Optimization strategies for binary transition metal selenides in high-performance supercapacitor-battery hybrid devices

Abstract

Transition metal selenides are revolutionizing the landscape of asymmetric supercapacitors due to their outstanding electrochemical characteristics and offering exceptional specific capacitance. But still crave for stability during cycling, limiting active sites, and conductivity balances that restrict rate capability. Herein, we present the optimization of binary metal selenides synthesized via a simple hydrothermal method for asymmetric supercapacitors. By fine-tuning the metal ratio, we enhance both energy storage capacity and cycling stability and significantly outperform conventional monometallic electrodes. X-ray diffraction (XRD) techniques, energy-dispersive X-ray spectroscopy (EDX), and scanning electron microscopy (SEM) were employed to characterize the phase composition, elemental and surface morphology of all synthesized nanomaterials. In a three-electrode configuration, Ni_0.5Co_0.5Se₂ demonstrated the superior electrochemical performance of all the selenide samples with a specific capacity of 1719.9 C/g and 805.6 C/g (1342.6 F/g) at 2 mV/s and 1.8 A/g, respectively. After that, Ni_0.5Co_0.5Se₂ was employed as a working electrode in an asymmetric supercapacitor, with counter carbon being a counter electrode. Electrochemical evaluation of an asymmetric device in a two-electrode setup showed a remarkable specific energy of 120.9 Wh/kg at the specific power of 1020 W/kg, and it maintained specific energy of 36.3 Wh/kg while achieving an exceptional specific power of 8512 W/kg. Additionally, the prepared device exhibited excellent capacity retention of 96.9 % after 4000 continuous galvanostatic charge/discharge cycles at 10 A/g. Further electrochemical analysis of the asymmetric device was conducted by using a simulation approach to assess diffusive and capacitive processes. The impressive performance of Ni_0.5Co0_.5Se₂ confirms its potential as a promising candidate for asymmetric supercapacitor applications, paving the way for future innovations in sustainable, high-capacity energy storage.