Prussian blue analogue (PBA) cathodes, built on nickel hexacyanoferrate and related hexacyanoferrate frameworks, are used mainly in sodium-ion batteries as a lower-cost, cobalt-free alternative to layered oxide cathodes. Their open framework structure allows sodium ions to move in and out during charge and discharge, which is central to the rate-capability claims that dominate this patent dataset. They are also explored in capacitor and water-treatment contexts, though those represent a small share of the filings tracked here (H01G and C02F together account for single-digit record counts).

The dataset shows a mix of Chinese universities, specialist sodium-ion battery makers and a small number of international names, with no single assignee showing sustained year-on-year growth in the most recent period. Filing activity is spread across many single-digit filers rather than concentrated at a dominant leader, which is consistent with a technology still being worked out at the process-engineering level rather than owned by one company. Recent-year momentum data suggests most previously active filers, including larger battery manufacturers, have slowed rather than accelerated.

Filings climbed from essentially zero in 2017 to a peak of 27 families in 2023, tracking the broader surge of interest in sodium-ion batteries as a cheaper alternative to lithium-ion chemistries during that period. The subsequent flattening does not necessarily mean interest has dropped: patent publication lags filing by roughly 18 months, so filings made in 2024 and 2025 may not be fully visible in this dataset yet. What the plateau does indicate is that the initial wave of foundational coprecipitation and defect-control claims has largely been staked out.

The core battery-application claims under H01M are heavily populated, but adjacent framings are thinner: capacitor-format hexacyanoferrate electrodes, wastewater-derived precursor routes, and surface-coating deposition methods each show only single-digit record counts in this dataset. Vacancy-defect quantification and crystal-water control are searched heavily as claim terms but the specific measurement and process-control methods within them are not uniformly covered. Anyone considering these branches should still run a targeted freedom-to-operate search, since low density is not the same as an open field.

Yes — of the receiving offices tracked, China accounts for 87 filings versus single-digit counts each for WIPO/PCT, the United States, Europe, India and South Korea. This means the enforceable claim scope most filers rely on has largely been examined under Chinese patent practice, and companies planning to compete in this space outside China should check separately whether equivalent protection exists, or is absent, in their target jurisdictions.