Enhancing Long−Cycle Stability of Sodium−Ion Cathode Materials via Interlayer Hydrogen Bonding Design

Abstract

Polyanionic cathodes hold great potential for high−rate sodium−ion batteries (SIBs), yet structural instability caused by phase transitions remains a fundamental challenge for long−term cycling. Here, a new layered hybrid framework, NaFePO3CH2PO3H·H2O (NaFe-MDP), is designed by incorporating molecular−scale hydrogen bonding (H−O−H∙∙∙∙∙∙O3P−) between coordinated water and organophosphonate groups. The bisphosphonate groups in layered structure can be used as organic ligands to stabilize the transition metals and produce directional and saturated interlayer hydrogen bonds, which reinforces interlayer stability and suppresses detrimental phase transitions during cycling. Consequently, the NaFe-MDP electrode demonstrates exceptional long−term cycling stability, maintaining 87.7% of its initial capacity after 1,000 cycles at a 4C rate. The hydrogen−bonding network's structural design, validated by DFT and crystal analysis, achieves one−dimensional Na+ pathways with record ionic conductivity (up to 1.69 × 10−9 cm2 s−1). This work demonstrates a generalizable molecular design strategy for stabilizing layered polyanion cathodes in SIBs, offering novel perspectives on how dynamic hydrogen bonding in regulating structural evolution and ion transport.