Enhanced high rate performance of Li[Li0.17Ni0.2Co0.05Mn0.58−xAlx]O2−0.5x cathode material for lithium-ion batteries

Abstract

Pristine Li[Li_0.17Ni_0.2Co_0.05Mn_0.58]O₂ (LNCM) and Li[Li_0.17Ni_0.2Co_0.05Mn_0.58−xAl_x]O_2−0.5x (x = 0.01, 0.02 and 0.04) (LNCMA) as Li-rich cathode materials for lithium ion batteries were synthesized via a sol–gel route. Inductively coupled plasma atomic emission spectrometry (ICP-AES), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to investigate the composition, structure and morphology of the LNCM and LNCMA samples. The homogeneous dispersion of the element Al in the LNCMA samples was confirmed using energy dispersive spectroscopic (EDS) mapping. Compared with LNCM, the larger crystal cell volume of LNCMA was verified by XRD and TEM analysis. A blue shift of O1s and Mn2p peaks in the A2 sample was observed via XPS, demonstrating the partial substitution of Al³⁺ for Mn⁴⁺ ions. The electrochemical properties are examined by means of cyclic voltammetry and charge/discharge tests. In general, the Al-substituted samples exhibit a better electrochemical performance. Especially for the A2 sample, it presents an enhanced initial discharge capacity of ∼300 mA h g⁻¹, accompanied with the better initial coulombic efficiency of 90.9%. For 5 C rate, the A2 sample delivers a higher discharge capacity of 168.9 mA h g⁻¹ in the initial cycle and 156.5 mA h g⁻¹ after 150 cycles, while for the pristine sample it is 126.5 and 98.8 mA h g⁻¹, respectively. The excellent electrochemical performance of the Al-substituted samples could be ascribed to the enlarged cell volume and improved structural stability resulting from the partial Al substitution.