Investigation of the structural and electrochemical performance of Li1.2Ni0.2Mn0.6O2 with Cr doping
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Cr-doped layered oxides Li[Li0.2Ni0.2 − x Mn0.6 − x Cr2x ]O2 (x = 0, 0.02, 0.04, 0.06) were synthesized by co-precipitation and high-temperature solid-state reaction. The materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (TRTEM), X-ray photoelectron spectroscopy (XPS), and electrochemical impedance spectroscopy (EIS). XRD patterns and HRTEM results indicate that the pristine and Cr-doped Li1.2Ni0.2Mn0.6O2 show the layered phase. The Li1.2Ni0.16Mn0.56Cr0.08O2 shows the best electrochemical properties. The first discharge specific capacity of Li1.2Ni0.16Mn0.56Cr0.08O2 is 249.6 mA h g−1 at 0.1 C, while that of Li1.2Ni0.2Mn0.6O2 is 230.4 mA h g−1. The capacity retaining ratio of Li1.2Ni0.16Mn0.56Cr0.08O2 is 97.9% compared with 93.9% for Li1.2Ni0.2Mn0.6O2 after 80 cycles at 0.2 C. The discharge capacity of Li1.2Ni0.16Mn0.56Cr0.08O2 is 126.2 mA h g−1 at 5.0 C, while that of the pristine Li1.2Ni0.2Mn0.6O2 is about 94.5 mA h g−1. XPS results show that the content of Mn3+ in the Li1.2Ni0.2Mn0.6O2 can be restrained after Cr doping during the cycling, which results in restraining formation of spinel-like structure and better midpoint voltages. The lithium-ion diffusion coefficient and electronic conductivity of Li1.2Ni0.2Mn0.6O2 are enhanced after Cr doping, which is responsible for the improved rate performance of Li1.2Ni0.16Mn0.56Cr0.08O2.
KeywordsLithium-ion battery Lithium-and manganese-rich oxides Cr doping Electrochemical performance
The authors gratefully acknowledge the National Natural Science Foundation of China (51304081, 51774150, 51604124, and 51604125) and Natural Science Foundation of Jiangsu Province (BK20140581, BK20150506, and BK20140558).
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