Manipulating thermodynamics and crystal structure modulates P2/O3 biphasic layered oxide cathodes for sodium-ion batteries

• The thermodynamic origin of P2/O3-Na 2/3 Li 1/18 Ni 5/18 Mn 5/18 Ti 5/18 Fe 2/18 O 2 is unravelled. • DFT calculations reveal the most thermodynamically favorable NLNMTF 3 . • Attractive reversible capacity, cycling performance and rate capability are achieved. • The maximum O3-phase content (70.27%) and enlarged Na interslab distance underpin the enhancement. Engineering high-performance layered oxide cathode materials is crucial for promoting the practical application of sodium-ion batteries (SIBs). One highly effective method by biphasic hybridization (such as P2/O3) is typically used to enhance reversible capacity and cycling stability. However, creating the optimal biphasic ratio is not yet well understood. Here, an insight into thermodynamics origin is unveiled within P2/O3 Na 2/3 Li 1/18 Ni 5/18 Mn 5/18 Ti 5/18 Fe 2/18 O 2 (NLNMTF) biphasic layered cathodes, in which thermodynamics and crystal structure are designed to improve reversible capacity and cycling performance. The NLNMTF 3 cathode optimized upon 15 h of calcination, which is the most thermodynamically favorable as revealed by density functional theory calculations, exhibits both the maximum O3-phase content (70.27%) and the enlarged Na interlayer distance. Significantly, the NLNMTF 3 cathode delivers a high reversible capacity of 97.8 mAh g −1 at 0.1C, superior rate capability of 78.8 mAh g −1 at 5C, and excellent capacity retention of 85.5% after 500 cycles at 1C. These results highlight the role of thermodynamics and crystal structure in optimizing high-performance biphasic P2/O3 layered oxide materials for SIBs. The most thermodynamically favorable P2/O3-Na 2/3 Li 1/18 Ni 5/18 Mn 5/18 Ti 5/18 Fe 2/18 O 2 is optimized to exhibit the maximum O3-phase ratio (70.27%) and the enlarged Na interslab distance, achieving an attractive reversible capacity (97.8 mAh g −1 at 0.1C), capacity retention (85.5% after 500 cycles at 1C), and rate capacity (78.8 mAh g −1 at 5C).