NiCo₅S₈ structure with unique morphology as a cathode active material for All-Solid-State Lithium-Sulfur batteries

Numerous attempts have been made to develop alternative materials to replace sulfur in all-solid-state batteries. Recently, transition metal sulfides(TMSs) have aroused researchers’ great interest to replace for extremely insulating sulfur and utilize as a cathode active material. In this study, a new TMS in ternary Ni-Co-S phase diagram with NiCo5S8 stoichiometry was synthesized in unique morphology and its electrochemical performance was evaluated in all-solid-state battery utilizing lithium and Li7P3S11 as anode and solid electrolyte, respectively. The cell was shown to deliver initial capacity of 884.8 mAh g−1 and 0.52 mAh capacity loss per cycle from 2nd to 120th charge and discharge at 0.3 mA cm−2 current density. Compared to sulfur, high electrochemical performance of the active material was attributed to the higher electronic conductivity of NiCo5S8, unique morphology and different reaction mechanism of TMSs. Besides, the discrepancy between the experimental and computational results for electronic state of the material was asserted by bandgap calculations through UV–Vis spectrometer and Density Functional Theory based calculations. Charge transfer mechanism of the cell was obtained through CV tests performed at different scan rates to distinguish surface mediated(capacitive) and diffusion-controlled(intercalation) processes. Moreover, in-situ Raman analysis was recorded to observe the reaction products at charge and discharge plateus to assert the reaction mechanism of the novel TMS cathode active material.