Cu-doped NaCu 0.05 Fe 0.45 Co 0.5 O 2 as promising cathode material for Na-ion batteries: synthesis and characterization

In this work, Cu-doped NaFe0.5Co0.5O2 was easily prepared by a one-step solid-state reaction and studied the effect of copper salt precursors including CuCl2 and Cu(OAc)2 on the structure and electrochemical properties. XRD patterns of the synthesized materials all exhibited diffraction peaks of O3-type layered oxide with high crystallinity and negligible impurity of halide compound. Using Cu(OAc)2 precursor showed a well-defined voltage profile feature of NaFe0.5Co0.5O2 material and a superior performance in sodium half-cell. Doped samples exhibited a capacity of 130 mAh g−1 which is higher than pristine NaFe0.5Co0.5O2 and good capacity retention for 100 cycles. Ex situ XRD results indicated the complex phase transition above 4 V on the first charge, but the structure of the Cu-doped materials remained O3-type layered after the end of cycling. Additionally, Cu-doping effectively enhanced Na+ diffusion coefficients also indicated using the cyclic voltammetry method.