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Page 4 of 16 Mu et al. Energy Mater 2022;2:200043 https://dx.doi.org/10.20517/energymater.2022.57

+
+
If a second Na source can be provided in addition to the cathode compensating for the Na loss during
charge and discharge, the capacity and energy density of SIBs can be further increased [33,43] . This process of
+
providing an additional Na source is defined as presodiation. Additionally, the presodiation process can
also increase the operating voltage and lower the electrolyte consumption during the formation of the SEI
film in SICs. Among the strategies to enhance the initial Coulombic efficiency, such as surface
engineering [54-56] , structural regulation and new materials design , the feasible presodiation technology
[58]
[57]
appears more effective and enables the irreversible capacity to be activated, maximizing the energy density
in SIBs. Presodiation methods vary in their benefits and drawbacks, and it is therefore crucial to
comprehend the underlying mechanism.

Self-sacrificing Na-containing additives for cathodes
Recently, presodiation has been performed with the addition of supplementary Na-containing additives and
a wide range of materials have been systematically investigated. Na-containing additives usually undergo
+
electrochemical oxidation during the first charge-discharge operation, irreversibly releasing extra Na to
+
compensate for the Na loss. For this, the decomposition potential of the additives should be lower than the
working potential of the full cell to ensure that the Na-containing additives can be thoroughly
electrochemically oxidized to release sufficient Na during the first charge .
[59]
+
There are many Na-containing additives that have been carefully studied for the presodiation of Na-ion full
cells, including Na C O , DTPA-5Na , NaCrO , Na O , Na S [63,64] , NaN , and NaNiO , which can
[66]
[65]
[59]
[62]
[60]
[61]
2
3
2
2
4
2
2
2
+
be combined with the active cathode materials and provide sufficient extra Na sources during the first
charge, as well as oxidizing the associated anions to release gases. Na C O , as a typical sacrificial additive, is
2 2
4
environmentally friendly, low cost and can achieve no additional residues after Na extraction. As shown in
+
Figure 2A, Sun et al. systematically evaluated the role of Na C O in the presodiation of SICs . They
[60]
4
2
2
concluded that Na C O could be oxidized at ~3.7-4.0 V (vs. Na /Na) to yield a specific capacity of
+
2
2
4
393.8 mAh g . Benefiting from the merit of “zero dead mass”, the boosted pouch-type SICs deliver
-1
remarkable energy and power densities of 91.7 Wh kg and 13.1 kW kg , respectively, when coupled with
-1
-1
commercially available activated carbon as the cathode and commercially available hard carbon (HC) as the
anode. Additionally, Zou et al. reported a labile organic sodium salt, Na C O , which could decompose to
2
6
6
[31]
produce abundant Na at high voltage to make up for the irreversible capacity .
+
There are many Na-containing additives that have been carefully studied for the presodiation of Na-ion full
[65]
[66]
[62]
[61]
[60]
[59]
cells, including Na C O , DTPA-5Na , NaCrO , Na O , Na S [63,64] , NaN , and NaNiO , which can
2
4
2
2
2
2
2
3
+
be combined with the active cathode materials and provide sufficient extra Na sources during the first
charge, as well as oxidizing the associated anions to release gases. Na C O , as a typical sacrificial additive, is
4
2 2
environmentally friendly, low cost and can achieve no additional residues after Na extraction. As shown in
+
Figure 2A, Sun et al. systematically evaluated the role of Na C O in the presodiation of SICs . They
[60]
2
2
4
concluded that Na C O could be oxidized at ~3.7-4.0 V (vs. Na /Na) to yield a specific capacity of
+
2
4
2
393.8 mAh g . Benefiting from the merit of “zero dead mass”, the boosted pouch-type SICs deliver
-1
remarkable energy and power densities of 91.7 Wh kg and 13.1 kW kg , respectively, when coupled with
-1
-1
commercially available activated carbon as the cathode and commercially available hard carbon (HC) as the
anode. Additionally, Zou et al. reported a labile organic sodium salt, Na C O , which could decompose to
6
2
6
produce abundant Na at high voltage to make up for the irreversible capacity .
+
[31]
As shown in Figure 2B, Jo et al. reported a new penta-sodium diethylenetriaminepentaacetic acid salt
(DTPA-5Na), which could be irreversibly oxidized to achieve an excellent charge capacity of nearly
363 mAh g -1[59] . By mixing 9 wt.% DTPA-5Na with a Na MnO cathode, the charge capacity delivers an
0.44
2