Öppna denna publikation i ny flik eller fönster >>2019 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]
The use of Li-ion batteries in portable electronic products is today widespread and on-going research is extensively dedicated to improve their performance and energy density for use in electric vehicles. The largest contribution to the overall cell weight comes from the positive electrode material, and improvements regarding this component thereby render a high potential for the development of these types of batteries. A promising candidate is LiNi0.5Mn1.5O4 (LMNO), which offers both high power capability and energy density. However, the instability of conventional electrolytes at the high operating potential (~4.7 V vs. Li+/Li) associated with this electrode material currently prevents its use in commercial applications.
This thesis work aims to investigate practical approaches which have the potential of overcoming issues related to fast degradation of LNMO-based batteries. This, in turn, necessitates a comprehensive understanding of degradation mechanisms. First, the effect of a well-known electrolyte additive, fluoroethylene carbonate is investigated in LNMO-Li4Ti5O12 (LTO) cells with a focus on the positive electrode. Relatively poor cycling performance is found with 5 wt% additive while 1 wt% additive does not show a significant difference as compared to additive-free electrolytes. Second, a more fundamental study is performed to understand the effect of capacity fading mechanisms contributing to overall cell failure in high-voltage based full-cells. Electrochemical characterization of LNMO-LTO cells in different configurations show how important the electrode interactions (cross-talk) can be for the overall cell behaviour. Unexpectedly fast capacity fading at elevated temperatures is found to originate from a high sensitivity of LTO to cross-talk.
Third, in situ studies of LNMO are conducted with neutron diffraction and electron microscopy. These show that the oxygen release is not directly related to cation disordering. Moreover, microstructural changes upon heating are observed. These findings suggest new sample preparation strategies, which allow the control of cation disorder without oxygen loss. Following this guidance, ordered and disordered samples with the same oxygen content are prepared. The negative effect of ordering on electrochemical performance is investigated and changes in bulk electronic structure following cycling are found in ordered samples, accompanied by thick surface films on surface and rock-salt phase domains near surface.
Ort, förlag, år, upplaga, sidor
Uppsala: Acta Universitatis Upsaliensis, 2019. s. 84
Serie
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1827
Nyckelord
LNMO, High-voltage spinel, FEC, Cross-talk, Cation ordering, Oxygen deficiency, Anionic redox
Nationell ämneskategori
Oorganisk kemi
Forskningsämne
Kemi med inriktning mot oorganisk kemi
Identifikatorer
urn:nbn:se:uu:diva-389848 (URN)978-91-513-0698-8 (ISBN)
Disputation
2019-09-13, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (Engelska)
Opponent
Handledare
2019-08-232019-07-292019-09-17