Stable High-Voltage Operation of Anionic Redox on P2-Type Na-Layered Cathode at Fast Discharge through Improved Kinetics

Sluggish kinetics and structural instability from oxygen redox can result in suboptimal electrochemical performance for cathode materials. This leads to a considerably lower operating voltage during discharge, especially at high current densities, and compromises power capability. Undesirable phase reactions during charge/discharge further hinder the electrochemical performance of oxygen-redox-based P2-type Mn-based layered oxide cathodes. Our study demonstrates the successful stabilization of oxygen redox in these cathodes through the cooperative synergy of Cu-Co. Specifically, this synergy significantly enhances the discharge operation voltage and energy density during fast charging. For instance, the discharge voltage difference for P2-type Na 0.67 [Cu 0.2 Co 0.2 Mn 0.6 ]O 2 between 10 and 1000 mA g − 1 is approximately ~0.18 V, contrasting sharply with P2-type Na 0.67 [Cu 0.2 Mn 0.8 ]O 2 , which exhibits differences of around ~0.36 V under the same conditions. Furthermore, after 100 cycles, the discharge capacity of P2-type Na 0.67 [Cu 0.2 Co 0.2 Mn 0.6 ]O 2 with oxygen redox remains at ~93% of the initial capacity. This is attributed to both a minimal volume change during charge/discharge (~0.6%) and the successful suppression of undesirable phase transitions in P2-OP4. These findings highlight the feasibility of utilizing oxygen-redox-based P2-type Na-layered oxide as an effective approach for achieving outstanding high-rate and high-voltage performance.