Cellulose nanofiber-derived carbon aerogel for advanced room-temperature sodium-sulfur batteries

Room-temperature sodium-sulfur (RT/Na-S) batteries are regarded as promising large-scale stationary energy storage systems owing to their high energy density and low cost as well as the earth-abundant reserves of sodium and sulfur. However, the diffusion of polysulfides and sluggish kinetics of conversion reactions are still major challenges for their application. Herein, we developed a powerful and functional separator to inhibit the shuttle effect by coating a lightweight three-dimensional cellulose nanofiber-derived carbon aerogel on a glass fiber separator (denoted NSCA@GF). The hierarchical porous structures, favorable electronic conductivity, and three-dimensional interconnected network of N,S-codoped carbon aerogel endow a multifunctional separator with strong polysulfide anchoring capability and fast reaction kinetics of polysulfide conversion, which can act as the barrier layer and an expanded current collector to increase sulfur utilization. Moreover, the hetero-doped N/S sites are believed to strengthen polysulfide anchoring capability via chemisorption and accelerate the redox kinetics of polysulfide conversion, which is confirmed from experimental and theoretical results. As a result, the assembled Na-S coin cells with the NSCA@GF separator showed a high reversible capacity (788.8 mAh g(-1) at 0.1 C after 100 cycles) and superior cycling stability (only 0.059% capacity decay per cycle over 1000 cycles at 1 C), thereby demonstrating the significant potential for application in high-performance RT/Na-S batteries.

Automated summary

A functional separator combining lightweight three-dimensional cellulose nanofiber-derived carbon aerogel and glass fiber separator is developed to address the challenges of polysulfide diffusion and slow reaction kinetics in room-temperature sodium-sulfur batteries. The multifunctional separator exhibits strong polysulfide anchoring capability and fast reaction kinetics, as well as acts as a barrier layer and expanded current collector to enhance sulfur utilization. Experimental and theoretical results confirm the mechanism of enhancing polysulfide anchoring capability and accelerating redox kinetics through chemisorption at hetero-doped N/S sites. The Na-S coin cells assembled with this separator show high reversible capacity and superior cycling stability, demonstrating their significant potential for high-performance energy storage systems.