Plasma-Assisted Amine-Functionalized BNNT Stabilizing the Ni-CoTe@Ti₃C₂T_x MXene Electrode for Flexible Supercapacitor

Developing supercapacitor electrodes that simultaneously exhibit rapid charge transport, high energy density, and prolonged electrochemical stability remains a critical challenge. In this work, we introduce a facile approach to fabricate a NiTe/CoTe heterostructure-based hybrid electrode combined with amine (-NH₂) functionalized boron nitride nanotube (f-BNNT) and Ti₃C₂T_x MXene (Ni-CoTe/f-BNNT@MXene) as a multidimensional electrode for asymmetric supercapacitor (ASC). A two-step Ar/NH₃ plasma engineering process was employed for efficient functionalization of BNNTs, enabling strong interfacial coupling, suppression of tellurides aggregation, and mitigation of MXene restacking to stabilize the composite electrode. Density functional theory reveals that -NH₂ functionalization generates electronic states near the Fermi level, facilitating charge transfer. The Ni-CoTe nanostructures provide abundant redox-active sites associated with Ni²⁺/Ni³⁺ and Co²⁺/Co³⁺ transitions. Through the synergistic contributions, the Ni-CoTe/f-BNNT@MXene nanohybrid offers decent structural integrity and balanced diffusion-controlled Faradaic reactions and surface-controlled charge-storage mechanisms. The assembled ASC using Ni-CoTe/f-BNNT@MXene reaches a maximum energy density of 44 Wh/kg with maximum power density of 5400 W/kg. The device retains ∼91% capacitance after 30 000 GCD cycles with ∼100% Coulombic efficiency. Furthermore, a flexible ASC fabricated with an ionic electrolyte demonstrates stable electrochemical performance under different bending angles.