Pyroprotein-Based Ultra-Thin Catalytic Layer for Sodium Metal Batteries

Abstract

In this study, a thin pyroprotein seed layer (PSL, ∼100 nm thick) was coated on a Cu substrate via spin-coating with a regenerated silk fibroin (RSF) followed by pyrolysis at 800 °C. The PSLs were composed of highly disordered carbon building blocks in which Na ions can diffuse and come into contact with numerous defective carbon sites. Therefore, the homogeneous deposition of Na metal can be induced on the PSL-coated Cu electrode (PSL-Cu) at a high areal current density of ∼4 mA cm−2. The nucleation overpotential of PSL-Cu remarkably decreases by ∼10 mV, which is a much lower value than that (∼26 mV) of a bare Cu foil electrode. In addition, the PSL-Cu achieved stable Na metal deposition/dissolution during ∼300 cycles with a mean CE of ∼99.96%, which is the highest value reported for metal anodes thus far. Moreover, the PSL-based Na metal anode has a significantly low cell-to-cell variation with a CE deviation of ∼0.43%. Considering the simple fabrication process and well-established chemistry of PSL-Cu, the electrochemical performance of PSL-Cu deserves significant attention. The feasibility of PSL-Cu was further demonstrated via a full-cell experiment using a reported polyanion cathode, which revealed a high specific energy of 402 W h kg−1 at 390 W kg−1, high specific power of 3800 W kg−1 at 275 W h kg−1, and stable cycling with a capacity retention of 86% after 30 cycles. This work proves that the electrochemical performance of a metal anode can be advanced by (1) increasing the number of catalytic nucleation sites for metal electrodeposition and (2) enhancing the wettability of the electrolyte through the introduction of a large number of nucleophilic functional groups.