Nanotwinned Copper Foil for "Zero Excess" Lithium-Metal Batteries

The "zero excess" lithium-metal battery cell concept, in which the pristine negative electrode consists only of the current collector, while all lithium is present only in the positive electrode active material, promises substantial improvements in energy density. However, the achievement of stable cycling for more than just a few cycles requires a careful design and adjustment of all cell components -especially the current collector at the negative electrode. Herein, we provide a comparative investigation of commercial, polycrystalline copper foil, characterized by a rather random [111], [200], and [220] orientation and a high concentration of grain boundaries, and nanotwinned copper foil, which has a solely [111]-oriented grain structure. Remarkably, the plated lithium on the foil with [111] orientation reveals a much more homogeneous morphology independent of the current density applied, while several dendritic lithium deposits are observed on the polycrystalline copper foil. This also translates into higher Coulombic efficiency and stabilized cycling performance of Cu[111]|| NMC811 cells, highlighting the important impact of the crystal orientation of the current collector.