Valence Regulation And Electrochemical Energy Storage Application Of Manganese Oxides

In recent years,transition metal oxides as anode materials for lithium ion secondary batteries have become an active research area due to their high theoretical capacity,environmental friendliness,high safety,etc,presenting great application prospects in lithium ion batteries.Manganese oxides have many advantages over other transition metal oxides,such as high specific capacity,non-toxicity and low cost.However,due to its low actual specific capacity,capacity attenuation and poor cycling performance during utilization,its application is limited.In order to overcome these problems,this thesis reports research on the strategy of promoting manganese oxide performance with metal-organic framework MOFs（Metal-Organic Frameworks）.That is manganese ion as the central ion of high specific surface area and high porosity MOF.By changing the synthesis conditions,the valence control of manganese oxides was realized,and different manganese oxides were prepared.When applied to the anode materials of lithium ion batteries,desirable energy storage performance was obtained.The specific research results are as follows:（1）MnO materials with different morphologies were prepared by using organic and inorganic solvents and applied to the anode of lithium ion batteries to obtain excellent electrochemical performance.Using deionized water and ethylene glycol as solvents,1,2,3,4-butane tetracarboxylic acid（BTCA）as the template agent and organometallic salt acetylacetonate manganese（III）as the reactant,MOF structural complexes containing carbon and manganese oxides were obtained.After heat treatment,the two resulting MnO materials were applied to the anode of lithium ion batteries.The comparative analysis illustrated that the change of solvent had a great influence on the morphology of the synthesized electrode materials,and the highly uniform nanosheets generated by the ethylene glycol solvent were more effective in improving the electrochemical behavior of the battery materials.（2）According to the results of（1）,ethylene glycol was selected as the solvent to regulate the valence of the material,obtaining different manganese oxides Mn₃O₄,Mn₂O₃and MnO₂,and their lithium ion storage performance was studied.As the anode of lithium ion batteries,the capacity of Mn₃O₄ is maintains at 950 mAh g^-1 after 150 cycles at 0.1 A g^-1,the capacity of Mn₂O₃ remains 1052.7 mAh g^-1 after 270 cycles at 1 A g^-1.The results reveal that manganese oxides still have excellent electrochemical properties after adjustment of valence.（3）On the basis of（1）,the two MnO materials were optimized,an effective strategy was developed to combine the materials with graphene.Due to the synergistic effect,electrochemical measurements showed that compound of MnO microcrystals combined with reduced graphene oxide（rGO）and amorphous carbon composites showed excellent lithium storage properties.At 2 A g^-1,the specific capacity of the MnO_Ⅰ@rGO electrode synthesized with deionized water remained 671.4 mAh g^-1 after 150 cycles,and the specific capacity of MnO_Ⅱ@rGO synthesized with ethylene glycol solvent remained 930mAh g^-1.It is further proved that the nano-flake structure synthesized by the organic solvent is more beneficial to improve the electrochemical performance.