Ionic Liquids for High Performance Solid-state Lithium Metal Batteries
Date
2023
Authors
Chen, Tianhua
Editors
Advisors
Losic, Dusan
Zhang, Haitao (Institute of Process Engineering, Chinese Academy of Sciences)
Zhang, Haitao (Institute of Process Engineering, Chinese Academy of Sciences)
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Thesis
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Abstract
The quest for high energy storages has driven the growth of high-performance lithium metal
batteries, but this has also raised serious safety concerns. In response, ionic liquids (ILs) have
become a popular choice due to their high ionic conductivity, non-flammability, and ability to
facilitate the formation of stable solid electrolyte interphase (SEI) layer. Understanding the
challenges faced by lithium metal batteries and the role of ILs in them is vital to improving their
performance. This study examines how ILs affect key factors such as ionic conductivity, Li⁺ ion
transference number, electrochemical stability window, and the lithium metal anode/electrolyte
interface. It also investigates the use of ILs with different types of cathodes, such as, including
LiFePO4 (LFP), LiNi0.6Co0.2Mn0.2O2 (NCM622), LiNi0.8Co0.1Mn0.1O2 (NCM811), and LiCoO2
(LCO).
A comparative study was made on the development of ionic liquid involved solid-state
electrolyte to achieve high performance solid-state lithium metal batteries. Three key aspects are
addressed in this thesis:
Firstly, an ionic liquid was injected into metal-organic framework (MOF-5) nanomaterials to improve
the poly(ethylene oxide) (PEO) solid electrolyte and enhance the performance of solid- state
lithium batteries. The results show that the formed nano-wetted interface structure can greatly
improve the interface stability, reduce the interface impedance, and inhibit the Li dendrite
growth. The MOF structure accelerates the transport of lithium ions by ion confinement effect
on anions inn the IL and large-size cations, thereby improving the lithium transference number.
As a consequence, the
overall performance of solid solid-state Li metal battery has been improved.
Secondly, using electrospun polyacrylonitrile PAN membranes, the ionic liquid and liquid
electrolyte monomers are combined and in situ polymerized to form a polymer electrolyte. In
this system, the decomposition of the ionic liquid is involved in the formation of the solid
electrolyte interface ( SEI mem brane. Through analysis at different current densities of the Li
symmetric cell , it was found that the ionic liquid can significantly suppress the formation and
growth of lithium dendrites. Moreover, due to the increased lithium affinity of the ionic liqui d,
Li ion transport is accelerated, resulting in a high lithium transference number, which improves
conductivity and allows the battery performing within a wide temperature range. Additionally,
L i F e P O 4 /Li batteries can run steadily for 100 0 cycles at high rate of 2 C.
T
hirdly, through the combined action of fluorine containing additives and ionic liquids, the in
situ formed polymer lithium battery can operate stably at high voltage. Analysis has shown that
the SEI membrane in this system is rich in LiF, whi ch effectively increases interface stability.
The ionic liquid enhances the electrochemical window of the polymer electrolyte, allowing this
system to match high voltage cathodes. Moreover, IL is beneficial to improve the interfacial
contact and provide st able components for the interfacial layer. Results show that at room
temperature, the NCM811/cell can perform at 1C, and the LCO/Li cell has good cycling
performance at 4.45 V, increasing the battery energy capacity.
This project contributes to the understanding of the application of ionic liquids in solid state
electrolytes, the knowledge of which can be used to design the solid state electrolyte. The chemical compositions of the SEI layers formed on
the surface of Li anode from this experimental work also provide valuable data that can be used in the future studies
School/Discipline
School of Chemical Engineering and Advanced Materials
Dissertation Note
Thesis (Ph.D.) -- University of Adelaide, School of Chemical Engineering and Advanced Materials, 2023
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