Research On Synthesis And Electrochemical Performances Of Germanium-base And MoO₂ Electrode Materials

In this paper,Ge/MWCNTs,Ge/C and MoO₂ are studied as anode materials for lithium-ion battery.The synthesis,modification and electrochemical properties of these materials are also studied.Several conclutions are obtained.The main contents are listed as follows:?1?The precursors of Ge/MWCNTs composite were synthesized through solvothermal method using multiwalled carbon nanotube?MWCNTs?and germanium tetrachloride?GeCl4?as raw materials,and anhydrous ethanol as solvent.The as-synthesized precursors were further heat-treated at 650? for 2 h under Ar/H2-5%atmosphere to obtain the expected Ge/MWCNTs composite.The structure and morphology of the expected samples are characterized by X-ray diffraction,Raman spectra,scanning electron microscopy,and transmission electron microscopy techniques.The results show that the average diameter of the Ge particles is about 100 nm and the Ge particles are buried in MWCNTs.The electrochemical properties of the samples were also investigated.The test results showed that Ge/MWCNTs composite have the lower charge transfer resistance,better electric conductivity and better cycling stability than that of the pure Ge.The specific capacity of Ge/MWCNTs composite was 1047 mAhg-1 after 50 cycles at a constant current of 100 mAg-1 in the voltage range of 0.01?1.5 V.The preparation principle for the formation and the electrochemical process of Ge/MWCNTs composite were also discussed.?2?The precursors of Ge/C composite were synthesized through freeze-drying method using germanium dioxide,citric acid,ammonia and oxalic acid as raw materials.The as-synthesized precursors were further heat-treated at 650? for 2 h under Ar/H2-5%atmosphere to obtain the expected Ge/C composite.The structure and morphology of the expected samples were characterized by X-ray diffraction,Raman spectra,scanning electron microscopy,and transmission electron microscopy techniques.The results show that the Ge/C composites were synthesized successfully.The Ge/C composites synthesized with oxalic acid as additive agent have better electric conductivity and cycling stability than that of Ge/C composites synthesized without adding oxalic acid.It has the specific capacity of 742 mAhg-1 after 80 cycles at a constant current of 200 mAg-1 in the voltage range of 0.01?1.5 V.The preparation principle for the formation of Ge/C composites and the electrochemical process of Ge/C composite were discussed also.?3?The precursors of Ge/C doped N composite were synthesized through electrospinning method using germanium tetrachloride?GeCl4?,polyvinyl pyrrolidone?PVP?and polycaprolactone?PCL?as raw materials,and anhydrous ethanol and N,N-Dimethylformamide?DMF?as mix solvent.The as-synthesized precursors were further heat-treated at 650? for 2 h under Ar/H2-5%atmosphere to obtain the expected Ge/C doped N composite.The structure and morphology of the expected samples are characterized by X-ray diffraction,Raman spectra,scanning electron microscopy,and transmission electron microscopy techniques.The results show that the Ge/C doped N composites synthesized with polycaprolactone have better electrochemical performance than that of Ge/C doped N composites synthesized without polycaprolactone.The Ge/C doped N composites posses the specific capacity of 858 mAhg-1 after 100 cycles at a constant current of 100 mAg-1 in the voltage range of 0.01?2 V.The preparation principle for the formation of Ge/C doped N composite and the electrochemical process of Ge/C-N composite were also discussed.?4?The MoO₂ was synthesized through hydrothermal method using ammonium molybdate and citric acid as raw mater:ials,sodium carbonate was used as mineralizer,and hexadecyl trimethyl ammonium bromide?CTAB?was used as dispersing agent,water was used as solvent.The structure and morphology of the expected samples were characterized by X-ray diffraction,scanning electron microscopy,and transmission electron microscopy techniques.The results show that the MoO₂ synthesized with CTAB has microspheres structure,while the MoO₂ synthesized without CTAB has morphology of nanorod structure.And the MoO₂ nanorods have good electrochemical performance with the specific capacity of 650 mAhg-1 after 50 cycles at a constant current of 100 mAg-1 in the voltage range of 0.01?3 V.The preparation principle for the formation of MoO₂ and the electrochemical process of MoO₂ were also discussed.