Vanadium nitride @ coconut shell carbon composite modified by carbon encapsulation as an anode material for symmetric supercapacitors

Among high-performance, clean, safe, and cost-effective energy storage technologies, supercapacitors have emerged as one of the most promising solutions for harnessing and delivering non-fossil energy. In this work, a sustainable biomass-derived carbon-coconut shell carbon (CSC) was employed as both a conductive scaffold and carbon source to support vanadium nitride (VN) via a hydrothermal synthesis route, yielding a CSC@VN composite. To further enhance electrochemical stability, the composite was subjected to a surface carbon-encapsulation treatment, resulting in a unique sandwich-structured CSC @VN@ amorphous carbon (CSC@VN@AC) material. The as-prepared CSC@VN composite delivered a specific capacitance of 122.3 F g⁻ 1 at a current density of 1 A g⁻ 1 and retained 79% of its initial capacitance after 8,500 charge–discharge cycles, demonstrating respectable cycling stability. Remarkably, the carbon-encapsulated CSC@VN@AC exhibited an improved specific capacitance of 129.81 F g⁻ 1 under the same conditions, along with significantly enhanced long-term cycling performance because of carbon-encapsulated. This enhancement is attributed to the protective amorphous carbon layer, which mitigates structural degradation and improves interfacial charge transfer during repeated electrochemical operation.