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. A porous yet dense freestanding carbon film was constructed through a self-assembly of graphene oxide and porous carbon sheet, which were stack in a laminated fashion to form the compact structure. It was demonstrated that the balance of porosity and density endowed the carbon film with improved compact sodium-ion storage performances. image