Study On The Lithium Rich Mixed-Metal Materials For Lithium Ion Battery

Lithium rich materials become the research focus for its high specific capacity, high voltage, high safety and environmental protectional, but also a popular candidate for one of the lithium ion battery cathode material for the next generation. This paper chose to study common manganese, nickel and cobalt three elemental Li rich material as the research object, in order to improve its electrochemical performance, the synthetic methods of material and process parameters, doping modification, effects of surface coating modification, transition metal component content on the electrochemical properties of materials, the relationship between the structure, morphology and the electrochemical properties of the materials have been studied deeply and systemly.The lithium rich materials Li1.2Mn0.54Ni0.13Co0.13O2 were synthesized by solid state reaction method, sol-gel method, microwave method and ultrasonic coprecipitation method. The sol-gel method with the surfactant CTAB, can make particle size uniformly. The initial specific discharge capacity was 282.7 mAh/g. The materials prepared by ultrasonic coprecipitation would be thinner than by the common ultrasonic method and solid state reaction method. Ultrasonic for 12 h, the first discharge specific capacity of the material reduced. There is an obvious activation process, the maximum discharge capacity appears at about the 10th time charge-discharge cycle. The materials have the bes cycle performance, the ratio of discharge specific capacity after 100 cycles than the maximum capacity is 89.7%. In this paper, for the first time prolonged the ultrasonic time to 12 h in coprecipitation method was applied to the preparation of lithium rich materials. The special role of ultrasound is exerted, makes the crystal properties of the material obvious and the particle integrated.The doping modification is used to improve structure of the lithium rich materials. A series of Li[Li0.2Mn0.54Ni0.13-xCo0.13Mox]O2 (x=0,0.01,0.03,0.05,0.07 and 0.09) materials were prepared by adding different amount of molybdenum. It is shown that the capacity of the materials was obviously increased after doping the appropriate amount of Mo, it could deliver discharge capacities of 296.8 mAh/g, at a charge/discharge current density of 20 mA/g in the voltage range of 2.0-4.8 V. The structure and morphology of the doped samples are characterized and compared by the results of XRD. The doped samples have bigger lattice volume, and better layer structure ordering, but also have higher aggregation of particles, resulting in bigger particle size and worse electrochemical performance. The value of x is 0.05 is found to be the optimal amount of Mo. In order to study the influence of the atomic radius of doping elements on the structure and properties of the material, three kinds of elements Cr, Mo and W were doped. Found that with the atomic radius increases, the lattice volume of lithium rich materials after doping is larger, but the W have larger atomic radius of than Cr and Mo is more difficult to enter the crystal lattice.The fluoride which is very stable in the electrolyte is in the treatment of surface coating modification. The lithium rich material were coated by NiF2 which itself contains Ni. The electrochemical properties of the material is improved. Also the earth rare La in the fluoride, as well as the heavy rare earth Y. YF3 modification of lithium rich materials have not been reported. The structure and properties after coating with the different YF3 were studid. The materials have better electrochemical performance when 5 wt.% coating.Considering the material composition optimization, study on the structure and electrochemical properties of high content for the single transition metal of lithium rich materials. We prepared the samples in the same synthesis parameters, the cobalt based lithium rich materials Li1.2Co0.54Mn0.13Ni0.13O2 has the best cycle performance, the capacity retention rate was 83.8% after 100 cycles. The manganese base lithium rich material Li1.2Mn0.54Co0.13Ni0.13O2 has the maximum specific capacity.