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Abstract: The goal of this research was to study the effect of various polymer-containing precursors on the performance of LiFePO4/C composite. A coprecipitation method was applied to prepare a series of LiFePO4/C materials by calcinating amorphous LiFePO4 with various polymer compounds at 600°C. The materials were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, particle size analysis, thermal analysis, BET specific surface area, Raman spectral analysis and electrochemical methods. The results showed that the structure of polymer precursors played an important role in improving the performance of LiFePO4/C composites. The residual carbon produced by the pyrolysis of polymers with functionalized aromatic groups exhibited a better capacity in the LiFePO4/C composites. A polyaromatic compound, e.g. polystyrene, with more functionalized aromatic groups displayed improved performance because its decomposition temperature was close to the temperature of the LiFePO4 phase transformation, which resulted in fine particle size and uniform carbon distribution on the composite surface. According to Raman spectral analysis, polystyrene with more aromatic groups has a lower I D/I G and sp3/sp2 peak ratio indicating more highly graphite-like carbon formation during polymer pyrolysis and exhibited a better capacity. [Copyright &y& Elsevier]

Abstract: Three types of spinel-based cathode powders, namely, LiMn2O4, Li1.07Mn1.93O4, and Li1.06Al0.2Mn1.74O4, are examined with rotating ring-disc collection experiments to measure manganese dissolution and capacity losses in lithium-ion cells. The cyclic voltammograms are similar at high scan rates for all three electrodes. Initially, all electrodes rapidly lose capacity during cycling. After about 25 cycles, the electrodes start to exhibit capacity retention, and the performance matches that of the best spinels. The cation-substituted spinel electrodes experience a moderate capacity loss of 0.2% per cycle over 200 cycles, which is half that suffered by a typical spinel electrode (LiMnO4). Manganese (Mn) dissolution from all the spinel-based samples is monitored in situ under various conditions. The ring cathodic currents for the cation-substituted spinel electrodes are similar to those for LiMn2O4, which shows that the Mn dissolution behaviour is the same for all spinel-based cathode powders. The ring currents reach maximum values at the end-of charge (EOC) and end-of discharge (EOD), with the largest peak at EOC. The results suggest that the dissolution of Mn from all spinel-based samples occurs during charge–discharge cycling, especially in a charged state at >4.0V and in a discharged state at <3.1V. In addition, lower ring cathodic currents are observed in the cation-substituted spinel cathodes and this indicates that the rate of dissolution of Mn has decreased in these materials. [Copyright &y& Elsevier]