| The perovskite-type materials with ABO3 structure have received tremendous attention due to their superior electric conductivity and superior electrochemical properties. In aqueous electrolytes, as the oxygen vacancies can extend to the bulk structure through a mechanism of oxygen intercalation, the observed redox reaction associated with the pseudo capacitive in perovskites can be attributed to a direct intercalation of oxygen ions transferred by oxygen vacancies. In this case, oxides with perovskite structure are considered as ideal electrode materials for supercapacitors as they can provide both a high specific capacitance and a superior energy density. However, many oxides with perovskite structure suffer from electrode kinetic problems due to its intrinsic material properties.In this thesis, we prepared a seirs of LaxSr1-xCoO3-?, LaxSr1-xNiO3-?, LaxSr1-xCu0.1Mn0.9O3-? and LaxSr1-xCo0.1Mn0.903-? (LSC-x, LSN-x, LSCM-x and LSOM-x) nanofibers. And the oxygen vacancies of these samples increased markedly with the growth of Sr-doping.(1)LaxSr1-xCoO3-?(0.3<x<1)perovskite nanofibers doped with Sr were prepared by a simple electrospinning method.The microstructure, morphology and electrochemical properties of LaxSr1-xCoO3-? (0.3?x?1) were systematically studied through SEM, XRD, TEM, HRTEM, BET, XPS and electrochemical analyzer etc. Furthermore, when 1 M Na2SO4 electrolyte was employed, a maximum capacitance of 747.8 F·g-1 at a current density of 2 A·g-1 was achieved for the La0.7Sr0.3NiO3-? as electrode material. Moreover, the symmetric supercapacitor (LSC-0.7//LSC-0.7) device using 1 M Na2SO4 aqueous solution was successfully assembled. It exhibited a high energy density of 38.4 Wh·kg-1 at a low power density of 400 W·kg-1 in a stable potential window of 0-1.6 V. And LSC-0.7//LSC-0.7 still remains 36.9 Wh·kg-1 at a power density of 50 kW·kg-1. More importantly, this symmetric supercapacitor can still show an excellent cycling performance with 97% specific capacitance retention after 2000 charging and discharging cycles.(2) The LaxSr1-xNiO3-? (0.3?x?1)perovskite nanofibers with different Sr-doping were synthesized by using the electrospinning process. The investigation on microstructure and electrochemical properties of LaxSr1-xNiO3-? samples were explored by the SEM, XRD,TEM, HRTEM, BET, XPS and electrochemical analyzer etc. In addition, the La0.7Sr0.3NiO3-? sample exhibited the highest specific capacitance value of 719.5 F·g-1 at a current density of 2 A·g-1 in 1 M Na2SO4 electrolyte.The symmetric supercapacitor (LSN-0.7//LSN-0.7) prepared by Lao.7Sro.3Ni03-? sample was operated reversibly at a high cell voltage of 2.0 V. Furthermore, the symmetric supercapacitor showed a low energy density of 37.5 Wh·kg-1 at high power density of 5 kW·kg-1 and a high energy density of 81.4 Wh·kg-1 were achieved at a power density of 500 W·kg-1. More importantly, this symmetric supercapacitor also showed an excellent cycling life (90% retention) after 2000 charging and discharging cycles. As a result, the LSN-0.7//LSN-0.7 sample showed a better performance than the LSC-0.7//LSC-0.7 device.(3) The preparation of LaxSr1-xCu0.1Mn0.9O3-? (0.1?x?1) electrospinning nanofibers with Sr and Cu substitution were presented in this study. As well, the structure and electrochemical properties of LaxSr1-xCu0.1Mn0.9O3-? were investigated in details. As a result, the La0.5Sr0.5Cu0.1Mn0.9O3 sample with high specific surface area possessed the maximum specific capacitance value of 553.5 F·g-1 at a current density of 2 A·g-1 in 1 M Na2SO4 aqueous electrolyte. In addition, a symmetric supercapacitor (LSCM-0.5//LSCM-0.5) was constructed using the La0.5Sr0.5Cu0.1Mn0.9O3 sample as electrode.The LSCM-0.5//LSCM-0.5 device with an extended operating voltage range of 0-2 V displayed excellent electrochemical performance with a high energy density of 48.7 Wh·kg-1 at a low power density of 500 W·kg-1.On the other hand, the device exhibited a low energy density of 30.9 Wh·kg-1 with a high power density of 5 kW·kg-1 Furthermore, the LSCM-0.5//LSCM-0.5 device could still maintain superior cycling stability with 93% specific capacitance retention after 2000 cycles.It suggested that LSCM-0.5//LSCM-0.5 sample had a better electrochemical property than LSC-0.7//LSC-0.7.(4) The double doping LaxSr1-xCo0.1Mn0.9O3-? (0.3?x?1) electrospinning nanofibers were successfully synthesized in this study. The SEM, XRD, TEM, HRTEM, BET and XPS results indicated that LSOM-x samples had good crystallinity and uniform morphology.As well, the electrochemical study demonstrate the La0.7Sr0.3Co0.1Mn0.9O3 sample had a maximum capacitance of 553.5 F·g-1 at a current density of 2 A·g-1 in 1 M Na2SO4 electrolyte. Furthermore, we had fabricated a symmetric supercapacitor (LSOM-0.7//LSOM-0.7) employing pseudocapacitive La0.7Sr0.3Co0.1Mn0.9O3 sample as electrode. And LSOM-0.7//LSOM-0.7 sample could operate at a cell voltage as high as 2 V.The LSOM-0.7//LSOM-0.7 delivered specific energy densities of 75.4 and 43.9 Wh·kg-1 at specific power densities of 500 W·kg-1 and 5000 W·kg-1, respectively. The symmetric supercapacitor possessed a good stability retaining more than 96% of its initial capacitance after 2000 consecutive cycles. The specific energy densities of LSOM-0.7//LSOM-0.7 is higher than LSN-0.7//LSN-0.7 sample at high power density of 5 kW·kg-1. It indicated that LSOM-0.7//LSOM-0.7 can exhibit better performance in a higher current intensity. |
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