The Three Sodium-Ion Cathodes: Layered Oxide, NFPP and Prussian Blue

Cell research · sodium-ion

"Sodium-ion" names the ion that moves, not the cathode it moves into. Three cathode families are on the market, and they behave very differently.

The cathode sets the voltage window, the shape of the discharge curve, the cycle life and the energy density. Check it before you set a BMS.

The lithium cousins

If you know NMC and LFP, you already know two of them

Layered oxide ≈ NMC
Same structure, sodium in place of lithium
Both are layered metal oxides: sheets of metal and oxygen with the ions sliding in between. NMC uses nickel, manganese and cobalt. Sodium layered oxide (often called NFM) usually uses nickel, iron and manganese, and no cobalt. Like NMC, it runs at a higher voltage, slopes steadily and packs more energy per kilogram than its phosphate cousin.
NFPP ≈ LFP
Both are iron phosphates
NFPP is sodium iron phosphate pyrophosphate; LFP is lithium iron phosphate. Iron plus phosphate is the common thread: no nickel or cobalt, and the phosphate holds its oxygen tightly. That is why both are known for thermal stability and long cycle life, at the cost of energy density.

Where the analogy breaks. The sodium versions run lower and swing wider than their lithium cousins. NFPP's flat plateau is much shorter than LFP's, and layered oxide slopes more than NMC. Low-cost layered oxide cells like ours lean on iron and manganese rather than nickel. Prussian blue has no common lithium cousin.

Side by side

Typical ranges by family

Layered oxide Polyanion (NFPP) Prussian blue
Lithium cousin NMC LFP none in common use
Nominal voltage 3.0 to 3.2 V about 3.0 V about 3.2 V
Voltage window about 1.5 to 4.1 V about 1.5 to 3.7 V about 2.0 to 4.0 V
Energy density 80 to 160 Wh/kg, by recipe 80 to 110 Wh/kg moderate
Discharge curve smooth, steady slope plateau, then slope sloping
Best for general use, mobility, weight-sensitive builds stationary storage, high current, long life low-cost bulk storage

Typical published ranges. Every cell's own datasheet wins over this table.

Layered oxide

A wide family, not one recipe

High-nickel versions chase energy density and land near the top of the range. Low-cost iron and manganese versions trade energy for price, rate and cycle life, and land near the bottom. Our current layered oxide 18650 measures about 89 Wh/kg on paper with a 15C rating, which puts it at the iron and manganese end.

On the bench

How to tell them apart

A slow discharge curve gives it away. Layered oxide slopes smoothly from top to bottom, like a gentler NMC. NFPP settles onto a flat plateau near 3.0 V before it slopes, a shorter version of LFP's flat line. You can see all three in our bench test of sodium 18650s against LFP.

Related: NFPP vs NFM · Is sodium-ion right for your build? · Layered oxide 18650 · NFPP 18650

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