An ultra-thin polymer electrolyte based on single-helical-structured agarose for high performance solid-state lithium batteries

Abstract

Solid-state lithium batteries are considered as a promising candidate for next-generation energy storage systems because of their high safety and energy density. The solid polymer electrolyte is a paramount component in solid-state lithium batteries. However, it is still a challenge to realize an ultra-thin electrolyte with both high ionic conductivity and mechanical strength. Herein, an ultra-thin polymer electrolyte (UTPE) is prepared by grafting agarose with polyethylene oxide (PEO) in the presence of isophorone diisocyanate (IPDI). The as-prepared electrolyte shows an ionic conductivity of 1.2 × 10⁻⁴ S cm⁻¹ at room temperature, a tensile strength of up to 5.5 MPa and a thickness lower than 32 μm. A Li symmetric cell using the UTPE can stably cycle for 600 h at room temperature. A solid-state LiFePO₄‖Li battery with the UTPE delivers a specific capacity of 131 mA h g⁻¹ over 600 cycles at a 1.0C rate at room temperature, showing a retention rate of 92.9%. Furthermore, a pouch solid-state battery shows good reliability and safety even after being folded, cut and penetrated by a nail. The present investigation offers a novel pathway to design ultra-thin electrolytes aiming for solid-state lithium batteries with high energy density and reliability.