Preparation And Modification Of Lithium Manganese Phosphate Cathode Material For Lithium-ion Battery

As lithium-ion battery cathode material, LiMnPO4 have some advantages of high voltage, high energy density, low cost, low toxicity et al.. But its electronic conductivity and lithium ion diffusion coefficient limit its practical application. In order to improve electronic and ionic conductivity of LiMnP04, This thesis was aiming at the improvement of performances of materials through surface coating and doping of divalent transition metal ions, while different experimental conditions on electrochemical properties of the materials were studied. Morphology, Structure and electrochemical performances of materials were characterized by scanning electron microscopy(SEM), x-ray diffraction(XRD) and electrochemical measurements respectively. The main results are summarized as follows:1. Solid state synthesis of LiMnP04 and the investigation on its electrochemical propertiesLiMnPO4 was prepared by solid state method, the effects of doping ions, carbon sources and pre-decomposition temperatures on morphology, structure and electrochemical properties were studied. The results showed that ion doping had significant influence on the electrochemical properties, the electrochemical performance of LiMn0.95Zn0.05PO4/C was better than that of LiMno.95Cu0.05PO4/C; their first discharge capacity were 131.7 mA·h·g-1,84.8 mA·h·g-1 at 0.02C respectively, which may be related with the doping ion radius. Meanwhile, the effects of carbon sources, doping concentration and different decomposition temperatures were discussed. The discharge capacity of 140.2 mA·h·g-1 could be achieved at 0.02C when the synthesis conditions were cyclodextrin as carbon source, decomposition tempreture at 500℃,0.05 for Zn2+ doping concentration(molar ratio) respectively. 2. Preparation precursor MnPO4 by precipitation method and the synthesis of LiMnPO4 with MnP04 as precursor.The precursor MnPO4 was prepared by precipitation method and LiMnPO4/C was synthesized with MnP04 as precursor by solid-phase reaction. The synthesized conditions of LiMnPO4/C were investigated. The results indicated that washing styles of precursor MnPO4 had important effect on electrochemical properties of the final product. The discharge capacity of the target compound with ultrasonic was higher than that of material without ultrasonic, which were 78.6 mA·h·g-1,58.1 mA·h·g-1 respectively. The material had the better performance when reaction temperature was at 600℃in the second step, and its initial discharge capacity was 65.5 mA·h·g-1. The result showed that Ni2+ doping could improve the electrochemical performance of composite material, however, the effect of Ni2+ doping was not significant.3. Hydrothermal synthesis of LiMnPO4 and its electrochemical propertiesReaction temperatures have effects on electrochemical properties of Cu2+ doped LiMnPO4/C material. Reaction temperature had great influence on the morphology and performance of the material, too. The LiMn0.95Gu0.05P04/C material synthesized at 240℃had the initial discharge capacity of 98 mA·h·g-1 at 0.02C.