Insight on the conversion reaction mechanism of NiCo2S4@CNTs as anode materials for lithium ion batteries and sodium ion batteries

Abstract

The three-dimensional network structure of NiCo2S4@CNTs electrode materials for LIBs and SIBs composing NiCo2S4 nanoflakes anchored on the surface of carbon nanotubes (CNTs), which was prepared by electrostatic adsorption through a two-step solvothermal method. This composite structure is helpful to alleviate the volume expansion effect of NiCo2S4 materials and enhance the conductivity of composite electrode materials. Therefore, NiCo2S4@CNTs anode materials exhibit good cycle stability (after 80 cycles, the NiCo2S4@CNTs electrodes deliver the capacities of 783.17 mAh g−1 for LIBs and 291.10 mAh g−1 for SIBs) and rate performance (the NiCo2S4@CNTs electrodes show 517.64 mAh g−1 in LIBs and 169.29 mAh g−1 in SIBs at 1000 mA g−1). Moreover, the conversion mechanism of NiCo2S4@CNTs electrode materials was revealed combined with in-situ XRD, ex-situ XRD, ex-situ Raman spectrum and HRTEM. The cycle reversibility of conversion products in lithium and sodium storage process were also proved. Furthermore, the energy storage behavior of NiCo2S4@CNTs electrodes (the combination of capacitance and diffusion) during the process of charge and discharge both in LIBs and SIBs was indicated by CV curves of different scanning scans. Such conversion reaction mechanism provides a reference for the research of this kind of materials in other alkali metal ion batteries.