The Research Of Electrochemical Properties Of O3-Phase Layered Oxide Material As Cathode For Sodium Ion Battery

Now,lithium-ion batteries?LIBs?have been widely used in mobile electronic devices ascribed to its higher energy and power density among various secondary batteries.However,lithium-ion batteries hardly support large-scale energy storage applications for the future because of rare lithium resource and increasing cost.So it is important to develop some alternative energy storage technologies for meeting the needs of the rapid development of electric vehicles?EVs?,smart grid and clean-energy industries?Relatively,more and more researchers pay more attention to sodium ion battery because of the abundant and cheap sodium resources.It makes oxide material to an ideal cathode material due to the advantages of low cost,simple synthesis,and high capacity.O3-phase oxide has higher initial capacity,but the shortcoming of bad rate and cycling performance limits the application of O3-phase oxide in sodium ion battery.So we improve the electrochemical performance by doping some element.?1?In this article,the effect of F-doping on structural and electrochemical properties of O3-type NaNi1/3Fe1/3Mn1/3O2-x Fx?x=0,0.005,0.01,0.02 and noted as NFM-F0,NFM-F0.005,NFM-F0.01,NFM-F0.02,respectively,united as NFM-Fx?were investigated systematically for the first time about sodium ion battery.As F-doping,the rate performance and capacity retention of O3-type cathode material are significantly improved.The best cycling performance is achieved in NFM-F0.01 with a capacity of¹10 mAh g^–1 at a current density of 150 mA g^–1 after 70 cycles.And it has a capacity of 62.2 mAh g^–1 even at 300mA g^–1.F-doping allows a high Na⁺diffusion and the electrical conductivity.Besides F-doping adjusts the ratio of Mn³⁺/Mn⁴⁺,which can suppress the John-Teller distortion of Mn³⁺and play the advantage of Mn⁴⁺that can keep structure stability.?2?NaNi_0.5-xMg_xMn_0.5O₂?x=0,x=0.05,x=0.1?was synthesized by a simple solid-state reaction method.Although the initial capacity of O3-NaNi_0.5Mn_0.5O₂ would decrease because the non-active Mg has substituted for Ni element,the cycling and rate performance would be improved.NaNi_0.4Mg_0.1Mn_0.5O₂ shows the best cycling and rate performance.It delivers capacity 108.2 mAh g^–1 in a voltage range of 2.0–4.2 V at 240 mAh g^–1 and also shows a capacity of 72.5 mAh g^–1 after 150 cycles.It also exhibits a reversible capacity of75 mAh g^–1 at 1440 mA g^–1.In a voltage range of 2.0–4.4 V,NaNi_0.4Mg_0.1Mn_0.5O₂ has better cycling and rate performance(the reversible capacity of 139.2 mAh g^–1 and 58.12%capacity retention after 100 cycles at 480 mA g^–1).The reason is that Mg-doping can improve the electrical conductivity and stable the structure.