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Mu et al. Energy Mater 2022;2:200043 https://dx.doi.org/10.20517/energymater.2022.57 Page 7 of 16

Figure 3. (A) Schematic illustrations of redox behavior of TM cations and oxygen anions of O3-type NaxTMO cathode (left) and
2
quenching process for self-presodiation cathode (right) [70] . (B) Schematic diagram of reaction mechanism of desodiation procedure for
cathode [71] .

[71]
In addition, another Na-rich cathode, Na V (PO ) , was systematically investigated by Mirza et al. . As
4 3
4
2
shown in Figure 3B, the electrochemical presodiation strategy was applied, in which Na V (PO ) (Na VP)
2
3
3
4 3
was first converted to Na V (PO ) (Na VP) by a sodium foil and then the desodiation process of Na VP was
2
4
4 3
4
4
performed below 2.2 V vs. Na /Na. The whole reaction process was characterized by operando XRD. During
+
this process, the additional Na per formula unit of Na VP is extracted into the electrolyte to compensate for
4
the irreversible Na depletion and the corresponding Na VP generated after desodiation from Na VP is
3
4
directly regarded as the cathode. As a result, the Na PV//HC full cell achieves an excellent energy density of
4
-1
265 Wh kg , which is 76% higher than that of the Na VP//HC full cell. The reversible capacities of the
3
Na VP//HC and Na VP//HC full cells are 103.76 and 51.02 mAh g , respectively, while the initial
-1
3
4
Coulombic efficiency of the Na VP//HC full cell is ~95%, which is nearly double that of the Na VP//HC full
4
3
cell.
Direct contact with sodium foil/powder
Learning from the prelithiation process of LIBs employing metallic Li or Li powder , metallic Na has also
[72]
been widely explored in direct contact with anode materials for presodiation. As shown in Figure 4A,
Liu et al. reported a presodiation method by spontaneous alloying between Na and Sn, where the Na and Sn
foils are in direct contact under pressure using a roller . After presodiation, the initial Coulombic
[73]
efficiency increases from 24.96% to 75.0% in the Na V PO F //NaSn full cell, which is attributed to the
4 3
2
3
release of extra Na from the NaSn alloy to compensate for the irreversible Na loss during the initial stage. In
addition to alloying presodiation, a potential-driven presodiation has also been reported, similar to
prelithiation in LIBs , in which Na metal was directly attached to an electrode separated with a small
[74]
amount of electrolyte and the potential gap between Na and the active materials, such as Na Fe Mn O
0.67
0.5
2
0.5
(NFMO) or commercial HC, could act as a driving force for the migration of Na ions and electrons. By
+
directly contacting Na metal with electrodes, Na will be introduced into the active electrode materials,
which can compensate for the Na loss during the initial cycle. Therefore, the PS-HC//NFMO full cell
exhibits a discharge capacity of 102 mAh g , representing a 60.0% increase over the HC//NFMO full cell
-1
[Figure 4B].
Similar to Li metal, metallic Na is extremely active and difficult to store stably and safely in air, so the
presodiation with Na metal or powder can only be performed in an oxygen- and water-free glove box.
Simultaneously, the manufacture of metallic Na powder is laborious and the risk of thermal runaway exists
when the anode and metallic Na powder are pressure coated. Additionally, excessive Na powder input will