Studies On Synthesis Of P2-type Manganese-based Oxide Cathode Materials And Their Sodium Storage Performance

In order to overcome the problems of short cycle life and low rate performance of manganese-base layered oxide as cathode materials for sodium-ion batteries.In this paper,Na_0.75Co_0.25Mn_0.75O₂ material with high sodium content was prepared by the conventional solid-state method.Eu and Ga elements are used to improve the pristine through the doping methode,respectively.XRD,FESEM,EDS,XPS,EIS,CV and galvanostatic charge-discharge tests are used to investigate the doping effects of these two elements on the pristine material’s morphology,structure and their electrochemical performence,respectively.XRD and FESEM results show that P2-type structure and layered hexagonal morphology of the pristine material is not changed by Eu-doping and Ga-doping,respectively.The results of Rietveld refinement show that Eu and Ga replace the Mn sites,respectively.After Eu-doping and Ga-doping,the lengths of a-axis and TM–O bonds are shortened,and the length of Na–O bond is increased,respectively,which makes the structure of the material more stable.The Jahn-Teller distortion effect is reduced,which is conducive to improving the cyclic stability of the prisitine material;and meanwhile,the Na layer spacing is enlarged,which gives the Na⁺broader insertion/extraction channels,thus improving the kinetic performance of the pristine material.EDS spectra show a uniform distribution of the elements.Electrochemical performance tests show that Eu-doped and Ga-doped materials present better performance than that of the prisitine material in the voltage range of 2.0–4.0 V,respectively.The Eu-doped sample Na_0.75Co_0.25Mn_0.73Eu_0.02O₂ exhibits a maximum discharge capacity of 141.70 m Ahg^-1 at 0.1 C(1 C=191 m Ag^-1),which is significantly higher than116.96 m Ahg^-1 of the pristine.The capacity retention of the Eu-doped sample after 1000cycles at 5 C is 65.65%,which is 25.69%higher than that of the pristine material.The Ga element-doped sample Na_0.75Co_0.25Mn_0.745Ga_0.005O₂ presents a high discharge capacity of 126.51 m Ahg^-1 at 0.1 C.The maximum discharge capacity of the doped sample is 60.50 m Ahg^-1 at a rate of 5 C.The capacity retention of the doped material is nearly 100%after 600 cycles,yet the capacity retention of the pristine material is 86.79%.After 1000cycles,the retention of the doped sample is 75.65%,which is significantly higher than 49.08% of the pristine material.