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Page 20 of 35 Tao et al. Energy Mater 2022;2:200036 https://dx.doi.org/10.20517/energymater.2022.46

resulting composite structure plays a critical role in improving the performance of the cathode. It has been
reported that the combined mechanical and liquid-phase mixing can increase the ionic conduction pathway
in cathode materials incorporating carbon replica, S and a solid electrolyte, resulting in improved
[148]
electrochemical performance of the composite cathode . A simple two-step dry/wet-mixing method was
reported by Chung et al. for preparing a cathode composite of homogeneous Li S-TiS -electrolyte , which
[103]
2
2
enables the composites to realize an intimate contact between the conductive TiS , active materials and the
2
SSE. Consequently, all these strategies are expected to construct favorable interfaces to alleviate stain/stress
and achieve ultrafast electronic and ionic pathways in solid-state battery systems.
Introducing a bifunctional ion-electron conducting layer between cathodes and SSEs
Intercalating a bifunctional ion-electron conducting layer between SSEs and cathodes offers another
[152]
practical method to improve the interfacial compatibility of batteries . The conducting layer is composed
of super P and PEO. An ASSLSB with a conducting layer thickness of 40 μm showed enhanced
-1
electrochemical properties(792.8 mAh g after 50 cycles) and interfacial compatibility. A novel bilayer
framework has been designed and fabricated by integrating a carbon nanofiber/sulfur composite with a
ceramic Li La 0.557 TiO nanofiber-PEO solid electrolyte, which showed an intimate and sufficient phase
3
0.33
contact of active materials and electrolyte and can function as both the cathode and electrolyte for high-
performance ASSLSBs . Furthermore, it has been demonstrated that modifying the interface between the
[118]
cathodes and SSEs with a highly concentrated solvate electrolyte as a Li -conducting interfacial layer,
+
acetonitrile-lithium-bis(trifluoromethane sulfonyl)imide:1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl
ether, can promote the sufficient interfacial contact of electrodes and electrolytes . A multi-channel
[119]
continuous electronic/ionic conductive network composed of the composite of a reduced graphene oxide-
vanadium tetrasulfide nanostructure coated with Li P S solid electrolyte nanoparticles can also contribute
7 3 11
to the improvement of the electronic/ionic conductivity and interfacial contact .
[153]

Based on the above research, it can be concluded that ASSLSBs based on composite cathodes exhibit higher
electrochemical performance than cells constructed with pure active materials. A suitable phosphorus/sulfur
(P/S) ratio of ISSEs in the composite cathodes is very important for a high ionic conductivity, which can
[154]
increase the reactivity of the sulfur, resulting in an improved battery performance . The interfacial
compatibility between SSEs and cathodes greatly depends on their composition and the structure of
composite cathode materials. The composite cathode materials composed of active materials and Li-ion and
electronic conductors can combine the advantages of each species to improve cathode/electrolyte interfacial
properties. The design and fabrication of smart cathode/electrolyte integrated architectures to decrease the
interfacial resistance will be the direction of future research. Further understanding of their interfacial
construction is important for accelerating the development of ASSLSBs.

Lithium anode side
In addition to the strategies conducted for the improvement of interfacial compatibility between SSEs and
cathodes, the issues related to the interface between Li anodes and SSEs should also be considered in
ASSLSBs. A solid electrolyte interphase layer is easily generated at the anode/SSE interface due to the
decomposition products of the SSE, which have lower ionic conductivity and result in increased interfacial
resistance. A “dot-dot” interfacial contact can cause non-uniform Li dissolution/deposition, reduce the
utilization of Li metal and result in a high interfacial resistance between a Li anode and SSEs, which is a
serious problem for ASSLSBs. Furthermore, the interfacial resistance is obviously related to the interface
voids and grain boundaries. In order to decrease the anode/SSE interfacial resistance and promote their
interfacial contact, numerous methods have been developed, such as introducing protective interlayers and
fabricating composite SSEs [Figure 4].