The Research Of Nickel-Manganese Binary Cathode Material For Lithium-ion Battery

Cathode material is one of the most important components for the lithium-ion battery(LIB) and plays an important role for the performance, safety and stability of the battery. Due to its high energy density, simple production process, rich resources, low cost, and environmentally friendiness, lithium nickel manganate cathode materials have attracted more and more attention in recent year. The materials include layered Li Ni0.5Mn0.5O2 material, spinel Li Ni0.5Mn1.5O4 material, layered lithium rich Li[Li1/3-2x/3NixMn2/3-x/3]O2 material. Because the production process of Li Ni0.5Mn0.5O2 material with high activity is extremely complex and realing mass production is very difficult, thus, most of the research works focused on the spinel Li Ni0.5Mn1.5O4 material and layered lithium rich Li[Li1/3-2x/3NixMn2/3-x/3]O2 material recently.In this paper, a series of Li NixMn2-xO4 cathode materials with various molar ratio of Ni/Mn have been prepared with a co-precipitation method, followed by a solid state reaction, and the effect of the molar ratio of Ni/Mn on the structure and properties of materials are intensively investigated by means of X-ray diffraction(XRD), fourier transform infrared spectrometer(FTIR), scanning electron microscopy(SEM), and performance measurements etc. It is found that the capacity at the 4.0 V plateau decreases while the capacity at 4.7 V plateau increases with the increase of the ratio of Ni/Mn, and the total discharge capacity shows growth trend with the increase of Ni content.Secondly, a series of lithium rich cathode materials, Li[Li1/3-2x/3NixMn2/3-x/3]O2(0<x<0.5), has been prepared and investigated, it is found that that the optimal Li[Li0.1Ni0.35Mn0.55]O2 material exhibits high capacity, more stable discharge plateau. Further, the effect of PEG addition on the performance of Li[Li0.1Ni0.35Mn0.55]O2 cathode is investigated, it is found that the material with 9 wt% PEG addition shows the most positive influence on the performance of the material. The 9 wt% PEG-Li[Li0.1Ni0.35Mn0.55]O2 exhibits well α-Na Fe O2 layered structure, making lithium ions embed in and out more easily,and resulting in the better electrochemical performance.Finally, we attempted to dop Co3+, Fe3+in the above cathode material to improve its electrochemical perpormance. Unfortunately, both Co3+ and Fe3+ doping exhibit negaitive influence on the electrochemical perpormance of the material. We suggest that the doping of Co3+ may result in the decrease of active lithium ions, resulting in the discharge capacity decreases from 187.1 m Ah/g to 150 m Ah/g. Meanwhile, new material phase may be generated in the layered structure of the material, blocking the Li+ diffusion channels after doping Fe3+, resulting in the decrease of the discharge capacity of the materials.