Preparation And Electrochemical Properties Of Perovskite Lanthanum Manganate Composite Electrode Materials

Developing electrode material with high energy density,high power density and long cycle stability is the key to improve electrochemical performance of supercapacitors.LaMnO₃ has been widely used in catalysts,sensors and other fields due to its stable structure,unique electronic characteristics,strong redox capability and catalytic activity,but it has been rarely studied as electrode material for supercapacitors.The OH^-in the electrolyte enters the oxygen vacancy and participates in reversible redox reaction of Mn^x+at B site to achieve energy storage and release charge.After doping appropriate amount of Sr at A site,the change of La-O-La bond length leads to distortion of Mn-O-Mn bond angle and mismatch of MnO₆ octahedron.The increase of oxygen vacancy concentration is beneficial to the improvement of charge storage capacity.There are few studies on its structure,morphology,element doping,energy storage mechanism,interface modification and electrolyte concentration.In this paper,LaMnO₃ is selected as electrode material of supercapacitor.By controlling doping amount of Sr,it is compounded with Ag and NiCo₂O₄ to improve electrochemical performance.An asymmetric supercapacitor with high energy density,high power density and excellent cycle stability was obtained by assembling LaMnO₃-based electrode material with activated carbon.The main contents of the study are concluded as follows:1.The strontium doping amount of 15%favours lattice distortion to produce more oxygen vacancies,delivering the highest specific capacitance of 102 F?g^-1 at current density of 1 A?g^-1and the lowest intrinsic resistance in 1 M KOH with the most excellent electrochemical performance.The OH^-ions of electrolyte were adsorbed to oxygen defect and generate O^2-and H₂O,while accompanied by the valence changes of Mn²⁺/Mn³⁺and Mn³⁺/Mn⁴⁺.Mn element constantly exudates into the electrolyte,resulting in deterioration of the overall stability.The energy density of LSM15//AC asymmetric supercapacitor is 3.9 Wh?kg^-1 when the power density is 120 W?kg^-1.2.Silver nanoparticles with good conductivity were modified on the surface of La_0.85Sr_0.15MnO₃（Ag@LSM15）.Ag nanoparticles not only facilitate to accelerate charge transfer but also contribute a small amount of pseudocapacitance in alkaline electrolyte by changing valence state.The as-designed Ag@LSM15 composite electrode with high conductivity shows high specific capacitance of 186 F·g^-1 at 1 A·g^-1.The Ag@LSM15//AC device delivers a maximum energy density of 20.6 Wh·kg^-1 at a power density of 1700 W·kg^-1 within the wide potential window of 1.7 V,as well as 13.4 Wh·kg^-1 at a power density of 8500 W·kg^-1.3.We designed a kind of core-shell nanoflowers structure of NiCo₂O₄ with good conductivity and excellent electrochemical performance to encapsulate LaMnO₃ nanoparticles,so that the element exudation can be inhibited.Morever,foam nickel was directly used as growth substrate,which reduced the additional contact resistance and improved the conductivity in the electrochemical reaction.The specific capacitance can reach 1560 F·g^-11 at 0.5 A·g^-1.The potential window of asymmetric supercapacitor is 1.6 V,and the maximum energy density and power density are 36.6 Wh·kg^-1and 25.6 kW·kg^-1,respectively.4.We prepared La_0.85Sr_0.15MnO₃@NiCo₂O₄（LSM15@NC）core-shell nanoflower electrode through hydrothermal method and systematically studied the effect of different KOH electrolyte concentration（1,3,6 and 9 M）on the electrochemical behavior of LSM15@NC electrode.It manifests high capacitance of 1341 F·g^-1 in 6 M KOH electrolyte at 0.5 A·g^-1.The assembled LSM15@NC//AC asymmetric supercapacitor has a wide potential window of 1.8 V,the highest energy density of 63.5 Wh·kg^-1 when the power density is 900 W·kg^-1,a super high power density of 57.6 kW·kg^-1 while the energy density remains 25.2 Wh·kg^-1 and the capacitance retention rate is 200%after 10000 cycles.