Complete conversion of Ni foam to Ni3S2 using diverse sulfur sources with a freestanding PPy binder-free hybrid electrode for asymmetric supercapacitors

Abstract

The development of high-performance asymmetric supercapacitors with enhanced energy density remains a critical challenge in energy storage research. In this work, we present, for the first time, a novel binder-free Ni₃S₂ hybrid composite electrode with incorporation of polypyrrole (PPy) synthesized via a straightforward hydrothermal method. This unique composite architecture effectively shortens ion diffusion pathways and tuning the morphology, resulting in superior electrochemical performance. The optimized PPy@Ni₃S₂ electrode exhibits primarily pseudocapacitive behavior driven by synergistic redox reactions between multiple oxidation states within the composite. It achieves a remarkable specific capacitance of 1860 F/g at 1 A/g, outperforming many previously reported Ni₃S₂-based materials. When assembled into an asymmetric supercapacitor device, it delivers a specific capacitance of 63 F/g at 1 A/g, with an energy density of 23 Wh/kg at a power density of 798 W/kg, alongside excellent cycling stability with ∼119 % capacitance retention over 6000 cycles. These results demonstrate a significant advancement in electrode design and provide a promising route toward efficient, durable energy storage systems.