Sodium-Ion 18650 Test Report v1: NFPP and Layered Oxide vs LFP
We put two sodium-ion 18650 cells and an LFP 18650 on our battery tester and ran each one through a full charge and discharge at about 0.5C, at room temperature.
All three cells delivered within about 5% of their rated capacity, and every bit of charge we put in came back out. The more useful part for builders is the shape of the curves: they explain why sodium-ion needs different BMS and inverter settings from LFP.
What we tested and how
Each cell was charged with the standard method from its datasheet: constant current until it reached its top voltage, then held at that voltage until the current fell to 0.1 A. After a short rest we discharged it at a constant current to its rated cutoff voltage. Room temperature, one cell at a time, on a ZKETECH EBC-A20 tester.
The sodium cells here are earlier batches (900 mAh NFPP and 1,300 mAh layered oxide). The cells we stock now are the 850 mAh NFPP and 1,100 mAh layered oxide; they are next on the bench.
Capacity at about 0.5C
| Cell | Window | Current | Capacity | Of rating | Energy |
|---|---|---|---|---|---|
|
Sodium-ion NFPP Rated 900 mAh (earlier batch) |
3.70 → 1.50 V | 0.45 A | 851 mAh | 95% | 2.34 Wh |
|
Sodium-ion layered oxide Rated 1,300 mAh (earlier batch) |
3.95 → 1.80 V | 0.65 A | 1,216 mAh | 94% | 3.51 Wh |
|
LFP (lithium reference) Rated 1,500 mAh |
3.65 → 2.50 V | 1.00 A | 1,446 mAh | 96% | 4.15 Wh |
Manufacturers rate capacity at a gentler 0.2C, so landing at 94–96% at 0.5C is normal. Each cell gave a little more when we continued at lower currents after the cutoff (another 35–155 mAh). Charge in matched charge out within 1–2% for all three.
Discharge voltage under load vs capacity delivered.
Three very different voltage curves
Scaling each curve to its own capacity shows the real difference between the chemistries. This is what your BMS, inverter and battery monitor will see.
Same discharges, plotted against depth of discharge.
How each cell charges
Constant-current, constant-voltage charge from empty, ending at 0.1 A.
- NFPP climbs to a plateau near 3.3 V, then rises steeply to 3.7 V in the last few percent. That sharp rise is an easy end-of-charge signal for a charger or BMS.
- Layered oxide rises almost in a straight line all the way to 3.95 V.
- LFP jumps quickly and spends most of its charge at the 3.65 V limit. Part of that early jump comes from our test leads (see below).
What this means for your pack
How to read this test
- The tester read voltage through its test leads and cell holder, which added roughly 0.3 Ω to the circuit. At 0.5–1 A that makes every voltage read about 0.15–0.35 V lower than the cell itself, and makes each cell reach its cutoff a little early. The capacities above are therefore slightly conservative.
- The energy figures are measured under load with the same lead loss, so they understate what the cells deliver in a well-built pack.
- The LFP cell was discharged at 1.0 A (about 0.67C) instead of exactly 0.5C.
- One cell of each type, one cycle each. This is a bench check, not a cycle-life study.
Test report v2
Next we test the cells we stock today, the 850 mAh NFPP and the 1,100 mAh layered oxide, at 0.5C and room temperature. We will use a 4-wire holder that measures voltage right at the cell terminals.
They will go on the same charts as the cells above, so you can compare all five side by side.
Results are from our own bench tests on individual cells and can vary between cells and batches. Always set pack limits from the datasheet for the cells you actually have. Related: NFPP 18650 review · Layered oxide 18650 review