Electrochemical performances of P2-Na2/3Ni1/3Mn2/3O2 doped with Li and Mg for high cycle stability

Sodium-ion batteries (SIBs) have great development potential in the field of grid energy storage thanks to the abundant sodium resources. The electrochemical performances of SIBs are mainly determined by cathode materials. Among them, P2-Na2/3Ni1/3Mn2/3O2 has high capacity and structural stability. The morphology and crystal structure are affected by Na sources, and the sample with Na2CO3 as Na source has better electrochemical performances. The electrochemical performances of P2-Na2/3Ni1/3Mn2/3O2 differ dramatically depending on the cut-off voltages. P2-Na2/3Ni1/3Mn2/3O2 exhibits an initial discharge capacity of 164.7 mAh g−1 in a voltage range of 2.0–4.3 V, while the capacity retention is only 27.6% after 100 cycles. The cycle stability can be significantly improved by Li and Mg doping, respectively. However, the initial discharge capacity is obviously reduced by doping. Na2/3Li0.1Ni0.23Mn0.67O2 and Na2/3Mg0.1Ni0.23Mn0.67O2 exhibit a capacity of 121.5 mAh g−1 and 114.6 mAh g−1, respectively. The capacity retention of Na2/3Mg0.1Ni0.23Mn0.67O2 reaches 89.7% after 100 cycles.