NiCo2S4 nanoparticles//activated balsam pear pulp for asymmetric hybrid capacitors

Abstract

Cauliflower-like NiCo₂S₄ nanoparticles (NPs) for use as battery-type materials have been synthesized via a simple one-step route solvothermal method with thioacetamide (TAA) as the sulfur source. The synthesis of the Ni–Co precursors and the S²⁻ anion exchange reactions occur at the same time, which is time-effective and cost-effective compared to other methods. The obtained NiCo₂S₄ NPs display very competitive electrochemical performance (a specific capacitance of 2480 F g⁻¹ is achieved at a current density of 0.5 A g⁻¹, excellent rate capability with 68% of the original capacitance remained at 10 A g⁻¹ and ideal cycle stability with 80% capacitance remained after 3000 cycles) with high mass-loading (5 mg cm⁻²). In addition, low-cost activated balsam pear pulp (ABPP) is developed as a capacitor-type carbon material for supercapacitors with ideal electrochemical performances. The asymmetric hybrid capacitors (AHCs) are further assembled into pouch cells using battery-type NiCo₂S₄ NPs as the positive electrode, capacitor-type ABPP as the negative electrode and flexible carbon papers as the current collector. The AHCs demonstrate high power density (3.52 kW kg⁻¹ at an energy density of 3.72 Wh kg⁻¹) and cycle stability (72.4% after 9000 cycles).