Preparation And Characterization Of Manganese Based Spinel Materials For Supercapaciors

The Supercapacitor is a kind of new environmental energy-storage devices, ranging from conventional capacitors to batteries. For its highlight of high charge-and-recharge efficient, large momentary discharge current and low maintain cost, supercapacitors have a wide range of application.,Especially in the field of（such as） electric vehicle, mobile communication, electronic equipment, aviation, supercapacitors have attracted much attention all over the world. It is difficult to improve the capacity of energy-storage through changing the active material of manganic oxide, since its poor electrical conductibility. To solve the problem that Mn O₂ and spinel Li Mn₂O₄ material with poor electrical conductibility, low ionic conductance and short cycle life, this article synthesize different tunnel structure manganese-based electrode material, including α-Mn O₂, δ-Mn O₂ combined carbon nanotubes（CNTs）, α-Mn O₂ combined CNTs、spinel Li Mn₂O₄、Li Mn₂O₄ combined CNTs and Li_0.8Mn₂O₄ combined CNTs, by hydrothermal method,and systematically research the structure and electrochemistry capacity of manganic oxide with the influence of different technological parameters and synthesis conditions, and employ the technology of X-ray diffraction and field emission scan electronic scope to identify the structure of manganic oxide.In the first chapter, potassium permanganate with strong oxidizing and CNTs which have huge contactable surface area and excellent electric conductibility react redox reaction. The obtained nano-size Mn O₂ particle can not only deposit on the surface of CNTs, but reach the tunnel gap of CNTs, since potassium permanganate sculpture the wall of CNTs in the reaction. By controlling different synthetic condition, obtained δ-Mn O₂ combined CNTs and α-Mn O₂ combined CNTs electrode material. Testing the electrochemistry capacity of different tunnel structure Mn O₂ combined CNTs electrode, we discuss the different reaction mechanisms of supercapacitors material. Compare the electrochemical performance of α-Mn O₂ combined CNTs electrodes with the different heat treatment temperatures in Na2SO4 solution. It is found α-Mn O₂ can store abundant Na+, and α-Mn O₂ combined CNTs material performs the most excellent conductivity with 200 ℃ heat treatment, specific capacitance reach 120 Fg-1 with the 0.5 Ag-1 current density, while with the condition of 300 ℃, it maintains 50 Fg-1 with the 5 Ag-1 current density. It is supported that the specific capacitance of α-Mn O₂ combined CNTs material can meet the practice require in the different current density. And synthesized δ-Mn O₂ combined CNTs electrodes have a good cycling stability, the specific capacitance reached 132.5 Fg-1 in the current density 0.5 Ag-1,after 1000 cycling, it still remained 86.83 percent.In the second chapter, we also adopt hydrothermal method to synthesize Li Mn₂O₄ combined CNTs electrode material with a different content of CNTs, and Li Mn₂O₄、Li Mn₂O₄ combined CNTs and Li_0.8Mn₂O₄ combined CNTs electrodes under the different heat treatment temperatures, and test their electrochemical capacity in the Li2SO4 solution. It is showed that high heat treatment temperature can improve the electrochemical capacity of spinel material. With 300 ℃ treatment Li Mn₂O₄ combined CNTs electrodes reach 230.5 Fg-1 in the current density of 1.5 Ag-1,it is 30 Fg-1 more than that of under 200 ℃,but after 100 cycling, capacity retention ratio is 78.21 percent. Li_0.8Mn₂O₄ combined CNTs electrodes perform double electric layer behavior and Faraday behavior. The obtained Li Mn₂O₄ combined CNTs electrodes with 300 ℃ treatment can prevent the producing of Jahn-Teller effect efficiently, specific capacitance is 286 Fg-1 in the 0.5 A g-1 current density, 55.5 Fg-1 more than that of Li Mn₂O₄ in the same condition. It reaches 170 Fg-1 in the 5 A g-1 current density, 65 Fg-1 more than that of Li Mn₂O₄ in the same condition. After 100 cycling, capacity retention ratio is still 90.69 percent. This all suggest Li_0.8Mn₂O₄ combined CNTs is one kind of ideal material for supercapacitors.Through comparing the electrochemical capacity of different manganic based combined CNTs material, obtained α-Mn O₂ precursor, two-step hydrothermal synthesis Li_0.8Mn₂O₄ combined CNTs electrode material, with a more excellent electrochemical capacity. But α-Mn O₂ combined CNTs still has wide practical value, for its high cost-effective、simple synthetic process and better specific capacitance in high current density.