Layered Li[NixCo1-2xMnx]O2 cathode materials for lithium-ion batteries

The structure and electrochemical behavior of Li[NixCo1-2xMnx]O-2 with x = 1/4 and 3/8 is reported for the first time, Li[NixCo1-2xMnx]O-2 (0 less than or equal to x less than or equal to 1/2) is prepared by the simultaneous substitution of Ni2+ and Mn4+ (1:1) for Co3+ in LiCoO2, X-ray diffraction patterns show these materials have a layered alpha -NaFeO2-type structure. Both Li[NixCo1-2xMn]O-2 with x = 1/4 or 3/8 can deliver a stable capacity of about 160 mAh/g between 2.5 and 4.4 V vs. Li using a specific current of 40 mA/g. If the upper potential of Li/Li[NixCo1-2xMnx]O-2 cells with x = 3/8 is reduced to 4.2 V vs. Li, its capacity retention behavior is improved and it gives a capacity of 136 mAh/g, which is very close to that of LiCoO2 in the same potential window. Studies of the thermal stability of Li1-y[NixCo1-2xMnx]O-2 in electrolyte using differential scanning calorimetry indicate that the samples with x = 1/4 and x = 3/8 are more thermally stable than LiCoO2. (C) 2001 The Electrochemical Society.