In Situ Growing BCN Nanotubes on Carbon Fibers for Novel High‐Temperature Supercapacitor with Excellent Cycling Performance

Carbon nanomaterials have elicited much research interest in the energy storage field, but most of them cannot be used at high temperatures. Thus, a supercapacitor with high energy and desired stability at high temperatures is urgently required. Herein, BCN nanotubes (BCNNTs) with excellent performance at high temperatures are generated on carbon fibers by optimizing the ratio of B and N. The nanotubes' morphology can effectively alleviate the structural damage caused by the rapid adsorption/desorption of the electrolyte during long-time charge/discharge cycles at high temperatures, thus improving the high-temperature cycle stability. The symmetric supercapacitors that are assembled with the binder-free BCNNT electrode in 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIM·BF₄ ) exhibited a high areal capacitance of 177.1 mF cm^-2 at a current density of 5 mA cm^-2 , and capacitance retention is maintained up to 86.1% for 5000 cycles at 100 °C. Moreover, the flexible supercapacitor based on BCNNTs in poly(vinylidenefluoride hexafluoropropylene)/EMIM·BF₄ /succinonitrile gel electrolyte also exhibits good volumetric capacitance (1.98 mWh cm^-3 at a current density of 5 mA cm^-2 ) and cycling stability (92.6% retention after 200 charge/discharge cycles) at a temperature of 100 °C. This work shows that binder-free BCNNTs are promising materials for high-temperature flexible energy storage devices.