Synthesis And Electrochemical Performances Of Anode Materials (Manganate And Tungstate)for Lithium-ion Battery

In this paper,we introduced two spinel type transition-metal oxides（ZnMn₂O₄、CoMn₂O₄）and two kinds of tungstates（MnWO₄、Bi₂WO₆）as anode materials for lithium-ion batteries.They were all successfully synthesized and studied furtherly.The crystal structure,morphology and electrochemical performances of the prepared compoundswere mainly investigated.The main details are listed as follows:（1）Using ZnAc₂·2H₂O、MnAc₂·4H₂O as reactants,and choosing the ammonium bicarbonate and urea as precipitant,respectively.Firstly,the precursor Zn_0.33Mn_0.67CO₃sample was synthesized successfully by solvothermal method.The final product ZnMn₂O₄was obtained by calciningtwo kinds of precursors at 600℃for 5h in the air,and the two corresponding products were marked as ZMO-1 and ZMO-2 respectively.Using the XRD,SEM and EDS etc.techniques to characterize the crystal structure,microcosmic morphology and composition of metallic elements for the two samples.The reaction mechanism of the prepared productions was also explained detailedly.The results illustrated that the prepared samples took spinel type as main structure.Besides,the prepared samples owned the morphology of microspheres and were equally distributed.Furtherly,the morphology of ZMO-1 prepared by using the urea as the precipitant present microspheres owing the smooth surface.Then,the morphology of ZMO-2 prepared by using the ammonium bicarbonate as the precipitant present microspheres composed by many nanoparticles.Electrochemical performances and mechanism of conversion reactions for the samples were investigated by the galvanostatic charge/discharge system and AC impedance measurement.At the current density of 100 mA g^-1between 0.01 and 3V versus Li/Li⁺,the reversible discharge specific capacities of ZMO-1 and ZMO-2 were still remained at 252 mAh g^-1and 602 mAh g^-1respectively after 100 cycles.Compared with the ZMO-1,ZMO-2 demonstrated the highest reversible capacity,the lowest charge transfer resistance and the highest Li⁺diffusion coefficient.In conclusion,the sample ZMO-2 using ammonium bicarbonate as the precipitant owns the best electrochemical performances.（2）Using MnSO₄·H₂O、CoSO₄·7H₂O as reactants,and choosing the ammonium bicarbonate as precipitant.The precursor was synthesized successfully by solvothermal method.The final product CoMn₂O₄ was obtained by calciningthe precursors at 600℃、700℃、800℃for 5h on muffle,and the three corresponding products were marked as CMO-1、CMO-2 and CMO-3 respectively.XRD,SEM and EDS techniques were used to characterize the crystal structure,microcosmic morphology and composition of metallic elements for the three samples.The reaction mechanism of the prepared productions was explained detailedly as well.The result show that as-prepared samples took spinel type as main structure.The morphology of CMO-1 prepared by calcining the precursors at 600℃present the microspheres composed by many nanoparticles which looks like hemp ball.However,the morphology of CMO-2 and CMO-3 prepared by calcining the precursors at 600℃and 700℃present the irregular shape,and the partical size is different with each other.Electrochemical performances and mechanism of conversion reactions for the samples were investigated by the galvanostatic charge/discharge system and AC impedance measurement.At the current density of 100 mA g^-1between 0.01 and 3V versus Li/Li⁺,the reversible discharge specific capacities of CMO-1、CMO-2 and CMO-3 were still remained at 1270 mAh g^-1、1003 mAh g^-1and 572 mAh g^-1respectively after 100 cycles.Among the three samples which were calcining at three temperatures,the sample CMO-1 demonstrated the highest reversible capacity,the lowest charge transfer resistance and the highest Li⁺diffusion coefficient,and owing the best electrochemical performances.We concluded that 600℃is the most suitable calcination temperature for synthesizing the sample CoMn₂O₄.（3）Using Mn（Ac）₂·3H₂O、NaWO₄·2H₂O as reactants,the final product MnWO₄ was synthesized successfully by a typical solvothermal method.XRD、TG、SEM and EDS tests were conducted to characterize the crystal structure,microcosmic morphology and composition of metallic elements for the samples.The results presents the morphology of the sample is flower-liked microspheres composed of nanosheets,owing a high initial capacity and a poor cycle performance.In order to improve the electrochemical performance of the pure sample,by using the glucose as the carbon source,we synthesized successfully the compound MnWO₄@C under the same experimental condition.Using the same test method to to characterize the crystal structure,microcosmic morphology and composition of metallic elements for the compound MnWO₄@C.It turned out that the composite material kept a similar flower-like microspheres and composed of nanorod.In addition,the content of carbon of the sample was about 23 wt%.Electrochemical performances and mechanism of conversion reactions of the sample were investigated.The reversible discharge specific capacity of the prepared MnWO₄@C was 1023mAh g^-1after 100 cycles at the current density of 100 mA g^-1between 0.01 and 3V versus Li/Li⁺.Through the study of the electrochemical reaction mechanism for the compound,we found that the change of charge and discharge platform is not obvious,and because of the carbon from the decomposition of glucose so that the conductivity of the compound MnWO₄@C was increased.In a word,MnWO₄@C has an excellent electrochemical performances.（4）Bi₂WO₆ was synthesized successfully using Bi（NO₃）₃·3H₂O、NaWO₄·2H₂O as reactants by a typical solvothermal method.XRD,TG and SEM tests were conducted to analyze the crystal structure and microcosmic morphology.The result shows that the morphology of the sample Bi₂WO₆ present smooth surface and aqually distributed.The reversible discharge specific capacity of the prepared Bi₂WO₆ was 936mAh g^-1after 139cycles at the current density of 100 mA g^-1between 0.01 and 3V versus Li/Li⁺.The sample Bi₂WO₆ demonstrated the lowest charge transfer resistance,the highest reversible capacity,and the highest Li⁺diffusion coefficient.In a word,it own the best electrochemical performances and expected to be widely used in Lithium ion batteries.