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Tao et al. Energy Mater 2022;2:200036 https://dx.doi.org/10.20517/energymater.2022.46 Page 13 of 35

materials, carbon-based groups afford relatively strong affinity for polar LiS species (calculated binding
energy of 0.30 eV); however, an electron source from carbon can accelerate the electrochemical
decomposition of sulfide-based SSEs, contributing to the formation of the cathode/electrolyte interface.

Computational studies can also be used to predict the electrochemical window of SSEs, as in the previous
sections, which is normally less than the redox potential of cathode active materials, indicating that most
SSEs show high instability in contact with cathodes during cycling. For sulfide SSEs, the calculated
oxidation potential is ~2.15-2.31 V and a series of the decomposed interfacial products can be
[90]
computationally confirmed (e.g., S, P S , Li P S and Li S for Li PS and Li PS , GeS , S, Li GeS , Li P S and
2
2
4
4 2 6
4
4
3
3
2 5
4 2 6
4
Li S for LGPS).
2
Although the interfaces between sulfide-based cathodes and SSEs could be very stable compared to oxide
cathodes because sulfide-based cathodes show similar chemical potential with sulfide-based SSEs, their
interface with limited ionic conductivity cannot be favorable for the development of ASSLSBs with high
electrochemical performance. In order to further understand the interface stability of sulfide-based
cathodes/SSEs, the prediction of their thermodynamic reaction energy, the exact reaction pathway and
possible interfacial reactions using theoretical calculations should be performed, the existence of a space-
charge layer confirmed and the interface modeled.
Lithium metal anode side
It has been found that theoretical calculations are very efficient and powerful tools for investigating and
analyzing the properties of anode/SSE interfaces and interfacial evolution behavior of ASSLSBs during
cycling, significantly contributing to understanding the role of interfaces in ASSLSBs. The Li metal anode
shows a high adhesion (W ) predicted by density functional theory calculations when exposed to SSEs,
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which can be used to reveal the possible working mechanism of the interfacial layer between the anode and
electrolyte . Furthermore, a series of interfacial reactions between anodes and electrolytes can be predicted
[93]
by theoretical calculations. The results show that sulfide-based SSEs, including Li PS , Li P S , Li P S I,
4
7 2 8
3
7 3 11
Li PS Cl and LGPS, have low thermodynamic stability against Li metal, are usually reduced during
6
5
assembling and cycling and possibly form Li-based interfacial products, such as Li S, Li P, Li-metal alloys,
2
3
LiCl and LiI.
Computational studies are also used to reveal the mechanical properties of the Li metal/SSE interface, such
as Young’s, bulk and shear moduli and estimate their effect on the formation and growth of Li dendrites at
the anode/SSE interface. The result indicates that Li dendrite propagation in the SSE should be suppressed if
the shear modulus of an electrolyte is higher than twice that of Li metal.
Ultimately, theoretical calculations, combined with experimental characterization methods, including
scanning tunneling microscopy, scanning transmission electron microscopy (TEM), X-ray diffraction
(XRD), X-ray photoelectron spectroscopy (XPS), infrared and Raman spectroscopy, nuclear magnetic
resonance spectroscopy, X-ray absorption spectroscopy and binding energy, can be the most efficient route
to exploring the interfacial properties between electrodes and electrolytes, analyzing their interfacial
resistance, predicting the structural and chemical information of the interface and providing essential
guidelines for screening and designing stable interfaces.