Synergistic Electrostatic and Mechanical Anchoring at Cathode-Current Collector Junctions for Durable Sodium-Ion...

Maintaining reliable physical and electrical contact at the cathode-current collector junction remains a critical yet underexplored challenge in sodium-ion batteries (SIBs). In particular, Na₃V₂(PO₄)₃ (NVP) cathodes undergo ∼8% volumetric fluctuations during biphasic (de)sodiation, progressively deteriorating the weak van der Waals-governed interface between the polyvinylidene fluoride (PVDF) binder and the aluminum substrate, causing electrical isolation and capacity loss. Despite the widespread industrial use of carbon-primed current collectors, a systematic understanding of their reinforcement mechanisms has been lacking. Herein, we elucidate three synergistic anchoring mechanisms through multi-scale characterization. The carbon primer enhances surface roughness to promote mechanical interlocking, provides a compliant interlayer accommodating cyclic volumetric strain without debonding, and establishes electrostatic bridging between carboxylate functional groups and the fluorinated polymer backbone, as independently confirmed by Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). Control experiments verify that the performance bottleneck lies at the junction rather than in bulk electronic conductivity, while cross-sectional wavelength-dispersive spectroscopy mapping reveals that junction integrity governs sodiation uniformity throughout the electrode thickness. The primer-integrated NVP//hard carbon full cells retain 88.7% capacity after 300 cycles, establishing a design framework for reliable cathode-current collector junctions in polyanion-based energy storage systems.