| Polyoxovanadate cluster compounds have attracted much attention because of low cost and large charge/discharge capability used as cathode material in li-ion batteries. In this work, different decavanadate lithium salt compounds have been prepared, and their structure, propertie and the interactions between them have been discussed detailed.[Li6(H2O)16V10O28]n, {[LiNa2(H2O)9]2V10O28}n, Li2(H2O)10(NH4)4V10O28, and (NH4)2[Ni(H2O)6]2V10O28·4H2O single crystals have been successfully synthesized by hydrothermal method. X-ray diffraction method has been used to determine the structure and find that [Li6(H2O)16V10O28]n, {[LiNa2(H2O)9]2V10O28}n and (NH4)2[Ni(H2O)6]2 V10O28·4H2O single crystals are firstly discovered in the world. By low temperature pyrogenation method, Li6V10O28, Li2Na4V10O28, H4Li2V10O28 and H2Ni2V10O28 compounds have been obtained, and their three-dimensional structures were determined by x-ray diffraction method. Various measurements have been carried out to determine the structure, appearance and propertie of the samples, especially used as cathode materials for lithium ion batteries. Some valuable results obtained are as follows.The structure analysis results indicate that, in these four single crystal compounds, different space frameworks of decavanadate salts are formed by the assemble of different cations, which forms a three-dimensional supermolecular structure by interactions of intermolecular hydrogen bond. All cations are the form of hydration ion and ammonium ion distributed in the framework structure of single crystals, and have much larger space volume than that of themselves.After dehydration or deammonium at low temperature, the obtained powder crystals was nano-sized particles with a large number of defects. The presence of large specific surface, tunnel effect and defects make the transfer of ion, insertion and extraction of Li ion readily during the charge/discharge processes used as cathode materials in Li ion betteries.The powder crystals still remain the primary framework structure after dehydration or deammonium, which provides a large number of ion passage as the model of tunnel or samdwich. It supplys preferable interspace for Li ion inseriton and extraction during charge/discharge processes.The negative charge distribution on oxygen is in the range of 0.450864 to 0.350250 obtained by the theoretical calculation with Gaussian03w quantification computational procedure based on the surface atoms of the decavanadate anion in [Li6(H2O)16V10O28]n compound. The results show that the transfer of Li ion has lesser resistance due to the interactions of the cation and anion, it is helpful to the insertion and extraction of Li ion during charge-discharge processes.The conductance of the pure material was studied using a resistance versus temperature, and internal resistances of the electrode and diffused coefficient of Li in the bulk of material were determined using exchange impedance spectroscopy techniques in a Li-ion battery model. The conductance of materials at room tempearture are in the range of 10-1～10Sm-1, and the diffusing coefficient is in the range of 10-7～10-9 cm2/s.The electrochemical behaviors and charge/discharge properties of materials are discussed by cyclic voltammetry and charge-discharge measurements. These materials show high Li-ion insertion capability. The largest Li-ion insertion capacity in H2Ni2V10O28 reaches 22.34 mole Li. The discharge capacity of H2Ni2V10O28 material can reaches 333mAh/g at the potential of 4.5～1.0V at 0.2mA/cm2 discharge current. The large discharge capacity at 4.5～0.2V is 556mAh/g. At the same time, these materials show good reversibility during charge-discharge processes. The excellent electrochemical properities of the materials could be attributed to the framework structure. All the results suggest that the polyoxovanadate cluster compounds would be a promising cathode materials for Li-ion batteries.
|
PDF Full Text Request