Magnetron Sputtering Fabrication of a Zn3N2–Ag Dual-Functional Coating on a Copper Current Collector toward Stable Anode-Free Lithium Metal Battery

Anode-free lithium metal batteries (AFLMBs) have attracted extensive research attention due to their high energy density and simplified manufacturing processes. However, key scientific issues such as the intrinsic lithiophobicity, high surface roughness, and poor interfacial stability of commercial copper foil lead to uneven lithium nucleation and dendritic growth on its surface, severely compromising the cycle life and safety of AFLMBs. Constructing a lithiophilic interface with a stable solid electrolyte interphase (SEI) is a crucial strategy for regulating lithium deposition/stripping behavior. In this study, a Ag-Zn3N2 bifunctional thin film was successfully introduced onto a commercial copper foil via magnetron sputtering technology. The inner Ag layer serves as a lithiophilic host, providing abundant lithiophilic nucleation sites, significantly reducing the lithium nucleation overpotential, and guiding uniform lithium deposition. Upon initial contact with lithium, the outer Zn3N2 layer is converted in situ into a LiZn alloy and Li3N, promoting the formation of a stable Li3N-enriched SEI. Electrochemical performance demonstrates that the cell equipped with the Zn3N2-Ag@Cu current collector exhibits excellent properties: the half-cell achieves a stable cycling over 770 cycles with an average Coulombic efficiency of 98.7% at a current density of 0.5 mA cm-2 and a capacity of 1 mAh cm-2; the symmetric cell operates stably for more than 5200 h under the same conditions with a polarization voltage of only 17 mV; the anode-free full cell paired with a LiFePO4 cathode retains 88.2% of its initial capacity after 100 cycles at 0.5 C. This study demonstrates that the magnetron-sputtered Zn3N2-Ag dual-functional coating provides a viable strategy for the interfacial engineering of copper current collectors, contributing to the realization of high-performance, long-lifespan anode-free lithium metal batteries.