Rational Selection of Sodium Layered Oxides for High Performance Na-Ion Batteries: P2 vs O3 vs P2-O3 Intergrowths

Sodium ion batteries (NIBs) are gaining importance as an energy storage technology complementary to the Li-ion batteries. In this regard, sodium-based layered oxides are recognized as one of the most suitable positive electrode candidate for NIBs, but vast variety of their chemical compositions and crystal structures complicates the selection of the best material. To shed light on different figures of merit that control the selection of layered oxide material for NIB applications, we compare here a P2, P2-O3 intergrowth and two O3 sodium layered oxides composed of the same transition metals (Ni, Mn, Ti and Zn) but in differing stoichiometries. The results show that the new P2-type Na_0.67Ni_0.3Zn_0.03Mn_0.52Ti_0.15O₂ phase reported here combines most of the advantages, such as stability towards moisture, reduced surface reactivity, better thermal stability and high rate capability, which are essential for commercialization, except for a limited capacity (∼125 mAh g⁻¹) compared to the O3 NaNi_0.45Zn_0.05Mn_0.4Ti_0.1O₂ phase (∼180 mAh g⁻¹), reported by our group previously. Altogether, this work enlarges the family of attractive Na-based positive electrodes and teaches us that we should not solely be obsessed with the capacity of a material to decide of its applicability.