Sodium sits just below lithium on the periodic table, and the resemblance is the whole pitch: a sodium-ion battery works much like a lithium-ion one, but with an element that is vastly cheaper and available almost everywhere. No lithium price exposure, no cobalt, no geopolitically fraught supply line. The catch is physics — sodium ions are bigger and heavier, so the cells store less energy per kilogram.

The 2022 grants show the chemistry being built out in earnest. Nippon Electric Glass's US11515534B2 claims a positive-electrode active material for a sodium-ion cell. The Research Foundation for the State University of New York's US11289700B2 claims a specific KVOPO4 cathode for sodium-ion batteries. Korea-linked work in US11251426B2 claims a sodium composite transition-metal oxide cathode. These are cathode patents — the same battleground as lithium-ion, refought for sodium.

“The present invention provides a novel positive electrode active material for a sodium-ion secondary battery having a high voltage and a high capacity.”— U.S. Patent No. 11,515,534 source

What that abstract leaves out, and the claims supply, is how unusual the Nippon Electric Glass material is. This is not a conventional powdered oxide cathode — it is a glass-ceramic. Claim 1 specifies a positive electrode active material "containing crystals having at least one crystal structure selected from monoclinic, triclinic, and orthorhombic" forms, with a composition (in mole percent of oxide) of "25 to 35% Na2O, 30 to 45% CoO, and 28 to 38% P2O5+SiO2+B2O3," and crucially "an amorphous phase, in terms of % by mass, 1% or more and 30% or less." Claim 11 confirms the route: the material is made by "melting a raw material batch to obtain a melt" and "cooling the melt to obtain a glass body," then firing it to crystallize. A company that makes glass for a living is attacking the sodium cathode with glass-making, not powder metallurgy — a reminder that sodium-ion is open enough as a field that very different process backgrounds can still find a defensible niche.

The composition itself is instructive about the trade-offs. The claim leans on cobalt (30–45% CoO) and phosphate/silicate/borate network formers rather than the nickel-heavy oxides of premium lithium cathodes, and an optional formula in claim 2 allows substituting "Cr, Fe, Mn, and Ni" for some of the cobalt. That flexibility — iron and manganese as cheaper stand-ins — is exactly the cost lever sodium-ion is supposed to pull, even if this particular high-voltage formulation keeps cobalt in the mix to chase capacity. The dependent claims even fold in "a sodium ion-conductive solid electrolyte" such as "beta-alumina or NASICON crystals," tying the cathode to the broader sodium solid-state toolkit.

Does it pencil? Not for a long-range EV, where energy per kilogram is king and sodium's lower density is disqualifying. It pencils for the opposite case: stationary grid storage, where the battery sits on the ground, weight is free, and the only number that matters is cost per kilowatt-hour over the asset's life. There, sodium's cheap, stable, abundant inputs are a genuine advantage — and a glass-ceramic cathode that can be melt-processed at scale fits a cost-driven application better than it fits a weight-driven one.

The assignee data around sodium-ion in this period is the real headline: CATL, the largest cell maker on earth, shows up heavily, alongside specialist Natron Energy. When the volume leader patents a 'lower-performance' chemistry, it is not slumming — it is segmenting. CATL can serve premium EVs with high-nickel lithium and cost-sensitive grid and entry-level applications with sodium, from the same factories. The presence of a glass maker (Nippon Electric Glass), a university foundation (SUNY), and Korea-linked cathode work in the same window says the supplier base is broadening, not consolidating — the signature of a chemistry crossing from lab to roadmap.

There is a safety bonus that does not show up in the energy-density number. Sodium-ion cells tolerate being fully discharged to zero volts, which simplifies shipping and storage, and many formulations are less thermally touchy than high-nickel lithium. For grid applications where a fleet of cells sits for years, that durability has real value — and it is part of why the cost-per-kWh-over-life math can favor sodium even when the per-kilogram energy looks unimpressive on a spec sheet.

It is worth being precise about what "lower energy density" costs in practice, because the trade is real but bounded. Commercial sodium-ion cells in this era landed roughly in the range of a low-end lithium iron phosphate cell on energy per kilogram, well below high-nickel lithium — which is why no serious player proposed sodium for a long-range car. But energy density is only one column of the ledger. For a stationary asset, the columns that decide the investment are installed cost per kilowatt-hour, cycle life, calendar life, and safety, and on several of those sodium is competitive or better. A grid operator does not pay a weight penalty; it pays a footprint penalty, which is far cheaper to absorb. The patents in this cluster are written for that buyer, not for the carmaker.

The contrast with the lithium cathode patents is the clearest way to read the segmentation. A high-nickel lithium cathode patent spends its claims on coatings and residual-lithium control to chase stability at high energy density; these sodium cathode patents spend their claims on cheap, abundant network formers and melt-processable glass-ceramics to chase low cost at adequate energy density. Same battleground, opposite objective function. When the same companies file in both spaces — as CATL does — it is direct evidence that they have concluded no single chemistry wins every application, and that owning a portfolio across the cost-versus-density curve is the durable strategy.

The CPC code H01M 10/054, the office's label for sodium secondary cells, is the one to track. Its climb through 2022, concentrated among cathode filings like these three, is the signal that sodium-ion had crossed from curiosity to a chemistry that serious players intended to ship — just not into the applications where lithium already wins. The patents describe high-voltage, high-capacity sodium cathodes built from cheap, abundant inputs; the market they pencil for is the one where weight is free and cost is everything.