Preparation And Electrochemical Properties Of La-and Sr-based Perovskite Oxide As Electrode Materials

Based on the anion intercalation mechanism,perovskite oxide(ABO₃)has been reported as a promising electrode material for supercapacitors.For perovskite oxides,the structure and defect(oxygen vacancy)content can be adjusted by partial replacement of the cations at the A and/or B positions,thus the conductivity and electrochemical performance.The modified perovskite oxides exhibit good electrical conductivity,a wide voltage window,and excellent cycle stability.Perovskite oxide LaMnO₃,and SrBO₃(B=Mn,Co)show the characteristics of electronic/ion mixed conductivity and redox activity,and have the potential to be used as electrode materials for supercapacitors.In this paper,LaMnO₃ prepared by electrodeposition method and SrBO₃(B=Mn,Co)perovskite oxide prepared by solid-state reaction method were used as the active materials combined with highly conductive transition metal oxides.The electrochemical performance of the electrode was tested and analyzed.Besides,liquid and all-solid supercapacitors were assembled,and their practical application as an all-solid-state device assembled in the laboratory was verified.Therefore,around the preparation and electrochemical properties of La-and Sr-based perovskite oxide as electrode materials,the specific research contents carried out in this paper were as follows:The perovskite-type LaMnO₃/MnO(LMO/MnO)supercapacitor electrode supported by carbon cloth was prepared by the electrodeposition method.By controlling the La/Mn ratio,the sample with the best deposition appearance and electrochemical performance was selected,and then the structure and electrochemical performance of the sample was studied in detail.Carbon cloth-supported LMO/MnO(La/Mn=20?1)electrode exhibited a specific capacitance of 260 F g^-1 at a current density of 0.5 A g^-1 in 0.5 M Na₂SO₄ electrolyte solution.The cooperative effects of LMO and MnO,as well as the uniform nano-array morphology,contribute to good electrochemical performance.Also,an asymmetric supercapacitor with a wide voltage window of2 V was fabricated,showing a high energy density of 28.15 Wh kg^-1 at a power density of 745 W kg^-1.The specific capacitance drops to 65%retention after the 5000 cycles due to the element leaching effect and partial flaking of LMO/MnO.(2)The 1/8 Nb⁵⁺ion-substituted Sr Mn_0.875Nb_0.125O₃(SMN)and SrCo_0.875Nb_0.125O₃(SCN)perovskite oxides were synthesized by solid-state reaction method,and their crystal structure and electrochemical properties were systematically discussed.After Nb⁵⁺substitution,the first reported SMN showed a 6H structure with{…hcchcc…}stacking sequence along the c-axis,while SCN exhibited a tetragonal perovskite-related superstructure phase with micro-twinned domains along[100]or[010]direction.Meanwhile,Nb⁵⁺substitution promoted the generation of oxygen vacancies and tended to improve conductivity,which in turn exerted a positive influence on the electrochemical performance of the materials.The electrochemical performance showed that the specific capacitance of SCN in 1 M Na₂SO₄ electrolyte was 894 mF cm^-2 when the current density was 1 mA cm^-2,which was 4.7 times that of SMN.The superiority of SCN was mainly ascribed to the higher oxygen vacancy content and more full use of the internal perovskite structure due to its shorter B-O bond length and large B-O-B bond angle.The energy density of SMN//AC and SCN//AC asymmetric supercapacitor at 1 mA cm^-2 was 46.81?Wh cm^-2 and 82.33?Wh cm^-2,respectively.After 10000 cycles,their respective capacitance retention rate of SMN//AC and SCN//AC was 98.62%and 88.88%,indicating excellent stability and long life.Also,after connecting two SCN//AC asymmetric capacitors in series and charging for 3 minutes,the 2.0 V red LED was successfully lit up.(3)The supercapacitor electrode material composed of SrCo_0.875Nb_0.125O₃@MnO₂ was synthesized by solid-state reaction and electrodeposition method.To better understand the electrochemical behavior of the SrCo_0.875Nb_0.125O₃@MnO₂,theoretical analysis of the density of states of SrCo_0.875Nb_0.125O₃ and MnO₂ were performed using Materials Studio 8.0 software to illustrate the high performance.In the three-electrode system with 2 M KOH as the electrolyte,SrCo_0.875Nb_0.125O₃@MnO₂ with a current density of 2 mA cm^-2 can achieve an ultra-high specific capacitance of 2066 mF cm^-2.Besides,the Randles-Sevick formula calculated that the diffusion coefficient of the SrCo_0.875Nb_0.125O₃@MnO₂ was 2.33×10^-12 cm² S^-1,and further analyzed the charge storage type and the capacitance contribution ratio through quantitative kinetics.The asymmetric supercapacitor composed of SrCo_0.875Nb_0.125O₃@MnO₂ and Cu S under a voltage window of 0?1.8 V had a specific capacitance of 114.6 mF cm^-2 when the current density was 3mA cm^-2.The energy density of SrCo_0.875Nb_0.125O₃@MnO₂//Cu S can reach 51.57?Wh cm^-2 at a power density of 4.86 mW cm^-2.