Boosting ion diffusion at Ni2P@3D nanostructure carbon network interface for superior and durable sodium-ion hybrid capacitor

Abstract

Sodium-ion hybrid capacitors (SIHCs) are a promising next-generation energy storage device because of their high energy and power density, long lifespan, and natural abundance of sodium. Ni2P is an appealing anode material for battery-type electrodes because of its high theoretical capacity (542 mAh g−1). This study proposes encapsulating Ni2P with carbon nanofibers (Ni2P@CNF) using a simple electrospinning method to produce an anode material suitable for high-performance SIHCs. The three-dimensional (3D) network of CNF interconnections delivers improved electrical conductivity and ion diffusivity. The CNF can efficiently reduce the stress repeatedly inflicted on the Ni2P because of the volume change, leading to superior stability. In the half cell, the Ni2P@CNF reveals a high specific capacity of 184 mAh g−1 than Ni2P (40 mAh g−1) and Ni2P/CNF (92 mAh g−1) at a current density of 0.1 A g−1. The Ni2P@CNF possesses a high-rate capability of 81 mAh g−1 at a current density of 2 A g−1. Furthermore, the ion diffusivity and electrochemical properties were investigated using electrochemical impedance spectroscopy. By integrating the Ni2P@CNF anode with an activated carbon (AC) cathode, the SIHC exhibits a high energy density of 136 Wh kg−1 and a high power density of 16.3 kW kg−1. The fabricated SIHC demonstrates high long-term stability with a capacity retention of 80% over 3,500 cycles.