Effect of polypyrrole-derived N-doped carbon coating on the sodium storage properties of NiCo2S4 synthesized by recycling discarded mobile phone batteries.

NiCo 2 S 4 with a spherical spinel structure was innovatively synthesized from discarded mobile phone batteries using a simple hydrothermal method, and the surface was coated with N-doped carbon to form NiCo 2 S 4 @NC. The products were used as anode materials of sodium-ion batteries to study the effect of the N-doped carbon layer on the electrochemical properties, structure and morphology. The results of XRD, FESEM and TEM revealed that the N-doped carbon layer derived by carbonizing polypyrrole had a minimal effect on the structure and morphology of NiCo 2 S 4 , but was coated on the surface of NiCo 2 S 4 with different thicknesses to adjust the electrochemical performance. The presence of N-doped carbon in NiCo 2 S 4 @NC was confirmed by Raman spectroscopy. The mesoporous structure of NiCo 2 S 4 and NiCo 2 S 4 @NC was corroborated by N 2 adsorption-desorption isotherm analysis, and the optimal specific surface area and pore size were 23.14 cm2/g and 18.0 nm, respectively. X-ray photoelectron spectroscopy indicated that Co2+/Co3+ and Ni2+/Ni3+ coexist in the spinel NiCo 2 S 4 @NC 50 synthesized upon adding 50 μL of pyrrole monomer. NiCo 2 S 4 @NC 50 outperformed other products in terms of its electrochemical properties, where its initial discharge specific capacity under the current density of 0.1 A g−1 was 1099.6 mA h g−1 and the specific capacity following 100 cycles reached 327.5 mA h g−1. NiCo 2 S 4 @NC 50 exhibited an optimal electrochemical performance and demonstrated a competent approach toward recycling discarded mobile phone batteries and building electrodes with high performance for use in energy equipment. [ABSTRACT FROM AUTHOR]