Ce-doping promotes the electrochemical performance of NaNi0.5Mn0.5O2

Abstract

Layered sodium ion cathode material is increasingly popular due to the superiority of low-cost and excellent rate performance. However, it usually suffers from poor capacity retention arising from microcracks during multiple-phase transitions. Herein, a Ce-doped O3-type cathode material NaNi0.5Mn0.5O2(NNM) was synthesized by high shear mixer-assisted precipitation of oxalate precursors. Using the characterizations of XRD, XPS, HRTEM, GITT, etc., the results indicate that Ce dopants can adjust the initial phase structure as well as postpone the phase transition in such O3-type material. The optimal NNM-0.06Ce shows a superior initial discharge capacity of 128.3 mAh g−1 and a retention of 85.96% after 100 cycles (1.5–4.0 V, 1 C, 25 °C), as well as superior rate performance of 107 mAh g−1 at 5 C. HAADF-STEM images disclose that the doped Ce atoms are probably located in the sodium layer of the cathode material, moreover, DFT calculations reveal that the Ce dopant is prone to occupy the Na site and cause charge rising of Ni and Mn. In-situ XRD tests indicate that the earlier formed O1 phase induced by Ce dopants can postpone the phase transition and increase the reversibility of the cathode, therefore improving the electrochemical performance of cathode materials.