Universität zu Köln

Wilhelm, Michael ORCID: 0000-0002-4764-6955 (2023). Chemically Engineered Metal Sulfides and Oxides as Electrode Materials for Li-Ion and Photochargeable Batteries. PhD thesis, Universität zu Köln.

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Abstract

Lithium-ion batteries have dominated battery technologies for portable electronic devices for decades, commanded by intercalation chemistry for electrochemical energy storage while pushing the limits of storage capacity worldwide to the terawatt-hour level. State-of-the-art intercalation cathodes for Li-ion batteries operate within the limits of transition metal oxide electrochemistry. However, conversion-redox processes have rich opportunities for substantially increasing energy densities. Due to the limitations of both the Li content and the extraction of one electron per transition metal, the target energy density of 500 Wh kg-1 of classical layered oxides at the cell level remains elusive. The diversity of compositions that exhibit high reversible capacities following a conversion redox reaction in the solid state has inspired the exploration of new materials for next-generation cathodes for lithium batteries and beyond. While thinking beyond, the electrification of the aviation sector is a game-changer for future transport. Therefore, the requirements on battery technologies must focus even more on high power density, high energy density with fast-charging capability and having low weight and compacted cell design. In addition, battery safety aspects and sustainability of energy materials are key challenges. To address some of the challenges, synthesis and surface engineering of high energy density and fast-charging materials, as well as the development and comprehensive characterization of metal-sulfur batteries for Li-S, Mg-S, and hybrid Li/Mg-S systems, were studied in this thesis. In terms of fast-charging electrode materials, TiNb2O7 was modified by a carbon-coating to improve the charge conduction and specific capacity at high current rates. Further, novel concepts towards photoresponsive cathode materials, such as vanadium pentoxide were investigated in a lithium-ion photo battery. This study reports on the optimization of dual functionality by chemical surface engineering of electrospun vanadium pentoxide fibers as photoresponsive cathodes in lithium-ion batteries. To meet the demand for high energy density in metal-sulfur batteries, lithium-sulfur and mag- nesium-sulfur batteries were explored. For Li-S system, a synthetic approach based on a new molecular precursor [(LiSC2H4)2NCH3] to form lithium sulfide/carbon nano- fibers as cathode was pursued. Suitable cathode materials based on metal sulfides, mainly copper, iron, and copper-iron-sulfides, were investigated in terms of their suitability for rechargeable magnesium batteries due to their high theoretical capacities (Mg: 3,833 mAh/cm3; 2,205 mAh/g) and high abundance in the earth’s crust (23,300 ppm). The influence of their crystal structures, particle morphologies, and nano-sized effects were tested to elucidate and further understand the electrochemical behavior with Mg2+ as the active ion. Introducing a small amount of Li-containing salts to the magnesium electrolyte, resulted in a hybrid electrolyte that showed great potential to improve the electrochemical behavior in combination with metal sulfides following a conversion reaction mechanism.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Wilhelm, Michael UNSPECIFIED orcid.org/0000-0002-4764-6955 UNSPECIFIED
URN:	urn:nbn:de:hbz:38-703912
Date:	2023
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Faculty of Mathematics and Natural Sciences > Department of Chemistry > Institute of Inorganic Chemistry
Subjects:	Chemistry and allied sciences
Uncontrolled Keywords:	Keywords Language Lithum-Ion Batteries English Magnesium Batteries English Lithium-Sulfur Batteries English Photochargeable Batteries English Chemical Engineering English Surface Chemistry English
Date of oral exam:	14 June 2023
Referee:	Name Academic Title Mathur, Sanjay Prof. Dr. Dr. (h.c.) Klein, Axel Prof. Dr.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/70391