Phosphorylated cellulose nanofibers establishing reliable ion-sieving barriers for durable lithium-sulfur batteries

The shuttle effect is among the most characteristic and formidable challenges in the pursuit of high-performance lithium-sulfur (Li-S) batteries. Herein, phosphorylated cellulose nanofibers (pCNF) are intentionally engineered to establish an ion-sieving barrier against polysulfide shuttling and thereby improve battery performance. The phosphorylation, involving the grafting of phosphate groups onto the cellulose backbone, imparts an exceptional electronegativity that repels the polysulfide anions from penetrating through the separator. Moreover, the electrolyte wettability and Li+ transfer can be significantly promoted by the polar nature of pCNF and the facile Li+ disassociation. As such, rational ion management is realized, contributing to enhanced reversibility in both sulfur and lithium electrochemistry. As a result, Li-S cells equipped with the self-standing pCNF separator demonstrate outstanding long-term cyclability with a minimum fading rate of 0.013% per cycle over 1000 cycles at 1 C, and a decent areal capacity of 5.37 mA h cm−2 even under elevated sulfur loading of 5.0 mg cm−2 and limited electrolyte of 6.0 mL g−1. This work provides a facile and effective pathway toward the well-tamed shuttle effect and highly durable Li-S batteries.