Potassium Pre-inserted Manganese Oxide Nanostructure And Their Application In Supercapacitors

In recent years,with the continuous development of technology and the continuous consumption of energy,traditional energy storage systems such as fuel cells,lithium ion batteries,etc.,are difficult to meet the current market demand for energy storage systems with both high power density and high energy density.The hybrid supercapacitor(HSC)is a newly developed new energy storage system.The positive and negative poles use traditional battery electrodes and capacitor electrodes,respectively,combining the advantages of batteries and supercapacitors.It has a higher energy density than electric double layer supercapacitors,while maintaining good cycle stability.However,due to its energy storage mechanism,the battery-type electrode of the hybrid supercapacitor is slow to charge and discharge,which limits its power density and prevents the hybrid device from being able to charge and discharge as quickly as a double-layer capacitor.Therefore,it is of great significance to study and improve the rate performance of battery-type materials.The nanostructure of the material structure is an effective way to improve the utilization rate and rate performance of the electrode material,because when using nanomaterials as the electrode material,its larger specific surface area can increase the full contact with the electrolyte and shorten the ion diffusion distance to increase the power density.Among them,manganese oxide materials are widely used as cathode materials for hybrid supercapacitors due to their advantages of large theoretical capacity,abundant reserves,and low cost.This thesis focuses on the study of manganese oxide material morphology control,crystal plane spacing control,different synthesis methods,etc.,so as to improve the power density and energy density of manganese oxide materials.The application of manganese oxide electrode materials in alkaline ion hybrid supercapacitors shows that they all have excellent electrochemical performance.The main research contents are as follows:(1)Preparation of pre-embedded potassium manganese oxide nanowires with high specific capacity and rate performance by hydrothermal method.A series of nano-structured pre-embedded potassium manganese oxide(KxMnO2)samples were obtained after mixing KOH with different proportions under a certain condition of precursor MnO2 and holding at 200℃ for 12h.The samples were characterized by SEM and XRD.The results showed that ultra-long ultra-fine KxMnO2(KMOx)nanowires with large specific surface area and structural stability were obtained,among which KMO6 had the best rate performance.The tunnel structure of the manganese oxide nanomaterials facilitates the insertion of large radius potassium ions and enlarges the crystal surface spacing,so that the cations in the electrolyte can be quickly detached and embedded in the crystal lattice.The use of KxMnO2 as the positive electrode material to assemble potassium ion hybrid capacitors can achieve excellent electrochemical performance,a high specific capacity of 250 F g-1 at a low scan rate of 0.5 mV s-1,and when the scan rate increases to 200 mV s-1,a higher specific capacity of 150.39 F g-1 can still be obtained.(2)Preparation of pre-embedded potassium manganese oxide nanomaterials by solid-phase method and explore the performance in different alkaline electrolytes.A certain amount of precursors MnO2 and K2CO3 are mixed and fully ground,and calcined at high temperature in a tube furnace under an air atmosphere to obtain a pre-embedded potassium manganese oxide material K1.04Mn8O16(KMO)with two structures of nanoparticles and nanowires.It can be seen from the morphological characterization that the nanowire agglomeration phenomenon is reduced and the distribution is more uniform compared to hydrothermal synthesis,which is conducive to the complete contact of the electrode material and the electrolyte and reduces the volume expansion during charging and discharging.KMO is used as a positive electrode material to assemble lithium ion and sodium ion hybrid capacitors and test their electrochemical performance.The results show that both have higher energy density and power density,and maintain high capacity after 10,000 cycles,almost no attenuation.