Research On Preparation And Electrochemical Performance Of Cobalt-based Perovskite Materials For Supercapacitor Electrode

Perovskite（ABX₃）has been proved to be a promising electrode material for supercapacitors due to its individual lattice structure.Through replacing the A or B ions in the structure,the structural defects and ionic electronic conductivity of the material can be effectively regulated.Particularly,the electrochemical properties of perovskite materials are mainly affected by the valence state of B-site elements.Cobalt（Co）has a polyvalent state,and the presence of polyvalent metal ions can lead to multiple redox reactions.Co was used as the key element in this paper,and we successfully synthesized the La Co O₃ perovskite oxides and Na Co F₃ perovskite fluoride as electrode materials for the supercapacitor by different preparation methods.The electrochemical performances of these electrode materials have been investigated in detail.Moreover,the electrochemical performance of the single perovskite electrode material was improved by B-site metal ion regulation and preparation of perovskite composite materials,and its energy storage application in supercapacitor was studied.The research work of this paper mainly includes:1.LaCoO₃ perovskite oxides with different morphologies were prepared by sol-gel method,metal-organic framework（MOFs）derivatization and electrostatic spinning.The La Co O₃ with nanofibrous shape showed good electrochemical performance.Then,the La Co O₃/Co₃O₄ composite electrode with nanofibers loaded with nanosheets was constructed.Compared with La Co O₃ electrode,the La Co O₃/Co₃O₄ composite electrode has better conductivity and faster ion diffusion rate.At the current density of 1 A g^-1,the specific capacity of La Co O₃/Co₃O₄ electrode was 446.76 F g^-1.At the current density of 10 A g^-1,the specific capacity of La Co O₃/Co₃O₄ electrode remains at 100.9%of the initial specific capacity value after 5000 charge and discharge tests,which shows excellent long cyclic stability.2.The optimum reaction condition for preparation of NaCoF₃ single-phase perovskite fluoride was investigated by solvothermal method at first.Then the B-site regulated Na Co_1-xNi_xF₃（x=0,0.3,0.5,0.8,1）perovskite fluoride with different Co/Ni ratios was successfully prepared by solvothermal method.When Co/Ni ratios was 2:8,the Na Co_0.2Ni_0.8F₃ electrode shows the best specific capacity(648.01-413.26 C g^-1,0.5-16 A g^-1),which is obviously better than Na Co F₃(82.95-66.10 C g^-1,0.5-16 A g^-1)and Na Ni F₃(574.82-309.69 C g^-1,0.5-16 A g^-1)electrode materials due to the improved conductivity.At the current density of 8 A g^-1,the coulomb efficiency of Na Co_0.2Ni_0.8F₃ electrode was close to 100%,and the specific capacity of Na Co_0.2Ni_0.8F₃ electrode remains at 75%of the initial specific capacity value after 5000 cycles.3.The bimetallic perovskite fluorides/reduced graphene oxide(NaCo_0.2Ni_0.8F₃/r GO)composite material was successfully synthesized by a simple solvothermal method.The addition of r GO could improve the long cycle stability and rate performance of Na Co_0.2Ni_0.8F₃ electrode by virtue of the great conductivity of the r GO and the uniform dispersion of Na Co_0.2Ni_0.8F₃ perovskite nanoparticles on it.The Na Co_0.2Ni_0.8F₃/r GO composite electrode displays the high specific capacity of 805.7 C g^-1,excellent rate performance(82%capacity retention from 0.5 to 16 A g^-1)and superior cycle stability（92%retention over 5000 cycles）.Furthermore,the active carbon（AC）//Na Co_0.2Ni_0.8F₃/r GO asymmetric supercapacitor exhibits a high energy density of 52.19 Wh kg^-1 under a power density of 750 W kg^-1,and the retention rate of specific capacity remains 82%after 3000cycles.It is believed that the above findings supply an efficient electrode design for the future practical application of perovskite fluorides in high-performance supercapacitor.