Zr4+-doped sodium manganese oxide: enhanced electrochemical performance as a cathode in sodium ion batteries†

Abstract

Sodium manganese oxides are regarded as a valuable class of cathode materials for sodium-ion batteries. By varying the stoichiometry of Na, Mn and O, it is possible to obtain layered, tunnel and spinel type structures, which can withstand the electrochemically-triggered sodiation–desodiation process. In this work, we report the electrochemical performance of Na₄Mn₂O₅, a sodium-rich manganese oxide, which has been previously reported to suffer from structural instability due to the Jahn–Teller distortion of the Mn³⁺ ion. It was observed that the Na₄Mn_2−xZr_xO₅ (x = 0.1) cathode delivered a discharge capacity of ∼203 mA h g⁻¹ post 250 cycles with a capacity retention rate of ∼82.8% on doping with Zr⁴⁺ ions. The improvement in cycling ability and rate capability is attributed to the enhanced structural stability and improved electronic conduction brought about by the substitution of Mn³⁺ by Zr⁴⁺ in Na₄Mn₂O₅. Density functional theory-based studies were conducted, which adequately support the obtained results.