Chitosan-coated hydroxylated BN nanosheets for polyetherimide-based high-temperature energy storage composites

Dielectric polymers are crucial basic materials for capacitive energy storage in power systems and electronic devices. However, the inherent performance degradation of conventional polymers at elevated temperatures greatly restricts their application in emerging energy storage fields. It is a key challenge to prepare polymer-based dielectrics that maintaining high energy storage density ( U e ) under elevated temperatures and high fields. In this work, the positively-charged chitosan (CS) and the negatively-charged hydroxylated boron nitride nanosheets (BNNS-OH) were self-assembled as the surface-charged BNNS-OH@CS hybrid nanostructure. Then it was filled into the polyetherimide (PEI) matrix to obtain the BNNS-OH@CS/PEI composite dielectrics. This hybrid nanostructure can construct trap energy levels in PEI matrix to capture charges, thereby restricting the charge migration. Furthermore, the localized reverse electric field formed at the interface between CS and BNNS-OH can reduce the kinetic energy of high-energy electrons within the composites, consequently disrupting charge transport pathways and mitigating space charge accumulation. Such features endow the composite dielectrics with significantly reduced leakage current and conduction loss under elevated temperatures and high fields. It is noteworthy that the highest U e of the 0.3 wt% BNNS-OH@CS/PEI composite with the charge-discharge efficiency ( η ) above 90 % is 4.2 J/cm 3 at 150 °C, which is 289 % higher than that of pure PEI (~ 1.08 J/cm 3 ). Consequently, this work provides a simple and feasible method for developing polymer dielectrics with high energy storage density under high temperatures and high fields.