Engineered Carbon Electrodes for High Performance Capacitive and Hybrid Energy Storage

Here we demonstrate, the use of a bio-material coconut sprout (CS) as a single precursor to prepare highly efficient carbon-based electrode materials and a separator with excellent mechanical properties and good chemical stability, for both capacitive and hybrid energy storage systems. A hybrid sodium ion capacitor is fabricated using hard carbon derived from CS (CSDHC) as Na⁺ intercalating anode and high specific surface area porous carbon (SSA ~2000 m² g⁻¹) derived through KOH activation of CS (CSDPC) as a cathode material. The full cell device delivered specific energy of 88 Wh kg⁻¹ at a specific power of 273 W kg⁻¹, when cycled in a potential window of 1.5 - 4.0 V, and showed remarkable rate capability along with excellent long-term cycling stability. Further, symmetric supercapacitor cells are assembled using CSDPC in both aqueous and organic-based electrolytes, which delivered maximum specific energy of 24.7 Wh kg⁻¹ at a specific power of 7.3 kW kg⁻¹. Most interestingly, we used the spongy sprout as the separator in all the assembled cells, which showed excellent mechanical properties and good chemical stability even after 10000 cycles of charge and discharge.