“Pore‐Hopping” Ion Transport in Cellulose‐Based Separator Towards High‐Performance Sodium‐Ion Batteries

Sodium‐ion batteries (SIBs) have great potential for large‐scale energy storage. Cellulose is an attractive material for sustainable separators, but some key issues still exist affecting its application. Herein, a cellulose‐based composite separator (CP@PPC) was prepared by immersion curing of cellulose‐based separators (CP) with poly(propylene carbonate) (PPC). With the assistance of PPC, the CP@PPC separator is able to operate the cell stably at high voltages (up to 4.95 V). The “pore‐hopping” ion transport mechanism in CP@PPC opens up extra Na+ migration paths, resulting in a high Na+ transference number (0.613). The separator can also tolerate folding, bending and extreme temperature under certain circumstances. Full cells with CP@PPC reveal one‐up capacity retention (96.97 %) at 2C after 500 cycles compared to cells with CP. The mechanism highlights the merits of electrolyte analogs in separator modification, making a rational design for durable devices in advanced energy storage systems. Immersion curing of a cellulose‐based separator (CP) with poly(propylene carbonate) (PPC) results in a cellulose‐based composite separator (CP@PPC) for sodium‐ion batteries. The “pore‐hopping” ion transport mechanism in CP@PPC allows a high Na+ transference number. PPC enhances the mechanical properties of the separator and the battery thermal safety, further promotes ion transport and improves the overall performance of the battery.