Modified Preparation And Performance Study Of Cathode Materials For NMO Sodium Batteries

Lithium-ion batteries have the advantages of high energy conversion efficiency and easy maintenance,and have been used in large-scale energy storage.However,with the application of lithium-ion batteries in the field of large-scale energy storage equipment,this has also accelerated the speed of lithium mining.The uneven distribution of lithium resources and low storage capacity have led to an increase in the production cost of lithium-ion batteries,and these factors have restricted the development of lithium-ion batteries.Due to the better safety of sodium batteries,sodium ion batteries will be easier to achieve large-scale applications in the future.Layered oxide is considered to be the most promising sodium ion cathode material due to its higher theoretical specific capacity,but its inherent low electronic conductivity and poor structural stability have affected its further development.In this paper,we first synthesize NaMnO₂ materials with different methods,and then improve the conductivity and structural stability through doping modification,test its electrochemical performance,further optimize the experimental conditions according to the results,and explore the optimal synthesis route.The main research contents are as follows:（1）Firstly,the NaMnO₂ materials were synthesized according to the co-precipitation method,and the electrochemical properties of the materials at different temperatures were investigated according to the orthogonal test,and the conditions were optimized according to the experimental results.Subsequently,the NaMnO₂ materials were prepared by different preparation methods（co-precipitation,liquid phase and solid phase）to investigate the influence of different preparation methods on the electrochemical properties of the materials and to improve the cycling performance.The electrochemical data showed that the NaMnO₂-assembled sodium ion battery obtained by co-precipitation method at 800℃could maintain a specific capacity of about 40 m Ah/g after 100 cycles at a current density of 2 C.The preparation method was better than the other two preparation methods.（2）In order to improve the capacity of NaMnO₂ materials and slow down the capacity decay caused by the structural deformation during the cycling process,they were firstly nickel-doped and some of the manganese elements were replaced by nickel to investigate the effect of nickel and manganese content on the electrochemical properties of the materials.The electrochemical data showed that the initial discharge capacity of Na Ni_0.4Mn_0.6O₂ was 141.2m Ah/g at a current density of 2 C.After 100 cycles,the specific capacity was 72.8 m Ah/g,and the capacity retention rate was about 79.7%.Subsequently,in order to further improve the cycling stability of the material,some manganese elements were replaced by cobalt.According to the results of electrochemical data,Na Ni_0.4Mn_0.5Co_0.1O₂ at a current density of 2 C had an initial discharge capacity of 142.9 m Ah/g and still maintained a specific capacity of 83.7 m Ah/g after 100 cycles,which was better than the other materials.This is mainly attributed to the moderate amount of nickel doping which can increase the capacity of the material,and the reduction of manganese content which helps to reduce the Jahn-Teller effect during the cycling process of the electrode material and reduces the capacity degradation.In addition,the electrochemical data shows that excessive nickel doping not only does not increase the capacity,but also leads to a decrease in the electrochemical performance,which may be due to the high content of nickel will quickly absorb water,which affects the performance of the organic system battery.Therefore,a moderate amount of ternary doping can help to improve the electrochemical performance.（3）In order to further enhance the long cycle stability and multiplicity performance of the anode materials,Na_1-xLi_xNi_0.4Mn_0.5Co_0.1O₂ materials were prepared by using Li⁺sodium doping.The effect of Li⁺doping on the electrochemical properties was investigated.The electrochemical data showed that Na_0.9Li_0.1Ni_0.4Mn_0.5Co_0.1O₂ could maintain a specific capacity of 94.2 m Ah/g after 100 cycles at a current density of 2 C.The capacity retention rate was76.6%,which was better than other doping ratios.The results show that the metallic Li+doping can effectively improve the electrochemical performance of the electrode material and reduce the polarization of the material.However,with the increase of Li content,the electrochemical performance of the material decreases.Therefore,an appropriate amount of Li doping can improve the electrochemical performance.（4）To further investigate the performance of the material in the full cell,a simple and low-cost method was used to prepare the phosphorus-doped carbon anode material by recycling waste tires and to investigate its sodium storage properties.Subsequently,Na_0.9Li_0.1Ni_0.4Mn_0.5Co_0.1O₂ was assembled with the phosphorus-doped carbon material in a whole cell to test the electrochemical performance.At a current density of 2 C,the initial discharge capacity was 72.4 m Ah/g,and the specific capacity of about 40 m Ah/g was maintained after 50 cycles with a specific energy of about 100 Wh/kg,proving the possibility of its full-cell application and laying the foundation for the further development of sodium-ion full-cell batteries in the future.