Research On Synthesis And Electrochemical Performances Of Spinel Type Transition Metal Oxides Anode Materials

In this paper,Three spinel type transition-metal oxides(ZnCo2O4,ZnMn2O4 and CuCo2O4),as anode materials for lithium-ion batteries,were synthesized.Especially,the ZnMn2O4 and CuCo2O4 were systematically studied by different synthesis methods.The crystal structure,morphology and the electrochemical properties and electrochemical mechanisms of the expected compounds were investigated.The main results are listed as follows:(1)ZnCo2O4 was synthesized through the rheological phase reaction method using zinc acetate dihydrate,cobalt(Ⅱ)acetate tetrahydrate as raw materials,and using citric acid as chelating agent.The precursors were heat-treated at 400℃ or 500 ℃,respectively.The samples were characterized by X-ray diffraction,scanning electron microscopy,and transmission electron microscopy.The results show that spinel ZnCo2O4 were synthesized successfully.The particles took on irregular quasi-spherical shapes,and the sizes of the particles were less than 100 nm.The electrochemical properties of the samples were investigated.The test results showed that the ZnCo2O4 synthesized at 400℃ behaved better reversible capacity than that of ZnCo2O4 synthesized at 500℃,and the specific capacity of two samples was 801 mAh/g and 736 mAh/g after 100 cycles at a constant current of 100 mA/g in the voltage range of 0.01-3 V.The ZnCo2O4 synthesized at 400℃ showed low charge transfer resistance and high Li+ diffusion coefficient.The preparation principle for the formation of ZnCo2O4 nanoparticles and the electrochemical process of ZnCo2O4 were also discussed.(2)The precursors of CuCo2O4 were synthesized by three methods(the rheological phase reaction method,the combustion method or oxalate precipitation method).The precursors were heat-treated at a suitable temperature to obtain the expected samples.The synthesized samples were characterized by X-ray diffraction,scanning electron microscopy,and transmission electron microscopy.The results show that spinel CuCo2O4 was synthesized successfully.The particles of CuCo2O4 were both irregular polyhedral.The sizes of the particles synthesized through three methods were different.Among them,the particle sizes of sample synthesized through combustion method were about 200 nm,which were the smallest among all samples,and the particle sizes of sample synthesized through oxalate precipitation method were about 1μm,which were largest among all samples.The electrochemical properties of the samples were investigated also.The test results showed that the CuCo2O4 synthesized through the combustion method featured highest reversible capacity and best cycling performance among three samples.The specific capacity of three samples was 510 mAh/g,618 mAh/g and 470 mAh/g respectively after 100 cycles at a constant current of 200 mA/g in the voltage range of 0.01-3 V.The preparation principle for the formation of CuCo2O4 nanoparticles and the electrochemical process of CuCo2O4 were also discussed.(3)The precursors of ZnMn2O4 were synthesized by different methods(the rheological phase reaction method or the mixed solvothermal method).The precursors were heat-treated at a suitable temperature to obtain the expected samples(ZnMn2O4).The synthesized samples were characterized by X-ray diffraction,scanning electron microscopy,and transmission electron microscopy.The results showed that spinel ZnMn2O4 was synthesized successfully.The particles of ZnMn2O4 were irregular quasi-spheres with sizes of about 50 nm.The ZnMn2O4 nanoparticles synthesized through the mixed solvothermal method were clustered together to form microspheres about 1μm in diameter.The electrochemical properties of the samples were investigated also.The test results showed that the ZnMn2O4 synthesized through the mixed solvothermal method featured higher reversible capacity and better cycling performance than that of sample synthesized by the rheological phase reaction method.The specific capacity of two samples was 569 mAh/g and 745 mAh/g respectively after 160 cycles at a constant current of 200 mA/g in the voltage range of 0.01-3 V.The charge transfer resistances of two samples were similar,but the ZnMn2O4 synthesized through the mixed solvothermal method behaved higher Li+ diffusion coefficient than that of sample synthesized through the rheological phase reaction method.The preparation principle for the formation of ZnMn2O4 and its electrochemical process of ZnMn2O4 were discussed also.