Li3V2（PO4）3 samples were synthesized by sol-gel route and high temperature solid-state reaction. The influence of Li3V2（PO4）3 as cathode materials for lithium-ion batteries on electrochemical performances was investigated. The structure of Li3Va（PO4）3 as cathode materials for lithium-ion batteries and morphology of Li3V2（PO4）3 were characterized by X-ray diffractometry （XRD） and scanning electron microscopy （SEM）. Electrochemical performances were characterized by charge/discharge and AC impedance measurements. Li3V2（PO4）3 with smaller grain size shows better performances in terms of the discharge capacity and cycle stability. The improved electrochemical properties of Li3V2（PO4）3 are attributed to the refined grains and enhanced electrical conductivity. AC impedance measurements also show that the Li3V2（PO4）3 synthesized by sol-gel route exhibits significantly decreased charge-transfer resistance and shortened migration distance of lithium ions.
The LiMnPO4/C composite material was synthesized via a sol-gel method based on the citric acid. The X-ray diffraction （XRD）, scanning electron microscopy （SEM） and electrochemical performance tests were adopted to characterize the properties of LiMnPO4/C. The XRD studies show that the pure olivine phase LiMnPO4 can be obtained at a low temperature of 500 °C. The SEM analyses illustrate that the citric acid used as the chelating reagent and carbon source can restrain the particle size of LiMnPO4/C well. The LiMnPO4/C sample synthesized at 500 °C for 10 h performs the highest initial discharge capacity of 122.6 mA-h/g, retaining 112.4 mA-h/g over 30 cycles at 0.05C rate. The citric acid based sol-gel method is favor to obtain the high electrochemical performance of LiMnPO4/C.
LiNi0.6Co0.2Mn0.2O2 was prepared from LiOH·H2O and MCO3(M=Ni,Co,Mn)by co-precipitation and subsequent heating. XRD,SEM and electrochemical measurements were used to examine the structure,morphology and electrochemical characteristics, respectively.LiNi0.6Co0.2Mn0.2O2 samples show excellent electrochemical performances.The optimum sintering temperature and sintering time are 850℃and 20 h,respectively.The LiNi0.6Co0.2Mn0.2O2 shows the discharge capacity of 148 mA·h/g in the range of 3.0-4.3 V at the first cycle,and the discharge capacity remains 136 mA·h/g after 30 cycles.The carbonate co-precipitation method is suitable for the preparation of LiNi0.6Co0.2Mn0.2O2 cathode materials with good electrochemical performance for lithium ion batteries.
LiVPO4F was synthesized by a novel sol-gel method under Ar atmosphere using V2O5·nH2O,LiF,NH4H2PO4,and citric acid as starting materials,and its physicochemical properties were characterized using X-ray diffractometry(XRD),SEM,and electrochemical methods.The XRD patterns show that LiVPO4F displays a triclinic structure with a space group of p1.The SEM results indicate that the particle size of LiVPO4F is about 0.8μm together with homogenous distribution.The optimal sintering temperature and sintering time are 600℃and 20 h,respectively,in order to obtain pure triclinic LiVPO4F with good electrochemical performance.LiVPO4F has the discharge capacity of 134 mA·h/g in the range of 3.0-4.4 V at the first cycle,and the discharge capacity remains 125 mA·h/g after 30 cycles.The sol-gel method is suitable for the preparation of LiVPO4F cathode materials with good electrochemical performance for lithium ion batteries.
