Skin-Like Coating Stabilizes the In Situ Forming Lithium Anode for High-Energy-Density Batteries.

In situ forming lithium metal batteries (IFLMBs) offer higher energy density and improved safety. However, lithiophobic Cu current collectors trigger nonuniform Li nucleation and dendrite growth, causing rapid Li inventory depletion and poor cycling stability. Herein, inspired by the selective transport regulation and barrier protection functions of the skin, a skin-like hydrolyzed collagen (HC) layer derived from biomass is constructed on Cu to stabilize IFLMBs. The ultrathin HC layer tightly covers the Cu surface as a biomolecular "skin", physically isolating deposited Li from the electrolyte and suppressing parasitic corrosion. Meanwhile, HC also serves as a durable lithiophilic nucleation scaffold. The abundant amide groups can act as lithiophilic active sites, redistributing Li+ flux and guiding uniform lithium nucleation. Accordingly, HC-coated Cu (HCCu) exhibits an increased Li+ transference number (0.71) and a reduced Li nucleation overpotential (13 mV). At a deposition capacity of 3 mAh cm-2, HCCu enables compact Li deposition with a thickness of 16.2 μm, which approaches the theoretical value of 15 μm. Consequently, Li||HCCu cells deliver a high average coulombic efficiency (CE) of 99.2% over 400 cycles. Moreover, a 6.4 Ah HCCu||LRMO pouch cell achieves a high energy density of 578.5 Wh kg-1, providing a viable pathway toward scalable, energy-dense IFLMBs.