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Glushenkov. Energy Mater 2023;3:300010 https://dx.doi.org/10.20517/energymater.2022.70 Page 5 of 6

oxide cathodes (higher than 250 Wh/kg). Thus, Tarascon reaches the same conclusion as in the previous
viewpoint: Na-ion batteries are clearly inferior in terms of their energy densities (or specific power) to some
of the more energy-dense Li-ion batteries but may be comparable to some of the more specialised long
[4]
stability or high power Li-ion battery cells such as graphite - LiFePO or Toshiba’s SCIB cells .
4
Another possible Na-ion battery chemistry based on the use of Prussian blue analogues (technology trialed
commercially, for example, by Novosis) is also mentioned briefly in the assessment by Tarascon . However,
[4]
the cell-level metrics are not provided, and the discussion is brief. It is mentioned that the morphology and
moisture content control may represent challenges for this cathode chemistry, and the energy density (in
Wh/L) may be on the lower side for such cells due to the low density of the cathode material.

As a researcher with first-hand knowledge of the commercialisation effort in Na-ion batteries, Tarascon
provides extra remarks on the specific advantages of these new cells not directly considered in the viewpoint
by Abraham . One of such remarks concerns the extra safety of Na-ion batteries. This characteristic
[4]
originates from the fact that, unlike Li-ion batteries, their sodium counterparts can be shorted by
connecting the opposite battery terminals without an irreversible consequence for the battery performance.
As a result of this very practical property, the transportation and storage of Na-ion batteries is much easier.
In the case of Li-ion batteries, they need to be treated as dangerous goods, with special safety measures
linked to their inherent flammability and ability to explode. In contrast, for the batteries that can be
temporarily shorted, the requirements for transportation and storage in the discharged state are much
[4]
softer, favouring the adaptation of Na-ion cells in practice .

One of the considerably advantageous attributes of Na-ion cells that Tarascon envisages in his commentary
is their capability of fast charge and performing as high power cells, particularly in the Tiamat’s cells with
vanadium fluorophosphate chemistry. Their specific power compares favourably with LFP-type Li-ion
batteries while offering, according to the author, better cost in terms of €/kWh or €/kW. The fast charge
ability is also not dissimilar to Toshiba’s SCIB cells. While this property is somewhat inferior in Tiamat’s
Na-ion cells, they offer an advantage of a higher voltage (3.7 V vs. 2.7 V) and better specific energy and
energy density parameters than those of SCIB batteries. The commentator envisages that sodium-based cells
may find applications in “power-hungry functions”, including regenerative braking and fast-charging public
[4]
transport .

In conclusion, both expert commentators assessed the expected performance, advantages and applications
of Na-ion batteries. It is highlighted that Na-ion cells are unlikely to be a true replacement for Li-ion
batteries in all applications. This is linked to their relatively limited energy density with respect to that
achievable by Li-ion batteries with layered cathodes (in LCO, NMC and NCA chemistries). Instead, Na-ion
batteries (pioneered commercially by Faradion and Tiamat and also those assessed by the researchers from
Washington State University and Pacific Northwest National Laboratory) with specific energies at the level
of 120-150 Wh/kg are more comparable to LFP Li-ion batteries or specialised fast-charge SCIB batteries
marketed by Toshiba. Specific advantages of Na-ion batteries include their excellent sustainability (the lack
of critical elements such as lithium and cobalt), increased safety (an ability to be shorted during storage and
transportation) and excellent fast charge capabilities and power densities for the Na V (PO ) F -based cells.
3
4 2 3
2
Possible applications for Na-ion batteries include regenerative breaking and other “power-hungry
functions” such as fast-charging e-buses, and the uses where LFP Li-ion batteries could have been otherwise
considered (electric vehicles with short range, power backup or energy storage systems used with localised
renewable energy generators).