Synergetic Modulation of Interlayer–Intralayer Spacings for P2-Type Layered Oxide Cathode with Superior Rate Performance

Abstract

P2-type layered transition-metal oxides have garnered considerable attention as cathode materials for sodium-ion batteries (SIBs); however, they suffer from limited capacity and structural instability during (de)sodiation processes, posing significant challenges for practical applications. Here, we address these issues by synergistically tuning the transition-metal (TM) interlayer and intralayer distances through the substitution of Na with K, achieving a stable structure denoted as Na0.62K0.05Ni0.33Mn0.67O2 (NKNMO). The K pillars induce the expansion of the TM interlayer and the contraction of the TM intralayer, which facilitates the transport of sodium ions and stabilizes the structure. Theoretical calculation and electrochemical measurements demonstrate that this P2-type cathode shows superior rate capability and enhanced anion redox activity. Specifically, the NKNMO demonstrates alleviated detrimental phase transitions and significantly reduced lattice strains during cycling at various rates, as directly revealed via advanced high-time resolution two-dimensional X-ray diffraction. The stable Na-storage lattice structure can prevent the layered structure from collapsing especially for high current density charging, leading to exceptional cycling stability with an outstanding capacity retention of 95.99% after 500 cycles at 3C. This work offers a fundamental understanding of material structure and provides important clues for developing structure-stabilized, high-performance cathode materials for SIBs.