Study on the effect of co-substitution of transition metals on O3-type Na-Mn-Ni-O cathode materials for promising sodium-ion batteries

The substitution of small quantity of electrochemically inactive and active elements described a propitious strategy for sodium-ion batteries (SIBs) to enrich the structural stability and electrochemical performance of O3-type cathodes. We prepared the co-substitution of (Cu and Ti) O3-Na0.9Mn0.60Ni0.30Cu0.05Ti0.05O2 (MNCT), (Ti and Mg) O3-Na0.9Mn0.60Ni0.30Ti0.05Mg0.05O2 (MNTM), (Mg and Cu) O3-Na0.9Mn0.60Ni0.30Mg0.05Cu0.05O2 (MNMC), and bare O3-Na0.9Mn0.60Ni0.40O2 (MN) cathode materials by typical solid state reaction for SIBs. From Rietveld refinement, the MNCT, MNTM and MNMC cathode materials revealed a rhombohedral structure with the space group (R-3m), in which sodium ions occupied octahedral site. The MNCT, MNTM, MNMC and MN electrodes have discharge capacities of 184, 179, 174, and 218 mAh g−1 in a voltage range of 2–4 V at 0.1C rate, respectively. The bare MN system suffered the structural stability, it was rectified upon co-substituting with two different combinations using the partial amount of copper (Cu), titanium (Ti) and magnesium (Mg). The substitution in transition metal oxide (TMO2) layers enriched structural immovability of the O3-type cathode materials during electrochemical reaction for rechargeable SIBs.