Preparation Of Manganese-based Oxide Micro-nano Structure And Investigation Of Its Capacitance Behavior

Manganese based materials have been considered to be one type of important electrode materials in energy storage and conversion devices,and have received widespread attention because of their price advantages and good theoretical electrochemical performance.However,the gap between actual performance and theory and the low utilization rate of manganese materials in electrochemistry have hindered its development.In this paper,manganese based materials with different morphologies and structures were synthesized by hydrothermal method,and the relationship between the prepared manganese-based materials and properties was explored by various characterization methods.?1?Two types of colloidal nanocrystal assemblies?CNAs?of MnFe₂O₄ had been investigated as the electrode materials by using aqueous electrolytes containing bivalent and trivalent metal ions.Experimental results showed that the capacitances of CNAs composed of large nanoparticles?MnFe-2Ac?is higher than CNAs assembled by 16 nm nanocrystals?MnFe-1Sf?in aqueous solutions containing Mg²⁺or Al³⁺ions.MnFe-2Ac and MnFe-1Sf have higher specific capacitances at 0.1 A g^-1 in electrolytes of Na₂SO₄ mixed MgSO₄ and MgSO₄ mixed ZnSO₄.MnFe-1Sf showed a better cycle stability than MnFe-2Ac either in MgSO₄ or in Al₂?SO₄?₃ electrolytes.The wide potential window during cyclic voltammetry brings the electrochemical diversification of the CNAs based electrodes in various electrolytes.Based on the experimental data and crystalline features of the CNAs,the structure-property relationship has been discussed and analyzed.?2?Both nanosheets and porous feature are two important factors to improve the capacitance of electrode materials.In this work,two types of MnO₂ nanosheets?MnO₂-NSs?,namely MnO₂-NS-K and Mn O₂-NS-N,are synthesized respectively from the starting systems containing potassium hydroxide and ammonia.The curved MnO₂-NS-N ultrathin nanosheets have a poor layered structure and a large surface area.The capacitance of MnO₂-NS-N is much higher at in aqueous MgSO₄ electrolyte than in Na₂SO₄ electrolyte.Flat MnO₂-NS-K thick nanosheets with a smaller surface area show the slightly higher capacitancesin MgSO₄ electrolytes.The capacitances of MnO₂-NS in MgSO₄ electrolyte dramatically decrease with the increase of current density,possibly due to the sluggish dynamics of intercalation and deintercalation of Mg²⁺ions compared with Na⁺ions.It is found that the surface capacitance plays a dominant role in the capacitance.Meanwhile,both of MnO₂-NS show a better cycle stability after 3000 cycles in aqueous Na₂SO₄ electrolyte.Based on the experimental data and features of the MnO₂-NS,the structure-property relationship has been discussed.?3?The normal temperature reaction is simple and easy,which simplifies the experimental steps and shortens the experimental preparation time.Through the comparison of the first group of experiments,the dosage of potassium hydroxide in the preparation process has a greater impact on the electrode electrochemistry of the product material.The cycle stability of the MnO-C-K-5 sample when the ratio with manganese acetate is 1:5 is good.When the ratio with manganese acetate is 1:10,the sample MnO-C-K-10 has high crystallinity and the best capacitance.Through the comparison of the second group of experiments,the ratio of manganese acetate Mn Mn?Ac?₂·4H₂O and potassium persulfate K₂S₂O₈ used in the samples with better synthesis performance at room temperature is MnO-C-23.Although the crystallinity of this sample is not as good as MnO-C-13,the electrochemical performance of all aspects is better.The third group of experiments confirmed its importance in the synthesis of manganese dioxide by adding potassium persulfate K₂S₂O₈ during the synthesis process.The comparison of the morphological characterization and electrochemical tests of these three sets of experiments has a great enlightening effect on the future preparation of high performance manganese dioxide materials by simple synthesis methods.