Research On Co、Mn Doped-V₂O₅Thin Film Electrode

Vanadium pentoxide (V2O5) has become a very promising cathode material forlithium-ion batteries because of its advantages like high voltage, high specific capacity,abundant resources, low price and so on. However, the poor structure stability and lowconductivity have limited its application in the field of lithium-ion batteries. In thispaper, both Co and Mn doped V2O5thin films were prepared by sol-gel method, whichmorphologies and electrochemical performances were systematic researched by meansof XRD, SEM, TEM, TG-DTA, CV and CP.Firstly, results from XRD, SEM, TEM and TG-DTA showed that the crystalstructure of V2O5has not been changed by doping Co and Mn. However, the V2O5thinfilm composed of nanosheet structure roundlike has been converted to rectangle andeach nanosheet was composed of nanorods with diameter less than30nm. While Coand Mn doped V2O5thin films are composed of nanosheets with the length of~500nm,width of~170nm, thickness of~85nm, and the length of~650nm, width of~120nm,thickness of~60nm, respectively. The morphology of doped V2O5thin film is helpfulto reduce the strain during Li+insertion/de-insertion and prevented the structure changes.Besides, it is beneficial to improve the discharge specific capacity and reduce capacityfading. In addition, some of V atoms are replaced by Co and Mn, resulting theenhancement of electrochemical properties due to the increases of layer gap between aaxis and c axis in crystal. And doping gives rise to the generation of oxygen vacancy,reasulting the improvement of materials’ specific capacity.Secondly, the sol-gel’s concentration and annealing time have effects on theelectrochemical performance of V2O5thin film. It is found that optimum concentrationof sol-gel is0.008mol/L. Under current density with400mA/g, the prepared V2O5thinfilm owns a discharge specific capacity of663mAh/g with1.09%fading per cycle. Thebest annealing time is2h and Co doped V2O5thin film has a discharge capacity of662mAh/g with1.15%fading per cycle with current density of800mA/g.In addition, it is found that with appropriate doping of Co and Mn can improve theelectrochemical capacity effectively. Both Co and Mn have a optimum doping at2.0%,where discharge specific capacities are758mAh/g and706mAh/g, with fading rate of1.26%and1.93%per cycle. The battery test results show that under current density with687mA/g, the electrochemical capacity of Co doped V2O5thin film can reach698 mAh/g and710mAh/g with the average of fading per cycle only0.62%after80cycles.When the current density increases20times larger, the discharge capacity of Co dopedV2O5thin film decreases59%and discharge capacity decreases43%with doping Mnwhen the current density increases12.5times.In conclusion, in spite of the unchanged crystal structure with doping Co and Mn,it influences the nanosheet morphology of thin film. This special morphology has bothgreatly improved the discharge specific capacity and reduced capacity fadingsimultaneously. Therefore, doped V2O5thin films can be a very promising cathodematerial for lithium-ion batteries...