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Page 2 of 6 Glushenkov. Energy Mater 2023;3:300010 https://dx.doi.org/10.20517/energymater.2022.70

A significant body of research and a degree of excitement is often followed by commercial efforts. Indeed, a
number of emerging industry players can be identified at the moment in the sodium-ion battery space,
including Faradion, Tiamat and Novosis, to name a few. Practical prototypes of the batteries appear, and
their metrics and the expected performance may be quantified with reasonable certainty levels. Experts in
the field can then analyze the available information and provide analytical commentaries able to define the
expected performance envelopes, strengths and limitations of the emerging technology. Two such
contributions have been recently published in the peer-reviewed literature, in the form of a viewpoint from
[3]
[4]
Prof. Abraham and a commentary from Prof. Tarascon . Both contributors are well-known expert
researchers in the field. Prof. Abraham has contributed to the development of lithium, Li-ion and Li-air
batteries, and served on the editorial board of Journal of Power Sources and as a Chair of the Battery
[4]
Division of the Electrochemical Society. Prof. Tarascon is a creator of the European Network of Excellence
ALISTORE-ERI and the French Network on Electrochemical Energy Storage (RS2E), and a strong research
participant in the field of Li-ion and Na-ion batteries. It is interesting to compare and discuss their two
opinions in the context of Na-ion batteries, as one of the expert commentators (Prof. Abraham) can be
regarded as an outsider in the field, while the second expert commentator (Prof. Tarascon) is a clear insider,
who significantly contributed to the sodium-based technology research and is also a shareholder and
development committee member in one of the emerging Na-ion battery companies, Faradion.

Both commentators comment on the choice of materials that enable Na-ion batteries. Hard carbon is
highlighted as the preferred material for negative electrodes (anodes) of these batteries. This type of carbon
is made up of disordered graphene layers and nanopores and has a typical sloping voltage region followed
by a plateau. Usually, optimal samples of hard carbon have reversible capacities of ~250 mAh/g, which
[3]
corresponds to the formation of Na C . The incorporation of sodium into hard carbon is usually
0.67
6
described in terms of a combination of its insertion between the disordered carbon layers and the filling of
nanopores present in the carbon host. Other negative electrode materials, such as Na Ti O , Na Ti (PO )
2
3
7
3
4 3
2
and materials that alloy with Na, have also been described; however, hard carbon remains the truly
[3,4]
dominant negative electrode material and is used in the vast majority of practical prototypes .
The choice of cathode materials is less singular and well defined. During the research activities on Na-ion
batteries, three main cathode material types have emerged, including layered sodium transition metal
oxides, typical for batteries produced by one of the industry pioneers Faradion, sodium vanadium
fluorophosphate Na V (PO ) F used in practical battery prototypes by Tiamat and Prussian blue analogues
3
2
4 2 3
such as Na MnFe(CN) •yH O, adopted in batteries developed by Novosis . These positive electrode
[3,4]
2
6
2-δ
materials have distinctly different capacities and average voltages (up to 150 mAh/g with varied average
voltages, depending on the materials, for sodium layered oxides; 128-135 mAh/g and 3.8-3.9 V for
Na V (PO ) F ; 80-160 mAh/g and 3-3.5 V for Prussian blue analogues) and enable three main types of
3
4 2 3
2
commercial cells adopted by the industry.
Electrolytes in Na-ion batteries are a variation of an appropriate salt [NaPF , NaN(SO CF ) or NaClO )]
3 2
2
6
4
and mixed organic carbonate solvents chosen from ethylene carbonate (EC), ethyl methyl carbonate (EMC),
propylene carbonate (PC), diethyl carbonate (DEC) and dimethyl carbonate (DMC). In order to enable
better stability in the cell, electrolyte additives may be used, which include, most commonly, fluoroethylene
carbonate (FEC) and sometimes other additives such as bis(2,2,2-trifluoroethyl) ether (BTFE). An
important point is that an electrolyte formulation cannot be simply copied from somewhat analogous Li-ion
batteries and need to be tailored for a particular combination of electrodes in a Na-ion cell .
[3,4]