Synthesis And Properties Improvement Of P2-Type Na_0.67(Mn_0.5Fe_0.25Co_0.25)O₂ Cathode Material For Na-Ion Batteries

As current energy issues become more prominent,sodium-ion batteries have received widespread attention due to their abundant sodium source.Among them,P2 type-Na₀.₆₇(Mn_0.5Fe_0.25Co_0.25)O₂ cathode material is a representative material of sodium ion battery cathode material.It has a high specific capacity（It shows a large initial discharge capacity of195 mAh g when cycled between 1.5 and 4.5 V at 0.1C）.However,the material also has the drawback of poor cycle performance（the capacity retention rate is only 74%after 20 cycles）.In this paper,the material was synthesized by solid-state method assisted by nano-ball mill in the laboratory,and the optimum technological parameters for the synthesis of the material were also determined as follows:the milling time was 1.5h,the calcination temperature was 900 C and the calcining time was 12h.Under this process parameter,the material has the best material properties.On this basis,the Li ion substituted method was adopted to improve the performance of the material,which significantly improved the cycle performance of the material（after 30cycles,the capacity retention rate increased by 15.3%）,and the rate performance has also been improved very well.At the same time,the decrease of polarization fo r the Li-substituted battery plates,the decrease of Rct value of charge transfer impedance and the increase of sodium diffusion coefficient are three important reasons for the improvement of material properties by using various kinds of test characterization methods（Such as XRD,SEM,CV,EIS,etc.）.Further studies have also found that Ti ion substitution can also improve the cycle performance of the material（after 30 cycles,the capacity retention rate increases by 16%）and the rate performance.Similarly,through the application of XRD,SEM,EIS and the calculation and analysis of the diffusion coefficient of sodium ions,it is proved that the substantial increase of the diffusion coefficient of sodium ions is an important reason which improve the material properties after Ti ion substitution.