| A modified citrate route with combustion for LiMn2O4, used for Li (ion) battery, has been developed. This processing is simpler and cost-cheaper than the normal route of preparing LiMn2O4. The nanometer and sub-micrometer LiMn2O4 synthesized by such a processing also has a good electrochemical performance, compared with LiMn2O4 produced by the normal citrate route and sold commercially, for the electrode application. XRD TEM and ICP were used to examine the structural characteristics. The single phase with the spinel structure can be easily obtained by optimizing the processing parameters. The typical synthetic product is Lio.95Mn2O4.18 with the cell constant a~ 8.2506A and powder size of 10-lOOnm, but the segregated granule size is about 611 m. The effects of glycol addition, pH value of solution on the precursor and calcining temperature on the phase structure have also been investigated. It is obtained that glycol promotes the homogeneous distribution of composition elements, which improves the electrochemical performances; pH=7.2 is a suited pH value for getting ideal product with good properties; the calcineing temperature is the key to transforming the precursor to a single spinel phase with the spinel structure and the calcination at 800C for 24h following 500C is considered as an optimized one. By typical processing, 2025 type button batteries were assembled using LiMn2O4 composite and Li metal foil as the positive and negative electrode respectively. Those batteries show the stable working voltage of about 4V and the reversible capacity of 1 29mAhIg for first cycle and remained of 82% after 20 cycles. Preliminary studies on the kinetic process of electrode reaction in full Li/LiMn2O4 battery system were also conducted by CV and EIS. Main feature of the CV curve is two reversible oxidation (reduction) peaks, which indicates that Li ions insert into (de-intercalation from) the LiMn2O4 lattice with two steps. EIS in different states of charge were also carried out for full LiMn2Q4/Li battery system. EIS has been resembly assigned and the semi-circle at middle frequency can be clearly attributed to the passive films from PTFE. For improving the cycling property, LiMMn2..O4 with substitution element B Al~ Cr Fe. Co. Ni-. Ga and x0.l and 0.2, respectively, were synthesized by the modified citrate route, which can make more homogeneous distribution of the substituted element. All substitution elements reduce the initial reversible capacity ,but except B,improve cycling characteristics. Among them, LiCro.iMni,904 has the best performance with the reversible capacity of 1 24mAhlg at first cycle and keeping 93.5% after 20 cycles. The resistance behaviors with temperature were examined for investigating the electron conducting and structural change of LiMn2O4. The resistivity of LiMn2O4..5 shows a semiconductor behavior with 103106 2 cm and could be described by Arrehnius law in the range of 200K-RT.The samples quenched from the equiliblium state at 400-.-700 in air, the electron conductivity activation energy Ea and the resistivity change little, but above 800CC, they decrease obviously with temperature increasing. It may be connected with the oxygen deficiency. The structural phase transition near room temperature was observed in some samples by resistance measurement. |
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