Unveiling Ni/Mn synergies in P2/O3 biphasic layered oxides for high‐performance sodium‐ion battery cathodes

Abstract P2‐type nickel–manganese‐based layered oxides are promising cathode materials for sodium‐ion batteries (SIBs), but their application is limited by initial specific capacity and anion redox instability. Herein, a P2/O3 biphasic Na 0.67 Ni 0.33 Mn 0.6 Cu 0.05 Mg 0.07 Ti 0.01 O 2 (Ni33Mn60) was prepared by adjusting the Ni/Mn ratio with as Na 0.67 Ni 0.23 Mn 0.65 Cu 0.05 Mg 0.07 Ti 0.01 O 2 (Ni23Mn65) matrix and is reported to exhibit high initial discharge capacity, cyclability and rate capability. The density functional theory (DFT) calculation and experimental data prove the enhancement of the Mn 3+ /Mn 4+ redox process to improve the specific discharge capacity and the P2/O3 biphasic structure to optimize the anion kinetics. The synthesized oxide Ni33Mn60 delivers a high initial discharge specific capacity of 140.21 mAh g −1 , a crucial discharge capacity of 76.07 mAh g −1 at 10C, a preferable capacity retention rate of 78.97% after 200 cycles at 5C and cycle stability at high voltages above 4.3V. In situ X‐ray diffraction (XRD) and galvanostatic intermittent titration technique (GITT) tests show that Ni33Mn60 has reversible structure evolution and fast Na + diffusion kinetics due to the ion effect and unique P2/O3 biphasic structure, respectively. This work provides a new thought about adjusting matrix ratio for the preparation of P2/O3 biphasic cathode materials for advanced SIBs.