Gradient nano-recipes to guide lithium deposition in a tunable reservoir for anode-free batteries

Anode-free batteries (AFBs) have the potential of ultra-high energy density, but lithium dendrite has largely hindered their practical applications. In this work, an in-situ grown gradient solid electrolyte interface (SEI) layer on pre-designed micro-hole-grid (MHG) Cu reservoir is proposed to guide uniform lithium deposition and propagation, by which the electrode interface is stabilized and the surface stress is considerably decreased endowing the AFBs with outstanding areal capacity and cycling performance. The gradient SEI is confirmed by cryogenic-transmission electron microscopy (Cryo-TEM) and XPS to be composed of (1) an elastic organic top layer to hinder non-Li species migration and withstand volume fluctuation, and (2) a lithophilic LiCl-rich bottom layer to render the rapid lithium supply. Operando electron paramagnetic resonance (EPR) shows a dynamic Li deposition, unambiguously demonstrating a dendrites-free behavior. As a result, the full cells of a gradient SEI modified Cu reservoir paired with a LiFePO₄ cathode exhibit high capacity of 95 mAh g^–1 and Coulombic efficiency (CE) of 99.5% after 100 cycles, much better than the control cells with planar current collectors (1.6 mAh g^–1, 2.6%). These findings are enlightening in engineering better interphases for high energy and safe rechargeable lithium metal batteries.