Electrochemical properties of 0.6Li[Li_(1/3)Mn_(2/3)]O_2-0.4LiNi_xMn_yCo_(1-x)O_2 cathode materials for lithium-ion batteries

摘要

Solid solutions between Li[Li_(1/3)Mn_(2/3)]O_2 and LiMO_2 (M = Ni_(1/3)Mn_(1/3)Co_(1/3), Ni_(0.4)Mn_(0.4)Co_(0.2), Nio.45 Mn_(0.45)Co_(0.1), Ni_(0.5)Mn_(0.2)Co_(0.3), and Ni_(0.5)Mn_(0.3)Co_(0.2)) have been synthesized by a solid-state reaction method. The as-prepared Li_(1.2)Ni_(0.13)Mn_(0.54)Co_(0.13)O_2, Li_(1.2)Ni_(0.16)Mn_(0.56)Co_(0.08)O_2, Li_(1.2)Ni_(0.18)Mn_(0.58)Co_(0.04)O_2, Li_(1.2)Ni_(0.2)Mn_(0.48)Co_(0.12)O_2, and Li_(1.2)Ni_(0.2)Mn_(0.52)Co_(0.08)O_2 solid solutions cathode materials can deliver discharge capacities of 267, 262, 253, 235, and 238 mAhg~(-1), respectively, at a charge/discharge current density of 25 mA g~(-1) in the voltage range of 2.5-4.7 V. These cathodes all have initial coulombic efficiencies larger than 80%, and show capacity loss less than 0.13% per cycle while cycling at 125 mA g~(-1) for 50 cycles. From Rietveld refinement results and electrochemical impedance spectra (EIS) analysis, it is found that the highest charge/discharge capacity values of Li_(1.2)Ni_(0.13)Mn_(0.54)Co_(0.13)O_2 cathode with the lowest Ni content among them are attributed to the lowest cation mixing. While both the Li_(1.2)Ni_(0.2)Mn_(0.48)Co_(0.12)O_2 and Li_(1.2)Ni_(0.2)Mn_(0.52)Co_(0.08)O_2 cathode materials with higher Ni content exhibit better rate capabilities due to their lower charge transfer resistances and higher electrical conductivities than those of other samples.