Stable high-voltage operation of oxygen redox in P2-type Na-layered oxide cathode at fast discharging via enhanced kinetics

Sluggish kinetics and structural instability caused by oxygen redox can lead to poor electrochemical performance of cathode materials, resulting in a much lower operating voltage during discharging than charging (especially at high current densities) and poor power-capability. Additionally, undesirable phase transitions during charge/discharge negatively affect the electrochemical performance of oxygen-redox-based P2-type Mn-based layered oxide cathodes. In this study, we demonstrate the successful stabilization of oxygen redox in P2-type Mn-based layered oxide cathodes through the synergy of Cu-Co. Particularly, the discharge operation voltage and energy density during fast charging are significantly enhanced. The average discharge voltage difference of P2-type Na_0.67[Cu_0.2Co_0.2Mn_0.6]O₂ between 10 and 1000 mA g⁻¹ is approximately ∼0.18 V, respectively, which is distinctly different from the case of P2-type Na_0.67[Cu_0.2Mn_0.8]O₂ showing differences of approximately ∼0.36 V under the same conditions. Moreover, after 100 cycles, the discharge capacity of P2-type Na_0.67[Cu_0.2Co_0.2Mn_0.6]O₂ with oxygen redox is retained to ∼93% of the initial capacity, due to both a small volume change during charge/discharge (∼0.6%) and successful suppression of undesirable phase transition of P2-OP4. The outcomes of this study underscore the viability of employing oxygen-redox-based P2-type Na-layered oxide as a reasonable method for achieving exceptional high-rate and high-voltage performance.