Sm-doped P2-type layered oxide with spherical secondary hierarchy as cathode material for sodium-ion batteries

Abstract

With the development of sodium ion battery which is considered as the alternative of lithium ion battery, better performance is required. However, its poor structure stability and rate capability due to the Jahn–Teller distortion of Mn³⁺ and poor charge transfer between transition metal and oxygen-ion limit its application. Here, Sm-doped P2-type layered oxide Na_0.67Li_0.1Mn_0.62Fe_0.18Cu_0.09Sm_0.01O₂ with spherical secondary hierarchy was obtained through microwave-assisted method. Pure P2-shaped layered oxide is obtained. And the tiny shift of the diffraction spectrum indicates the effect of doping. The electrochemical performance of the doped oxide improves obviously. Even at a high current density of 1.0A g⁻¹, the capacity is still as high as 60.3 mAh g⁻¹, much higher than that of undoped one. The cycle stability is also improved. Electrochemical impedance spectroscopy (EIS) and Distribution of relaxation times (DRT) are taken to further study the mechanism. It reveals that the doped samarium not only serves as the pillar to stable the structure of the layered oxide, but also makes faster charge transfer between transition metal ions and oxide ions due to the Multielectron structure of samarium. Thus, such Sm-doping strategy may offer a solution toward the application bottleneck of layered oxides for sodium-ion batteries.