Deconvolution of capacitive and diffusive charge/lithium storage in lyophilized NiCo2S4–NiCo2O4 composite for supercapattery and lithium-ion battery

Abstract

In this work, a spinel-type metal sulfide/oxide (NiCo₂S₄–NiCo₂O₄) composite in which NiCo₂S₄–NiCo₂O₄ anchored on graphene oxide was synthesized via a simple freeze-drying method was explored as an electrode for both supercapattery and lithium-ion battery applications. Materials characterization revealed the formation of a NiCo₂S₄–NiCo₂O₄ composite material. Electrochemical studies, including cyclic voltammetry (CV), galvanostatic charge–discharge (GCD) cycling and electrochemical impedance spectroscopy (EIS), were performed for both the lithium-ion battery (LIB) and supercapattery in the form of a CR-2032 coin cell featuring the NiCo₂S₄–NiCo₂O₄ electrode. The lithium storage performance of the NiCo₂S₄–NiCo₂O₄ anode in a half-cell exhibited a high reversible capacity of 674 mA h g⁻¹ at a rate of 0.2C with high reversibility and excellent cycling stability over 500 cycles at a rate of 1C. The supercapattery device delivered a high specific energy of 86 W h kg⁻¹ at a specific power of 320 W kg⁻¹ with excellent cycling stability and Coulombic efficiency. In both the LIB and supercapattery, using a power law and Dunn's method, deconvolution of the capacitive and the diffusive charge/lithium storage were examined. The high capacitive contribution was attributed to the nanostructured features of the freeze-dried composite material.