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Mu et al. Energy Mater 2022;2:200043 https://dx.doi.org/10.20517/energymater.2022.57 Page 9 of 16

In contrast to conventional wet chemical presodiation, Liu et al. proposed a continuous presodiation
process by solution spraying, where 0.1 M Na-Naph in tetrahydrofuran (THF) solvent was sprayed with a
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precise dosage of Na-Naph (38 µL cm ) onto commercially available HC anodes, followed by drying to
[32]
eliminate any remaining Naph and THF [Figure 5A] . The results indicate that the presodiation treatment
boosts the reversible capacity by 60 mAh g , the initial Coulombic efficiency by 20.0% and the energy
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density from 141 to 240 Wh kg for the Na [Cu Fe Mn ]O //HC full cell. Interestingly, after chemical
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0.48
0.22
0.9
0.30
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presodiation, a stable SEI film is generated on the surface of the HC anodes, which effectively reduces the
irreversible loss of Na during the initial stage. To suppress the decomposition of electrolytes during battery
assembly, Zheng et al. used Na-Naph in a DME solvent as the presodaition reagent to perform an ultrafast
[80]
chemical pretreatment, as shown in Figure 5B . Presodiation treatment successfully raises the initial
Coulombic efficiency of rGO to 96.8% and results in the decomposition of the Na-containing complex to
generate an artificial SEI layer on the anode surface. As a result of the suppressed decomposition of the
excessive electrolyte by the artificial SEI, a homogenous and inorganic-rich SEI film generated on the
surface of rGO, facilitated rapid interfacial ion transfer. Therefore, an outstanding capacity of 198.5 mAh g
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at 5 A g is displayed by the presodiated rGO anode.
Referring to the traditional prelithiation process, Cao et al. reported a liquid-phase immersion presodiation
method, as shown in Figure 5C . To finish the presodiation process, a Na Ti O cathode was submerged
[81]
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into the stable liquid Na-Naph-DME for 10 min, followed by rinsing with a DME solution. As a result, the
initial Coulombic efficiency of Na Ti O in the half cell is significantly boosted to 100% from 65%. The
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2
presodiation treatment could raise the initial efficiency from 40% to 80% in a Na V (PO ) //Na Ti O full
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13
2
2
4 3
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cell and the electrode after presodiation still exhibited high rate capability and cycle performance. To raise
the initial Coulombic efficiency of commercial HC, Liu et al. developed a feasible and efficient chemical
presodiation method, in which the HC anode was submerged into a DME solution containing Na-Bp and
[30]
the presodiation level could be carefully regulated by varying the immersion time [Figure 5D] . The
presodiated HC anode shows a dramatically increased initial Coulombic efficiency by 30%, originating from
the provided extra Na sources by presodiation treatment. The Na V (PO ) //Na HC full cell demonstrates a
2
4 3
x
3
significantly improved energy density and capacity retention using this presodiated HC anode.
The chemical presodiation strategy can easily regulate the presodiation degree by changing the soaking time
+
and Na concentration in the solution. Compared with Na metal, the safety of liquid sodium sources is
significantly improved, which can remain safe even in harsh conditions with water.
Electrochemical presodiation
The electrochemical presodiation involves two steps of assembling and disassembling the half cell . Firstly,
[43]
the anode is assembled with Na metal in a half cell and then pre-cycled to generate the stable SEI film on the
anode surface before disassembling. During electrochemical presodiation, the current density should be
sufficiently low to ensure the integrity and uniformity of the SEI film. The detailed electrochemical
presodiation process is given in Figure 6A . By assembling a Na//PH5 (or Na//HC) half cell, the PH5 and
[82]
HC are both successfully presodiated during the first discharge process. Consequently, the full cell
(Na-PH5//NVP) assembled with presodiated anode exhibits an excellent reversible capacity of nearly
107 mAh g and an energy density of 150 Wh kg . In addition to HC anodes, other anode materials can also
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be presodiated by the electrochemical procedure. Recently, Liu et al. proposed a novel Na-Sb@ZMF/C
anode with excellent cycle stability and attractive Coulombic efficiency . In the course of in-situ
[83]
presodiation, Na-Sb and Na-Sn intermediates were introduced and dispersed in the Na O matrix, which not
2
only induced directed Na flux and electron transfer but also facilitated Na absorption through the uniform
+
+
alloying process, as shown in Figure 6B. When paired with a NaVPO F cathode, the Na-Sb@ZMF/C anode
4
reduced the polarization voltage of the full cell to 31 mV and exhibited an outstanding rate performance