Making use of the inherent nitrogen content of spent coffee grounds to create nanostructured activated carbon for supercapacitor and lithium-ion battery applications

Nitrogen-containing carbonaceous materials were synthesized from spent coffee grounds (SCG) without the addition of nitrogen doping agents. The synthesis process included pre-treatment by hydrothermal carbonization (HTC) to incorporate inherently present nitrogen atoms into carbon structures followed by activation with different KOH ratios at 800 °C under N2 atmosphere to form the activated product (A-SCG). The optimum ratio of biochar to KOH was 1:3 (A-SCG 1:3) with 1.2 at.% nitrogen content remaining along with a high surface area of 1835 m2 g−1. The electrochemical performance of the obtained materials was then characterized for supercapacitor and lithium-ion battery applications. In a two-electrode system, high specific capacitance of 312 F g−1 and energy density of 10.84 Wh kg−1 was observed at a current density of 0.1 A g−1. The material possessed a high-power density of 4589 W kg−1 at a current density of 3 A g−1. In addition, good cycling stability of 97% capacitive retention (up to 10,000 cycles) at 0.5 A g−1 was observed. Furthermore, high performance was demonstrated in lithium-ion battery applications with the sample A-SCG 1:3. As an anode material, the batteries showed a specific capacity of 592 mAh g−1 at a current density of 100 mA g−1 which is ~1.6 times higher than the theoretical capacity of graphite (372 mAh g−1). This system also demonstrated excellent cycling stability up to 500 cycles, while still providing capability retention of 96% and columbic efficiency of 97%. As a result, nitrogen containing nanostructured carbon derived from spent coffee grounds could be a promising electrode material in both supercapacitor and lithium-ion battery applications.