Synthesis and characterization of LiNi_0.6Co_xMn_0.4-xO₂ (x = 0.05, 0.1, 0.15, 0.2, 0.25 and 0.3) with high-electrochemical performance for lithium-ion batteries

A series of Ni_0.6Co_xMn_0.4-x(OH)₂ hydroxide precursors with x = 0.05, 0.1, 0.15, 0.2, 0.25 and 0.3 are prepared by co–precipitation method from sulfate solutions using NaOH and NH₄OH as precipitation and complexing agents. Then, well–ordered layered LiNi_0.6Co_xMn_0.4-xO₂ are synthesized by sintering the mixture of as–prepared precursors and LiOH · H₂O at 820 °C for 12 h in flowing oxygen. Their structural and electrochemical properties are investigated using X–ray diffraction(XRD), scanning electron microscope(SEM), X–ray photoelectron spectroscopy(XPS), charge–discharge test, Cyclic voltammetry(C–V) and electrochemical impedance spectroscopy (EIS). The increase of the Co content in LiNi_0.6Co_xMn_0.4−xO₂ leads to the decrease of the tap–density of the powders, the increase of discharge capacity and the deterioration of cycling performance. It also leads to the enhancement of the ratio Ni³⁺/Ni²⁺ in LiNi_0.6Co_xMn_0.4−xO₂, confirmed by the XPS analysis. The results show that the sample with x = 0.2 has the highest tap–density, delivers an initial discharge capacity of 172.3 mAh g⁻¹ at 1C rate between 2.8 and 4.3 V, more than 94.1% of that is retained after 100 cycles, and also with excellent rate capability and high-temperature performance