Bottom-Up Li Deposition by Constructing a Multiporous Lithiophilic Gradient Layer on 3D Cu Foam for Stable Li Metal Anodes

Metallic current collectors with three-dimensional (3D) porous structures have been considered as ideal hosts for Li metal anodes because of their ability to accommodate anode volume fluctuations and suppress Li dendrite formation. However, in a conductive 3D porous framework, Li preferentially deposits at the top surface, resulting in uneven deposition, and ultimately forms Li dendrites. Herein, we propose a deposition regulation strategy by fabricating a lithiophilic nanoporous CuSnAl layer at the bottom of a porous Cu foam to induce bottom-up and dense Li deposition. The as-prepared CuSnAl@Cu foam demonstrates enhanced Li deposition reversibility with a lifespan over 2000 h in symmetrical cells at 1 mA cm-2. Full cells coupled with lithiated CuSnAl@Cu foam and a LiFePO4 cathode exhibit outstanding electrochemical performance, with a Coulombic efficiency (CE) of 99.6% over 300 cycles, which is much better than that using a pure Cu foam or Cu foil. Moreover, the electric field distribution at the CuSnAl layer has been directly observed to disclose the intrinsic mechanism of bottom-up Li growth. This design of 3D metallic current collectors with a lithiophilicity gradient provides new insights into stable Li metal anodes, and thus, into Li metal batteries.