Effect of 3D Metal on Electrochemical Properties of Sodium Intercalation Cathode P2-Na_xMe_(1/3)Mn_(2/3)O2 (M = Co, Ni, or Fe)

摘要

This research aims to evaluate the influence of different 3D metals (Fe, Co, and Ni) substituted to Mn on the electrochemical performance of P2-Na_xMe_(1/3)Mn_(2/3)O2 material, which was synthesized by the coprecipitation process followed by calcination at high temperature. X-ray diffraction (XRD) results revealed that the synthesized Mn-rich materials possessed a P2-type structure with a negligible amount of oxide impurities. The materials possessed their typical cyclic voltammogram and charge-discharge profiles; indeed, a high reversible redox reaction was obtained by Na_xCo_(1/3)Mn_(2/3)O2 sample. Both Na_xCo_(1/3)Mn_(2/3)O2 and Na_xFe_(1/3)Mn_(2/3)O2 provided a high specific capacity of above MOmAh·g~(-1); however, the former showed better cycling performance with 83% capacity retention after 50 cycles at C/10 and high rate capability. Meanwhile, the Ni-sub Na_xNi_(1/3)Mn_(2/3)O2 exhibited excellent cycling stability but a low specific capacity of 110 mAh·g~(-1) and inferior rate capability. The diffusion coefficient of Na~+ ions into the structure tended to decrease with a depth of discharge; those values were in the range of 10~(10)-10~(-9) cm~2·s~(-1) and 10~(-11)-10~(-10) cm~2·s~(-1) in the solid solution region and biphasic region, respectively.