Alloying Interlayers for Anode‐Less Lithium‐Metal Polymer Batteries

Anode-less lithium-metal batteries potentially offer further increased energy densities. However, the Coulombic efficiency (CE) of lithium plating and stripping, as a classical measure of Li inventory reversibility, is commonly still insufficient for achieving long-lasting rechargeable batteries. Herein, the potential benefits of employing thin (20 nm) metal interlayers of Ag, Pt, and Au on Cu to alloy with Li in Cu||Li half-cells and induce homogeneous Li plating with poly(ethylene oxide)-based electrolytes are investigated. Interestingly, not all alloying interlayers enable a higher CE compared to neat Cu foil with 84%—specifically Ag@Cu with only 81%, while the best performing one, Au@Cu, provides a substantially increased CE of 91%. While generally the formation of “dead lithium” is found to be the major source of CE, this appears to be less pronounced in the case of Au@Cu, indeed. Further improvement can be achieved by carefully adjusting the cell voltage to a region in which the continuous de-/alloying is suppressed, yielding a further enhanced CE of 94%, thus highlighting the need for a comprehensive approach to design suitable electrode chemistries and designs beyond a “simple” material improvement.