Strengthening the susceptible interphase of layered oxide cathodes via eco-friendly aqueous binders

Layered oxides present compelling potential as cathode materials for sodium-ion batteries (SIBs). However, challenges including interfacial instability and sluggish reaction kinetics critically limit their rate capability and cycling performance. Herein, we introduce the water-soluble sodium polyacrylate (NaPAA) binder as a promising approach to mitigating these issues in P2-type layered oxides. The NaPAA binder facilitates the formation of a uniform Na⁺ conductive interfacial film, which protects the cathode against electrolyte-induced corrosion and effectively inhibits the dissolution of transition metals in P2-Na_0.85Li_0.12Ni_0.22Mn_0.66O₂ (NLNMO). Furthermore, we elucidate the mechanism by which the NaPAA binder dynamically regulates the coordination of free anions at the electrode–electrolyte interface. This regulation reduces solvent decomposition and promotes the formation of a stable, ionically conductive layer. Consequently, the P2-NLNMO@NaPAA integrated electrode exhibits enhanced electrochemical performance, achieving an 89.2 % capacity retention after 200 cycles at 0.2 C and delivering an initial capacity of 102.9 mA h g⁻¹ even at 0 °C. This study advances the fundamental understanding of binder-mediated interface engineering and demonstrates a scalable and eco-friendly manufacturing pathway for high-performance SIBs.