Boosting Lithium Ion Conduction of Carboxylate‐Type Single‐Ion Conducting Polymers through Complexation with Ionic Liquids for Lithium‐Ion Batteries

Abstract

Single‐ion conducting (SIC) polymers, wherein anions are covalently bonded to the polymer chain, selectively facilitate the movement of lithium ions, making them promising polymer electrolytes for lithium‐ion batteries because only lithium ion acts as a charge carrier. Carboxylate‐type SIC polymers offer cost advantages and are facilely prepared compared to conventional types like sulfonylamide‐type SIC polymers. However, they are known to suffer from inefficient dissociation of lithium ions due to their high basicity. In this study, enhancement of lithium‐ion dissociation in carboxylate‐type SIC polymers is investigated by complexing them with ionic liquid (IL). Incorporation of IL with the SIC polymer significantly improves electrochemical properties, achieving a high ionic conductivity close to 2 mS cm–1 and a critical current density of 2.1 mA cm–2 in a Li symmetric cell at 25 °C. The interaction between the SIC polymer and IL is confirmed through infrared and Raman spectroscopy. Electrochemical tests of the Li/LiFePO4 cell exhibit a high reversible capacity of 128.6 mAh g–1 with a cycle retention of 89.9% after 100 cycles at 1C (1C = 170 mA g–1) and an excellent recuperation even after rate tests at 6C.