The effect of sintering temperature on the electrochemical property of LiMn2O4 was investigated. Results showed that the particle size was increased at higher sintering temperatures while the initial capacity was decreased after high temperature sintering. Capacity fading, on the other hand, was suppressed at lower sintering temperatures since the sintering at higher temperatures (≥ 800 o C) increased the Mn ions with a lower oxidation state (Mn +3 ), which induced structural instability during cycling due to dissolution of Mn ions into the electrolyte. In particular, LiMn2O4 sintered above 830 o C showed severe capacity fading (capacity loss was 38% of initial capacity) by lower coulombic efficiency due to the abnormally increased particle size.
This study reports the origin of the electrochemical improvement of LiFePO4 when synthesized by wet milling using acetone without conventional carbon coating. The wet milled LiFePO4 delivers 149 mAhg -1 at 0.1 C, which is comparable to carbon coated LiFePO4 and approximately 74% higher than that of dry milled LiFePO4, suggesting that the wet milling process can increase the capacity in addition to conventional carbon coating methods. UV spectroscopy, elemental microanalysis, and evolved gas analysis are used to find the root cause of the capacity improvement during the mechanochemical reaction in acetone. The analytical results show that the improvement is attributed to the conductive residual carbon on the surface of the wet milled LiFePO4 particles, which is produced by the reaction of FeC2O4· 2H2O with acetone during wet milling through oxygen deficiency in the precursor.
This study addresses the controversial issue of the effect of metal ion doping on the electrochemical performance of LiFePO 4 . Metal doping is claimed to be a possible cause for the capacity improvement of LiFePO 4 as carbon coating. Results obtained inthis study show that dry-milled LiFePO 4 and LiFe 0.9 Cr 0.1 PO 4 deliver 119 mAh g −1 and 101 mAh g −1 , while wet-milled LiFePO 4 and LiFe 0.9 Cr 0.1 PO 4 deliver 149 mAh g −1 and 138 mAh g −1 , respectively. This indicates that the capacity improvement by metal doping is due to the carbonaceous materials produced during fabrication and not by the enhancement of ion diffusion. On the other hand, cycle test results show that metal doping enhances the rate capability at high C-rates by accelerating lithium ion diffusion.
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