Study Of Electrochemical Energy Storage Based On Na_xMnO₂ Electrode Materials

In this thesis, the poor diffusion of electrolyte Na⁺ions in the bulk of manganese dioxide（MnO₂） was soloved through synthesis of intercalation of sodium into MnO₂ （NayMnO₂）; the electronic conductivity and electrochemical capacitance performance of Na_xMnO₂ were improved by modifying with reduced graphene oxides（rGO）; excellent cycling stability and electrochemical capacitance performance at high current density were obtained by dipping rGO-Na_xMnO₂ on the surface of TiN substrate.（1）The synthesis of Na_xMnO₂. MnO₂ have prepared by a hydrothermal method, and the intercalation compounds Na_xMnO₂ was synthesized through a solid-state route using MnO₂ and NaOH as raw materials. X-ray diffraction（XRD） pattern shows the composition of intercalation of sodium into MnO₂ included Na0.70MnO₂.05 and Na0.55Mn2O4·1.5H2O. Scanning electron microscope（SEM） reveals the morphology of Na_xMnO₂ was belt and have wideths of 1-2μm, lengths of about 2μm. The occurrence of redox peaks implies that the charge storage mechanism is mainly based on the intercalation/deintercalation of Na⁺ions into Na_xMnO₂ interlayers; but the CV curves of MnO₂/NF were quasi-rectangular shapes show the surface Faradaic reaction. The specific capacitance of Na_xMnO₂ and MnO₂ were separately 133.2 F g^-1,18.3 F g^-1 at a constant current density of 0.2A g^-1. The specific capacitance and IR drop value of Na_xMnO₂/NF were separately 65.7 F g^-1,0.24V at a constant current density of 2.0A g^-1. The charge-transfer resistance Rct of Na_xMnO₂, were 3.44 Ω,18.78Ω, respectively; diffusion resistance W of electrolyte ions were 18.34Ω, 1048 Ω respectively. Experiment datas show a good diffusion of electrolyte Na⁺ ions in the bulk of MnO₂.（2）The synthesis of rGO-Na_xMnO₂. The rGO-Na_xMnO₂ was synthesized through a simple thermo-chemical reduction reaction after the Na_xMnO₂ was dispersed in the GO solution. XRD pattern shows the characteristic peak of rGO was 24 degree. SEM reveals the Na_xMnO₂ was gathered and wrapped rGO layer after a thermo-chemical reduction process. The CV curves of rGO-Na_xMnO₂/NF were quasi-rectangular shapes. The specific capacitance and IR drop value of rGO-Na_xMnO₂/NF were separately 177F g^-1,0.1V at a constant current density of 2A g^-1. The specific capacitance of rGO-Na_xMnO₂/NF was 164F g^-1 after cycled 380 cycles at a constant current density of 2A g^-1 and have a 92.6% capacitance retention. Experiment datas show the conductivity and electrochemical capacitance performance of Na_xMnO₂ were enhanced after modifying with rGO materials.（3）The synthesis of rGO-Na_xMnO₂/TiN. rGO-Na_xMnO₂/TiN was prepared by dipping TiN substrate in the ethanol and rGO-Na_xMnO₂ solution. The specific capacitance and IR drop value of rG0-Na_xMnO₂/TiN were separately 244.2F g^-1,0.04V at a constant current density of 2.0A g^-1. The specific capacitance of rGO-Na_xMnO₂/TiN was 241.4F g^-1 after 580 cycles at a constant current density of 2A g^-1 and retained about 98.9%. The specific capacitance of rGO-Na_xMnO₂/TiN decreased from 184F g^-1 to 128F g^-1 when the current density increased from 3A g^-1 to 20A g^-1. Experiment datas show the rGO-Na_xMnO₂/TiN electrode materials have good electrochemical capacitance performance at high current density, the capacitance loss was very low and the crossion problem of substrate material was disappear even after long time cycles.