A polyanionic cathode is a positive-electrode material built around a polyanion group — phosphate, fluorophosphate or a related sulfate/silicate structure — that hosts sodium ions within a stable framework. The polyanion group's strong covalent bonding gives these cathodes structural stability across repeated charge cycles, which is why the search terms behind this dataset centre on structural stability and long cycle life. Sodium vanadium phosphate (Na3V2(PO4)3) and its fluorophosphate variant are the two most heavily filed compositions in this corpus, largely because vanadium's multiple oxidation states support a workable operating voltage for sodium-ion cells.

NASICON stands for Sodium (Na) Super Ionic CONductor, and a NASICON cathode uses a rigid three-dimensional framework of corner-sharing polyhedra to create open channels for fast sodium-ion transport. This differs structurally from layered oxide cathodes, which store sodium between stacked transition-metal-oxide sheets and tend to suffer more from structural collapse over long cycling. The NASICON structure's rigidity is precisely why carbon-coating and doping claims dominate this dataset — the framework itself is stable, so the remaining engineering problem is boosting its comparatively low intrinsic electronic conductivity, most often addressed with carbon coatings.

Vanadium phosphate and fluorophosphate frameworks have low intrinsic electronic conductivity, and carbon coating is the most direct, low-cost way to raise conductivity without altering the underlying crystal structure. The two most-cited records in this dataset, CN106328911A and CN106058202A, both centre on carbon-coated, ion-doped vanadium phosphate, which signals that combining a coating method with a dopant strategy is the claim structure the field has converged on. That combination is also why it is one of the harder claim areas to design around — most conductivity fixes touch either the coating method or the dopant choice, and the leading claims cover both.

China accounts for the large majority of receiving-office filings in this dataset, 75 of 95, with India, the United States, WIPO/PCT and the United Kingdom making up the rest in much smaller numbers. This concentration means Chinese filings set the practical boundaries of freedom-to-operate for anyone planning to manufacture or sell in China, regardless of where a company is headquartered. Filers targeting US or European markets have comparatively more open claim space, though the US-filed families in this corpus, including a highly cited fluorophosphate composite patent, show the region is not empty.

Filing activity peaked in 2025 at 26 records after rising steadily from a single filing in 2017, but the growth curve is closer to flat than accelerating once the partial, still-undercounted 2026 year is excluded. The midpoint year, 2022, already sat at 16 filings, which is not far below the eventual peak — a sign that the field found its current claim density some years before the peak rather than scaling continuously into it. Because publication lags filing by around 18 months, the most recent one to two years in any such trend will always look lower than they eventually turn out to be, so this apparent plateau should be read with that lag in mind rather than as a definitive slowdown.