The rational design of lithium insertion materials for battery applications

University dissertation from Uppsala : Acta Universitatis Upsaliensis

Abstract: The transition-metal oxide spine1 LiMn2O4 is a promising cathode material for high-capacity lithium-ion batteries. Structure-property relationships pertaining to the electrochemical cycling behaviour of LiMn2O4 have been studied. The techniques exploited have been in situ X-ray and neutron diffraction, in combination with quantum-mechanical band-structure calculations. The results obtained lay the ground for an improved basis for designing new insertion materials.Substitution of Mn by Ni in LiMn2O4 and by Li in Li1+xMn2-xO4 give qualitatively different results: Ni is found to replace Mn directly, while Li takes up entirely new sites not observed earlier. Band-structure calculations have been used to better understand the crystallographically observed x-dependence of the Li1+xMn2-xO4 structure, and the underlying mechanisms of lithium-ion extraction/insertion.Quantitative observation of charge passed through the cell has also been related to the amount of lithium extracted to indicate possible sources of irreversible capacity loss, and how synthesis technique can influence cell performance.The LiMn2O4 structure has also been studied by neutron diffraction after treatment in strong-acid solutions, where Li ® H ion-exchange has been observed to take place. This process has strong implications for the dissolution of Mn2+ ions from the cathode into the electrolyte, especially at elevated temperatures, and the related corrosion process occurring at the cathode surface.

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