Influence of cobalt content on the electrochemical properties of sheet-like 0.5Li2MnO3·0.5LiNi1/3+xCo1/3−2xMn1/3+xO2 as lithium ion battery cathodes

Abstract

The promising cathode materials of serial 0.5Li₂MnO₃·0.5LiNi_1/3+xCo_1/3−2xMn_1/3+xO₂ (x = 1/12, 1/24, 0, −1/24 and −1/12) solid solutions have been synthesized by a polymerization–pyrolysis-assisted crystallization route. X-Ray diffraction (XRD) and scanning electron microscope (SEM) characterization show that all the powdered solid solutions possess a two-dimensional sheet-like superstructure composed of crystalline nanoparticles. Galvanostatic charging–discharging tests exhibit that, as high-capacity cathodes, the initial coulombic efficiency and cycling stability of these sheet-like configurations depend upon the cobalt content (i.e., the value of (1/3 − 2x) difference) in chemical formula 0.5Li₂MnO₃·0.5LiNi_1/3+xCo_1/3−2xMn_1/3+xO₂, giving an optimal x value in the range of 0 and 1/12. Considering the initial activation of component Li₂MnO₃ and the unwanted phase change of Co-contained component LiNi_1/3+xCo_1/3−2xMn_1/3+xO₂ at a charging voltage higher than 4.55 V, the cyclability and electrode polarization of serial sheets have also been estimated within a narrow electrochemical window of 2.0 and 4.3 V. To compare with the electrochemical parameters of serial solid solutions obtained within 2.0 and 4.7 V, therein an extremely high capacity retention ratio of 99.2% (x = 1/12) or 95.4% (x = 0) is observed at 0.5 C over 50 charge–discharge cycles.