Preparation And Electrochemical Properties Of Layered Manganese-based Cathode Materials For Sodium Ion Batteries

Due to the advantages of environmental friendliness and rich reserves,sodium-ion batteries have become the successor of lithium-ion batteries,and have great potential for application in energy storage materials.Layered oxide cathode materials give them high theoretical capacity and reversible sodium ion removal due to the wide sodium ion channel in the structure,which is one of the important directions of sodium ion battery research.Among them,the manganese-based cathode material has the advantages of high theoretical capacity and easy production to make it stand out,but the influence of Jahn-Teller effect on the material structure makes their electrochemical performance in practice not ideal in practice.In view of the problem of irreversible phase transition caused by Jahn-Teller effect in sodium-ion batteries,two types of Na_0.7Fe_xMn_（1-x）O₂（NFMO）and Na_0.7Co_yFe_xMn_（1-x-y）O₂（NCFMO）manganese cathode materials were synthesized by solid phase and sol gel respectively,and assembled into batteries for electrochemical testing.SEM,XRD,XRD,XRF,XPS characterization methods and charge and discharge,cyclic voltammetry and electrochemical performance test methods were used to investigate the influence of the preparation method,doping amount（iron,cobalt）,calcination temperature on the microstructure and electrochemical properties of cathode materials,The main research contents are as follows:（1）Na_0.7Fe_xMn_（1-x）O₂（0<x≤0.5）was prepared by high temperature solid phase and sol-gel to investigate the influence of ferromanganese mole ratio and calcination temperature on the microstructure and electrochemical properties of Na_0.7Fe_xMn_（1-x）O₂materials.The results show that the iron doping stabilizes the material P2 phase crystal type,and increases the sodium layer spacing;For lamellar and P2 phase cathode material Na_0.7Fe_0.2Mn_0.8O₂（F）synthesized by solid phase method,the first-week capacity at 2-4 V is132.20 m Ah/g and 118.57 m Ah/g,and the capacity retention rate after 100 weeks is53.08%;The cathode material Na_0.7Fe_0.2Mn_0.8O₂（F1）synthesized by sol gel method has a first-week charge-discharge specific capacity of 109.61 m Ah/g and 103.61 m Ah/g at the level of 2-4 V voltage range and 0.2 C current,and the capacity retention rate after 99weeks was 46.79%.（2）The Na_0.7Co_xFe_（0.2-x）Mn_0.8O₂（0<x<0.2）manganese cathode material was prepared by high temperature solid phase,and the influence of cobalt iron manganese mole ratio（0.05:0.15:0.8,0.1:0.1:0.8 and 0.15:0.05:0.8）on the microstructure and electrochemical properties of the materials was investigated.The results show that:cobalt and iron codoping,increase the sodium layer spacing and better stabilize the material P2 phase crystal type;The molar ratio of cobalt-layered and P2 phase Na_0.7Co_0.1Fe_0.1Mn_0.8O₂materials is 0.1:0.1:0.8,and the charge-discharge capacity is 125.83 m Ah/g and 139.58m Ah/g at 2-4 V and 0.2 C current,and the capacity retention rate is increased to 58.68%after 100 weeks.The laminated,P2 phase Na_0.7Co_0.1Fe_0.1Mn_0.8O₂cathode material was prepared by sol gel method,with a capacity retention rate of 96.31%for 100 weeks within the voltage range of 2-4 V;The charge-to-discharge specific capacity of the first week in0.2 C current and 1.5-4.5 V wide voltage range reaches 226.08 m Ah/g and 159.32 mAh/g,and has good multiplier performance.