Modulating the oxygen redox activity of an ultra-high capacity P3 type cathode for sodium-ion batteries via beryllium introduced

Abstract

Sodium-ion batteries (SIBs) show great potential for energy storage due to their good electrochemical properties and intrinsic cost performance, and sodium-ion cathode materials with high capacity and stable structure are the inevitable future development trend. While conventional anionic redox-active layered oxide cathode materials offer the advantage of extra capacity, challenges such as irreversible oxygen release still need to be addressed. Herein, beryllium is successfully introduced into P3-NaxLiyMn1-yO2 series of layered oxide materials for the first time, and the developed P3-Na0.6Li0.2Be0.25Mn0.675O2 (NLBMO) with the modulation of lattice oxygen activity can reach an ultra-high reversible capacity of 212.6 mAh g−1, significantly surpassing the P3-Na0.6Li0.2Mn0.8O2 (NLMO, 165.7 mAh g−1). Based on a comprehensive comparison with the P3-NLMO, the effect of beryllium on the Mn/O charge complementary mechanism is revealed. Since the strong covalency of beryllium can inhibit the oxidation of excess O through the formation of stable Be-O bonds, while irreversible peroxidation of partially unstable (O2)n− occurs to stimulate more Mn4+/Mn3+ to replace O for charge compensation. As a result, pollution and structural damage caused by O peroxidation are effectively suppressed while achieving ultra-high capacity. In-situ XRD reveals that P3-NLBMO exhibits high structural reversibility during charging and discharging processes, indicating that the formation of Be-O bonds can also further stabilize the crystal structure during cycling. Therefore, beryllium modification strategy proposed in this work provides a novel route to synthesize novel SIBs cathode materials with higher performance.