High-Performance Alkaline Battery-Supercapacitor Hybrid Based on Bimetallic Phosphide/Phosphate

Abstract

Transition metal-based materials explored for energy storage applications viz. batteries, supercapacitors and more recently battery-supercapacitor hybrids (BSHs) abundantly involve Co-based materials. However, the supply chain issues and low electronic conductivity force us to look for alternative options. In this regard, Co-free binary metal phosphide/phosphate consisting of Ni and V metal (NiVP/Pi) microspheres as the positive electrode of BSH which shows a high specific capacity of 502 C g⁻¹ (1004 F g⁻¹) at 2 mV s⁻¹ while retaining a high specific capacity of 214 C g⁻¹ (428 F g⁻¹) at 12 A g⁻¹ is reported. The high electronic conductivity of binary metal phosphide in NiVP/Pi electrode and the rich electrochemical active sites due to Ni and V metal centres results in exciting performance. More interestingly, the hybrid device is successfully developed by employing NiVP/Pi as the positive electrode and carbon nanotubes (CNTs) as the negative electrode. The hybrid device (NiVP/Pi//CNT) is able to achieve a maximum energy density of 22.17 Wh kg⁻¹ and a power density of 5 kW kg⁻¹ with 91.7% capacitance retention after 7500 continuous galvanostatic charge–discharge cycles.