An Investigation On Tunnel Controlling And Electrochemical Cation Storage Performance Of Manganese Dioxide

Manganese dioxides are important functional materials. Since having a variety ofcrystal structures and manganese changeable valence, manganese oxides are widelyused as electrode materials in electrochemical storage energy devices. The basic crystalstructure of manganese dioxide consists of MnO6octahedral units, which form1D,2Dand3D tunnel structures, it possesses H2O or cations such as Li+, K+, NH4+in the tunnelstructures. The electrochemical energy storage mechanism of MnO2is using the tunnelas host and monovalent or divalent ion (Na+or Zn2+) as media to store energy, thereforethe tunnel structures and cations in tunnel determine its electrochemical energy storagebehavior. The influence of cation species and concentration on electrochemical energystorage of Na+or Zn2+performances of MnO2was studied systematically in this work.First, a common liquid co-precipitation method based on the redox reactions of Mnwas used to synthesize α-MnO2, δ-MnO2, γ-MnO2, β-MnO2, MnOOH, Mn2O3andMn3O4by controlling the proportion of the oxidant and reductant, the synthesiscondition and synthesis method in this dissertation,. The transformation mechanism oftunnel structure of MnO2and its storage of Na+or Zn2+performances were discussed.The results indicated that all types MnO2with tunnel structure could store Na+, sinceα-MnO2with large tunnel old store large amounts of Na+, it had the highest storagecapacity of all manganese dioxides..The battery behavior of zinc ions stored by manganese dioxides with differenttunnel structures was study, the result showed that of Zn2+could be stored bymanganese dioxide with different tunnel structure in an aqueous solution. Manganesedioxide storage Zn2+by the redox reaction between Mn4+and Mn3+. Further studyindicated that adding Mn2+in aqueous ZnSO4electrolyte inhibited thedisproportionation reaction of Mn3+changing to Mn2+, which caused manganesedissolved. Through reducing the dissolution the active materials of manganese dioxideto improve the capacity during the charging and discharging cycle. Since Zn2+couldinsertion/extraction into the positive MnO2tunnel rapidly, the discharge time could befrom several tens of seconds to several hours, which made it can be used in the newtype zinc ion battery having a high power density and energy density at the same time.The effect of different ions such as Li+, Na+, K+or NH4+on the stability of tunnel structure of α-MnO2and storage performances of Na+or Zn2+was studied systematicallyin this dissertation. It was found that K ion has the best stabilizing effect of α-MnO2tunnel with approximate ionic radius of O2-and OH-. Since the MnO6octahedral chaindisorder lap provides more space, amorphous α-MnO2can store more Na+and Zn+,exhibit better capacitor performance. In addition, introducing K ions in the tunnel ofα-MnO2changed its specific surface area and pore structure greatly, which provided anew method for getting amorphous α-MnO2with different density.