Benan Hu

Synthesis and characterization of a Li-rich layered cathode material Li1.15[(Mn1/3Ni1/3Co1/3)0.5(Ni1/4Mn3/4)0.5]0.85O2 with spherical core–shell structure

A Li-rich layered cathode material Li1.15[(Ni1/3Co1/3Mn1/3)0.5(Ni1/4Mn3/4)0.5]0.85O2 with a spherical core–shell structure was firstly synthesized by a co-precipitation route. In this material, the Li1.15[Ni1/3Co1/3Mn1/3]0.85O2 core was completely encapsulated by a Li1.15[Ni1/4Mn3/4]0.85O2 shell. The structure and morphology of the as-prepared core–shell structured material were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD results indicate that the core–shell structured material has a typical layered structure with the existence of a Li2MnO3-type integrated component. Spherical morphologies with an inner core and outer shell layer are clearly observed by SEM. A half cell using the core–shell structured cathode material showed a high capacity of 242 mA h g−1 at a rate of 0.1 C in a voltage range of 2.0–4.8 V. Especially, the core–shell structured cathode material represents excellent lithium intercalation stability compared to the Li1.15[Mn1/3Co1/3Mn1/3]0.85O2 core, and an improved rate capability compared to the Li1.15[Ni1/4Mn3/4]0.85O2 shell. A synergetic effect of the positive attributes of the two materials is achieved by the formation of the core–shell architecture. Therefore, the as-prepared core–shell structured Li1.15[(Mn1/3Ni1/3Co1/3)0.5(Ni1/4Mn3/4)0.5]0.85O2 is very effective for improving the electrochemical behavior of Li-rich layered cathode materials in the high-performance lithium ion batteries.

Spherical concentration-gradient LiMn1.87Ni0.13O4 spinel as a high performance cathode for lithium ion batteries

A novel spherical concentration-gradient material with an average composition of LiMn1.87Ni0.13O4 is successfully synthesized via a co-precipitation route, in which the homogeneous LiMn2O4 core is encapsulated by a continuously Ni increasing concentration-gradient layer, and the composition of the outmost layer of the spherical LiMn1.87Ni0.13O4 is LiMn1.5Ni0.5O4. The physicochemical and electrochemical performances of the spherical LiMn1.87Ni0.13O4 sample are investigated by X-ray diffraction (XRD) and electrochemical tests, and using a scanning electron microscope (SEM) with an energy-dispersive X-ray spectroscope (EDXS). The results show that the LiMn1.87Ni0.13O4 sample has a typical Fd3m spinel structure. It can be found from the cross-sectional SEM images and EDXS analysis that the LiMn1.87Ni0.13O4 particles are quite homogeneous without any apparent gap between the inner core and the outer concentration-gradient layer. Especially, the LiMn1.87Ni0.13O4 sample has excellent performance at an elevated temperature. It delivers a discharge capacity of 108.2 mA h g−1 between 3.0 and 4.4 V vs. Li/Li+ with a retention of 90.2% over 200 cycles at a rate of 0.5 C (74 mA g−1) at 55 °C. Besides, it has an exceptional capacity of 129.1 mA h g−1 between 3.0 and 4.9 V with a retention of 91.9% over 100 cycles at a rate of 0.5 C at 55 °C. Apparently, the LiMn1.87Ni0.13O4 sample shows excellent capacity stability even at an elevated temperature, i.e. 55 °C, where a traditional LiMn2O4 sample inevitably fails. Thus, the LiMn1.87Ni0.13O4 sample with a homogeneous LiMn2O4 core material and an isotropy concentration-gradient outer layer shell will be a promising cathode material for advanced lithium ion batteries.