Enabling fast Li+ transport in cellulose nanocrystals polymer electrolytes via grafting flexible acrylates for stable solid-state lithium metal batteries.

Cellulose nanocrystals (CNC), as an abundant and renewable biopolymer, are highly promising for suppressing lithium dendrites due to their outstanding mechanical strength. However, their intrinsically high crystallinity severely impedes Li+ transport, limiting practical deployment in battery electrolytes. Here, we report a CNC polymer electrolyte (CM-SSE) fabricated by grafting flexible, ether-rich acrylate side chains onto the rigid CNC backbone to provide abundant Li+ transport sites. The as-obtained CM-SSE exhibits a high ionic conductivity of 2.37 × 10-4 S cm-1 at 30 °C, a superior Li+ transference number of 0.78, and a mechanical strength of 6.1 MPa. Combined experimental and theoretical analyses reveal that the grafted chains form continuous ion-conduction pathways, while the CNC framework ensures mechanical integrity and its -OSO3H groups promote LiTFSI dissociation. This molecular-level synergy effectively suppresses dendrite growth, enabling Li/Li symmetric cells to cycle stably over 1000 h at 0.1 mA cm-2. The LiFePO4/CM-SSE/Li cells deliver 154.8 mAh g-1 at 0.1C with 98.4% retention after 200 cycles, and 92.4% after 490 cycles at 1C. Furthermore, the CM-SSE shows preliminary compatibility with high-voltage LiNi0.8Co0.1Mn0.1O2 (NCM811) cathodes. This work highlights the significant potential of cellulose in plasticized polymer electrolytes and offers a promising avenue toward sustainable energy storage systems.