High-Performance Structural Supercapacitors Based on Solid Polymer Electrolytes via Hydroxylated Boron Nitride Nanosheet Doping

A supercapacitor is a type of energy storage device that integrates the characteristics from traditional capacitors and secondary batteries. The main components that determine its performance are the electrolyte and electrode. Compared with traditional liquid electrolytes, the solid polymer electrolyte (SPE) has better safety, higher strength, lighter weight, and unique flexibility, which has become a research hotspot in related fields. First, boron nitride nanosheets (BNNs) were prepared by a liquid-phase ultrasonic reflux exfoliation method. Atomic force scanning probe microscopy (AFM) analysis showed that the boron nitride layer thickness was 87.62 nm, indicating that the prepared BNNs were on the nanoscale. With that, an epoxy-based solid polymer electrolyte (EP-SPE) with good conductivity, high modulus, and good thermal stability was prepared by melt casting and blending epoxy resin (EP), ionic liquid 1-butyl-3-methylimidazole tetrafluoroborate (C8H15N2BF4), and BNNs with m-phenylenediamine (m-PDA). The ionic conductivity reached 0.394 mS·cm–1, and the modulus was 728.6 MPa. Meanwhile, the initial decomposition temperature (Tinitial) was 384 °C. Finally, the SPE was assembled with activated carbon (AC) electrodes to form a symmetrical supercapacitor. The cyclic voltammetry (CV) and cyclic charge–discharge (GCD) tests showed that the prepared supercapacitor had a stable electrochemical window near 3.5 V and a specific capacitance of 119 F/g at a 0.1 A/g current density. Meanwhile, a maximum energy density of 83.7 Wh/kg at 156.1 W/kg was obtained for our symmetric supercapacitor and revealed a high cyclic retention of 83.7% at 0.5 A/g up to 650 cycles. The performance of this solid electrolyte can meet the performance requirements of supercapacitors in the load-bearing field. It is significant in the field of preparing energy devices.