Various artificial interlayers like metal/metallic oxides have been introduced to improve Li wettability through alloy reaction for the Li/garnet interface. However, huge volume change during the continuous alloying/dealloying process is detrimental to the rigid solid-to-solid contact of Li/garnet and subsequently leads to instability of the polarization voltage. Herein, we demonstrate an improved artificial interlayer of Cu 6 Sn 5 to simultaneously restrict the volume change and ensure the intimate contact of the Li/garnet interface. It is proved that the Cu atom in Cu 6 Sn 5 cannot only mitigate the volume change but also restrain the diffusion of Sn. Intimate solid contact of Li with garnet can still be realized after Li stripping due to upholding of the Li 2+x Cu 1−x Sn framework. Moreover, the Li/garnet/Li symmetric cell with Cu 6 Sn 5 modification displays smaller voltage polarization and impedance change than the pure Sn modified counterpart.

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