Internal microstructural design and characterization of metal selenides anode for efficient sodium storage / Wang Jian

Wang , Jian (2024) Internal microstructural design and characterization of metal selenides anode for efficient sodium storage / Wang Jian. PhD thesis, Universiti Malaya.

	PDF (The Candidate's Agreement) Restricted to Repository staff only Download (614Kb)
	PDF (Thesis PhD) Download (11Mb)

Abstract

The new energy storage system represented by sodium-ion devices has become a promising candidate in large-scale energy storage due to its low cost and fast response kinetics. However, the larger radius of sodium ions relative to lithium ions results in complex reactions and slow transport in the bulk electrode phase, leading to lower energy and power density. Therefore, it is necessary to develop microstructural designs for electrodes to enhance sodium-ion storage capacity and improve transport kinetics. Metal selenides (MSes) can provide higher capacity output through multi-electron reactions, making them promising candidates for efficient sodium ion storage anodes. However, the considerable diffusion energy barriers and narrow active interfaces of MSes are unfavorable for long-range sodium ions transport, making it difficult to achieve both high capacity and fast reaction. Therefore, optimizing the bulk phase microstructural of MSes anodes can help intrinsically improve their electrochemical performance. In this thesis, it is demonstrated that significant enhancement in energy density and power density are achieved through the synthesis of specific MSes and their engineering into heterostructures (analogous cationic heterostructures, analogous anionic heterostructures, and dissimilar heterostructures) and introduction of carbon composite (metal-organic framework (MOF)-derived carbon, monosaccharide-derived carbon (ribose), and polymer-derived carbon (PPy and PAN) carbon coating). Additionally, this thesis details the electrolyte selection, electrochemical reaction process, and electrode activation behavior applicable to MSes anodes. The main findings are as follows. Firstly, the one-pot method selects Mo and W, which have similar metal properties, to construct bimetallic MOF precursors with different morphologies. Afterward, analogous cationic heterostructure design and homogeneous carbon introduction are achieved through a selenization/carbonization at different temperatures. The final obtained composites have abundant heterogeneous interfaces and homogeneous carbon distribution, exhibiting significant enhancement in electrochemical performance, relative to the unmodified samples. Secondly, analogous anionic heterostructures of similar S and Se are constructed using metal polysulfides (VS4 and WSx) precursors. Meanwhile, ribose-derived carbon sphere and polymerderived carbon coatings (PPy and PAN) are introduced. The obtained composites show expanded lattice spacing and abundant anionic heterogeneous interfaces. Theoretical calculations and physical characterization demonstrate that the constructed anionic heterostructures have improved metal properties and strong adsorption of transformation products, exhibiting excellent cycling lifetimes and electrochemical capabilities relative to unmodified polysulfide electrodes. Thirdly, dissimilar cationic heterostructures with varying crystal structures, based on Mo and Fe bimetallic MOFs as well as Sb and W bimetallic MOFs, were synthesized. On one hand, the significant electronegativity difference between MoSe₂ and FeSe, coupled with the flexible valence changes of the Fe atom, creates abundant heterogeneous interfaces and induces distinct crystalline transitions in MoSe₂. On the other hand, the Sb₂Se₃ and WSe₂ heterostructures, with their large crystal structure differences, form perfectly parallel interlayer structures. Exploring these two dissimilar heterostructures suggests that their construction leads to rich heterogeneous interfaces and stimulates more pronounced heterogeneous effects. This generates higher asymmetric built-in electric fields and promotes more efficient storage of Na+.

Actions (For repository staff only : Login required)