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We have succeeded in obtaining good cycle performance by control cutoff voltage suitable for an ambient temperature in Li-ion full cells with carbon-coated SiO (C-SiO) anode. The optimized cells showed that the retention ratio of discharge capacity was above 90% after 500 cycles at 20°C. We also found that the origins of capacity fading were very different at 20°C and 60°C. In the former, C-SiO electrode caused the phase separation of Li concentration during charge-discharge due to the slow diffusion rate of the Li ion, and the thick heterogeneous phase was formed on C-SiO particles. In the latter, the decomposition of electrolyte became the main deterioration factor. The improved performance of full cell and the elucidation of the deterioration mechanism can accelerate the practical application of next generation high capacity Li-ion cells.

We carried out a deterioration analysis in Li-ion cells using SiO anode at high temperature, i.e., 60 • C. The capacity retention at the upper cutoff voltage (UCV) of 4.0, 4.1, and 4.2 V after 400 cycles was about 80, 80, and 20%, respectively. The cell deterioration depended strongly on the upper cutoff voltage and proceeded drastically at 4.2 V. This was because the internal resistance of cell increased by the decomposition of the electrolytic solution during cycles. From depth profile of XPS on the anode, the thick layer containing Li and F has been formed only for UCV = 4.2 V, implying that the electrolyte of LiPF 6 is enough to break down carbonate electrolyte at 60 • C. Therefore, we found that the optimization of the threshold of UCV for high temperature need to attain the good cycle performance at high temperature in a Li-ion battery using a SiO anode.

LiMn2O4 has a phase transition at room temperature, which is caused by Jahn-Teller distortion. DC resistivity of LiMn2O4 shows an anomaly at the transition temperature, while no such anomaly is observed in samples with excess lithium. X-ray diffraction patterns of LiMn2O4reveal that the crystal structure changes from cubic at higher temperature to orthorombic, as a first approximation, at lower temperature. However, no differences in initial charge-discharge curve are observed, which means that the Jahn-Teller distortion has no effect on electrochemical characteristics. The authors have succeeded in mass-producing lithium ion secondary batteries with a manganese spinel cathode.

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