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PhD student, The University of Sydney


Looking for and systematically characterise new battery material candidates with high performances

As a result of increased energy demand, energy storage has become a growing global concern over the past decade. Electrochemical energy storage (EES) technologies based on batteries are beginning to show considerable promise as a result of many breakthroughs in the last few years due to their appealing features include high round-trip efficiency, flexible power, and energy characteristics to meet different grid functions, long cycle life, and low maintenance. My PhD project focuses on the discovery, characterisation and optimisation of electrode and solid electrolyte materials in both lithium ion batteries and sodium ion batteries, in which the investigation of materials nuclear & magnetic structures and the dynamics of Li+/Na+ is a key issue. Three techniques below are heavily utilized in my project: (1) Ab initio calculations. It is employed to identify and compare the energies of framework structures (for both nuclear and magnetic) with hosting Li/Na from materials data mining, which give an improved understanding of how the experimentally determined structures arise and how they will evolve with mobile ion concentration under electrochemical cycling. Knowledge of the ground-state magnetic structure also permits the accurate calculation of redox potentials, in conjunction with electrochemical measurements. (2)Neutron scattering technique. It concerns new crystalline materials for light metal-ion batteries, in several ways. Neutron diffraction reveals the location and occupancies of Li/Na sites in the crystal lattice, and hence conduction pathways. In situ experiments explicitly reveal Li/Na ion mobility, as well as phase changes under operating conditions that undermine long-term stability. Inelastic and quasielastic neutron scattering probe the dynamics of the mobile ions and the supporting lattice. Besides, low-temperature neutron diffraction reveals the spin-ordered ground states of the transition metal counter-cations, which are not only fundamentally fascinating due to their complex super-super-exchange pathways, but also characteristic of their electrochemical states in batteries. (3) In-situ transmission electron microscopy characterization. It is performed to study materials degrade on a larger scale over repeated cycling: nanocrystallisation, and changes in the roughness of the interfaces. The information of the materials failure collected by virtue of this technique will help to effectively design the accurate ways to optimise the materials.


In situ TEM probing of crystallization form-dependent sodiation behavior in ZnO nanowires for sodium-ion batteries

Abstract: Development of sodium-ion battery (SIB) electrode materials currently lags behind electrodes in commercial lithium-ion batteries (LIBs). However, in the long term, development of SIB components is a valuable goal. Their similar, but not identical, chemistries require careful identification of the underlying sodiation mechanism in SIBs. Here, we utilize in situ transmission electron microscopy to explore quite different sodiation behaviors even in similar electrode materials through real-time visualization of microstructure and phase evolution. Upon electrochemical sodiation, single-crystalline ZnO nanowires (sc-ZNWs) are found to undergo a step-by-step electrochemical displacement reaction, forming crystalline NaZn13 nanograins dispersed in a Na2O matrix. This process is characterized by a slowly propagating reaction front and the formation of heterogeneous interfaces inside the ZNWs due to non-uniform sodiation amorphization. In contrast, poly-crystalline ZNWs (pc-ZNWs) exhibited an ultrafast sodiation process, which can partly be ascribed to the availability of unobstructed ionic transport pathways among ZnO nanograins. Thus the reaction front and heterogeneous interfaces disappear. The in situ TEM results, supported by calculation of the ion diffusion coefficient, provide breakthrough insights into the dependence of ion diffusion kinetics on crystallization form. This points toward a goal of optimizing the microstructure of electrode materials in order to develop high performance SIBs.

Pub.: 13 Sep '16, Pinned: 30 Aug '17