Synthesis and Electrochemical Study of New P3 Type Layered Na_0.6Ni_0.25Mn_0.5Co_0.25O₂ for Sodium-Ion Batteries

The room temperature stable P3 type Na_0.6Ni_0.25Mn_0.5Co_0.25O₂ phase was studied as an interaction material for Na ion batteries. The phase was synthesized by mixed hydroxide co-precipitation method followed by heating at 750 °C in air. The phase purity was analyzed by means of Rietveld refinement using GSAS software. X-ray photoelectron spectroscopy (XPS) analysis showed that Co, and Mn are in oxidation states of 3+ and 4+, respectively, and Ni is in 2+ and 3+ oxidation states. The electrochemical properties of this layered material as a cathode delivered the reversible discharge capacity of 105 and 130 mAh/g at C/10 rate in the voltage window of 1.5-3.6 and 1.5-4.0 V vs. Na⁺/Na, respectively. The good capacity retention and nearly 99 % of coloumbic efficiency was observed. The Na insertion and de-insertion was occurred by reversible phase transitions as evidenced by ex-situ powder X-ray diffration. With increasing cutoff voltage to 4.4 V, the ex-situ powder X-ray diffration pattern indicated that the existence of P3 phase at high Na de-insertion.