Preparation and electrochemical properties of LiCoO2–LiNi0.5Mn0.5O2–Li2MnO3 solid solutions with high Mn contents

The solid solutions LiCoO2–LiNi1/2Mn1/2O2–Li2MnO3 with higher Mn content have been prepared by a spray drying method between 750 and 950 °C and their electrochemical performances have also been characterized. The effects of the Li content on the structure and electrochemical performance of the samples have been studied. It was found that their lattice parameters a, c and V increase with the increase in Ni content and the decrease in Co content. The solid solutions xLiCoO2–yLiNi1/2Mn1/2O2–(1−x−y)Li2MnO3 with x = 0.18, 0.27 and y = 0.2 have the largest discharge capacity, which is more than 200 mAh/g in the voltages of 3.0–4.6 V. It is believed that the optimum Co content x in xLiCoO2–yLiNi1/2Mn1/2O2–(1−x−y)Li2MnO3 is between 0.2 and 0.3 in the charge–discharge voltage range of 3.0–4.6 V. The solid solutions xLiCoO2–yLiNi1/2Mn1/2O2–(1−x−y)Li2MnO3 with x = 0.18–0.36 and y = 0.2 have the excellent cycling performance and the capacity retention attains to almost 100% after 50 cycles. Moreover, it is found that the discharge capacity gradually increases with the increment of cycle number especially in the initial 10 cycles. XRD showed that the layered structure has been kept all the time in 20 cycles, which is perhaps the reason why the sample has the excellent cycling performance.