Synthesis and electrochemical properties of layered lithium transition metal oxides

Abstract

Layered lithium transition metal oxide cathode materials (Li_1.2Ni_0.2Mn_0.6O₂, LiNi_1/3Co_1/3Mn_1/3O₂ and LiNi_0.5Mn_0.5O₂), 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 Li_1.2Ni_0.2Mn_0.6O₂, LiNi_1/3Co_1/3Mn_1/3O₂ and LiNi_0.5Mn_0.5O₂ 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 Li_1.2Ni_0.2Mn_0.6O₂ and LiNi_1/3Co_1/3Mn_1/3O₂ showed an initial discharge capacity of 150 and 166 mAh g⁻¹; as for the LiNi_0.5Mn_0.5O₂, the discharge capacity decreased to 67 mAh g⁻¹. After 150 cycles at a current density of 250 mA g⁻¹, both LiNi_1/3Co_1/3Mn_1/3O₂ and LiNi_0.5Mn_0.5O₂ showed a capacity decay rate of >25%, while the Li_1.2Ni_0.2Mn_0.6O₂ exhibited an excellent cycling performance with almost no capacity decay.