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Structural and electrochemical data of xLi2MnO3•(1-x)LiMn0.5Ni0.5O2 electrodes, as a function of Li2MnO3 content, x, are presented. Three distinct processes have been identified and tracked during extended electrochemical cycling. In addition to the standard intercalation behavior typical of layered metal oxide electrodes, two additional electrochemical phenomena, manifest as hysteresis and continuous voltage fade, are found to be directly related to one another. These two processes are a consequence of the Li2MnO3 component in the electrochemical reaction. This finding, coupled to X-ray absorption data, reveals that lithium and manganese ordering plays a significant role in the voltage degradation mechanisms of high-capacity lithium-and manganese-rich composite electrode structures. In general, all xLi2MnO3•(1-x)LiMO2 (M = Mn, Ni, Co) electrode materials possess this feature and are subject to similar degradation after activation (>4.5 V) and during high voltage (>4.0 V) cycling. The data highlight the practical importance of limiting the amount of Li2MnO3 and/or the extent of activation in these composite structures, thereby providing electrode stability to counteract voltage fade and hysteresis.
Croy et al. (Tue,) studied this question.