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The poor cycling stability of Li- and Mn-rich layered oxide cathodes used in lithium-ion batteries (LIBs) has severely limited their practical application. Unfortunately, current strategies to improve their lifecycle sacrifice initial capacity. In this paper, we firstly report the synergistic improvement of the electrochemical performance of a Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O 2 (LNCMO) cathode material, including gains for capacity, cycling stability, and rate capability, by the partial substitution of Li + ions by Mg 2+ ions. Electrochemical performance is evaluated by a galvanostatic charge and discharge test and electrochemical impedance spectroscopy (EIS). Structure and morphology are characterized by X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). Compared with the substitution of transition metal (TM) ions with Mg 2+ ions reported previously, the substitution of Li + ions by Mg 2+ ions not only drastically ameliorates the capacity retention and rate performance challenges of LNCMO cathodes but also markedly suppresses their voltage fading, due to the inhibition of the migration of TM ions during cycling, while also increasing the capacity of the cathode due to an increased abundance of the Li 2 MO 3 phase. [ABSTRACT FROM AUTHOR]

Li- and Mn-rich layered oxide (LMRO) cathode materials deliver a reversible capacity over 280 mAh g −1 , which is almost two times higher than that of traditional cathode materials. However, the improved mechanism of high capacity for the LMRO cathode material has not been elaborated clearly so far. In this work, the relationship between the structures and the electrochemical performance in the Li (2x+2)/(2+x) Ni (2-2x)/(6+3x) Co (2-2x)/(6+3x) Mn (2+4x)/(6+3x) O 2 (XLNCMO) (0 ≤ X ≤ 1) cathode materials is systematically studied. Electrochemical performance is evaluated by a galvanostatic charge and discharge test and electrochemical impedance spectroscopy (EIS). Structure and morphology are characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS) technologies. Results demonstrate that there is an obvious synergistic effect between the Li 2 MO 3 ( C 2/ m ) phase and the LiMO 2 (R-3m) phase in the XLNCMO cathode with a mutual doped composite structure. In this composite structure, the LiMO 2 (R-3m) phase plays a role of an “activator” to activate the electrochemical activity of the Li 2 MO 3 ( C 2/ m ) phase and also provides electrochemical capacity, and the Li 2 MO 3 ( C 2/ m ) phase can be seen as an “stabilizer” to enhance the cycling stability of the LiMO 2 (R-3m) phase. Moreover, the Li 2 MO 3 ( C 2/ m ) phase can also be seen as a major contributor for enhancing the electrochemical capacity of the XLNCMO cathodes. [ABSTRACT FROM AUTHOR]