Master of Science in Mechanical Engineering (MSME)


Mechanical Engineering

Document Type



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 master thesis, we introduce several research works on novel design and synthesis of nanostructured electrode materials with high performance for lithium-ion batteries. The exploration of new inexpensive rechargeable batteries with high energy-density electrodes is a key to integrate the renewable sources such as solar and wind, and address the sustainability issues. Herein, we also introduce a scalable method to prepare hierarchical graphene-encapsulated hollow SnO2@SnS2 nanostructures by in-situ sulfuration on the backbones of hollow SnO2 spheres via a simple hydrothermal method followed by a solvothermal surface modification. The as-prepared hierarchical SnO2@SnS2@rGO nanocomposite can be used as anode material in lithium ion batteries, exhibiting excellent cycleability with a capacity of 583 mAh/g after 100 electrochemical cycles at a specific current of 200 mA/g. This material shows a very low capacity fading of only 0.273% per cycle from the 2nd to the 100th cycle, lower than the capacity degradation of bare SnO2 hollow spheres (0.830%) and single SnS2 nanosheets (0.393%). Even after being cycled at a range of specific current varied from 2000 mA/g to 100 mA/g, hierarchical SnO2@SnS2@rGO nanocomposite maintains a reversible capacity of 664 mAh/g, which is much higher than single SnS2 nanosheets (374 mAh/g) and bare SnO2 hollow spheres (177 mAh/g). Such significantly improved electrochemical performance can be attributed to the unique hierarchical hollow structure, which not only effectively alleviates the stress resulted from the lithiation/delithiation process and maintains structural stability during cycling but also reduces aggregation and facilitates ion transportation. This work thus demonstrates the great potential of hierarchical SnO2@SnS2@rGO nanocomposites for application as high-performance anode material in next-generation lithium ion battery technology. Rational design composite material is a main way to improve the performance of lithium ion batteries. Co3O4, attracted by the high theoretical capacity, has long suffered from low electrical transportation and dramatic large volume variations. Herein, to overcome these challenges, we report a scalable method to fabricate integrated Co3O4/TiO2 composite hollow polyhedrons through a cation-exchange approach in metal-organic framework. In this synthesis, well-defined ZIF-67 particles not only serve as the host to accommodate exchanged titanium cations but also act as the template to form the hollow polyhedron structure. The obtained integrated Co3O4/TiO2 composite hollow polyhedrons exhibit a high reversible capacity of 630 mAh/g at a rate of 500 mA/g after 200 cycles, accounting for 96.9% of the initial capacity, much higher than that of pure Co3O4 hollow polyhedrons, which can only maintain a specific capacity of 200 mAh/g and a capacity retention of only 40%. The optimized integrated Co3O4/TiO2 composite hollow polyhedrons display significant improvements in electrochemical performance, demonstrating great potential as advanced anodes in future lithium ion batteries.



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Committee Chair

Wang, Ying