In Situ Chemical Lithiation Transforms Diamond‐Like Carbon into an Ultrastrong Ion Conductor for Dendrite‐Free Lithium‐Metal Anodes

Abstract Lithium (Li)‐metal anodes are of great promise for next‐generation batteries due to their high theoretical capacity and low redox potential. However, Li‐dendrite growth during cycling imposes a tremendous safety concern on the practical application of Li‐metal anodes. Herein, an effective approach to suppress Li‐dendrite growth by coating a polypropylene (PP) separator with a thin layer of ultrastrong diamond‐like carbon (DLC) is reported. Theoretical calculations indicate that the DLC coating layer undergoes in situ chemical lithiation once assembled with the lithium‐metal anode, transforming the DLC/PP separator into an excellent 3D Li‐ion conductor. This in situ lithiated DLC/PP separator can not only mechanically suppress Li‐dendrite growth by its intrinsically high modulus (≈100 GPa), but also uniformly redistributes Li ions to render dendrite‐free lithium deposition. The twofold effects of the DLC/PP separator result in stable cycling of lithium plating/stripping (over 4500 h) at a high current density of 3 mA cm⁻². Remarkably, this approach enables more than 1000 stable cycles at 5 C with a capacity retention of ≈71% in a Li || LiFePO₄ coin cell and more than 200 stable cycles at 0.2 C in a Li || LiNi_0.5Co_0.3Mn_0.2O₂ pouch cell with cathode mass loading of ≈9 mg cm⁻².