Electrochemical and kinetic studies of Li1.156Mn1.844O4

The electrochemical and kinetic properties of a lithium-rich spinel material, Li1.156Mn1.844O4, were investigated to illustrate the impact of the excessive lithium on the performance of spinel-based lithium-ion cells. It was found that the capacity retention of such mesocarbon microbead/spinel cells was significantly deteriorated when the upper cutoff voltage was raised from 4.1 to 4.3 V at 55 degrees C. The significant difference on the capacity retention was attributed to the irreversible reaction at about 4.22 V, which was further related to the electrochemical reaction of lithium-rich spinel at high voltages. The low rate cycling of Li/spinel cells at different temperatures showed the evolution of at least three irreversible peaks above 4.2 V. Moreover, the Li/spinel cells showed continuous impedance growth after extraction of the excessive lithium. The kinetic study showed that the irreversible peaks shifted toward low potential as the temperature increased. It is predicted that the first irreversible peak shows up at about 4.25 V vs Li/Li+ at 55 degrees C. It suggests that the upper cutoff voltage of such graphite/ spinel cells should be limited to 4.1 V at 55 degrees C. The kinetic study also indicates that such graphite/spinel cells can be cycled up to 4.4 V at 25 degrees C without triggering any detrimental impact. (c) 2006 The Electrochemical Society.