THESIS
2022
1 online resource (xxi, 194 pages) : illustrations (some color)
Abstract
Lithiated silicon-sulfur (Si-S) battery is a promising next-generation energy-storage
technology due to the raw materials’ high theoretical capacities, earth-abundance, and
environmental benignity. Nonetheless, their overall electrochemical performance cannot meet
the requirements for large-scale implementation, mainly caused by the internal polysulfide
shuttle effect and inferior solid-electrolyte interphase (SEI) stability. Therefore, the primary
objective of this thesis is to tackle these issues by electrode structure design and SEI
optimization through electrolyte manipulation.
The thesis begins with structure engineering of host materials to address the polysulfide
migration and volume change of Si. Hollow carbon nanoshells are proposed to accommodate
the S and Si nanoparticles, wh...[
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Lithiated silicon-sulfur (Si-S) battery is a promising next-generation energy-storage
technology due to the raw materials’ high theoretical capacities, earth-abundance, and
environmental benignity. Nonetheless, their overall electrochemical performance cannot meet
the requirements for large-scale implementation, mainly caused by the internal polysulfide
shuttle effect and inferior solid-electrolyte interphase (SEI) stability. Therefore, the primary
objective of this thesis is to tackle these issues by electrode structure design and SEI
optimization through electrolyte manipulation.
The thesis begins with structure engineering of host materials to address the polysulfide
migration and volume change of Si. Hollow carbon nanoshells are proposed to accommodate
the S and Si nanoparticles, which function as physical barriers and provide sufficient conductive
pathways to improve the reaction kinetics. More compact pomegranate-like micro-clusters are
then developed for both S cathode and Si anode to further improve the full cell performance.
The S is encapsulated in titanium nitride-carbon dual-layer hollow nanospheres assembled as
micro-clusters, wherein the inner titanium nitride layer anchors the polysulfides and catalyzes
their conversion reaction, while the outer carbon layer facilitates the electron transfer.
Additionally, the multiple-layer barriers of the cluster further prevent the polysulfides escape,
thus mitigating the side reactions and material loss. Si nanoparticles are hosted in pomegranate
carbon clusters with internal void spaces to buffer the volume change, enabling stable SEI
formation on the outmost layer. As a result, the lithiated Si-S full cell with the proposed
structures achieves a high reversible capacity of 940 mAh g
-1 at 0.3 A g
-1 and a high areal
capacity of 3.5 mAh cm
-2.
To further alleviate the side reactions and improve the cycling reversibility of lithiated Si-S
batteries, the thesis then focuses on optimizing the solid-electrolyte interphase (SEI) by
electrolyte engineering. A fluorinated ether electrolyte is proposed, which renders the formation
of a robust lithium fluoride-rich SEI on both the anode and cathode. The SEI not only buffers
the volume variation of Si microparticles over repeated cycles, but also renders the direct quasi-solid-state conversion of S, drastically reducing the polysulfides generation. The newly
developed electrolyte endows the full cell with superior cycling performance to the conventional one and a high areal capacity of 4 mA h cm
-2 with a low electrolyte/S ratio of 7.4 μL mg
-1.
Finally, to enhance the safety level, all-solid-state batteries are developed using polyethylene
oxide (PEO)-based composite electrolytes. To tackle the polysulfide dissolution in the PEO, an
artificial SEI is constructed on the S cathode by pre-cycling it in the concentrated liquid
electrolyte. The compact SEI isolates the S from direct contact with PEO, leading to the one-step solid-solid transition of S without generating dissolved polysulfide. The Li-half cell with
the artificial SEI exhibits much better capacity retention than the pristine one (85% vs. 42%).
However, the inferior dendrite suppression capability of PEO limits the actual areal capacity of
Li metal, so a metal-organic framework (MOF) hosted Si anode is then fabricated to replace the
metallic Li, which shows excellent interfacial stability toward the PEO-based composite
electrolyte for over 1000 h and achieves a high reversible areal capacity of 3 mAh cm
-2. At last,
an all-solid-state full battery is assembled using the proposed S@SEI and Si@MOF electrodes,
which achieves a high capacity of 850 mAh g
1 at 0.1 A g
-1.
Keywords:
lithiated silicon-sulfur battery; polysulfide shuttle effect; fluorinated ether electrolyte; solidelectrolyte
interphase; polyethylene oxide
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