The Preparation And Electrochemical Properties Of Ternary Transition Metal Perovskite Fluoride Electrode Materials

The traditional fossil fuel energy with limited reserves,heavy pollution and low conversion efficiency will be gradually replaced by efficient,environmental friendly and green sustainable energy,the most important part of which is energy storage technology.As one of the key devices for energy storage,aqueous electrochemical energy storage equipment has been deeply studied by scientists,and the electrode material is the key factor that affects the device performance.Traditional transition metal compound electrode materials have poor specific capacity,rate and cycle performance due to their low electronic conductivity.Therefore,the development of pseudocapacitive conversion cathode materials with fast kinetics characteristics is a research idea to improve the specific capacity and rate performance of the cathode and build an efficient aqueous electrochemical storage device.In this paper,two novel pseudocapacitive ternary transition metal perovskite fluoride materials were synthesized and used as the cathode of aqueous electrochemical storage devices by taking advantage of the strong ionic properties of metal-fluorine bond and the synergistic effect of multi-metals.The kinetics behavior characteristics and conversion mechanism of these two materials were discussed.The main contents are as follows:（1）The ternary transition metal perovskite fluoride KNi_0.8Co_0.1Mn_0.1F₃（KNCMF-811）with different synthesis conditions and the same metal proportion was screened out and the synthesis conditions with the best comprehensive electrochemical performance were screened out by single electrode test.The original KNCMF-811powder and KNCMF-811（8^#）electrode after full charge and full discharge were characterized by XPS,TEM,SAED and other test methods to explore the charge storage conversion mechanism of KNCMF-811（8^#）material in alkaline medium.Aqueous supercapacitors based on activated carbon（AC）anode and KNCMF-811（8^#）cathode were constructed to test their performance in alkaline and neutral electrolyte systems.By adding bipolar redox electrolytes[Cu（NH₃）₄]²⁺and[Fe（CN）₆]^3-to the electrolyte of AC negative electrode and KNCMF-811（8^#）positive electrode respectively,a strategy to improve the energy density of supercapacitors was explored.In this study,a small amount（1.0wt%）of Na₂Mo O₄ anti-polarization additive was added to the electrolyte to improve the cycling performance of the supercapacitor at this temperature.（2）Twoternarytransitionmetalperovskitefluoride K_0.9Ni_0.3Zn_0.3Mn_0.4F_3.0（KNZMF）and K_0.8Ni_0.3Co_0.3Mn_0.4F_3.5（KNCMF）were synthesized by one-step solvothermal method.The physical properties of KNZMF were characterized by XRD,TEM,SEM,BET and BJH,the bulk phase transformation mechanism and the pseudocapacitance-dominated kinetics of KNZMF electrode in alkaline electrolyte were revealed by XPS,TEM,SAED and CV tests.The Zn-based aqueous battery（ZABs）was constructed with Zn sheet as negative electrode and active electrode material as positive material.The ion diffusion coefficient,OH^-adsorption on redox active Ni/Mn species,deprotonation process and surface electroactive sites were studied by electrochemical test,ex situ characterization and density functional theory（DFT）.The results show that the Co-free KNZMF and Zn//KNZMF exhibit remarkable properties,which are superior to the Co-rich KNCMF and Zn//KNCMF.This work provides a new idea for developing new environment-friendly cathode materials.