UV-Assisted Rapid Polymerization of Poly(Tannic Acid)-Silver Layers for Design Lithiophilic Layers in Anode-Free Lithium Metal Batteries

Anode-free lithium metal batteries (AFLMBs) enhance energy density by using bare copper (Cu) foils as the anode. However, they face challenges due to irreversible lithium (Li) plating caused by the inherent lithiophobicity of the materials. In this study, we present an ultraviolet-assisted in-situ polymerization strategy to create a poly(tannic acid) film embedded with silver (Ag) nanospheres (PTA@Ag-Cu) in just 15 minutes. The PTA film improves the wettability of the electrolyte, reducing the contact angle by 50.6%, and accelerates Li⁺ desolvation. The Ag nanoparticles (21 nm) lower the nucleation overpotential to 10 mV compared to 150 mV for bare Cu, through the formation of a lithiophilic LiAg alloy. The charge-transfer dynamics and embedded electric fields, which are verified by density functional theory (DFT), contribute to the uniform deposition of Li, as evidenced by in situ optical microscopy. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) indicates a synergistic regulation of Li⁺ flux at the atomic level by the combination of Ag and molecular-level interactions from PTA. The PTA@Ag-Cu||LiFePO₄ configuration achieves 61.2% capacity retention after 100 cycles at a rate of 1 C-rate without pre-lithiation. The preparation of PTA@Ag-Cu using UV-assisted polymerization is economical, time-saving, and suitable for large-scale production. This work introduces a photo-induced dual-functional interface that addresses AFLMB degradation through integrated electric field engineering, making it compatible with roll-to-roll battery manufacturing.