Nitrogen-Doped tannin carbon dots anchored NiCo-LDH composites for high-performance asymmetric supercapacitors

Abstract

This study demonstrates the synthesis and application of nitrogen-doped tannin carbon dots (TCDs) derived from condensed tannin of grapestone through a single-step hydrothermal method. The TCDs were employed to enhance the electrical conductivity, active site availability, structural stability, and charge storage mechanisms of NiCo-LDH composite electrodes. Density Functional Theory (DFT) calculations reveal that the incorporation of TCDs increases the density of states (DOS) near the Fermi level, thereby improving charge transport properties and contributing to the enhanced cycling stability. In a three-electrode system, the NiCo-LDH@TCDs_3.0 electrode exhibits an exceptional specific capacitance of 1804.2F g⁻¹ at 1 A g⁻¹, with a capacitance retention of 77.4 % at a high current densities of 10 A g⁻¹. As button cell of asymmetric supercapacitor (ASC) assembled with tannin-based activated carbon (TAC600-4) as the negative electrode and NiCo-LDH@TCDs_3.0 as the positive electrode, the device demonstrates a maximum energy density of 87 Wh kg⁻¹ at a power density of 800 W kg⁻¹, and maintains a high energy density of 61.6 Wh kg⁻¹ even at an ultra-high power density of 8000 W kg⁻¹, significantly surpassing devices composed solely of NiCo-LDH. Durability assessments further revealed 78.6 % capacitance retention and 100.9 of coulombic efficiency after 10,000 cycles, underscoring its applicability in high-performance energy storage. This study not only advances the synthesis of carbon dots from sustainable tannin sources but also provides valuable insights into optimizing the specific capacitance, rate capability, and cycling durability of LDH-based supercapacitors.