Here is the some kind of current "final conclusion" based solely on the VTT report curves and numerical behavior (without relying on any Donut’s marketing claims):
1) Most likely category: Li-ion intercalation cell (not a supercapacitor)
The voltage range 2.7–4.15 V, maximum 4.3 V, nominal 3.6 V, together with the characteristic CC→CV transition and exponential-like CV current decay, are highly consistent with a Li-ion intercalation cell (such as NMC/NCA/LNMO family or a closely related chemistry).
Based on the voltage vs time and CC-CV behavior alone, this device does not resemble a pure capacitive storage device, nor does it exhibit a fundamentally different voltage profile that would indicate an entirely new electrochemical storage mechanism.
2) What it most likely is: a very low-polarization Li-ion cell with optimized internal structure
Published VTT paper curves clearly show that:
CC phase continues unusually far even at very high C-rates (up to 11C), meaning the terminal voltage does not immediately hit the CV limit.
This implies low total polarization, i.e. low effective internal resistance and/or very efficient ion transport and charge transfer.
Voltage curves remain smooth and stable even at very high current.
This strongly suggests the cell is still fundamentally a Li-ion intercalation system, but with exceptionally well-optimized internal structure, such as:
improved electrode conductivity,
optimized electrode thickness,
enhanced ion transport pathways,
or improved electrode surface structure.
3) Thermal behavior follows classical Li-ion physics
Difference between the one-heatsink and two-heatsink cases behaves exactly as expected from electrochemical and thermal theory:
Hotter cell (one heatsink) shows lower polarization, so during CC charging its voltage can remain lower and the CV phase shortens.
Cooler cell (two heatsinks) maintains higher polarization, so the voltage reaches the limit earlier and the CV tail is longer.
This behavior is entirely consistent with conventional Li-ion cells and does not require any exotic explanation.
4) CV decay time constants ("tau") do not indicate fundamentally new storage mechanism
Calculated CV current decay time constants were approximately:
~2.4–3.9 minutes at 11C,
~4.5–5.8 minutes at 5C (two-heatsink case),
and importantly, the time constant increases at lower current levels, which is characteristic of diffusion-limited behavior near full charge.
This is exactly what is expected from Li-ion intercalation systems.
If this were primarily a supercapacitor-like (including chemical pseudocapacitor) storage mechanism, one would typically expect either:
significantly different voltage vs charge profile, or
very different CV decay behavior.
That is not observed here.
5) What this does NOT rule out
This cell could still be "special" within the Li-ion family. For example:
Anode may be a nanostructured carbon or other advanced structure.
Cathode may be a different composition than conventional NMC111/NMC811.
Internal architecture may be highly optimized for fast ion transport.
This is fully compatible with the observed voltage behavior.
VTT report also does not rule out the possibility that this is a particularly well-performing individual sample rather than representative mass-production performance.
6) What the VTT report does NOT yet provide (and what is critical)
Following key information is missing:
cycle life data at high C-rates,
capacity retention after stress tests,
internal resistance change after cycling,
statistical variation across multiple cells,
energy density (Wh/kg),
differential capacity plots (dQ/dV).
Without these, the long-term durability and true technological novelty cannot be determined.
And then also other note about test arrangement (in these the customer defines what is being tested and possibly also defines at least partially the desired test protocol)
What the minimal cooling setup may implicitly suggest
From an engineering perspective, the relatively modest or even sloppy cooling arrangement*) could be interpreted as a signal that the developer is not overly concerned about the cell’s immediate thermal stability under high charge rates. If the cell were extremely sensitive to temperature, one would normally expect very careful thermal control to avoid overheating or unstable behavior during validation testing.
*) Also note that this is a pouch type cell.
By contrast, demonstrating high-rate charging with only passive heatsinking may implicitly suggest that the cell can tolerate significant thermal stress, at least over short durations, without catastrophic failure or severe instability.
However, there are several possible explanations for this choice of setup:
It may simply reflect a cell-level characterization test, intended to observe the intrinsic limits of the cell rather than demonstrate a production-ready thermal system.
It may be intended to show that the cell’s performance is not highly dependent on sophisticated cooling, which could be advantageous in practical applications.
It may also be a way to demonstrate robustness under less-than-ideal thermal conditions.
At the same time, this type of test alone does not establish long-term durability, cycle life, or degradation behavior at elevated temperatures, which are equally important considerations for real-world use.
In summary, the cooling setup could reasonably be interpreted as suggesting that the developers are confident in the cell’s short-term thermal tolerance, but additional data would be needed to determine its long-term thermal robustness and operational limits.
Next small part of the entire ordered test has been promised to be released on Monday next week. This way of releasing things is not very nice. But it is their chosen strategy, the reasons for which can be varied, both good and bad.
Home
Help
Search
Login
Register
