Investigation of solid-state host materials for Zn-ion insertion

Date

2021-04-27

Authors

Park, Min Je

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Abstract

Multivalent-ion batteries (Mg-, Zn-, Ca-, and Al-ion) based on insertion chemistry like lithium-ion batteries have been explored as a potential alternative energy storage technology because of the high earth abundance of those elements. Many crucial impediments still need to be overcome, one of which is the slow diffusion kinetics of multivalent ions in solid-state host materials, which has hampered the search for identifying novel host materials. Ever since the discovery of Chevrel phase Mo₆S₈ as a reversible host for multivalent-ion insertion, various classes of materials have been explored, but there are only a few known reversible hosts for multivalent-ion insertion thus far. In order to improve the diffusion kinetics of multivalent ions in solid-state hosts, different approaches, including charge shielding through water incorporation have been attempted. The approach of water incorporation has demonstrated significantly improved electrochemical charge storage, which was attributed to the shielding of the positive charge of the multivalent ions by water in the electrolyte or in the host structure, thereby weakening their electrostatic interaction with the host material. However, increasing number of studies recently have unveiled that such enhancement in electrochemical charge storage is significantly or even completely due to insertion of protons supplied by water in the system, which would be favored over the insertion of much charge dense multivalent ions. These studies highlight the critical need to conduct more fundamental research to clarify and broaden our understanding of multivalent-ion insertion in solid- state hosts for the future discovery of candidate host materials. Thus, in this dissertation, Zn-ion insertion behavior in different solid-state host materials have been explored. In Chapters 3 and 4, polyanionic V₂(PO₄)₃ and Na₃V₂(PO₄)₂F₃, respectively, are investigated as host materials for reversible Zn-ion insertion to assess whether Zn-ion insertion can be facilitated with their open-framework structure. In Chapter 5, Zn-ion insertion in layered transition metal dichalcogenide 2H-NbS₂ is explored to understand the limited Zn-ion insertion in 2H-MoS₂ and 2H-WS₂, and in Chapter 6, a facile Zn-ion insertion behavior observed with 2H-NbSe₂ is studied.

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