Influence of Manganese Content on the Performance of LiNi_0.9−yMn_yCo_0.1O₂ (0.45 ≤ y ≤ 0.60) as a Cathode Material for Li-Ion Batteries

The layered oxide cathode material LiMO 2, where M = Ni 0.9− y Mn y Co 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 stoichiometric 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 O 2 and LiNi 0.45 Mn 0.45 Co 0.1 O 2 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 O 2 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.