Synthesis and Characterization of Oxide Cathode Materials for Lithium Power Sources

[D. Jugović]

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Fizička hemija / Physical chemistry

U okviru ove doktorske disertacije su izloženi različiti načini sinteze najnovijih oksidnih katodnih materijala za litijumske izvore struje LiFePO4 i LiCr0.175Mn1.825O4 kao i osobine ovih materijala koje su važne sa stanovišta hemijskih izvora struje. Prikazana su tri načina sinteze prahova: sinteza pomoću reakcije u čvrstoj fazi, ultrazvučna sprej piroliza i sinteza pomoću sonohemijske reakcije. Svaka sinteza praćena je metodom rendgenske difrakcije na polikristalnim uzorcima. Podaci dobijeni rendgenskom difrakcijom su iskorišćeni za rendgenostrukturnu analizu prahova, dok je morfologija prahova ispitana skenirajućom i transmisionom elektronskom mikroskopijom. Magnetna merenja su rađena pomoću magnetometra SQUID. Elektrohemijske osobine prahova kao katode u litijum-jonskoj ćeliji su ispitivane galvanostatskim punjenjem i pražnjenjem. Dobijeno je da različiti načini sinteze rezultuju u prahovima različitih strukturnih, mikrostrukturnih i elektrohemijskih osobina. Za dobijanje fazno čistih uzoraka litijum gvožđe fosfata neophodna je kontrola temperature i atmosfere, a kompoziti sa ugljenikom se mogu dobiti dodatkom organske komponente u prekursorski rastvor. Utačnjavanjem strukture je bilo omogućeno određivanje praktično svih relevantnih parametara kristalne strukture i kristalne građe. Najbolje elektrohemijske osobine je pokazao kompozit LiFePO4/C dobijen sintezom pomoću sonohemijske reakcije, koji je prilikom cikliranja C/10 strujom pokazao kapacitet pražnjenja od 125 mAh/g. Ultrazvučna sprej piroliza se pokazala pogodnom za dobijanje Cr-supstituisanog praha litijum manganata. Detaljna analiza magnetnih merenja je pokazala da može biti izuzetno važna i moćna tehnika u proučavanju strukture i kristalne građe čistih materijala i njihovih primesa koji sadrže 3d jone. Uporedna analiza dobijenih rezultata je pokazala jaku korelaciju transportnih osobina prahova i njihovih strukturnih i mikrostrukturnih parametara

This PhD. thesis describes different ways of syntheses of the most recent oxide cathode materials for lithium power sources, LiFePO4 and LiCr0.175Mn1.825O4, as well as their properties that are significant in the light of chemical power sources. Three synthesis procedures were shown: solid state reaction, ultrasonic spray pyrolysis, and sonochemical reaction. Each synthesis was followed by X-ray powder diffraction (XRPD). XRPD data were used for the structural analysis of the synthesized powders, while the particle morphology was revealed by both scanning and transmission electron microscopies. Magnetic measurements were carried out with SQUID-based magnetometer. In order to examine the electrochemical properties of synthesized powders as cathode materials for lithium-ion battery galvanostatic charge/discharge tests were performed. It was demonstrated that various synthesis procedures result in powders with different structural, microstructural, and electrochemical properties. Optimization of both temperature and atmosphere is necessary for obtaining monophased lithium iron phosphate samples, while composites with carbon can be easily attained by the addition of an organic component in a precursor solution. Crystal structure refinement was used for the determination of all relevant structural and microstructural parameters. Sonochemically derived LiFePO4/C composite showed the best electrochemical performances, reaching discharge capacity of 125 mAh/g while cycling with current density of C/10. Ultrasonic spray pyrolysis has been proven to be a proper method for obtaining Cr-substituted lithium manganate powder. It has been shown that magnetic measurements are very efficient in crystal structure study of pure materials as well as their impurities that contain 3d ions. Parallel analysis of the obtained results showed a strong correlation between transport properties of powders and their structural and microstructural parameters.

LiFePO4, LiMn2O4, litijum jonski akumulatori, utačnjavanje kristalne strukture, galvanostatsko cikliranje

LiFePO4, LiMn2O4, lithium-ion batteries, crystal structure refinement, galvanostatic cycling

544.6:66.017(043.3)

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