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Yan et al. Energy Mater 2023;3:300002 https://dx.doi.org/10.20517/energymater.2022.60 Page 17 of 32

[121]
behavior . More recently, Luo and co-workers proposed a 3D MXene aerogel MIEC scaffold for a Li metal
[122]
anode with excellent electrochemical performance under high current density . Represented by Ti C ,
2
3
such MXene aerogels have both high electronic conductivity and fast ionic transport capability due to the
abundant lithiophilic oxygen- and fluorine-containing functional groups.
In addition, some IC frameworks, such as Li La Zr Al O (LLZO), were incorporated into the 3D EC
3
12
0.2
2
6.4
framework of carbon nanofibers via an electrospinning process, followed by heat treatment, fabricating a
3D MIEC composite framework . The outstanding performance of this framework could be attributed to
[123]
the improved electrolyte wettability caused by decreased interface energy and homogenized Li flux to
+
compensate Li depletion in the vicinity of the electrode. Li et al. developed a 3D crosslinked porous
+
polyethylenimine sponge (PPS), which was capable of providing strong Li-ion affinity and promoting
[124]
+
electrokinetic phenomena [Figure 6E] . The lithiophilicity of the PPS concentrates Li ions in the sponge,
leading to a higher local concentration of Li ions at the electrode/electrolyte interface compared to that in
+
the bulk electrolyte. Chen et al. reported that a prelithiated Li Si anode can effectively suppress the
x
formation of dead Li when the total lithiation/delithiation capacity in each cycle is higher than the Li
plating/stripping capacity on Li Si because the slight delithiation from Li Si shows a higher potential than
x
x
the stripping of deposited Li from Li Si [Figure 6F] .
[35]
x
Fabrication of artificial interfaces
Fabricating artificial SEIs (ASEIs) is one of the most attractive solutions to overcome the shortcomings of
spontaneously formed interphases. Due to multiple degrees of freedom, ASEIs with unique properties and
compositions created outside an electrochemical cell can be precisely tuned. A stable and homogeneous
ASEI with a specific composition on the electrode surface is favorable for the definition and characterization
of structure-property relationships. Ideally, as shown in Figure 7A, an ideal ASEI must meet several intrinsic
requirements: (1) chemically and electrochemically stable to avoid parasitic reactions with the electrolyte;
(2) mechanically flexible and robust to withstand the volume change and retard dendrite growth during
repeated cycles; and (3) uniform and abundant ion conductive pathways to facilitate facile single Li-ion
diffusion [125,126] .

An ideal ASEI must be stable to the Li metal anode, preventing electrolyte component decomposition apart
[127]
from the reduction of Li ions . Polymer networks have shown the ability to stabilize Li metal anodes and
+
block electrolyte penetration to some extent. In addition, ASEIs are attractive due to the polymer networks,
[129]
[130]
[128]
such as polyethylene oxide , Nafion and polyvinylidene fluoride , having a maximum limit in
swelling due to the balance between the entropy of mixing and the entropy of the polymer chain
configuration . Huang et al. integrated tether cations onto a polymer backbone to form a polyionic liquid
[131]
coating that is chemically stable even at ultranegative potentials below Li reduction (< -3.04 V vs. SHE),
resulting in an improved Li deposition morphology, as well as superior cycling performance of LMBs
[132]
[Figure 7B] . A Li metal electrode featured with an air-stable and waterproof surface using a PEO-based
composite ASEI film was also prepared by Yang and co-workers for Li-S battery applications [Figure 7C] .
[133]
The mechanical modulus of the interphase can be tuned by modulating the physical structure and chemical
compositions of the ASEI. During the electrodeposition process, mechanically unstable SEIs are prone to
fracture and allow dendritic penetration when confronted with large amounts of stress and strain, leading to
+
[134]
the generation of hotspots in which uneven diffusion of Li ions aggravates dendritic Li growth . Even
without dendrites, the mechanical degradation of the SEI will expose fresh Li to solution, leading to the
consumption of both electrolyte and Li metal. Therefore, the degradation of mechanical stabilities
accelerates the failure of batteries. Tamwattana et al. showed that the considerably high tensile strength and