Potassium gluconate-derived N/S Co-doped carbon nanosheets as superior electrode materials for supercapacitors and sodium-ion batteries

Hard carbon has attracted enormous attentions as electrode materials for various energy storage devices owing to its low cost, abundant sources and high theoretical capacitances/capacities. However, it still suffers poor electrical conductivity and unsatisfying rate performance. Herein, N/S co-doped ultrathin carbon nanosheet is reported as high performance electrode material for both supercapacitors and sodium-ion batteries. The symmetric supercapcitors assembled with the as-synthesized materials (1.0 M Na₂SO₄ as electrolyte) deliver a high energy density of 24.5 Wh kg⁻¹ at a power density of 500 W kg⁻¹ within a wide voltage range of 0–2.0 V. When being served as anode for sodium-ion batteries, the electrode exhibits a high reversible capacity (371.2 mAh g⁻¹ @ 0.1 A g⁻¹) and superior rate capability (180.9 mAh g⁻¹ @ 10.0 A g⁻¹). Besides, the as-fabricated electrodes display stable cycling performance in both energy storage systems. Subsequent mechanism studies further shed light on the excellent electrochemical performance.