Toyota is the most active recent filer in absolute terms, with 23 filings in the latest tracked year, though that count is down 89% year-on-year. Other large historical filers include Panasonic, Samsung SDI, Murata and LG Energy Solution, all of which show double-digit percentage declines in the latest year. Because publication lags filing by roughly 18 months, the most recent year understates true filing activity for every one of these companies.

No — filings peaked in 2023 at 2,170 records and have flattened since, with the 2022 midpoint at 2,046 confirming the plateau rather than continued acceleration. Recent-year momentum data reinforces this: every major assignee tracked shows a sharp year-on-year decline. This pattern is consistent with a field where the core claim space is already occupied, prompting filers to consolidate rather than expand their portfolios.

H01M (batteries, cells & fuel cells) carries the largest share of records in this corpus at 19,832, but a search limited to H01M alone misses meaningful prior art. H01B (cables, conductors & insulators) adds 2,787 records tied to ionic conductor materials, while C01B and C01G together contribute 2,630 records covering inorganic electrolyte and cathode compounds; C04B (ceramics) and C08L/C08G (polymer compositions) add further coverage for garnet processing and composite electrolytes respectively.

The thinner-density areas sit outside the core H01M cell-architecture block: polymer-ceramic composite electrolyte interfaces, garnet electrolyte sintering process control, and oxide-coating adhesion at nickel-rich cathode interfaces all show lighter filing density relative to core electrode and cell claims. This does not mean these areas are technically easier — it means the claim space is less crowded, which is different from being unclaimed outright. A freeing-to-operate and prior-art search focused specifically on these interface and process claims is more likely to surface open ground than a general cell-architecture search.

Both file heavily, and they increasingly co-file together — the Hyundai-Kia pairing alone accounts for 373 shared filings, the strongest co-assignee relationship in the dataset. Toyota's own filings, plus its co-filing with Panasonic (106 shared records), show the automaker-cell-maker alliance pattern extending across at least two major groups. Pure battery makers such as Samsung SDI and LG Energy Solution also file independently, but co-assignee pairs remain rare overall — only 10 pairs appear at scale across the entire corpus.