Strategies Of Regulating Internal Lectric Field Of Manganese Oxides Electrode Materials For Supercapacitors

Advanced energy storage technologies,such as supercapacitors(SCs),have been widely investigated due to the exhaustion of non-renewable energy and the continuously increased energy requirements.Manganese oxides(MnOx),as typical electrode materials for SCs,have attracted extensive attention because of their characteristics of low price,abundant earth reserves and high theoretical capacitance.However,MnOx have poor electrical conductivity and low practical capacitance,thus limiting their applications in SCs.In this thesis,we introduced the interfacial electric field and local electric field into manganese oxide materials by preparing carbon coupled MnOx composite and Cu doped MnOx,respectively.The electrochemical properties of the resultant manganese oxide electrode materials were investigated,and the effect of internal electric field on the capacitive performance of MnOx was deeply discussed.(1)The g-C3N4 coupled manganese oxide composite(CN@MnOx)with heterogeneous structure was successfully prepared by in-situ growth method.The CN@MnOx electrode material has an open two-dimensional lamellar structure.Compared with the counterpart sample of pure MnOx,CN@MnOx shows higher electrical conductivity,higher capacitance,and faster charge transfer kinetics.DFT calculations show that,on the one hand,the electrons distribution around Fermi energy level of CN@MnOx improve the electrical conductivity,on the other hand,a formed interfacial electric field in CN@MnOx lowers the diffusion energy barrier of sodium ions.An fabricated ASCs(CN@MnOx//AC)delivers a maximum energy density of 46.7 Wh kg-2 at a power density of 1000 W kg-1.(2)Cu doped MnO2 nanosheets(Cu-MnO2)were successfully synthesized to regulate the electronic structure of MnO2.Compared with the counterpart of undoped MnO2,Cu-MnO2 has higher electrical conductivity,higher capacitance,and faster charge transfer kinetics.DFT calculations reveal that the promising electrical conductivity of Cu-MnO2 is attributed the regulated electronic structure by the copper atom doping.Moreover,a local electric field formed by the charge redistribution around the atoms substantially facilitates the Na ions transport.An assembled ASCs(Cu-MnO2//AC)delivers a maximum energy density of 44.7 Wh kg-1 at a power density of 1000 W kg-1.In summary,CN@MnOx and Cu-MnO2 electrode materials were prepared aiming to introduce internal electric field.Based on the experimental and calculations results,the effect of internal electrical field on the capacitive performance of MnO2 was thoroughly investigated.This work provides basic understanding of the internal electric field associated electrochemical performance of metal oxides electrode materials for energy storage applications.