| Monoclinic lithium vanadium phosphate (Li3V2(PO4)3) is a highly promising the third generation cathode materials of Li-ion batteries cathode material proposed for lithium ion batteries, due to stabilized framework, a high work voltage up to 4.5 V and a high theoretical capacity of 197 mAh-g-1 et. The development of Li3V2(PO4)3 cathode material was reviewed in detail. The aims of present study were to focus on the preparation processes and technics, the structural characterization, the electrochemical properties, the modification of materials.A novel synthesis process was developed to prepare Li3V2(PO4)3 cathode material by using N2H4 as reducer without via hydrogen reduction method. Firstly low value vanadium precursor was obtained by N2H4 reducing. After high-temperature sintering in argon atmosphere, Li3V2(PO4)3 product can be obtained. Various surfactants were using in precursor preparation process, scanning electron microscopy (SEM) shows that product powders have a spherical or spherical-like shape. Among of them, the products by using surfactants of PEG and PVP have regular shape, pretty good electrochemical properties and felicitous reversible capacity. Base of above all, pure LiVPO4F was attempted to be synthesized in two steps method using N2H4 reducer and electrochemical properties of LiVPO4F were performed.The rheological phase reaction was introduced to synthesize Li3V2(PO4)3/C cathode material by using sucrose, PEG, graphite and acetylene black as carbon source and reducer. The result shows that the end products by using sucrose and PEG have smaller and more uniform dispersed particles. The solid particle surface of products was coated by carbon decomposed by organic compound, which showed pretty good electrochemical properties and felicitous reversible capacity in different voltage ranges.The improved Solution method to prepare the precursor is established to synthesize Li3V2(PO4)3/C and PEG is chose as carbon source and reducer. It is found that compared with traditional solid method by using Solution method the materials can confect in molecule level and the precursor reacts drastically in heat treatment process and product configuration fully developed. The ideal reaction condition of preparing the end product is that the precursor processed by the pre-calcining is calcined at 750℃for 8h and the amount of PEG in75g/mol is better. The material particles are better dispersed and more uniform (4.165μm). The surface area of the particles can be utilized efficiently due to the close and uniform contact between solid particles. Electrochemistry performance in different rate and voltage ranges was studied.For the first time, mixture solvent of sol-gel method was employed tosynthesize a serious of Ti doped Li3V2(PO4)3 by using tetra-n-butyl titanate as Ti source. The modification of Li3V2(PO4)3 by doping Ti was studied. The results indicate that 0- 0.4 doped-Ti does not affect the monoclinic structure of the material. The charge-discharge curves of the substituted samples have change obviously (1) new gradient plateaus appear in 2.0-2.5 V range, which contribute little capacity of material; (2) the first two plateaus in 3.0- 3.8 V range slightly sloping in the substituted samples and to 0.3 doped-Ti sample the boundary gradually became ambiguous. The charge-discharge tests show that 0.3 doped-Ti sample exhibits improved capacity, cycling stability. |
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