Arrayed silk fibroin for high-performance Li metal batteries and atomic interface structure revealed by cryo-TEM

Abstract

Lithium (Li) metal anode has been extensively studied due to its ultrahigh theoretical capacity and lightweight nature. However, the inherent uncontrolled growth of Li dendrites evokes serious safety issues and leads to compromised electrochemical reversibility. Here, we report an upright silk fibroin/Li foil (SF–Li) alternant array as the anode for Li metal batteries. The arrayed structure reduces the local current density so that the fast dendrite growth is suppressed while the three-dimensional porous SF effectively accommodates the volume expansion of the anode during cycling. More importantly, SF with rich polar groups participates in the formation of the solid electrolyte interphase (SEI) as the lithiophilic phase and regulates the SEI structure. In particular, the SEI on the Li grown between upright SF and Li foil shows an unexpected robust layered structure (as revealed by cryogenic transmission electron microscopy), which is rarely seen among the SEIs formed in ether-based electrolytes at room temperature. The low-impedance, mechanically stable SEI together with the architectural design of the SF–Li anode guarantee a superior cycling lifespan over 3800 h at 1 mA cm⁻² with a capacity of 5 mA h cm⁻² in symmetric cells. As such, we suggest a structured-biomass strategy towards smooth Li metal anodes, as well as regulating the nanostructures of SEI atomically.