Modification And Electrochemical Properties Research Of Layered Manganese Base Cathode Materials For Sodium Ion Batteries

Sodium ion battery has attracted a lot of attention due to the abundent original materials and low-lost compared with lithium ion battery.And O3 type layered manganese base NaMn_0.5Fe_0.25Ni_0.25O₂ has been favored by people on account of the high theoretical capacity and enough Na content.However,there are always some irreversible phase change occurred in NaMn_0.5Fe_0.25Ni_0.25O₂ during the charge/discharge processing,which lead a low structural stabilization.The problem still exists and restrict the development of NaMn_0.5Fe_0.25Ni_0.25O₂material.In this paper,we have synthesized the NaMn_0.5Fe_0.25Ni_0.25O₂ material.by nano ball mill spray method.owning to it’s simple operation,environmental friendly and suitable for industrial production.And we obtained that ball milling for 40min and sintering at 900℃are the optimal synthetic process.The sample synthesized through the optimal way exhibited a first discharge capacity of 149.9 mAh g^-1 at 0.1C rate.On the basis of the optimal synthetic route,we used the Zn²⁺subsititution in the transition metal layer positions to improve the structural stabilization of NaMn_0.5Fe_0.25Ni_0.25O₂material,and then reducing the irreversible phase change.The results showed that the electrochemical proformance of NaMn_0.5Fe_0.25Ni_0.25O₂ material had a distinctly enhancement through the Zn²⁺subsititution.When the Zn²⁺subsititution content was 4%,the NaMn_0.46Fe_0.25Ni_0.25Zn_0.04O₂ material exhibited a highest first discharge capacity of 165.9mAh g^-1 at 0.1C and a best cycle performance with retention of 90.12%after 50 cycles at 1C.Accroding to the tests and results,we found the Zn²⁺went into the transition metal layer by replacing the Mn³⁺positions,and meanwhile,in order to maintain a balance valence,a part of Mn³⁺（0.645?）has changed into Mn⁴⁺（0.53?）.On the one hand,it may lead a thickness reduction of transtion metal layer and a increase of Na layer.which help to reduce the Jahn-Teller distortion cased by Mn³⁺.On the other hand,it may alleviate the Jahn-Teller effect made by Mn³⁺.And meanwhile,Zn²⁺was invariable during the sodiun ion insertion and extrication process to stabilize the structure,which lead a good structural stabilization.Finally,we have improved the structure stability of NaMn_0.5Fe_0.25Ni_0.25O₂ material during the charge./discharge process through the NiO surface coating in the paper.The NiO/NaMn_0.5Fe_0.25Ni_0.25O₂ exhibited a higher discharge capacities especial at 5C current,which increased it by 35.7mAh g^-1 compared with NaMn_0.5Fe_0.25Ni_0.25O₂,and the retention increased it by 6.81%after 50 cycles at 1C.On the one hand,the enhancements may cause by that NiO surface coating increase the conductivity and ion diffusion coefficient,which lead a good electrochemical proformance.On the other hand,NiO surface coating avoided the immediate contact between NaMn_0.5Fe_0.25Ni_0.25O₂ material and electrolyte to decrease the unnecessary side cffects...