Page 149 - Read Online

Shipitsyn et al. Energy Mater 2023;3:300038 https://dx.doi.org/10.20517/energymater.2023.22 Page 11 of 37

3% vol. DMCF shows the appearance of similar compounds [Figure 4D-F] as it was mentioned for
electrolytes with FEC additive [Figure 4A-C]. However, the increase of the CO peak (BE ≈ 290 eV) suggests
3
a larger quantity of Na CO on the HC surface which could be the reason for the cell capacity decay. It is
3
2
unfortunate that Fondard et al. did not clearly report the fluorination degree of the DMCF used in this
[24]
work. According to Yu et al. , such a factor could determine the cell performance through additive
[76]
decomposition routes.
Sulfur-containing Additives
Table 4 listed a few sulfur-containing additives that have been reported for protecting HC anode materials.
1,3-Propane sultone (PS, Table 4) is known as an MIB additive, which reacts with radicals in electrolytes,
forming sulfite or sulfate inorganic species . This additive can also be used to decrease the gas evolution in
[69]
[77]
LiNi Mn O /graphite full cells at the state of full charge . Moreover, it was mentioned that PS can repair
1.5
4
0.5
broken SEI layers at high temperatures . Yan et al. found that electrolytes with 3% PS create a SEI layer
[78]
[69]
with a lower impedance and good capacity retention. In recent studies, authors stated that the reduction
[59]
peak for PS is observed at 2.02 V vs. Na /Na, which means that PS can prevent decomposition of other
+
solvents in the electrolyte. Zhang et al. tested PS as an additive in the electrolyte [1M NaPF + EC/
[59]
6
DMC(1/1) + 2% wt. FEC], and the results showed that 2% wt. PS increased initial CE from 72.3% to 76.7%
and capacity retention from 58.7% to 82.0% after 50 cycles in full-cells Na(Ni Mn Cu Ti ) La O /HC
0.001
0.4
2
0.1
0.1 0.999
0.4
full-cells. XPS characterization showed that the electrolytes with PS form ROSO Na, RSO Na, Na SO , and
2
3
2
3
Na SO on the surface of HC.
4
2
Using density functional theory (DFT) calculations, Liu et al. calculated free energies during
[72]
decomposition of 1,3-Propylene sulfite (1,3-PS, Table 4) through the formation of a 1,3-PS-Na complex,
ring opening, and the production of simpler species. Here, reduction reactions are provided:
C H O S + Na + 1ē → OCH CH CH OSONa ΔG = -146.88 kcal/mol (2)
+
3
2
2
6
2
3
After ring opening, there are two paths. The first goes through SO gas evolution:
2
2C H O S + 2Na + 2ē → NaO(CH ) SO Na + SO ↑ ΔG = -372.75 kcal/mol (3)
+
2 6
3
3
3
2
6
The second path leads to the formation of CH CH=CH gas and inorganic Na SO :
3
2
2
3
+
C H O S + 2Na + 2ē → CH CH=CH ↑ + Na SO ΔG = -357.62 kcal/mol (4)
3
3
2
6
3
2
3
Based on the calculations, the authors [72,79] concluded that the two-electron reduction of 1,3-PS takes more
effort to form Na SO compared to the reduction of carbonate esters, such as EC, PC, and vinylene
3
2
carbonate (VC). But it is easier for a one-electron reduction of 1,3-PS to produce an organic layer on the
HC anode compared to EC, PC, and VC.
Che et al. showed that the additive of 1% wt. prop-1-ene-1,3-sultone (PES or PST, Table 4) in the
[70]
electrolyte [1M NaPF + EC/EMC(1/1) + 2% wt. FEC] increased capacity retention after 1,000 cycles from
6
76.6% to 84.4% in pouch cells (NaNi Fe Mn O /HC). However, in recent studies, Zhang et al.
[59]
1/3
1/3
2
1/3
concluded that increasing the PES amount in the electrolyte [1M NaPF + EC/DMC(1/1) + 2% wt. FEC]
6
leads to the formation of a high-resistance SEI layer, so the amount of the additive should not exceed
0.2% wt. In any case, even the small amount of PES in the electrolyte worsens the electrochemical
performance because the magnitude of SEI impedance (R ) and charge transfer impedance (R ) after 50
SEI
ct