Multi-Ion Doping Modification And Electrochemical Performance Of Layered Cathode Materials For Sodium Ion Batteries

Due to high abundance,low cost,and similar chemical properties to Li,sodium-ion batteries are considered as an ideal alternative to lithium-ion batteries and are expected to be used in large-scale energy storage devices.The positive electrode material is the key to sodium ion batteries,which determines its energy density,cycle life,and safety.However,the larger the radius of Na⁺ is,the more difficult to find the host material suitable for Na⁺ intercalation.Layered transition metal oxides have become hotspots in the field of cathode materials due to their high discharge capacity,abundant electrochemically active elements,and wide Na⁺ diffusion channels.Although layered metal oxides have obvious advantages,there are still some problems that need to be solved urgently,such as obvious irreversible phase transition at high voltage,poor structural stability and cycle stability.In this paper,materials are modified by polyion doping,and the structure,morphology,and electrochemical performance of a series of materials are investigated by SEM,TEM,XRD,XPS,and electrochemical testing methods.The main research contents and conclusions are as follows:Aiming at the problem of poor long-cycle stability of the P2-sodium layered cathode material,Mg/Al/Fe and Mg/Al/Ti were used to co-dopped Na_2/3Mn_2/3Ni_1/3O₂ with multiple ions.The research results show that the multi-doping method can stabilize the crystal main structure of the material and improve the reversibility of the electrochemical reaction.Among them,the multicomponent material Na_2/3Mn2/3Ni_0.21Mg_0.05Al_0.03Fe_0.03O₂ has the best electrochemical performance.The discharge capacity of the material at 1 C rate for the first cycle was 128.1 mAh·g-1,and after 100 cycles,the discharge capacity was 98.8 mAh·g-1,and the capacity retention rate was still 79.5%.Effectively improve the electrochemical performance of materials.In order to further improve the structural stability of the P2-sodium layered cathode material and achieve a long cycle life,Zr⁴⁺?0.79 A?and Ce⁴⁺?0.87 A?with larger ionic radius were selected to replace the Fe3+?0.66?in the previous multi-component material.A)and Ti⁴⁺?0.605 A?for multi-ion doping.The results show that the doping of Zr⁴⁺ and Ce⁴⁺ make the structure of the transition metal layer more stable,effectively inhibits complex phase transitions,reduces the shrinkage and expansion of the volume of the material,enhances the structural stability of the material,and thus enhances the cycle stability of the material.The initial cycle discharge capacity of the multi-component materials at 1 C are 105.4 and 103.4 mAh·g-1,after 300 cycles,with a specific capacity of 89.3 and 90.2 mAh·g-1,the capacity retention rates are as high as 84.7%and 87.2%,which are showing excellent long cycle life.Based on the above research results,the problems of poor cycle stability and rate performance of the 03-sodium layered cathode material are addressed.O3-NaMn0.5Ni0.5O2 was modified by Fe/Ti co-doping.At the same time,by further optimizing the Na content,the phase structure and crystal structure of the material are optimized.The results show that the charge-discharge curves of the multi-ion doped O3-NaxMn0.3Ni0.25Fe0.3Ti0.1O2 material are relatively smooth,indicating that the multi-ion doping is very good at inhibiting the complex phase transition of the material,and Na 1.0 material has the best electrochemical performance.The discharge capacity of the material at 1 C rate in the initial cycle is 112.5 mAh·g-1,and the capacity retention rate can still reach 79.8%after 200 cycles,and its stability is higher than that of most 03 materials reported in the literature.