P2-S01 voltage-window note
This article treats the P2-S01 chart as a voltage-window selection problem rather than another generic half-cell capacity note. The useful question is not simply whether 4.3 V gives the largest number; it is whether the extra capacity unlocked above 4.0 V is worth carrying into the next round of electrolyte, cycling, and full-cell validation. In the supplied 2320 coin-cell data, capacity increases from 78.88 to 112.04 mAh/g as the upper cut-off voltage moves from 4.0 to 4.3 V, while first-cycle efficiency remains within 96.47-98.18%.
The Figure Is a Four-Step Voltage Experiment
The strength of this dataset is that one variable is easy to see: the upper cut-off voltage. The same P2-S01 material label, 13.5 mg/cm2 loading, sodium-metal counter electrode, carbonate-based electrolyte, 0.1C/0.1C rate, and 25 +/- 1 C test temperature are shown across four upper limits. That makes the chart more useful for protocol planning than a single best-capacity claim. Researchers comparing ready-to-test cathodes can start from the exact P2-Type NMTO single-sided cathode at 13.5 mg/cm2, then use the voltage-window logic below to decide which ceiling deserves repeat testing.
Capacity Gain by Voltage Ceiling
The voltage ceiling changes the accessible capacity in a stepped way. The gain from 4.0 to 4.1 V is moderate, the gain from 4.1 to 4.2 V is larger, and the jump from 4.2 to 4.3 V is the largest in this chart. The first-cycle efficiency decline is comparatively small across the same sequence, dropping 1.71 percentage points from 98.18% to 96.47%.
| Upper cut-off window | Reported capacity | Reported ICE | How to read the point |
|---|---|---|---|
| 2.5-4.0 V | 78.88 mAh/g | 98.18% | Conservative reference window with the lowest delivered capacity and highest first-cycle efficiency. |
| 2.5-4.1 V | 85.26 mAh/g | 97.53% | Adds 6.38 mAh/g over 4.0 V, showing a modest gain with only a small ICE decrease. |
| 2.5-4.2 V | 96.36 mAh/g | 96.97% | Adds 11.10 mAh/g over 4.1 V and looks like the practical middle window for follow-up work. |
| 2.5-4.3 V | 112.04 mAh/g | 96.47% | Adds 15.68 mAh/g over 4.2 V and gives the highest capacity, but it is also the highest-voltage stress case. |
The total reported capacity gain is 33.16 mAh/g from the 4.0 V ceiling to the 4.3 V ceiling, or about a 42% increase relative to the 4.0 V window. If the 13.5 mg/cm2 loading is used directly as the areal-capacity basis, the same sequence corresponds roughly to 1.06, 1.15, 1.30, and 1.51 mAh/cm2. That conversion is useful for experiment design, but the loading basis should be confirmed before using it for N/P balancing.
Why 4.2 V May Be the Practical Checkpoint
The 4.3 V curve is the headline result because it reports 112.04 mAh/g. For an early material screen, however, the more useful decision may be to treat 4.2 V as the control window and 4.3 V as the challenge window. The 4.2 V point has already recovered much of the extra capacity above 4.0 V, while reducing the uncertainty that comes with pushing a carbonate electrolyte and layered oxide cathode to the highest tested voltage.
This distinction matters when ordering samples or planning a coating run. The broader sodium-ion cathode electrode sheets category is useful for comparing P2-type materials with NFM, NVP, NFPP, and other sodium cathode formats, but P2-S01 should be evaluated with its own voltage ladder rather than copied from another cathode family. A higher cut-off can increase delivered capacity and still create different demands on electrolyte oxidation, current collector stability, gas generation, and long-term impedance.
Protocol Details That Decide Whether 4.3 V Is Worth Keeping
A single first-cycle chart cannot prove that 4.3 V is the final operating window. The next test should compare at least two branches: a 4.2 V reference branch and a 4.3 V stress branch. Both should use the same electrode diameter, electrolyte amount, rest time, separator, sodium source, pressure condition, formation steps, and data-integration settings. The comparison should then add repeat cells, extended cycling, rate testing, impedance tracking, and post-cycle inspection.
Because the highest point in this article reaches 4.3 V, the test channel should have enough voltage headroom and stable data export. For labs building that method, battery test equipment and instruments are the relevant Atomfair route, and a 5 V multi-channel coin-cell tester is directly aligned with voltage-window screening rather than low-voltage qualification alone.
From Half-Cell Window to Full-Cell Design
In a sodium-metal half cell, the sodium counter electrode isolates the cathode response from hard-carbon inventory limits. That is useful for locating the cathode voltage window, but it does not answer the full-cell question. Once the 4.2 V and 4.3 V branches are compared, the selected cathode condition should be paired with a measured hard-carbon anode, an explicit N/P target, and a capacity-matched formation plan.
For that later step, a hard carbon anode sheet or sodium-ion pouch-cell route should be chosen from measured areal capacity, not nominal material capacity. The Battery Research hub can serve as the parent workflow for moving from cathode-window screening to electrode pairing, cell assembly, and validation reporting.
Data Boundaries for Publication
The supplied chart supports a clear article claim: P2-S01 delivered more reported capacity as the upper cut-off voltage increased from 4.0 to 4.3 V, while first-cycle efficiency remained high in the first cycle. It does not support cycle-life claims, rate-performance claims, electrolyte-stability claims, gas/safety claims, full-cell energy claims, or a recommendation that 4.3 V should be used without validation. Those claims require repeat-cell and longer-term data.
For publication quality, this page should keep the article centered on voltage-window selection. It should not be expanded with unsupported general statements about all P2 cathodes or all sodium-ion batteries. The value for readers is the decision logic: use 4.0 V as a conservative baseline, 4.2 V as a practical checkpoint, and 4.3 V as a high-capacity branch that must pass stability testing before it becomes the default window.