High-Performance Ionic Liquid-Based Gel Polymer Electrolyte Incorporating Anion-Trapping Boron Sites for All-Solid-State Supercapacitor Application

A high-performance boron-containing gel polymer electrolyte (GPE) with semi-interpenetrating polymer network structure was successfully prepared by a rapid and easy one-step polymerization process assisted with UV light, exploiting poly(ethylene oxide) as a polymer host, the novel borate ester monomer as the cross-linker, and LiClO₄ and EMIMBF₄ both as the plasticizer and electrolytic salt, respectively. Owing to the incorporation of anion-trapping boron sites, the ionic conductivity of the as-prepared GPE at room temperature can be up to 5.13 mS cm^-1. In addition, the boron-containing GPE (B-GPE) exhibits favorable mechanical strength, excellent thermal stability, and extremely low flammability. Moreover, the all-solid-state symmetric supercapacitor using B-GPE as the electrolyte and reduced graphene oxide as the electrode was fabricated and exhibited a broad potential window (3.2 V). The all-solid-state symmetric supercapacitor based on B-GPE can still reach a high energy density of 27.62 W h kg^-1 with a power density of 6.91 kW kg^-1 at a high current density of 5 A g^-1. After 5000 cycles at a current density of 1 A g^-1, the all-solid-state supercapacitor with B-GPE displays a decent capacitance retention of 91.2%.