High-performance sodium-ion storage: multi-channel carbon nanofiber freestanding anode contrived via ingenious solvent-induced phase separation

Abstract

As a promising anode material of sodium ion batteries (SIBs), hard carbon (HC) still faces challenges of inadequate active storage sites and sluggish ion-diffusion kinetics. To improve these issues, herein, we introduce a solvent-induced phase separation (SIPS) method to produce multi-channel carbon nanofibers (MCCFs) as a freestanding anode for SIBs. The channel structures can be precisely designed by simply tuning the mass ratio of the soluble polymer and insoluble carbon precursor, thereby affecting the microstructures of carbon nanofibers. Such tactics permit the first-displayed multi-channel structures in carbon nanofibers with expected defects/pores, and greater ascending rate performance compared to conventional materials. In particular, an outstanding reversible capacity (365.4 mA h g⁻¹ at 0.1C) and excellent cycling stability (90% retention rate after 300 cycles at 0.4C) benefit from the increased active sites and enhanced electrode kinetics. Meanwhile, abundant ultra-micropores allow only the entry of sodium ions and the expanded interlayer spacing makes the sodium insertion easier, and a high plateau capacity (231.2 mA h g⁻¹) below 0.1 V is acquired. When matched with an O₃-NaNi_1/3Fe_1/3Mn_1/3O₂ cathode, the full cell delivers excellent energy density of ca. 270 W h kg⁻¹ with reliable cycle performance. Moreover, relevant sodium storage behaviors and kinetics mechanisms are elaborated in detail. This work not only delivers a feasible strategy to construct multi-channel carbon-based materials, but also serves as a theory guide for designing other superb HC electrodes.