Metal Sulfides for High Performance Lithium Ion and Sodium Ion Battery Anodes

Abstract

The research described in this dissertation aims to develop facile synthetic routes to fabricate carbon coated metal sulfides (SnS, SnS2, MoS2) with sophisticated nanostructure to achieve high capacity and long cycle life in Li-ion and Na-ion batteries, and provide in-depth understanding on their electrochemical behavior.

In this study, a simple solid-state reaction method to synthesize carbon coated tin sulfides (SnS/C, SnS2/C) nanomaterials was developed, which enables feasible large-scale production for the wide application of battery technology. The as-prepared SnS/C nanospheres exhibit high capacity (900 mAh/g) and long cycle life (200 cycles) at a current density of 227 mA/g in lithium ion batteries. Tin disulfide (SnS2) with larger layer distance (5.9 Å) as compared with SnS (3.4 Å) was chosen as an anode material in Na-ion batteries. The as-prepared SnS2/C nanospheres from solid-state synthesis deliver a high reversible capacity (~600 mAh/g) for hundreds of cycles, demonstrating one of the best cycling performances in all reported SnS2/C anodes for Na-ion batteries to date. Mechanism studies demonstrate that the superior cycling stability of the SnS2/C electrode is attributed to the stable nanosphere morphology and structural integrity during charge/discharge cycles.

The MoS2/C composite with nanoflower morphology was fabricated from a hydrothermal method. MoS2/C nanomaterials deliver a reversible capacity of 520 mAh/g at 67 mA/g and maintain at 400 mAh/g for 300 cycles at a high current density of 670 mA/g. The stable cycling performance and high coulombic efficiency (~100%) of MoS2/C nanospheres are ascribed to the highly reversible conversion reaction of MoS2 during sodiation/desodiation and the formation of a stable solid electrolyte interface (SEI) layer. The MoS2/C nanomaterial is also synthesized using a one-step spray pyrolysis in which sucrose serves as a carbon source. The MoS2/C nanomaterials from spray pyrolysis exhibit higher capacity and stable cycling performance in Na-ion batteries. Spray-pyrolysis synthesized MoS2/C nanomaterials are robust to withstand the volume change during charge/discharge cycles, as evidenced by the stable interface resistance in electrochemical impedance spectroscopy (EIS) analysis and good morphology maintenance after cycling in scanning electron microscopy (SEM) image.