期刊
JOURNAL OF MATERIALS SCIENCE
卷 43, 期 14, 页码 4701-4706出版社
SPRINGER
DOI: 10.1007/s10853-007-2355-6
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Layered lithium metal oxide cathodes typically exhibit irreversibility during the first cycle in lithium cells when cycled in conventional voltage ranges (e.g., 3-4.3 V vs. Li(+)/Li). In this work, we have studied the first-cycle irreversibility of lithium cells containing various layered cathode materials using galvanostatic cycling and in situ synchrotron X-ray diffraction. When cycled between 3.0 and 4.3 V vs. Li(+)/Li, the cells containing LiCoO(2), LiNi(0.8)Co(0.15)Al(0.05)O(2), and Li(1.048)(Ni(1/3)Co(1/3)Mn(1/3))(0.952)O(2) as cathodes showed initial coulombic efficiencies of 98.0, 87.0, and 88.6%, respectively, at relatively slow current (8 mA/g). However, the lost capacity could be completely recovered by discharging the cells to low voltages (< 2 V vs. Li(+)/Li). During this deep discharge, the same cells exhibited voltage plateaus at 1.17, 1.81, and 1.47 V, respectively, which is believed to be associated with formation of a Li(2)MO(2)-like phase (M = Ni, Co, Mn) on the oxide particle surface due to very sluggish lithium diffusion in Li(epsilon)MO(2) with epsilon -> 1 (i.e., near the end of discharge). The voltage relaxation curve and in situ X-ray diffraction patterns, obtained from a Li/Li(1.048)(Ni(1/3)Co(1/3)Mn(1/3))(0.952)O(2) cell, showed that the oxide cathode reversibly returned to its original state [i.e., Li(1.048)(Ni(1/3)Co(1/3)Mn(1/3))(0.952)O(2)] during relaxation following the deep discharge to achieve 100% cycle efficiency.
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