Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Mechanical and Materials Engineering

Supervisor

Xueliang(Andy) Sun

Abstract

The practical applications of lithium ion batteries are highly dependent on the choice of electrodes, where boosting the materials innovations to design and achieve high capacity, excellent cycling performance, rate capability, low-cost and safe electrode materials provide the best solution. Based on this, tin-based anodes have gained great attention due to its high theoretical capacity, low cost and nontoxic nature to environment. Nevertheless, it undergoes significant volume variation(259%)during the operation of the battery, leading to pulverization and significant capacity fade. Thus, the practical application of tin-based anodes is still quite challenging. This thesis tackles issues related to tin-based anodes. It is demonstrated that designing hierarchical nanostructured tin and tin-based carbon composites particular tin-based graphene composites are the most effective routes to achieve excellent electrochemical properties.

In this thesis, we reported the rational design and fabrication of nanostructured tin-based anodes which began with the synthesis of relevant electrode materials as well as evaluation of their electrochemical performance. Further, synchrotron based X-ray absorption spectroscopy was conducted to unveil the electronic structure of these composites for better understanding of the mechanism behind the performance. Various strategies of material design have been used. These include:

(i) SnO2 nanowires on conducting substrates are successfully obtained using hydrothermal process. The electronic structure and the optical properties study revealed the different crystallinity and surface/defect states related luminescence. (ii) Further we extend the research to fabricate the hierarchical tin-based graphene composites such as graphene-SnO2 nanoparticles and SnO2 nanowire/graphene/carbon composites using hydrothermal method. The hierarchical nanocomposites exhibit better performance in both high and stable capacity benefitting from the buffering effect of carbonaceous materials as well as high capacity of tin dioxide. (iii) In addition, Sn@C-graphene was obtained using chemical vapor deposition method. The core-shelled Sn@C nanoparticles are well embedded in graphene matrix with superior electrochemical performances. (iv) Refer to Sn@C nanowires on metallic substrates obtained by the same route, the high cyclic capability is achieved benefitting from the one dimensional core-shell structure. (v) Most interestingly, through surface coating of Al2O3 on SnO2 electrodes via atomic layer deposition, we found that the well defined and optimized Al2O3 layer could relieve mechanical degradation and form an artificial SEI layer, leading to improved electrochemical performances compared with bare SnO2 electrodes. The element specific X-ray absorption spectra uniquely characterize the Sn, C and O specified edge of target samples, providing the information of the cystallinity and surface/defect states, revealing the strong chemical bonding and interactions between Sn or SnO2 with graphene or carbon layer, allowing for better understanding of the performance. The study in this thesis demonstrates nanostructured tin-based anodes can be alternative high performance anodes in the next generation lithium ion batteries.

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