Materials design of potassium-ion pre-intercalated cathodes for sodium-ion batteries

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Materials design of potassium-ion pre-intercalated cathodes for sodium-ion batteries

Wei, Runzhe; (2024) Materials design of potassium-ion pre-intercalated cathodes for sodium-ion batteries. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

Lithium-ion battery (LIB) is currently the most popular energy storage form from mobile devices to large-scale grids because of its high energy density, long cycle life, low maintenance and versatile. However, due to the increasing demand and cost, limited resources and environmental concerns, it is essential to explore the feasibility of new battery technologies, which can potentially reduce the pressure of LIB or even replace it in the future. Among various choices, sodium-ion battery (SIB) is regarded as one of the most promising candidates due to its low cost and abundance. More importantly, as another member of alkali metal, Na has similar characteristics as Li does, which leads to much transferable knowledge. Since SIB is still at early stage, many challenges, especially for cathode materials, need to be overcome, because of the larger ion size and higher standard redox potential. This project offers some solutions and insights by applying K+ pre-intercalated cathode materials for SIB, which is different from the mainstream research of SIB cathodes. The focus of the project is to investigate the role of K+ in the process of ion intercalation and diffusion. The first work is applying potassium iron hexacyanoferrate (K-FeHCF Prussian blue with a tunnel structure) as cathode for SIB. Compared to Na+, K+ can better fit in the Prussian blue structure, resulting in better structural stability. Additionally, the lower standard reduction potential of K over Na leads to a higher cell voltage. The K+ pre-intercalated KFeHCF makes it a hybrid-ion battery system when being used in a SIB cell. Introducing a level of [Fe(CN)6]4- vacancy can regulate the intercalation mechanism, therefore maximize the enhancement provided by K+ pre-intercalation. The second work is using potassium vanadyl phosphate (KVOPO4 with a layered structure) as cathode for SIB. Benefiting from the even larger size of K+ over Na+, the presence of K+ in the interlayer space of KVOPO4 acts as a “pillar” to provide extra space for Na-ion intercalation in KVOPO4. KVOPO4 exhibits robust Na kinetics and improved structural stability, resulting in a higher cycling capacity and better rate capability compared to NaVOPO4. Finally, full cell test is carried out to further verify the two designs described above, where hard carbon is used as the anode electrode. The roles of K+ remain in the full cell and both cathode materials exhibit comparable performance to half cell test. This indicates the feasibility of K+ pre-intercalated cathode materials in SIB cells and both materials can be even more promising in the future by optimizing the designs.

Type:	Thesis (Doctoral)
Qualification:	Ph.D
Title:	Materials design of potassium-ion pre-intercalated cathodes for sodium-ion batteries
Open access status:	An open access version is available from UCL Discovery
Language:	English
Additional information:	Copyright © The Author 2024. Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) Licence (https://creativecommons.org/licenses/by-nc/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request.
UCL classification:	UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Chemistry
URI:	https://discovery.ucl.ac.uk/id/eprint/10185647