High-Density and Freestanding Porous Carbon Film for Compact Sodium-Ion Storage

Porous carbon materials are often difficult to achieve high density while possessing high porosity, which limits their application in compact energy storage. Here, a design of freestanding porous-yet-dense carbon films with a tunable density (1.08–1.33 g cm⁻³) and porosity (specific surface area of 0–423.8 m² g⁻¹) is presented through an assembly of porous carbon nanosheet with graphene oxide under vacuum filtration. The typical freestanding carbon films simultaneously deliver a high density of 1.08 g cm⁻³ and a high specific surface area of 423.8 m² g⁻¹ when the porous carbon nanosheet content is 75 wt.%. As anode materials for sodium-ion batteries, the optimized freestanding carbon films deliver high volumetric capacity (270 mAh cm⁻³ at 20 mA g⁻¹), high initial capacity efficiency (81 %) and superior long-term cycling stability (1300 cycles with a capacity decay rate of 0.012 % per cycle). This study provides a promising direction for creating freestanding electrodes that meet both high-porosity and high-density requirements for compact sodium-ion batteries.