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Tao et al. Energy Mater 2022;2:200036 https://dx.doi.org/10.20517/energymater.2022.46 Page 21 of 35

Introducing interface layers between lithium anodes and SSEs
Metal-based thin films

Since the Li metal anode has the most negative electrochemical potential, it can easily react with most SSEs
to form a metastable interface, resulting in poor Li-ion diffusion. In order to alleviate the interfacial
reactions between the SSE and lithium electrode , metal thin films were introduced on the SSE surface,
[155]
[126]
[158]
[136]
[156]
[159]
including Li , Au , Al , In , Ge , Sn and Mg . These are effective in constructing
[160]
[157]
homogeneous interfaces between the anode and SSEs, because the metal can react with Li to form a Li-metal
alloy layer, effectively decreasing the generation of grain boundaries and voids at the SSE/anode interface
and improving their interfacial compatibility. For example, Au thin films were employed as an ideal
[161]
interface between the SSE and anode, because Au shows good interfacial wetting with them . In addition,
an ultrathin, artificial intermediary Al layer was used to modify the interface of the garnet solid electrolyte
and Li metal, and the formed Li-Al alloy interface layers play a key role in improving the Li wettability of
SSE and reducing their interfacial resistance . Similarly, a favorable interface between the SSE and anode
[158]
can be constructed by alloying Li metal with Ge, and the formed Li-Ge alloy interface layer has a high Li-ion
conductivity . Since Sn has a high lithium diffusion rate and ductility, it can be inserted into the
[136]
electrode/anode interface to construct a suitable interfacial phase and decrease the interfacial resistance .
[159]
A Li-rich Li-Mg alloy was deposited on the surface of a SSE and employed as an anode for ASSLSBs,
because the Li-Mg framework can construct continuous Li-ion/electron dual-conductive pathways at the
[160]
anode/SSE interface [Figure 11A-J]. Therefore, it is expected that more metals that are miscible with Li
can be used as suitable interphases to construct ideal anode/electrode interfaces.
Inorganic materials
Many inorganic materials, including Al O 3 [158,159] , ZnO , amorphous Si , graphite [32,167,168] , LiH PO 4 [169] ,
[166]
[113]
2
2
BN and Li N , have outstanding reactivity with molten lithium, which can serve as a surface
[170]
[161]
3
modification layer of garnet SSE to fill the gap between the SSE and lithium electrode. The resulting
intimate contact between lithium and garnet SSE leads to a low interfacial resistance decrease. Inserting an
ultrathin Al O layer into the anode/electrolyte interface can promote the molten Li metal to be uniformly
3
2
deposited on the surface of SSE and prevent the generation of interfacial void space, resulting in an
improvement in the interfacial wetting and stability [156,157] [Figure 11K and L]. Furthermore, the surface
wettability of a SSE can be significantly improved by a ZnO coating layer, because it can react with the
molten Li metal to form a Li-Zn alloy layer to enhance the interfacial contact between the SSE and lithium
electrode . In addition, an electron/ion dual-conductive framework formed by a reaction between
[113]
graphite and the molten Li metal can ensure good interfacial contact with the SSE [32,167,168] . Since a LiH PO
2
4
protective layer in situ constructed by a manipulated reaction between Li anode and Li GeP S can
2 12
10
effectively prevent uncontrollable interfacial layer growth, enhance the contact area of electrode/electrolyte
and benefit the diffusion of mixed ionic-electronic reactants into the inner of electrolyte, it is considered as
[169]
an ingenious interfacial reengineering strategy for reducing the anode/SSE interfacial resistance . A BN
nanofilm, which has good insulation and ionic conductivity, was also employed as a protecting layer to
[161]
reduce the reduction of the SSE by Li metal and stabilize the electrolyte/anode interface . Coating Li N
3
onto the Li metal surface could be an effective method for constructing better SSE-lithium wetted
interfaces because Li N has high Li-ion conductivity and is easily prepared by a direct reaction between
[170]
3
Li metal and nitrogen at room temperature. Consequently, the surface reactions between the introduced
protective interlayers and the Li metal play an essential role in improving the electrode/anode interfacial
[171]
compatibility and Li-ion and electronic conductivity .