Preparation And Properties Of Manganese-based Ternary Compounds As Binder-free Electrode

Electrochemical capacitors attract much attention as an energy storage device with highenergy density, high current charge and discharge characteristics, and friendly to the environment.Electrochemical performance of capacitors strongly depends on the electrode materials. In recentyears, research on transition metal oxides aroused widespread attention. Ternary compoundsbecame one of the hotspots due to their high specific capacitance and excellent cyclicperformance. On the other hand, binder-free electrodes cause great interests whereelectrochemically active materials grow on the collector surface directly.In this thesis, ternary compounds, CoMn2O4and MnCo2O4were synthesized by a simplehydrothermal method, which were deposited on the surface of Ni foam to establish a binder-freeelectrode. The composition and morphology of electrode were characterized by Scanningelectron microscope (SEM), X ray diffraction (XRD) and energy dispersive spectrometer (EDS).The electrochemical performance of the electrode was evaluated by cyclic voltammetry (CV),galvanostatic charge-discharge testing, and electrochemical impedance spectroscopy (EIS). Theconclusions are as following:（1）CoMn2O4, a transition metal oxide with spinel structure (AB2O4), was synthesized by ahydrothermal method using Mn(CH3COO)2·4H2O, Co(CH3COO)2·4H2O and urea as reactants.The synthetic parameters were investigated, such as the concentration of the urea, thehydrothermal time and the hydrothermal temperature. As a result, the optimal parameters areobtained as follows: n(Mn):n(Co):n(urea)=2:1:1, n(Mn)=20mmol, hydrothermally reacted at60°C for20h. In the optimized condition, amorphous CoMn2O4nanosheets were deposited onthe surface of Ni foam. The size of the nanosheets is about200nm. The obtained binder-freeelectrode has better electrochemical performance than the traditional ones, with the specificcapacitance of625.00F·g-1and the retention of the capacitance was65.50％, while thetraditional electrode is252.00F·g-1and60.54％, respectively.（2）MnCo2O4is another transition metal oxide with spinel structure, where the valencestate of Mn and Co is2+and3+, respectively. Co(CH3COO)2·4H2O and Mn(CH3COO)2·4H2O were used to synthesis MnCo2O4. The optimal synthetic parameters are obtained as follows:n(Co):n(Mn):n(urea)=2:1:1, n(Co)=10mmol, hydrothermally reacted at60°C for20h. Underthis condition, petal–shaped MnCo2O4nanosheets are compact coating on the surface of the Nifoam uniformly. The size of the nanosheets is around300nm. The specific capacitance of thebinder-free electrode is740.00F·g-1and the retention of the capacitance after500charge-discharge cycles is71.00％, which are much higher than that of the traditional electrode,251.66F·g-1and37.26％, respectively.In this thesis, we provide a facile hydrothermal method to fabricate binder-free electrode,where electrochemically active ternary compounds CoMn2O4and MnCo2O4have been designedto deposite on the surface of Ni foam. The binder-free electrode exhibits excellentelectrochemical performance compared with the traditional ones. The results of the study arevery meaningful for our future work on binder-free electrodes.