Structure-Controlled Synthesis And Electrochemical Performance Of Anode Materials For Lithium Ion Batteries

In recent years, electrochemical energy-storage devices with high energy and power densities and long lifespan, especially rechargeable Li batteries and supercapacitors have stimulated global research interests due to the ever-growing demands for grid storage, electric vehicles and portable electronics.Owing to unique morphological and structural advantages and favorable physicochemical properties including large surface-to-volume ratios, high electrical conductivity, and excellent chemical and thermal stabilities, hollow carbon spheres (HCSs) have been proved to be promising candidates in the applications for batteries, electric double-layer capacitors, catalyst-supports, and adsorbents for water treatments. In this dissertation, we designed and synthesized two kinds of hollow carbon sphere composite materials with novel structure to study the electrochemical performance.1. We designed and synthesized a hollow carbon sphere composite materials with novel structure to study the electrochemical performance. The obtained graphene-wrapped graphitic hollow carbon spheres (G-graphitic HCS) demonstrate the admirable multifunctions in energy storage devices including Li-ion battery, Na-ion battery and supercapacitor. It delivers an unprecedentedly high initial discharge capacity of 2007 mAh g-1 at 0.1 A g-1, while also preserving 92.4% of the initial charge capacity after 100 cycles in a prototype Li half cell. Herein, the thin carbon shell and the hollow and hierarchically porous structure of G-graphitic HCS facilitate the ionic transport and provide more active sites for the storage of ions. Moreover, both of its graphitic components (graphene shell and graphitic HCS) result in a seamless and highly-efficient transmission pathway for electrons.2. We presented the synthesis of a novel nanocomposite, in which ultrathin MoS2 nanosheets were grown on graphene-wrapped polystyrene sphere by a facile hydrothermal route. After the removal of the PS core via high-temperature calcinations, hollow nanostructured MoS2/C coated-graphene spheres (MoS2/C-G) were obtained. MoS2/C shell as a host for Li storage shortens the mass diffusion path and internal graphene shell improves conductivity effectively. The cooperation of several active components effectively solves the problems of volume expansion and poor conductivity during the charge-discharge process. Electrochemically evaluated as an anode material for LIBs, the MoS2/C-G spheres exhibit outstanding performances, especially at high rates, and deliver a high reversible capacity of 2016.4 mA h g-1 after 500 cycles at a current density of 1 A g-1, promoting the high power applications.