Synthesis, Modification And Electrochemical Performance Of Novel Electrodes For Lithium Ion Battery

In this paper, SnWO4and SnMoO4as the anode materials for lithium ion battery, as well as Li6V3(P2O7)3(PO4)2being a novel cathode material, were synthesized and modified, among which, the SnWO4and SnMoO4were systematically studied by carbon-coating and ion-doping(Mg2+,Zn2+). The crystal structure, morphology and the electrochemical properties of the expected compounds were investigated. It was found that the modifications could improve electrochemical performances of the original materials effectively, which could be applied in lithium ion battery industry. The main results are listed as follows:(1) a-SnWO4and SnWO4/C composites materials were synthesized by solvothermal and rheological phase methods respectively, using hydrated stannous chloride (SnCl2-2H2O) and sodium tungstate dihydrate (Na2WO4-2H2O) as the main raw material, ethylene glycol as solvent, glucose as the carbon source, The crystal structure and microstructure were characterized by XRD and SEM techniques. And the electrochemical properties of the samples were investigated by constant-current charge-discharge system and AC impedence spectroscopy testing method. The results showed that the performances of α-SnWO4/C composites synthesized by this method were better in particle size distribution, high-rate charge/discharge ability and cycling stability than those of pure SnWO4synthesized by solvothermal method. SnWO4/C-50composite material has a high initial specific capacity (1050mAh/g) and good cycle performance, after charging and discharging30cycles, the capacity was maintained at600mAh/g. Even increase the current density to100mA/g, after30cycles, the charge-discharge capacity remained at500mAh/g, significantly better than the pure SnWO4as an anode material.In addition, SnWO4was synthesized by adding surfactants. The composites were synthesized by solvothermal method with different surfactants (polyethylene glycol PEG), and to study effects of different type of surfactants, it was found that reaction time have relation to the SnWO4structure and performance. The results show that different surfactant has a different effects on the electrochemical performance of SnWO4, to add polyethylene glycol (PEG) can improve SnWO4as the electrochemical properties of the negative electrode material, the sample SnWO4-PEG-18, which use PEG-4000as surfactant and kept reaction for 18h, has the best the performance among the all samples. At the current density of100mAg-1, the first discharge capacity was up to1108mAh/g and reversible capacity reached790mAh/g, the discharge capacity is320mAh/g after30curves, which was improved than that of pure SnWO4.(2) SnMoO4and SnMoO4/C composites, were synthesized by solvothermal and Theological phase method, using stannous chloride hydrated, ammonium molybdate tetrahydrate as raw materials. The factors on the effects of the SnMoO4mophplogy and performance were studied. The results show that the type of surfactants (PEG and CTAB), the quality of each surfactant, the molecular weight of surfactant (PEG) and the different reaction time have effects on electrochemical properties of expected compouds. For example, the surfactants (both PEG and CTAB) are favor in improving the electrochemical performance, but the PEG is better than the CTAB in it. The suitable quality and the molecular weight as well as the reaction time were presented also. Such as that the sample SnMoO4-PEG-0.1sample in which the molecular weight of PEG is4000and the reaction time is18h, has a high initial specific capacity (1280mAh/g) and good cycle performance, after charging and discharging30times, the capacity was maintained at580mAh/g.The doping of metal ion (Mg2+) can improve electrochemical performances, solo-element doping is better than multi-doping in improving electrochemical properties. For example, sample Sn0.9Mg0.1MoO4behaves a high initial specific capacity (998mAh/g) and good cycle performance, after charging and discharging30times, the capacity is maintained at63OmAh/g, which is as much as the twice of capacity for the pure SnMoO4. After heat treatment, Sn0.9Mg0.1MoO4behaves a higher initial specific capacity and better cycle performance. It is promising anode material for lithium ion battery application.(3) Li9V3(P2O7)3(PO4)2was synthesized by three different reaction methods which are rheological phase reaction method(the sample maked as LVP-1), solid phase ball milling(the sample maked as LVP-2) and sol-gel synthesis(the sample maked as LVP-3), in which Lithium acetate, vanadium pentoxide, ammonium dihydrogen phosphate as the main raw materials, citric acid as a chelating agent and carbon source. The results showed that the sample LVP-1used by Theological phase reaction method, take on morphology of sheets structure. When at the current density (30mA/g), the initial first discharge specific capacity of 2) is109.35mAh/g, after10charge-discharge cycles, discharge capacity still has103.35mAh/g, at last after40curves, the discharge capacity is83.26mAh/g. This is due to the LVP-1has a smaller size, and is benificial to the intercalation and deintercalation of lithium ions, so it has a high discharge capacity.