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

Abstract

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_2/3Li_1/18Ni_5/18Mn_5/18Ti_5/18Fe_2/18O₂ (NLNMTF) biphasic layered cathodes, in which thermodynamics and crystal structure are designed to improve reversible capacity and cycling performance. The NLNMTF₃ 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 NLNMTF₃ 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.