| The principle and the development of lithium ion batteries and the survey of cathode materials have been described in this dissertation. The physicochemical properties, the preparation methods, and some existing problems of LiMn2O4 have been introduced with emphasis. On the basis of this, the LiMxMn2-xO4 (x=00.5) cathode materials were prepared and their structure and electrochemical performance were investigated in detail. Meanwhile, the electrode dynamics, electronic structure and the effects of substituted metal ions on the open circuit potential of LiMxMn2-xO4 electrode were theoretically explored.Firstly, the LiMn2O4 samples were prepared by a liquid precipitation-calcination method and the effects of calcinations temperature and time on their physicochemical properties were investigated. It was found that the LiMn2O4 phase is formed when the precessor is calcined at 350 ℃, and the pure LiMn2O4 is obtained over 700 ℃. The cell parameter and unit cell volume decrease with the increase of the calcination temperature due to the volatilization of a little lithium, but the vibration frequency of Mn-0 bond does not change with the variety of calcination time and temperature. FWHM(311) and FWHM(400) decrease at first and then increase with the increase of calcination temperature, which have the minimum values at 750 ℃. The discharge potential and discharge capacity increase at first and then decrease with the increase of calcination temperature. The sample calcined at 750 ℃ has higher discharge potential, larger discharge capacity and better cycle stability due to lower electrochemical and diffusion polarizations which result from smaller unit cell volume, better crystallinity and smaller particle size. The increase of calcination time can contribute to the improvement on the discharge capacity.Secondly, the LiMxMn2-xO4 (M=Ni, Co, Ni/Co) samples were prepared by the liquid precipitation-calcination method and their physical properties and electrochemical performance were investigated in detail. Due to the introduction of Ni, the vibration frequencies of Mn(Ⅳ)-O and Mn(Ⅲ)-O bonds shift to higher and lower wave number, respectively. The new vibration of Ni-O bond appears and its strengthgradually increases with increasing the nickel content in the samples. The vibration frequencies of both Mn(IV)-0 and Mn(III)-0 bonds shift to higher wave number with the increase of Co doping. For the samples with Ni/Co, the vibration frequency of Mn(IV)-0 shifts to higher wave number, and the one of Mn(III)-0 bond almost keeps unchange. The vibration frequencies of Mn-0 bonds in LiMxMn2-xO4 (M=Ni, Co, Ni/Co) do not change with the variety of calcination time and temperature, but the cell parameters decrease with the increase of calcination time and temperature. The cell parameters of LiMxMn2-x04 (M=Ni, Co, Ni/Co) decrease with the increase in the contents of the substituted metal ions due to the stronger M-0 (M=Ni, Co, Ni/Co) bond and the smaller radius of substituted metal ions. The addition of Ni leads to the increase in the extent of cation disorder, the decrease of particle size and the improvement of dispersivity, and the addition of Co leads to the increase in the extent of cation disorder, the decrease of particle size and the improvement of dispersivity. The trace impurity occurs when the content of the additives (Co, Ni/Co) exceeds 0.2. The increase of calcination time contributed to the improvement on dispersivity and uniformity of samples. The new current peaks and the potential flat appear at about 4.7 V for LiNixMn2-xO4 and LiNixCoxMn2-2xO4 due to the introduction of Ni, but they do not occur for LiCoxMn2-xO4 sample. The new current peak values increase and the peak values at about 4.0 V decrease with the increase of Ni contents in samples. The LiNio.05Mn1.95O4 sample has higher discharge potential, larger discharge capacity and better cycle stability due to the introduction of Ni, which decreases Rs, Rf and Warburg impedance and increases the diffusion coefficient of Li+. The values of Rs, Rf, Rt and Wo are greatly decreased by the introduction of Co. With the increase of Co contents, Rs decreases, Rf and Rt first decrease and then increase, and Wo increases. This may be the reason why the charge flat potential increases, and the current peak, the discharge flat potential and discharge capacity decrease for LiCoxMn2.xO4 samples. The LiCoo.1Mm.9O4 sample with smaller Rs, Rf, Rtand Wo values has higher discharge potential, larger discharge capacity, better rate capability and longer cycle life. The addition of Ni/Co leads to the decrease of Rs, Rf, Rt and Wo values, which results in the current peak values first increase and then decrease in 4 V potential range and the peak values in the 4.7 V increase. The LiNio.osCoo.osMni 9O4 sample has larger current peak, lower charge potential, higher discharge potential, larger discharge capacity, better rate capability and longer cycle life due to its minimum Rt and Wo values. The electrochemical performance of LiNio.1Coo.1Mn1.gO4 sample is improved by the increase of calcination time, which decreases the charge transfer resistance anddiffusion resistance, namely, electrochemical and diffusion polarizations. The effects of calcination time on the samples with various Co contents are different. With the increase of calcination time, the polarization of the LiCoo.iMni 9O4 electrode is sharply decreased, but the electrode polarization of the LiCoo.2Mn1.gO4 sample is increased, which is unfavorable to the intercalation-deintercalation of Li+ and then results in the decrease of electrochemical performances. It was also found the LiMn2O4 sample with appropriate content of the additives (Ni, Co and Ni/Co) display better electrochemical-cycling performance at 55°C.Finally, the band structure and density of states of LiMr^Cn materials were explored by ab initio calculation method, and the effects of substitution of various metal ions on the open circuit potential were also studied. In general, the calculation results are close to the experimental ones.
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