Synthesis and characterization of Nickel-rich layered LiNi1-xMnxO2 (x=0.02,0.05) cathodes for lithium-ion batteries

In this paper, LiNi0.98Mn0.02O2 and LiNi0.95Mn0.05O2 binary materials were synthesized by chemical co-precipitation method. The phase characterization and electrochemical performance analysis of Ni-Mn binary materials were carried out by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and electrochemical tests, and the action of Mn element on the material was studied. XRD analysis shows that LiNi0.95Mn0.05O2 material has the better layered structure (1.47 of the (003)/(104) peak intensity ratio), and the lower Li-Ni mixing ratio (1.98%). The initial discharge capacity of LiNi0.95Mn0.05O2 material at 1 C is 189.6 mAh/g, and the capacity retention rate is 89.93% after 100 cycles at 1 C, which is much higher than LiNiO2 of 177.4 mAh/g and 60.26%. In addition, the initial discharge specific capacity of LiNi0.95Mn0.05O2 can reach 205.8 mAh/g at 0.5 C under the high temperature of 50 °C, and the capacity retention rate is 78.7% at 0.5 C for 100 cycles, while the discharge specific capacity of LiNiO2 is 191.1 mAh/g at 0.5 C and the capacity retention rate is only 63.9%. Excellent electrochemical properties of Ni-Mn materials than LiNiO2 at room and high temperature is because Mn4+ without electrochemical activity is stabilized in the transition metal layer during the charge and discharge process of the materials, alleviating the structural collapse caused by the Li/Ni mixing. By comparing the cross-section of the materials before and after 100 cycles at 1 C, LiNi0.95Mn0.05O2 has fewer microcracks due to the high reversible phase transformation of H2-H3 according to the analysis of the dQ/dV versus voltage curves. Meanwhile, the stable layered structure and lithium-ion diffusion channel also make LiNi0.95Mn0.05O2 has the better lithium-ion conductivity.