Nanometric P2-Na2/3Fe1/3Mn2/3O2 with controlled morphology as cathode for sodium-ion batteries

P2-Na2/3Fe1/3Mn2/3O2 was synthesized by an emulsion-based method. This preparative route provides a crystalline and high-purity sample with homogeneous distribution of the elements. The polycrystalline material contains nanometric particles and the morphology is controlled by the surfactant content. The effect of the nanometric texture on the performance in sodium test batteries was clearly evidenced by better coulombic efficiencies and lower cell polarization of nanometric P2-Na2/3Fe1/3Mn2/3O2 as compared to a sample of the same composition with micron-size particles. The kinetic improvement was related to low internal cell impedances and higher sodium diffusion coefficient. The superior performance found for the nanorod-like layered oxide assembled in a full Na-ion test cell allows envisaging this material as a potential candidate for the positive electrode of future Na-ion batteries.