Mg-Doped O3-Na[Ni0.6Fe0.25Mn0.15]O2 Cathode for Long-Cycle-Life Na-Ion Batteries

The O3-type layered oxide materials have the advantage of high specific capacity, which makes them more competitive in the practical application of cathode materials for sodium-ion batteries (SIBs). However, the existing reported O3-type layered oxide materials still have a complex irreversible phase transition phenomenon, and the cycle life of batteries needs, with these materials, to be further improved to meet the requirements. Herein, we performed structural characterization and electrochemical performance tests on O3-NaNi0.6−xFe0.25Mn0.15MgxO2 (x = 0, 0.025, 0.05, and 0.075, denoted as NFM, NFM-2.5Mg, NFM-5.0Mg, and NFM-7.5Mg). The optimized NFM-2.5Mg has the largest sodium layer spacing, which can effectively enhance the transmission rate of sodium ions. Therefore, the reversible specific capacity can reach approximately 148.1 mAh g−1 at 0.2C, and it can even achieve a capacity retention of 85.4% after 100 cycles at 1C, demonstrating excellent cycle stability. Moreover, at a low temperature of 0 °C, it also can keep capacity retention of 86.6% after 150 cycles at 1C. This study provides a view on the cycling performance improvement of sodium-ion layered oxide cathodes with a high theoretical specific capacity.