Characterization of a thin, uniform coating on P2-type Na_2/3Fe_1/2Mn_1/2O₂ cathode material for sodium-ion batteries

A thin, uniform carbon coating on Na_2/3Fe_1/2Mn_1/2O₂ (NFMO) using 2,3-dihydroxynaphthalene (DN) was prepared. Pristine and DN-coated samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). An amorphous nanolayer coating of carbon is obtained on the surface of the layered pristine material. The 0.2 wt% DN-coated NFMO exhibits excellent electrochemical performance. An initial discharge capacity of 178 mA h g^-1 was obtained at a C-rate of 0.1 C; this capacity is 20% higher than bare NFMO. Capacity retention (77.8% at the 50th cycle) is also maintained comparable to bare NFMO (77.7% at the 50th cycle). The thin and uniform carbon layer leads to improvement of charging and discharging kinetics and protects against direct contact between cathode and electrolyte.