Rapid self-healing, highly conductive and near-single-ion conducting gel polymer electrolytes based on dynamic boronic ester bonds for high-safety lithium metal batteries

Abstract

Polymer electrolytes with high ionic conductivity and good self-healing capability are crucial for the development of lithium metal batteries with enhanced rate capability and safety. However, the application of self-healable polymer electrolytes is hindered by low ionic conductivity and slow self-healing speed. Herein, boronic ester based self-healing gel polymer electrolyte (PBAD-PEG) with high ionic conductivity and fast self-healing speed is developed. PBAD-PEG is fabricated by thiol-ene click reaction of a multifunctional monomer 2,2′-(1,4-phenylene)-bis (4-allyloxy-1,3,2-dioxaborolane) (PBAD) consisting of two dynamic boronic ester bonds, pentaerythritol tetra(3-mercaptopropionate) and polyethylene glycol diacrylate. Abundant reversible boronic ester bonds endow PBAD-PEG with good flexibility and excellent self-healing ability. PBAD-PEG can self-heal within 1 h at room temperature after damaged, which effectively restores the ionic conductivities and mechanical properties. PBAD-PEG possesses high ionic conductivity of 8.67 × 10−4 S cm−1 at 25 °C. Lewis acid-base interactions between anions and boron atoms of PBAD-PEG contributes to ultrahigh lithium-ion transference number of 0.71. PBAD-PEG exhibits significant resistance to the growth of Li dendrites. The fabricated LiFePO4/Li batteries with PBAD-PEG achieve significantly boosted cycle stability (capacity retention of 92.6 % after 150 cycles). More importantly, LiFePO4/Li cells with the healed PBAD-PEG also show excellent cycle performance.