Preparation Of High Specific Energy Supercapacitor And Its Energy Storage Mechanism

Supercapacitor is a new type of energy storage device between traditional capacitor and secondary battery.It has many advantages of high power density,high energy density and long cycle life.At present,the research on supercapacitors is mainly focused on the preparation of high performance electrode materials,aiming at improving the energy density and power density of supercapacitors to meet the needs of modern electronic devices.In this paper,low-cost pseudocapacitor electrode materials are used as supercapacitor materials,combined with a variety of electrochemical research methods,material research and test methods,to research the high specific energy supercapacitors from the aspects of crystal structure design,defect charge compensation,and oxygen vacancies.The main research contents and innovations are as follows:1.Ultralong single-crystal V₂O₅ wires?W-V₂O₅?and V₂O₅ nanoparticles?P-V₂O₅?with similar physicochemical properties were compared to investigate the possible stimulative factors for pseudocapacitive enhancement.By comparing the capacitive behaviors and analyzing the crystal structures,we clarified that beside the most-discussed specific surface area,the crystal structures such as facet orientation and interlamerllar spacing distance also affect greatly to the intrinsic pseudocapacitive performances by influencing the electrons transport and charge carriers intercalation.First the single-crystal V₂O₅ wire with robust ultralong structure can free up the electron transportation along the wire direction?the[001]facet orientation?;second,the enlarged interlamellar spacing of W-V₂O₅ ensure the rapid intercalation of Li⁺into the crystal lattice;Third,the layer structure is vertical to the wire direction,which will shorten the diffusion distance for Li⁺inserting into the 2D layer structures.Using this material as a positive electrode to prepare an asymmetric supercapacitor device,when the current density is 0.4 A/g,the specific capacity is 100.8 F/g,the power density is 1542 W/kg,and the energy density is 22.98 Wh/kg.This new insight presented here provides guidance for the design of pseudocapacitive metal oxides and opens new opportunities in the development of high-performance pseudocapacitors.2.The transition metal oxides?MnO₂,Co₃O₄,NiO,NiS,Co?OH?₂,CuO?were treated under air and hydrogen,and the effects of oxygen vacancies on the properties of the materials were studied through electrochemical tests.As a result,it was found that the electrochemical performance after hydrogen treatment was improved to a different degree than in an air atmosphere.We believe that due to the hydrogen treatment,more oxygen vacancies are generated,and the oxygen vacancies as their acceptor energy levels attract more hydroxide ions to participate in the electrochemical reaction,which ultimately leads to improved electrochemical performance.Taking MnO₂ as an example,when the current density is 1 A/g,the specific capacitance increases from 1520 F/g to 2165 F/g.This research can help develop supercapacitors with high energy density,high power density and long cycle life.3.We proposed the synthesis of Co doped oxygen-vacancy abundant?-MoO_3-x(Co-MoO_3-x)nanosphere through a novel defect-engineering method.The introduction of the oxygen-vacancies could not only extremely lead to a larger interlayer spacing and improve the electrical conductivity of?-MoO₃,but also significantly enhance the electrochemical activity to enable the?-MoO₃ structure to be maintained during the insertion and removal of K ions.we fabricated an asymmetric supercapacitor which assembled by utilizing the Co-MoO_3-x-x electrode as the cathode and the AC as the anode.it exhibits an ultrahigh energy density of 55Wh/kg at a power density of 763 W/kg,and excellent cycling stability.In addition,this novel synthetic method can be extended to other metal oxide composites,which will have great potentials in not only the energy storage field,but also in numerous other frontiers.