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

An important consideration in Na-ion batteries is the possibility of avoiding the use of copper current
collectors in the negative electrodes and aluminium can be used instead as a cheaper alternative. This is
related to the lack of parasitic alloying of sodium with aluminum, which is, unfortunately, a problem that
exists for lithium in Li-ion cells.

In his viewpoint published in ACS Energy Letters, Abraham raises a question on how comparable Na-ion
[3]
batteries are to their Li-ion counterparts . This is discussed through the consideration of actual and
hypothetical batteries assembled in the format of 18650 cells and the analysis of their specific energies
(Wh/kg) and energy densities (Wh/L). Li-ion batteries [graphite - LiCoO (3.7 V, 206 Wh/kg, 530 Wh/L),
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graphite - LiNi Mn Co O (3.6 V, 210 Wh/kg, 530 Wh/L), graphite - LiNi Co Al O (3.6 V,
0.15
0.33
2
0.05
0.33
2
0.8
0.33
285 Wh/kg, 785 Wh/L), graphite - LiFePO (3.4 V, 126 Wh/kg, 325 Wh/L) and graphite - LiMn O (3.8 V,
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2
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132 Wh/kg, 340 Wh/L)] are used as established benchmarks. In turn, three Na-ion battery prototypes are
considered - a commercial Na-ion battery prototype from CNRS CEA (90 Wh/kg and estimated 250 Wh/L),
a Na-ion battery prototype from the joint work of Washington State University and Pacific Northwest
National Laboratory utilising an O3-type layered oxide NaNi Mn Co O (2.7 V, 150 Wh/kg, 375 Wh/L)
2
0.10
0.68
0.22
and a Na V (PO ) F -based Na-ion cell built by European research centre ALISTORE (3.5 V, 75 Wh/kg). It
4 2 3
2
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should be noted that the specific energy of the latter cell is likely underestimated in Abraham’s
consideration, as a value of energy at a high 1C rate is taken into account.
Considering the above values, it is concluded in Abraham’s viewpoint that Na-ion cells are not comparable
to high-energy Li-ion batteries such as those with LiCoO (LCO), LiNi Mn Co O (NMC) or
2
0.33
0.33
0.33
2
LiNi Co Al O (NCA) cathode chemistries . However, some of the emerging Na-ion batteries may have
[3]
0.05
2
0.15
0.8
specific energies and energy densities close to those of Li-ion cells with LiFePO (LFP) cathode chemistry. It
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may be therefore expected that similar applications (e.g., electric vehicles with short range, power backup or
energy storage systems used with localised renewable energy generators) may be envisaged for Na-ion
batteries. Moderate energy contents per mass or volume in Na-ion batteries may be traced to the behaviour
of many cathode materials; it is commonly observed that Na-containing cathode candidates have a reduced
capacity and a smaller average operating voltage than their lithium counterparts. As an example, the voltage
[1]
- capacity profiles for Na CoO and Li CoO may be compared [Figure 1] . Concluding his assessment,
2
1-x
2
1-x
Abraham also envisages that some cost reduction may be possible in Na-ion batteries (10%-20% cheaper
than their Li-ion counterparts) in the long term and cites the sustainability (Li- and Co-free nature) as the
major advantage of these new batteries. He also emphasises that their energy densities are much superior to
those offered by old-school battery types in the form of lead-acid, nickel-cadmium and nickel - metal
hydride cells .
[3]
Similarly, the commentary by Tarascon is concerned with distinguishing between the hype associated with
the earlier development of Na-ion batteries and reality . His discussion is based on the cells publicized by
[4]
three start-up companies in this space, Faradion (layered oxide cathode chemistry) Tiamat (Na V (PO 4 ) F
2
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2 3
cathode chemistry) and Novosis (using Prussian blue analogue as a cathode). These cells are compared with
graphite - LiFePO batteries and, importantly, with Toshiba’s Super Charge Ion Battery (SCIB) cells. The
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latter benchmark is new in our discussion (not considered previously in Abraham’s viewpoint ) and is very
[3]
interesting as these batteries represent another category of Li-ion cells - specialised low energy, high power
batteries. A spider diagram [Figure 2] represents a comparison of various parameters of the cells under
[4]
consideration . One minor criticism addressed to Figure 2 may be the specific energy and energy density of
LFP cells, which seems lower than the usually publicized data. In the opinion of the author of this Research
Highlight, higher values should have been used for the LFP cells in the benchmarking exercise.