Lithium-ion Battery Cathode Material Spinel Of Limn <sub> 2 </ Sub> O <sub> 4 </ Sub> Material Modification

The spinel LiMn₂O₄ has not been commercialized to date because of its capacity fading that occurs with charge-discharge cycles.The capacity fading has been linked to several problems, including electrolyte oxidations, manganese dissolution and distortion of the crystal lattice due to the Jahn-Teller effect on discharge. doping the spinel with F and Co was introduced in this paper to improve performace of material.The doped spinel LiMn₂O₄ was synthesized by sol-gel-complexation method . Citric acid was used as a complexing reagent. At first, the citrate precursor formed and was heated to remove water. After drying ,the precursors were decomposed at 300℃to eliminate organic contents. The decomposed powders were slingtly ground and then sintered at different temperatures in air.The performace of material was tested by DSC,XRD,SEM,EIS and charge-discharge cycles . The influences of various synthesized condition , sintering time and the amount of F were studied and correlative technics parameter to improve performance of material were optimized. DSC shows that three endotherimc peaks and one large exothermic peak are observed in the temperature range 150-400℃, which is because of the removal of water,the decomposition of the organic constituents and the formation of spinel. Only the citrate precursor is sintered at least 450℃, the crystallinity of spinel phase could be formed intactly.SEM shows that the samples calcined at 600℃ consist of smaller particles. As the calcination temperature increases, the particle size also increases. In particular, at 800℃ the particles exhibit uniform crystal shape and good crystallinity with an average size of 4.90μm. EDAX shows that there are F and Co in the material synthisezed with sol-gel-complexation method.XRD shows that doped LiMn₂O₄ belongs to spinel also. The crystallinity of spinel phase calcined at 300℃ is poor.The crystallinity is increased with increasing temperature as indicated by the sharpness of the intensities of the XRD Peaks and 700-800℃ is the better temperature. The impurity peaks observed in the XRD patterns are due tothe formation of Mn2O3 or some other substances during firing. the crystallinity is independent of the amount of F. The lattice parameter increases with the increase of temperature and the amount of F.The electrode reaction of doped LiMn₂O₄ is the insertion of Li-ion between the cathode and anode and the performance of these electrodes can be studied by application of EIS. The equivalent circuits must be considered to describe the diffusion and accumulation of lithium at the very low frequency.The Nyquist and fitresults show that the resistance of doped material is uniform to the undoped LiMn₂O₄ before charge and discharge. At the initial stage of charge and discharge, Rdoped is larger than Rundoped, however, Rdoped is smaller than Rundoped with the cycles. This indicates that the performance of former is better than the latter.There are two semicircles in the Nyquist during cycling, which is due to the electrolyte decomposition product formed as a result of oxidation-reduction processes occurring on the surface of the electrode. The cycling recults show the initial rate-capacity of doped LiMn₂O₄ is 119.278mAh/g, which is near to that of the undoped LiMn₂O₄ . The capacity fading rates of doped spinel and undoped one are 23.8% and 42.5% respectively after 60 cycles. So the cycling performance of LiMn₂O₄ has been improved effectively after modification by doping.