymer Electrolytes Comprising Camphor-Derived Chiral Salts for Solid-State Batteries

Abstract

Solid polymer electrolytes (SPEs) with both excellent processability and flexibility have been deemed as an auspicious alternative to develop safe solid-state lithium metal (Li°) batteries (SSLMBs). The electrochemical performance of SSLMBs is ultimately associated with the nature of the Li-salt anion and the widely used bis(trifluoromethanesulfonyl)imide anion (TFSI) is "slippery" due to its perfluorinated nature and therefore highly mobile, which leads to severe polarization upon battery cell charge/discharge cycles. In this work, we report on a new type of chiral salts, synthesized from commercially available camphorsulfonic acid, used in poly(ethylene oxide) (PEO)-based SPEs. The impact of the chirality of the anions on the fundamental physical properties of the SPEs is extensively studied in terms of thermal stability, phase transition and ionic conductivity, etc. We demonstrate that the resulting SPEs exhibit agreeable ionic conductivities (ca. 10 -4 S cm -1 ) accompanied by high cation transference numbers (ca. 0.5) at 70 °C. Whether either the R or the S enantiomers are used the ion transport properties are the same, as expected, but rather surprisingly the artificial racemic mixture is within the errors of the measurements just as conductive. We discuss how this opens a new avenue to design novel salts for reaching high-performant SSLMBs.