Effect of the Linker and Substituents on the Ionic Conductivity of Borate Single-Ion Polymers for Lithium Batteries

Abstract

Polymer electrolytes with high ionic conductivity are actively searched for their application as solid electrolytes in lithium batteries. Here, we show new borate single lithium-ion conducting polymers with high ionic conductivity and lithium transference number values. For this purpose, eight new methacrylic lithium borate polymers were synthesized and characterized with varying chemical compositions focusing on the linker between the polymer chain and the pendant borate ionic group and its substituents. The polymers with the optimum ethoxy linker and fluorinated pendant groups show a low Tg value and the highest ionic conductivity value of 1.29×10-4 S.cm-1 at 60 °C. This value is among the highest ionic conductivity reported for a single lithium-ion conducting homopolymer. These polymers show a high lithium transference number (between 0.88 and 0.96) and electrochemical stability close to 4.2 V vs Li+/Li, making them promising candidates for application as solid electrolytes in lithium batteries.