Degree

Doctor of Philosophy (PhD)

Department

Department of Mechanical & Industry Engineering

Document Type

Dissertation

Abstract

Nowadays, the fast-increasing energy demand for efficient, sustainable and environmentally-friendly energy storage devices remains a significant and challenging issue. Lithium ion batteries (LIBs) have been widely used as commercial energy devices in portable electronics and also shown great promise in upcoming large-scale applications due to their advantages of environmental safety, efficiency in energy delivering and light weight. However, due to their limited capacity, energy densities and cycle ability, LIBs still need further improvement to expand their applications to a larger field, especially electric vehicle (EVs) and hybrid electric vehicles (HEVs), in which energy storage devices with large capacity and high energy density are urgently required. The increasing demand for their emerging applications in hybrid electric vehicles (HEVs) and electric vehicles (EVs) requires us to develop LIBs with higher energy density and power density. Significant improvements have been achieved on researching materials with high capacity to replace current commercial cathode material (LiCoO2) and anode material (graphite). In this report, we introduce several research works on novel design and synthesis of nanostructured electrode materials with high performance for lithium-ion batteries.

Our work concentrates on boosting electrochemical performance of both cathode and anode materials for lithium ion batteries. The first project is focused on synthesis of KFe3(SO4)2(OH)6/rGO hybrid as high-performance cathode materials for Li-ion batteries, we found single-layer graphene sheets can serve as both structure-directing agents and growth platforms to directly grow monocrystalline KFe3(SO4)2(OH)6 nanoplates with unique hexagonal shapes, forming KFe3(SO4)2(OH)6/rGO hybrid that exhibits significantly improved performance. Moreover, we also investigated electrospinning method, the new technique to fabricate nanostructures. We synthesized spinel-structured LHMNCO TBA nanowires using an electrospinning method followed by facile ion-exchange promoted phase transition. The spinel-structured LHMNCO TBA shows improved capacity retention and improved rate capability as cathode for lithium ion batteries. In addition, we also developed various several strategies to improve the performance of anode materials. Coral-like SnO2/C composite electrodes has been fabricated through a top-down strategy followed by a sol-gel method of carbon coating, showing significant improvements in rate capability. We also fabricated crystalline-Co3O4-carbon@amorphous-FeOOH interwoven hollow polyhedrons through thermal treatment paired with solution-phase growth. The improve anode performance is attributed to the synergistic effect of integrated crystal and amorphous components as well as the unique interwoven heterostructure. We also investigate the oxygen evolution reaction performance of nanostructured materials. Co3O4-x-carbon@Fe2-yCoyO3 heterostructural hollow polyhedrons have been fabricated by facile thermal treatment followed by solution-phase growth for application as efficient OER electrocatalyst. The last two projects switch to design novel cathode materials for zinc ion batteries. Compared with lithium ion batteries, zinc ion batteries are more attractive for large-scale application due to their low cost, environmental friendliness and safety. However, the development of zinc ion batteries is seriously impeded by the limited choice of suitable cathode materials owing to their low reversibility and slow diffusion of divalent zinc cations in cathodes. We first developed porous MoO2/Mo2N heterostructured nanobelts cathode via electrochemical activation method. During the electrochemical activation, it is interesting to find that MoO2 grains in-situ generate in Mo2N matrix. The improved performance is attributed to the synergistic effect of integrated MoO2 grains and Mo2N nanobelt matrix. In addition, we further studied defect engineered MoS2-x nanosheets as cathode for zinc ion cells. These MoS2-x nanosheets show a preferential insertion of Zn ions into sulfur vacancies, allowing a much greater capacity to be obtained compared to pure MoS2.

Date

11-2-2018

Committee Chair

Wang, Ying

DOI

10.31390/gradschool_dissertations.4726

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