Capacitance Properties And Lithiation Behavior Of Layered MnO₂ Nanomaterials

Manganese dioxide?MnO₂?is a traditional material widely used for electrode.Two-dimensional?2D?nanosheets process unique properties such as ultra-thin thickness and potential quantum size effect,which was intense researched recently.The utmost feature of these nanosheets is their large surface area,rendering them promising candidates for many applications,especially as electrodes in electrochemical devices.In this thesis,the capacitive performance and lithium intercalation behavior of MnO₂ are studied on the purpose of combining the advantages of MnO₂ and nanosheets.Firstly,Na⁺intercalation MnO₂ materials?Na-MnO₂?were prepared by hydrothermal method.MnO₂ nanosheets was then obtained by ion exchange reaction.The colloid MnO₂suspension was freeze dried to obtain the reassembled MnO₂ nanosheets?FD-MnO₂?.Meanwhile,Na⁺were inserted into MnO₂ nanosheets to obtain another reassembled MnO₂?rNa-MnO₂?.From the electrochemical tests,the specific capacitances of FD-MnO₂ and rNa-MnO₂ are 143 F/g and 141 F/g,respectively.This result shows nanolayered inorganic materials can be used in electrochemical energy storage.Secondly,a new type of layered Li-MnO₂ with heavy stacking faults has been synthesized via MnO₂ nanosheets reacting with Li ions.MnO₂ nanosheets were obtained by chemical oxidation of Mn²⁺ions in the presence of tetramethylammonium cations in an aqueous solution.ICP results show that the atomic ratio of Li/Mn is 0.6:1.The Li-Mn O₂ has a disordered mesoporous texture formed during the stacking of MnO₂ nanosheets.The discharge capacity of a Li-MnO₂ was 188.8 mAh/g initially,the specific discharge capacity could reach 90.6 mAh/g after 100 cycles.Even the current density was increased to 1 A/g,Li-MnO₂ exhibited the discharge capacity of 84.3 mAh/g,which shows excellent high rate and load performance.This synthetics route of Li-MnO₂ material opens a new way for the preparation of similar material.Nanosheets embedded lithium is expected to be used as cathode material in high performance Li-ion battery.Embedding different ions and nanostructures,the prepared nanomaterials extended its application to other energy storage system.