Na0.67Mn1−xMgxO2 (0 ≤ x ≤ 0.2): a high capacity cathode for sodium-ion batteries

Abstract

Earth-abundant Na_0.67[Mn_1−xMg_x]O₂ (0 ≤ x ≤ 0.2) cathode materials with the P2 structure have been synthesized as positive electrodes for sodium-ion batteries. Na_0.67MnO₂ exhibits a capacity of 175 mA h g⁻¹ with good capacity retention. A Mg content of 5% is sufficient to smooth the charge/discharge profiles without affecting the capacity, whilst further increasing the Mg content improves the cycling stability, but at the expense of a lower discharge capacity (∼150 mA h g⁻¹ for Na_0.67Mn_0.8Mg_0.2O₂). It was observed that the cooling process during synthesis, as well as Mg content, have an influence on the structure.