Influence of Manganese Content on the Performance of LiNi_(0.9-y)Mn_yCo_(0.1)O2 (0.45 ≤ y ≤ 0.60) as a Cathode Material for Li-Ion Batteries

摘要

The layered oxide cathode material LiMO2, where M = Ni_(0.9-y)Mn_yCo_(0.1) and 0.45 ≤ y ≤ 0.60, was synthesized by a coprecipitation method. X-ray diffraction analysis shows that the maximum manganese content in the sloichiometric material, i.e. with Li:M = 1, cannot exceed 50; otherwise, a second phase is formed. Rietveld refinement reveals that increasing manganese content suppresses the disorder between the lithium and nickel ions. Magnetic measurements show that part of the Mn~(4+) ions in the manganese rich compounds is reduced to Mn~(3+); this results in a larger hysteresis loop due to the increased magnetic moment of the resulting ferrimagnetically ordered clusters. LiNi_(0.4)Mn_(0.5)Co_(0.1)O2 and LiNi_(0.45)Mn_(0.45)Co_(0.1)O2 show similar electrochemical capacities of around 180 mAh/g (between 2.5 and 4.6 V at 0.5 mA/cm~2) for the first discharge. However, subsequent cycling of LiNi_(0.4)Mn_(0.5)Co_(0.1)O2 results in faster capacity loss and poorer rate capability indicating that manganese rich compounds, with Li:M = 1:1, are probably not suitable candidates for lithium batteries.