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Page 4 of 12 Cui et al. Energy Mater 2023;3:300034 https://dx.doi.org/10.20517/energymater.2023.19

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approximately 2,300 cm , which indicates that isocyanate has been completely consumed by the
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polyaddition reaction. The existence of C-SO -N bonds (1,195 cm ) and C-S bonds (1,061 cm ) is
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associated with LiTFSI. The existence of the -CH - component (2,918 cm ) and C-O-C bonds (1,135 cm ) is
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assigned to PU segments. We also recorded FTIR spectra of the PO membrane and PU-LITFSI (PO-PU-
LITFSI electrolyte without PO membrane). After adding the PO skeleton to PU-LiTFSI, the peak positions
of PU-LiTFSI did not shift and no additional peaks were observed, indicating that the PO skeleton does not
react with other components and exists stably in the PO-PU-LiTFSI electrolyte [Supplementary Figure 1].
Furthermore, TGA reveals that the PO and PU contents were 5 wt% and 15 wt%, respectively
[Supplementary Figure 2] .
[23]
The PO-PU-LiTFSI electrolyte shows high mechanical strength. As shown in Figure 2 A and
Supplementary Figure 3, the puncture resistance of the PO-PU-LiTFSI electrolyte is as high as 4.6 N, and its
tensile strength is 145.1 MPa. The tensile strength of the PO-PU-LiTFSI electrolyte is one of the best
performances among reported SPE [Supplementary Table 1]. The high strength of the electrolyte is related
to the high strength of the PO membrane. The puncture resistance and tensile strength of the PO-PU-
LiTFSI electrolyte are about 10% higher than those of the PO membrane, which indicates that PU-LiTFSI
modification can improve the strength of the PO skeleton.

The PO-PU-LiTFSI electrolyte exhibits high adhesion. The adhesive force between the PO-PU-LiTFSI
electrolyte and S cathode is 4.15 N, and the value between the electrolyte and Li anode is 2.36 N [Figure 2B
and Supplementary Figure 4A]. The high adhesion is related to high mobility of PU segments and the
strong interactions (such as H-bonding) between urethane/urea groups and other polar groups . The high
[24]
mobility of PU segments was reflected by the differential scanning calorimetry (DSC) curves and X-ray
diffraction (XRD) patterns. As shown in the DSC curves [Figure 2C], the peak at approximately -35 °C
corresponds to the glass transition temperature (T ) of the amorphous PU segments and the peak at
g
[23]
approximately 45 °C corresponds to the melting point (T ) of the crystalline PU segments . The DSC
m
curve of the PU-LiTFSI (LiTFSI: 80 wt%) shows no obvious peak at approximately 45 °C, indicating that the
PU segments in the electrolyte are amorphous. Meanwhile, no sharp diffraction peaks are detected at the
XRD pattern [Supplementary Figure 5], which also indicates the low crystallinity of PU segments.

The high mobility of PU segments is associated with the plasticizing effect of dissociated LiTFSI in the PO-
PU-LiTFSI electrolyte [Figure 3A]. The plasticizing effect enhances with increasing LiTFSI content
[Supplementary Figure 4B]. In contrast, LiTFSI in the PO-PEO-LiTFSI electrolyte cannot be dissociated at a
high content. Therefore, the PEO segments in the PO-PEO-LiTFSI electrolyte exhibit poor mobility,
resulting in poor contact with electrode [Figure 2B and C, Supplementary Figures 4A and 6]. The high
LiTFSI dissociation in the PO-PU-LiTFSI electrolyte is related to a strong interaction between
urethane/urea groups and TFSI . Density functional theory (DFT) calculations indicate that the binding
-
energies (E ) between the urethane/urea group and TFSI are 0.76 eV, respectively, which is higher than the
-
ads
-
values between ether oxygen of PEO and TFSI [Figure 3B]. The high binding energy can promote the
dissociation of LiTFSI [25,26] . The interaction between urethane/urea groups and TFSI was also reflected by
-
the FTIR spectra of PU and PU-LiTFSI [Supplementary Figure 6]. After adding LiTFSI to PU, the N-H peak
of PU shifted from 3,543 to 3,560 cm , while the C-N peak shifted from 1,360 to 1,348 cm . In addition, the
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C-O-C peak shifted from 1,107 to 1,135 cm . These peak shifts indicated the interaction between urethane/
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urea groups and TFSI . -
The PO-PU-LiTFSI electrolyte exhibits high ionic conduction. The room-temperature ionic conductivity
+
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+
(σ = 1.8 × 10 S cm ), Li t r a n s f e r e n c e n u m b e r ( t = 0 . 5 4 ) a n d Li d i f f u s i o n c o e f f i c i e n t
+