High-voltage ionic liquid-based flexible solid polymer electrolyte for high-performance Li-ion batteries

Abstract

Imidazolium ionic liquid-based solid polymer electrolyte (SPE) membrane was developed for Li-ion batteries. The low viscous 1-ethyl-3-methylimidazoilium bis(trifluoromethane sulfonyl)imide [EMIM][TFSI] ionic liquid was found to be more compatible with the polymer matrix of poly (ethylene glycol) methyl ether methacrylate (PEGMA) and cellulose triacetate (CTA) offering excellent mechanical strength, thermal and electrochemical stabilities, and improved flexible nature to the SPE membrane. Linear sweep voltammetry study showed that the SPE membrane was highly stable up to 4.8 V and could be employed in high-voltage applications. The impedance analysis of SPE displayed ionic conductivity of the order 1.24 × 10⁻³ S cm⁻¹ at room temperature, while the ionic conductivity increased to 6.2 × 10⁻³ S cm⁻¹ at a temperature of 70 °C. The performance of the cell tested with the configuration LiFePO₄/SPE/Li showed an initial discharge capacity of 167 mA h g⁻¹ at room temperature with 99% efficiency. The ionic liquids played a significant role in tuning the mechanical as well as electrochemical properties of SPE and most importantly the safety of Li-ion batteries.