| With the wide spread application of Li-ion battery, one of specific requirements is positive electrode material with high capacity, high security, cycle stability and rate capability. However, in present cathode materials can’t meet the requirements of the market, cathode materials become the bottleneck of commercial lithium ion batteries.Recently, Li-rich cathodes have caught the great attention for the novel electrode materials of lithium ion batteries with high capacity and high discharge plateau. In addition, anode material Li4Ti5O12(LTO) have the excellent thermostability, cycle stability and no volume change during charge and discharge process. LTO has been the most promising anode material. Due to the characteristics of Li-rich layer-structure and LTO, we have done some works as follows:1. Li-rich layer-structure xLi2MnO3·(1-x)LiNi0.5Mn0.5O2(x =0.2, 0.4, 0.6, 0.8)cathode materials has been synthesized by coprecipitation-high temperature solid-state method, the influence of x value and sintering temperature on morphology and electrochemical properties. The crystal structureand and morphology are characterized by X-ray diffraction(XRD), SEM, EDS and so on, the electrochemical properties are studied by charge-discharge tests and Zview Rietveld and so on. XRD patterns indicate that the as-synthesized material is pure. SEM shows the aggregation of particles into class sphere and sphere average particle size(3 μm). The charge/discharge results indicate that the Li-rich 0.4Li2MnO3·0.6LiNi0.5Mn0.5O2 have the best electrochemistry properties are synthesized via coprecipitation-high temperature solid-state method. Within the cut-off voltage between 2.5 and 4.8 V, the initial discharge capacity is 226.8 mAh·g-1 at 0.1 C rate; and after 50 cycles the discharge capacity remains 215 mAh·g-1, with good reversibility(94%).2. To improve the high-rate capacity and cycle ability, Li2ZrO3 successfully coat the particles of 0.4Li2MnO3·0.6LiNi0.5Mn0.5O2 via high temperature solid-state method. The adding mode and amount were investigated on morphology and electrochemical properties. The lattice structure of 0.4Li2MnO3·0.6LiNi0.5Mn0.5O2 is remained after coating layer. After Li2ZrO3 coating, the best proportion is 2%, the discharge capacity is 253 mAh·g-1 at 0.1 C rate, which are much higher than 226.8mAh g-1of intrinsic 0.4Li2MnO3·0.6LiNi0.5Mn0.5O2. Even at the current density of 1 A g-1, 2%-Li2 Zr O3 offers capacity of 145.5 mAh g-1, which are much higher than 116.9mAh g-1 of 0.4Li2MnO3·0.6LiNi0.5Mn0.5O2.3. Zr doped sample of Li4Ti4.99Zr0.01O12(LTZO) and Li2 Zr O3(LZO) coated Li4Ti5O12(LTO) are prepared by a solid-state method. The lattice structure of LTO is remained after doping element of Zr and coating layer. The crystal structure and electrochemical performance of the material are investigated by X-ray diffractometry(XRD), high-resolution transmission electron microscopy(HRTEM),cyclic voltammetry(CV), galvanostatic intermittent titration technique(GITT) and charge-discharge tests. Zr-doping and LZO coating play the positive role in improving the diffusion ability of lithium cations. LTZO and LZO-LTO show much improved specific capacity and rate capability compared with pristine LTO. LZO-LTO has the smallest ?V of the redox peaks because the coating of Li2ZrO3 is helpful for the extraction/reinsertion of lithium ions during charge/discharge processes. LTZO and LZO-LTO as electrode deliver the initial capacities of 164.8, 168.1 mAh g-1, which are much higher than 150.2 mAh g-1of intrinsic LTO. Even at the current density of 2A g-1, LTZO and LZO-LTO offer capacity of 96 and 106 mAh g-1, which are much higher than 33 mAh g-1 of LTO. The improved electrochemical performance is attributed to the improved diffusion ability of lithium. During the whole discharge process, the lowest value of LTO is 5.97×10-17 cm2 s-1 which is much lower than7.80×10-16 cm2 s-1 in LTZO and 1.85×10-15 cm2 s-1 in LZO-LTO, respectively.4. Li-rich layer-structure 0.4Li2MnO3·0.6LiNi0.5Mn0.5O2 and LTO have been made into total battery, cathode restricted capacity and anode restricted capacity on electrochemical properties. We have found total battery with poor cycle stability,capacity attenuation serious and low capacity. The experimental results is not ideal,total battery should be studied further.Through the studies of this paper, we have realize the preparation process of Li-rich cathode material and LTO, the structure characteristics and electrochemical performance of the relationship. All these provide basic research and practical application for Li-rich cathode material and LTO in the future. |
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