Synthesis and electrochemical properties of self-doped solid polymer electrolyte based on lithium 4-styrene sulfonate with BF3-THF

Poly(lithium 4-styrene sulfonate)-based self-doped solid polymer electrolytes were prepared by radical polymerization and ion-exchange reactions of sodium 4-styrene sulfonate and oligo(ethylene oxide) methyl ether methacrylate. The crystalline melting temperature of ethylene oxide was reduced by increasing the lithium-ion concentration, which resulted in a reduction in the size of the crystalline domains due to the improved coordination between lithium ions and oxygen. Alternating current (AC) impedance measurements showed that the ionic conductivity was 15 times higher after the introduction of boron trifluoride-tetrahydrofuran (BF3-THF), and up to 1.22×10−5 S cm−1 was achieved at 25 °C in all the solid-state self-doped polymer electrolytes. Furthermore, although some oxidation current was observed due to the reaction with lithium metal after the addition of BF3-THF, electrochemical stability up to 4.5 V was obtained. For the same reason, the lithium-ion transference number decreased from 0.9 to 0.59 after the addition of BF3-THF. However, since the anion is immobilized in the polymer chain, it can be expected as a single-ion conductor regardless of the addition of BF3-THF. [Display omitted] •The crystallite size and melting temperature of polymer electrolyte decreased after BF3-THF addition.•The ionic conductivity increased 15 times after BF3-THF was added.•The electrochemical stability up to 4.5 V was observed.•The lithium ion transference number decreased from 0.9 to 0.59 after addition of BF3-THF.