Multiple Strategies toward Advanced P2-Type Layered Na_xMnO₂ for Low-Cost Sodium-Ion Batteries

Due to the high specific capacity and fast sodium-ion diffusion path, P2-type transition layered oxides have become the most promising cathode material for sodium-ion batteries (SIBs). However, poor service life, irreversible phase transitions, sensitivity to moisture, low energy density, and inevitable high-cost metals (nickel, cobalt, etc.) have slowed their development. In this work, on account of low-cost cathode alternatives to SIBs, an example of P2-type layered NaxMnO2 (NLCM) has been demonstrated, in which Li+ and Cu2+ cosubstituted in transition metal layer sites suppressed the ordered arrangement of Na+/vacancies and stabilized the structure. Furthermore, the electrochemical performance of the layered transition metal oxide was improved by optimizing the Na content in the P2-type material to 0.83 per mole. The high content of Na in the host improves the structural stability during the high-voltage stage. Li and Cu cosubstitution also activates the anion redox reaction and reduces the first-cycle coulomb efficiency, which is beneficial for commercial applications. P2-Na0.83Li0.13Cu0.2Mn0.67O2 (NLCM-083) provides a reversible capacity of 150 mA h g–1 in the voltage window of 2–4.5 V at 26 mA g–1 and 90.7 mA h g–1 at 1.0 C rate after 200 cycles with a capacity retention of about 84.6%, which demonstrated the potential of NLCM-083 as a high-performance working electrode for high-voltage SIBs.