Hybrid Nanostructured Carbon-based Materials for High Performance Rechargeable Lithium Batteries

用於高性能可充電鋰電池的復合納米結構碳基材料

Student thesis: Doctoral Thesis

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Award date24 Aug 2017

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Abstract

Metal oxides and sulfur are promising candidates for the next-generation rechargeable lithium battery electrode materials as substitute for existing commercial LiCoO2-graphite system because of their high theoretical specific capacities, abundance, easy preparation, and low cost. Although these candidates have many advantages, their poor electrical conductivity and slow Li-ions diffusion in solid bulk materials greatly limit the rate capabilities for fast charge/discharge. In addition, the dramatic volume change in these elements during charge/discharge results in pulverization of the active material and the exfoliation from the current collector, leading to poor cycling performance and rapid capacity decay. More severe challenges are lithium polysulfides intermediates(Li2Sn, 4≤n≤8) generated during electrochemical-reduction reaction would dissolved in organic liquid electrolytes and shuttled between the sulfur cathode and the metallic lithium anode. The sulfur loss originated from this shuttle effect leads to poor cycling capability and low coulombic efficiency. As a result, the practical applications of metal oxides and sulfur are greatly challenged until today given their poor rate and cycling capability.
Considering for aforementioned challenges, this thesis is aim to rational combine sulfur or metal oxides with various carbon to achieve hybrid nanostructured electrode materials for high performance rechargeable lithium batteries. This thesis focuses on the synthetic methodology, characterization and electrochemical investigation of the hybrid nanostructured carbon-based materials integration with electroactive materials for high performance rechargeable lithium batteries. Serval hybrid nanostructured carbon materials were successfully fabricated by multiple strategies and they were incorporated with metal oxides or sulfur for high performance rechargeable lithium batteries. Firstly, ZnFe2O4 nanoparticles anchored on acetylene black to form hierarchical porous granule and coated with a thin carbon layer were synthesized by heat induced self-assembly and then they were used as anodes for Li-ion batteries. Secondly, a nitrogen and phosphorus co-doped hierarchical porous carbon was fabricated by simple pyrolysis of polyaniline aerogels in the presence of phytic acid and subsequently activation treatment by KOH and then this carbon was employed as host for sulfur impregnation. Thirdly, a nitrogen doped carbon nanotubes-hierarchical porous carbon hybrids as cathode for Li-S batteries were prepared and simultaneously in-situ nitrogen doped by simple pyrolysis of the low-cost raw material melamine-formaldehyde resin in the presence of nano-CaCO3 as template and bimetallic combination of Fe-Co as catalyst. Fourthly, sulfur encapsulated inside nitrogen doped hollow carbon sphere and graphene networks were synthesized by self-template method. Benefiting from the advantages of high conductivity, optimal hierarchical porosity, fast ion transportation, physical confinement and chemical adsorption of hybrid nanostructured carbon materials, these composites as electrodes exhibit favorable electrochemical performance, including high reversible capacity, good cycling stability, and high rate performance, which suggest that these rational hybrid materials have alluring prospect for superior rechargeable lithium batteries.