Synthesis and electrochemical properties of layered lithium transition metal oxides

Layered lithium transition metal oxide cathode materials (Li1.2Ni0.2Mn0.6O2, LiNi1/3Co1/3Mn1/3O2 and LiNi0.5Mn0.5O2), of spherical morphology with primary nanoparticles assembled in secondary microparticles, were generally synthesized through a simple carbonate co-precipitation method. In this method, various carbonates such as Na2CO3, NaHCO3 and (NH4)2CO3 could be employed as the precipitants without careful control of the pH value. Aging treatment on the carbonate slurries at 80 °C could yield spherical microparticles assembled with very fine primary nanoparticles. The carbonate microparticle precursors were calcined at 500 °C and further lithiated at 900 °C to prepare the layered cathode materials. The as-prepared Li1.2Ni0.2Mn0.6O2, LiNi1/3Co1/3Mn1/3O2 and LiNi0.5Mn0.5O2 cathode materials could deliver a capacity of 230, 190 and 153 mAh g−1, respectively, at a charge–discharge current density of 25 mA g−1 in the voltage range of 2.5–4.6 V. When the charge–discharge current density was increased to 250 mA g−1, the Li1.2Ni0.2Mn0.6O2 and LiNi1/3Co1/3Mn1/3O2 showed an initial discharge capacity of 150 and 166 mAh g−1; as for the LiNi0.5Mn0.5O2, the discharge capacity decreased to 67 mAh g−1. After 150 cycles at a current density of 250 mA g−1, both LiNi1/3Co1/3Mn1/3O2 and LiNi0.5Mn0.5O2 showed a capacity decay rate of >25%, while the Li1.2Ni0.2Mn0.6O2 exhibited an excellent cycling performance with almost no capacity decay.