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.
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
Abstract: Currently known organic electrode materials for lithium-ion batteries have severe cost and resource constraints and are difficult to implement in applications for large-scale electrical energy storage. Compared to lithium-ion battery electrode materials, sodium-ion battery electrode materials are more abundant and more cost effective. However, methods for the prediction of organic electrode materials for sodium-ion batteries are not perfect at present. A fast and accurate theoretical method for finding possible candidates for organic electrode materials for Na-ion batteries is urgently needed. In the present work, dispersion-corrected hybrid density functional theory is applied to study five organic electrode materials for Na-ion batteries. The results of this study show that the D2 dispersion-corrected hybrid functional method (HSE06-D2) can precisely calculate the potential of organic materials with a small average error of approximately 3.68%. The band gap values are approximately lower than 2.5 eV, which proves that the materials have good conductivity and are expected to be candidates for organic electrode materials for sodium-ion batteries.
Pub.: 31 Mar '17, Pinned: 30 Aug '17
Abstract: As lithium-ion battery technology becomes widely popular with increasing demand for efficient energy-storage devices for a wide range of applications, the scarcity of lithium resources poses a concern for increasing costs. Replacing lithium with much more abundant sodium in combination with abundant transition metals such as iron (instead of traditionally used cobalt or nickel) as the charge compensation center in the cathode materials is expected to make large-scale battery technology a reality. To activate iron as a reversible redox center, oxyanions (XO4)n− have been introduced to stabilize the structures and raise the redox potentials, and silicates (X = Si, n = 4) form the best candidate group in terms of abundance and cost. In this regard, we explored the Na2O-FeO-SiO2 pseudoternary system and identified a new phase, Na2Fe2Si2O7, with an efficient chemical composition for charge accumulation (Na/Fe = 1), providing a large one-electron theoretical capacity of 164.5 mAhg–1 as a sodium-ion battery cathode.
Pub.: 28 Apr '17, Pinned: 30 Aug '17
Abstract: Sodium-ion battery (SIB) technologies are known to suffer from kinetic problems associated with the solid-state diffusion of Na(+) in intercalation electrodes, which results in suppressed specific capacity and degraded rate performance. Here, a controllable selective etching approach is developed for the synthesis of Prussian blue analogue (PBA) with enhanced sodium storage activity. Based on time-dependent experiments, a defect-induced morphological evolution mechanism from nanocube to nanoflower structure is proposed. Through in situ XRD measurement and computational analysis, this unique structure is revealed to provide higher Na(+) diffusion dynamics and negligible volume change during the sodiation/desodiation processes. As a SIB cathode, the PBA exhibits a discharge capacity of 90 mAh g(-1), which is in good agreement with the complete low spin Fe(LS)(C) redox reaction. It also demonstrates an outstanding rate capability of 71.0 mAh g(-1) at 44.4 C, as well as unprecedented cycling reversibility over 5000 times.
Pub.: 01 Jul '17, Pinned: 30 Aug '17
Abstract: Ever-growing energy needs and depleting fossil-fuel resources demand the pursuit of sustainable energy alternatives, including both renewable energy sources and sustainable storage technologies. It is therefore essential to incorporate material abundance, eco-efficient synthetic processes and life-cycle analysis into the design of new electrochemical storage systems. At present, a few existing technologies address these issues, but in each case, fundamental and technological hurdles remain to be overcome. Here we provide an overview of the current state of energy storage from a sustainability perspective. We introduce the notion of sustainability through discussion of the energy and environmental costs of state-of-the-art lithium-ion batteries, considering elemental abundance, toxicity, synthetic methods and scalability. With the same themes in mind, we also highlight current and future electrochemical storage systems beyond lithium-ion batteries. The complexity and importance of recycling battery materials is also discussed.
Pub.: 18 Dec '14, Pinned: 30 Aug '17