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Page 10 of 12 Cui et al. Energy Mater 2023;3:300034 https://dx.doi.org/10.20517/energymater.2023.19

The excellent performance of the solid-state Li-S battery can be explained by the following factors: (1) High
+
+
room-temperature ionic conductivity, high Li transference number, high Li diffusion coefficient, and low
+
activation energy reduce battery internal resistance and polarization, thereby achieving fast Li transport.
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Fast Li transport is critical for the excellent electrochemical performance of Li-S batteries. (2) The high
adhesion allows the electrode and electrolyte to maintain tight contact and even enables the broken
electrode/electrolyte interface to self-heal during cycling, leading to stable Li transport [Figure 6G]. (3) The
+
high mechanical strength of the PO-PU-LiTFSI electrolyte inhibits the growth of lithium dendrites and
prevents damage to the electrode/electrolyte interfaces [Figure 1B]. (4) For Li-S batteries, the shuttle of
polysulfides between the Li anodes and S cathodes results in irreversible loss of active materials and
capacity. The PO-PU-LiTFSI can prevent polysulfides from reaching the Li anode, reducing capacity loss.
This effect was confirmed by DFT calculations. The binding energy between the PU segment and Li S is
2 6
1.43 eV, which is higher than that of the PEO segment and Li S (1.05 eV) [Supplementary Figure 10]. The
2 6
Li-S batteries using the PO-PU-LiTFSI electrolyte showed much lower shuttle currents. The results suggest
that the PO-PU-LiTFSI electrolyte can effectively prevent polysulfides from reaching the Li anode and thus
depressing the shuttle effect. Indeed, the Li-S batteries using the PO-PU-LiTFSI electrolyte also exhibited a
lower self-discharge rate at the open circuit voltage (OCV) than the Li-S batteries using the PO-PEO-LiTFSI
electrolyte [Supplementary Figure 11].

A solid-state Li-S pouch cell was assembled to evaluate application prospects of the PO-PU-LiTFSI
electrolyte. As shown in Figure 7A, the solid-state Li-S pouch cell delivers a specific capacity of 608 mAh g
-1
after 100 cycles. During the subsequent 0.1 C rate, it can still cycle for 150 cycles, exhibiting a specific
capacity of approximately 400 mAh g and an average Coulombic efficiency of 99.8%. The solid-state
-1
battery also exhibits good safety. As shown in Figure 7B, a solid-state Li-S pouch cell can power light-
emitting diode (LED) bulbs even after it is folded, penetrated, cut, and lit.

CONCLUSIONS
In summary, we proposed a high ionic conduction and high adhesion PO-PU-LiTFSI electrolyte for solid-
state Li-S batteries with fast and stable Li transport. The symmetric Li||Li cell using the PO-PU-LiTFSI
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electrolyte exhibited a stable overpotential of about 40 mV during cycling for 800 h. The solid-state Li-S
-1
battery using the electrolyte maintained a discharge capacity of about 610 mAh g after 125 cycles at the S
loading of about 4 mg cm . The excellent performance was attributed to the high ionic conduction and high
-1
adhesion of the electrolyte. The high ionic conductivity ensures fast Li transport in the electrolyte, while its
+
high adhesion enables tight contact with electrodes and even enables the broken electrode/electrolyte
interface to self-heal, resulting in stable electrode/electrolyte interfaces and stable Li transport during
+
cycling. The robust electrode/electrolyte interface during cycling was confirmed by in-situ observation using
a laser confocal microscope. Our work demonstrates that Li transport problems of solid-state Li-S batteries
+
can be solved by using electrolytes with polar groups. This design concept has the potential to solve similar
interfacial problems of other solid-state batteries.