Synthesis, Modification And Electrochemical Performance Of Lithium Iron Phosphate, Tungsten Oxide And Molybdenum Oxide

In this paper, LiFePO4as the cathode material for lithium ion battery, WO3and MoO3as well as MoO2being the anode materials, were synthesized and modified in our research work. The main results are listed as follows:(1) FePO4·2H2O materials were synthesized by liquid-phase co-precipitation method, using Fe(NO3)3·9H2O and NH4H2PO4as raw materials. The effect of different molar ratio of Fe and P to the crystal structure and morphology of the expected materials were investigated. Then the samples of LiFePO4and LiFePO4/C composite were synthesized through a facile rheological phase reaction method by using the FePO4of micro-sphere micrography and Li2CO3materials. The glucose as the carbon source. The effects of different carbon coated ratios on LiFePO4materials were studied. The test results showed that the LiFePO4/C composite behaved good performance. In the voltage range of2.5to4.2V, the initial discharge capacity of the LiFePO4/VC composite (synthesized with the20wt.%of glucose) reached133.68mAh/g at current density of17mA/g. Besides, the materials also showed better cycling performance. After50cycles, the discharge capacity of the sample remained specific capacity at137mAh/g.Fe3(PO4)2·8H2O materials were synthesized through liquid-phase co-precipitation method, using FeSO4and NH4H2PO4as raw materials. Then the LiFePO4-1and LiFePO4/C-1composite were synthesized through a facile rheological phase reaction method by using the Fe3(PO4)2·8H2O, Li3PO4and different mass ratios of glucose as raw materials. LiFePO4-2and LiFePo4/C-2composite were synthesized through the same method by using the Fe3(PO4)2·8H2O of analytical grade and Li3PO4as raw materials. The effects of different carbon coated ratios on LiFePO4materials were also studied. The test results showed that carbon coated LiFePO4(LiFePO4/C-1-20and LiFePO4/C-2-20) synthesized with20%mass ratio of glucose exhibited better electrochemical performance than that of pure LiFePO4. The initial discharge capacity of LiFePO4/C-1-20and LiFePO4/C-2-20) reached154and137.74mAh/g respectively at current density of17mA/g, This two materials also showed better cycling performance. After50cycles, the discharge capacity of LiFePO4/C-1-20and LiFePO4/C-2-20composites remained at151.6and137mAh/g respectively. (2) WO3materials were synthesized through a hydrothermal method by using the (NH4)10H2(W207)6and H2C204as raw materials. The effects of different carbon coated ratios on WO3materials were also studied. The test results showed that the carbon coated WO3exhibited superior electrochemical performance than that of pure WO3, especially the sample of WO3/C-10exhibited the best electrochemical performance among all the WO3materials. The initial discharge specific capacity of WO3/C-10reached998.82mAh/g at current density of50mA/g. After50cycles, the discharge capacity of WO3/C-10composites remained specific capacity at631.25mAh/g.(3) MoO2micro-sphere were synthesized through a hydrothermal method by using the (NH4)6Mo7O24·H2O and H2C2O4as raw materials. In addition, the effect of surfactant (CTAB) on MoO2materials was investigated. The testing results showed that both MoO2and MoO2-CTAB were taken on the morphologies of micro-sphere. But to be compared with MoO2, The particles of MoO2-CTAB sample were more uniform and bigger than that of MoO2. In terms of the electrochemical performances, the initial discharge capacity of the MoO2-CTAB (783.237mAh/g) was higher than that of MoO2(1009.34mAh/g). But the performance of the electrochemical cycling stability became worse. The effects of different carbon coated ratios on MoO2-CTAB were also studied. The test results showed that the carbon coated MoO2-CTAB exhibited superior electrochemical performance than that of MoO2-CTAB, especially the sample of M0O2/C-3O exhibited the best electrochemical performance among all the MoO2-CTAB materials. The initial discharge capacity of MoO2/C-30reached at1216.45mAh/g under current density of50mA/g. After50cycles, the discharge specific capacity of MoO2/C-3O composites remained at519.82mAh/g.The MoO3/C nanofibers and MoO3nano-sheets were synthesized through the electrospinning method.(NH4)2MoO4and PNA were dissolved in DMF to form sol-gel. The precursor of sol-gel was heated under different atmosphere to form expected compounds. The electrochemical properties of MoO3/C nanofibers and MoO3were studied. The initial discharge capacity of MoO3/C reached1550mAh/g at40mA/g. Although the initial discharge capacity of pure MoO3(1560mAh/g) was higher than that of the MoO3/C, loss of discharge capacity is remarkable. The MoO3/C composite retained a discharge capacity of710 mAh/g after100cycles. When load current density is increased to800mA/g, the MoO3/C composite still keep a discharge capacity of280mAh/g after100cycles.