This dataset is best read as a collector-design screen, not as a simple NFM-versus-NFPP ranking. Both traces use a customized Al@C current collector on the anode side, so the central question is whether the collector can support sodium plating and stripping while the cathode still delivers meaningful capacity. The NFM branch reports 122.31 mAh/g with 87.02% first-cycle efficiency, and the NFPP branch reports 100.46 mAh/g with 85.12% first-cycle efficiency. Those numbers are promising enough for follow-up, but the first-cycle loss is also the main engineering warning.
What the Al@C Collector Is Being Asked to Do
In an anode-free sodium cell, the anode is not a preloaded hard-carbon electrode. The cathode provides the sodium inventory, and sodium must deposit onto the Al@C current collector during charge, then strip back during discharge. That makes the collector surface part of the active electrochemical design. Researchers moving from material screening toward format work can compare this approach with broader sodium-ion dry pouch cells, but the coin-cell trace should first be treated as a controlled current-collector experiment.
Two Branches, Two Different Jobs
The two panels should not be read as a direct material contest because the cathode chemistry, loading, and voltage window are different. Their value is comparative in another way: they show whether the same customized anode-side concept can be tested against both a layered-oxide NFM cathode and a higher-loading NFPP cathode. That is a useful early screen for laboratories deciding whether to continue anode-free sodium work.
| Design branch | Cathode loading | Voltage window | Reported capacity | Reported ICE | Interpretation |
|---|---|---|---|---|---|
| NFM / Al@C | 10 mg/cm2 | 2.0-4.0 V | 122.31 mAh/g | 87.02% | Higher-voltage layered-oxide branch; useful for checking whether the collector supports sodium plating while the cathode still accesses usable capacity. |
| NFPP / Al@C | 20 mg/cm2 | 2.5-3.8 V | 100.46 mAh/g | 85.12% | Higher-loading polyanion branch; useful for testing collector compatibility under a different cathode profile and sodium-inventory demand. |
For a cathode-first workflow, the starting point is still the electrode family. The sodium-ion cathode electrode sheets category helps researchers choose NFM, NFPP, NVP, P2, or related cathodes before committing to a custom collector experiment. Once an anode-free branch is selected, existing cell-format references such as the 1Ah NFM dry pouch cell and 1Ah NFPP anode-free dry pouch cell show how the question can later move from coin-cell screening toward larger sample formats.
Why First-Cycle Efficiency Is the Key Signal
The reported capacities are useful, but the first-cycle efficiencies of 87.02% and 85.12% deserve just as much attention. In an anode-free design, irreversible sodium loss does not have a large anode reservoir to hide behind. A capacity value near 100 mAh/g can still become difficult to scale if plating reversibility, interphase formation, electrolyte consumption, or collector-side dead sodium are not controlled.
That is why the claim should stay narrow: the customized Al@C collector enabled measurable first-cycle capacity recovery in both NFM and NFPP coin-cell branches. The chart does not prove long-cycle stability, commercial energy density, uniform sodium morphology, or safety behavior. Those require repeat-cell statistics, voltage efficiency, impedance tracking, post-test morphology, and longer cycling.
Customization Variables to Lock Before Scaling
The next experiment should separate collector effects from cathode effects. If too many variables change together, a later failure cannot be assigned to the Al@C surface, electrolyte, cathode loading, stack pressure, or formation sequence. A useful custom request should therefore specify the collector surface, cathode type, loading, voltage window, electrolyte, current, pressure condition, and expected validation endpoint.
| Variable to lock | Reason in anode-free testing |
|---|---|
| Al@C collector surface | The collector is the sodium-hosting side; surface chemistry and carbon layer consistency affect nucleation, stripping, and first-cycle loss. |
| Cathode areal capacity | The cathode supplies the sodium inventory, so loading and usable capacity define how much sodium must plate and strip. |
| Electrolyte and wetting | The chart uses 1 M NaPF6 in DEGDME. Any solvent, salt, additive, or wetting change can alter plating morphology. |
| Formation protocol | Current, rest, pressure, and cut-off settings decide whether first-cycle loss comes from material behavior or setup drift. |
| Replicate and post-test checks | Anode-free claims need repeat cells, impedance, morphology, retention, and failure-mode inspection before scaling. |
For repeat testing, use battery test equipment and instruments that can keep the same current, rest, cut-off, recording interval, and export rules across both cathode branches. The wider Battery Research hub is the better navigation path when a team needs to connect material selection, electrode preparation, coin-cell testing, and pouch-cell validation into one project.
Publication Boundary
This article should be published as an early anode-free sodium-cell customization note. It may state the reported NFM and NFPP first-cycle capacity and efficiency values under the listed conditions. It should not state that Al@C collectors solve sodium plating, that either chemistry is fully validated, or that the coin-cell data already represent pouch-cell performance. The strongest public value is the engineering logic: anode-free cells must be designed around the cathode sodium inventory, the collector surface, and first-cycle reversibility together.