Revisiting the Closed‐Pore Formation and Interfacial Micro‐Environment Modulation Mechanisms of Polyacrylonitrile‐Derived Carbon Nanofibers Toward Efficient Sodium Storage

Abstract

Polyacrylonitrile‐based carbon nanofibers (CNFs) are widely regarded as promising sodium‐storage anodes owing to their high carbon yield/axial conductivity and superior mechanical flexibility. Nevertheless, the ambiguous understandings into the temperature‐dependent micro‐structure evolution, particularly the closed‐pore formation over pyrolysis, and the electrolyte induced electrode‐electrolyte interface micro‐environments, along with the involved influence mechanism upon sodium‐storage behaviors should be reasonably clarified. With systematical in(ex)‐situ physicochemical/electrochemical characterizations, it is first established that the optimal pyrolysis temperature of 1400°C combined with a “zipper‐like” point‐line‐plane solid‐phase fusion evolution effectively modulates micro‐structures, endowing the optimized pseudo‐graphitized CNFs film (i.e., GCNFs‐1400) with a synergistic balance among ions transport pathways (interlayer spacing), active storage sites (closed pores), and 3D conductive supporting framework (solid‐phase fusion). Concurrently, compared to the ester‐based electrolyte, the ether‐based electrolyte favors the formation of a thinner, more uniform, and chemically stable solid electrolyte interphase layer. It is the dual‐engineering of both material micro‐structures and interfacial micro‐environment that fully guarantees the competitive sodium‐storage properties of GCNFs‐1400 in terms of ultra‐high initial Coulombic efficiency (96.2%), rate capability, and long‐term stability toward presodiation‐free sodium‐ion batteries and sodium‐ion capacitors. More essentially, our in‐depth insights here provide meaningful guidance for future design of advanced hard carbon anodes toward efficient sodium storage.