Construction And Performance Study Of Supercapacitors Based On Manganese Oxide Composites

In recent years,to meet carbon peaking and carbon neutrality goals,the green,low-carbon,and sustainable development model is accelerating the transformation of the energy consumption structure of China.At the same time,it also puts forward higher requirements for high-performance energy storage equipment.As a representative of environment-friendly energy storage devices,lithium-ion batteries are widely used in current social production,but their low power density and poor cycle performance are gradually showing signs of fatigue in the face of increasingly stringent market demands.As a new energy storage device with the high-power density and long cycle stability,super capacitors have the potential to supplement lithium-ion batteries in practical applications,but their low energy density has been a key problem restricting their development.According to the energy density formula E=CV2/2 of the supercapacitor,there are two breakthroughs to further improve its energy density:specific capacity and voltage window.Manganese oxide is considered a promising electrode material for supercapacitors because of its abundant reserves and high theoretical capacity.However,its low intrinsic conductivity hinders the improvement of its actual capacitance.In this paper,manganese oxide was optimized and modified in depth from the aspects of morphology regulation,composite high conductivity materials,electrochemical activation,structural design,and positive and negative electrode matching,so as to improve the conductivity of manganese oxide and enhance its capacitance,and then assemble supercapacitor devices with high energy density.The main research work is as follows:(1)α-MnO2 nanomaterials with different morphologies were prepared by controlling the concentration of surfactant during a hydrothermal reaction,and the effect of different morphologies on their capacitance storage was investigated.The test results of morphology,phase,and composition confirmed the successful preparation of α-MnO2 materials with the morphology of nanosheets and nanowires.Nitrogen isothermal adsorption and desorption test showed that the α-MnO2 nanosheet morphology showed a larger specific surface area(66.93 m2 g-1).The electrochemical performance tests show that the α-MnO2 material with nanosheet morphology(212.80 F g-1)has a specific capacitance about twice that of nano wire morphology(113.34 F g-1),but its agglomeration phenomenon reduces the rate performance and conductivity.The experimental results show that the capacitance storage performance ofα-MnO2 material is related to the specific surface area infiltrated by electrolyte,and the nanocrystalline manganese oxide material can expand the specific surface area and shorten the electron transport distance,and effectively improve the capacitance storage and electric conductivity.However,it is noteworthy that nanomaterials with high specific surface area tend to agglomerate,which also provides guidance for subsequent related studies.(2)Based on large-area graphene(rGO)material,NiMnO3/rGO composite with multilayer structure was prepared by hydrothermal method,and its energy storage performance and electrochemical kinetics in supercapacitor were studied.Morphology characterization confirmed that NiMnO3 nanosheets uniformly grow on the rGO substrate to form a multilayer structure,which alleviated the self-aggregation phenomenon of the nano sheets.The corresponding structural characterization confirmed the successful preparation of NiMnO3/rGO composites and the close bonding between them.Nitrogen isothermal adsorption and desorption tests show that the composite has a high specific surface area of 371.60 m2 g-1.The electrochemical results show that the composites can achieve a high specific capacitance of 529.92 F g-1 at the current density of 1.00 A g-1,and exhibit excellent rate performance.Furthermore,the kinetic process shows that the surface capacitance behavior is dominant in the storage process.Moreover,the assembled asymmetric supercapacitor(ASC)exhibits excellent energy density(40.27 Wh kg-1)and ultra-long cycle stability(capacitance retention up to 94.60%after 10000 cycles).The experimental results show that the introduction of rGO substrate provides a strong conductive network for manganese oxides,which accelerates electron transport,reduces the internal resistance,improves electrochemical kinetics,and can further enhance capacitance.This provides a new idea for improving the agglomeration of manganese oxide nanosheets and improving their electric conductivity and energy storage performance.(3)NiMn2O4 nanosheets were grown in situ by hydrothermal reaction on carbon cloth(CC)substrate with good electric conductivity,and NiMn2O4-active/CC self-supporting materials were prepared by electrochemical activation.The mechanism of electrochemical activation on the improvement of energy storage performance of manganese oxide materials was studied.The influence of different electrolytes on the energy storage performance after electrochemical activation was further summarized.The morphology reconstruction of NiMn2O4 nanosheets during electrochemical activation was confirmed by SEM.Then,XRD and XPS characterization indicates that the amorphous materials formed after electrochemical activation are favorable for pseudocapacitance reaction.Electrochemical tests show that the activated NiMn2O4-active/CC electrode has a high specific capacity of 707.54 F g-1,which is twice that before activation.Furthermore,the effects of cationic and anionic groups in different neutral electrolytes on the energy storage performance of NiMn2O4 nanosheets after electrochemical activation were further compared and analyzed,which laid a good foundation for the preparation of high-performance electrode materials by electrochemical activation.At the same time,the asymmetric supercapacitor device was assembled with the positive electrode of NiMn2O4-active/CC electrode,and the maximum energy density of 54.27 Wh kg-1 and 2.20 V voltage window was obtained,which greatly expanded the voltage window of the water supercapacitor and further promoted the development of water supercapacitor with high energy density.(4)A high mass loading amorphous NiMnOx/TiN/CC self-supporting material with a leaf-branch structure was designed and fabricated,and its application in flexible supercapacitors was explored.Morphology and phase characterization showed that the branch-leaf structure avoided the formation of dense materials during the in-situ growth of high-quality loaded amorphous NiMnOx materials,thus improving the wettability of the electrode surface and electrolyte,and introducing more reactive sites.The crystal phase and composition test results indicate the successful preparation of amorphous NiMnOx/TiN/CC materials and confirms the strong bonding between NiMnOx nanosheets and TiN nanowires.The results of electrochemical tests showed that the NiMnOx/TiN/CC electrode had excellent area capacity(4882.62 mF cm-2),and excellent rate performance(63.42%capacitance retention),and low impedance at a mass load of 10.12 mg cm-2.In addition,the assembly NiMnOx/TiN/CC//FeOOH/TiN/CC flexible device has a high working voltage,2.20 V at the same time has excellent energy density(0.65 Wh cm-2)and power density(32.40 W cm-2).The experimental phenomenon of this design idea proves that the strategy of the branch-leaf structure plays an important role in the development of high-performance electrode materials with high mass loading.