Sn-based Metal Oxide Cooperates With The P-N Junction For Asymmetric Supercapacitors

High-efficiency energy storage devices have stimulated tremendous attention from researchers,because of the exhaustion of nonrenewable resources and their increasing damage to the environment.Supercapacitors(SCs).also known as electrochemical capacitors,are considered to represent a new class of energy storage devices,because they are capable of storing more energy than conventional capacitors and providing greater power than batteries.However,in order to meet the increasing energy requirements for the next-generation electronic devices,the energy density of current SCs must be further improved without sacrificing the power density and cycling life.According to the equation of energy density E=1/2CV2,two strategies that are aimed at extending the voltage window(V)and increasing the capacitance(C)have been proposed to achieve the target.Currently,most commercial supercapacitors are based on two symmetric activated carbon(AC)electrodes separated by a polymeric membrane impregnated with an organic electrolyte.The organic electrolytes,have many disadvantages including low ionic conductivity,high cost,tedious purification processes and flammability.On the contrary,aqueous electrolytes ha e merits in terms of high ionic conductivity low cost.inflarmmabilitvy and environmental benignity,which make the supercapacitors using aqueous electrolyt(;more desirable for practical applications.However,the restriction of aqueot electrolytes is a limited operating voltage of about 1.23 V at which water decompose;To further improve the energy density of aqueous electrolyte-based supercapacito;widening the voltage window is the key.One strategy is to select electrode material that have high overpotentials for hydrogen and/or oxygen evolutions.Another one i:to combine different positive and negative electrode materials that have well-separated potential windows to make asymmetric supercapacitors,enabling widening of the cell voltage.Development of high-energy and high-power asymmetric supercapacitors(ASCs is still a tremendous challenge due to the low capacitance of anode(100?200 F.g-1 for carbon materials)and smaller voltage window(1.6?1.8 V in aqueous electrolytes)compared with Li ion battery.In this paper,a simple one-step hydrothermal method was used to obtain ultra-thin tin dioxide nanosheets,and the nanostructures of the nanostructures were obtained by the secondary hydrothermal process,and tin oxide composite with different contents can be prepared from the next annealed at different temperatures in argon atmosphere.The nanometer sheet and the high specific surface area of the secondary structure and the P-N junction with different band gap of tin oxide and tin dioxide interface effect of the two kinds of materials to achieve a substantial increase in capacity and cycle stability.The results showed that the fractionated SnO2 nanostructures were improved from 112 F·g-1 to 540.3 F·g-1 at a scanning rate of 10 mV·s-1.which was a relatively high capacity storage.This simple experimental process with clever structural design.supercapacitor energy density and power density of the coordinated development of a new idea.At the same time,we designed a simple and feasible one-step hydrothermal method to obtain the defective manganese oxide electrode material with ultrahigh working potential,and matched the tin oxide electrode material with large specific capacity after treatment.as positive and negative electrodes are assembled into asymmetric supercapacitors,manganese oxide mainly to broadening the entire operating voltage of the entire capacitor.tin oxide after treatment mainly to enhance the capacity of the entire capacitor in the structure and matching,the comprehensive realization of the high Energy density and high power density harmonized with excellent overall quality of the asymmetric supercapacitor.Herein,we demonstrate the rational design of conductive hierarchical nanostructured SnO@SnO2 anode with high charge storage capability(342 F·g-1 at 5 mV·s-1)and wide potential window working(0?1.3 V vs.SCE)MnO2 nano sheets cathode for high-energy and high-power ASCs.The construction of hierarchical nanostructures of SrnO@SnO2 composites can provide not only large surface area for fast ion transportation but also efficient path for charge transfer.Moreover,our results have shown that the expanded wide working potential window of cathode surely have enlarged the stable voltage of as-assembled ASC(up to 2.2 V),which further achieves a volumetric energy density of 2.29 mWh·cm-3 at 196 mW·cm-3 and significantly retains 1.08 mmWh·cm-3 at 2063 mW·cm-3,opening up new opportunity for advancing high-performance ASCs.