Internal microstructural design and characterization of metal selenides anode for efficient sodium storage / Wang Jian
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...
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| Format: | Thesis |
| Published: |
2024
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| Online Access: | http://studentsrepo.um.edu.my/15799/2/Wang_Jian.pdf http://studentsrepo.um.edu.my/15799/1/Wang_Jian.pdf http://studentsrepo.um.edu.my/15799/ |
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| Summary: | 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+.
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