Multifunctionalized Safe Separator Toward Practical Sodium‐Metal Batteries with High‐Performance under High Mass Loading

Introducing sodium as anode to develop sodium metal batteries (SMBs) is a promising approach for improving the energy density of sodium‐ion batteries. However, fatal problems, such as uncontrollable sodium dendrite growth, unstable solid electrolyte interphase (SEI) in low‐cost carbonate‐based electrolytes, and serious safety issues, greatly impede the practical applications. Here, a multifunctionalized separator is rationally designed, by coating PP separator (200 µm) and successfully solves all of the above problems, and for the first time creats high performance SMBs by using Na3V2(PO4)3 (NVP) cathodes in pouch cell. The Na||NVP full cells can stably cycle over 1200 times with capacity retention of 80% at a high rate of 10 C and deliver a specific capacity of 80 mAh g−1 even at high rate of 30 C, indicating extraordinary fast‐charging characters. The full SMBs can also stably cycle 200 times with a retention of 96.4% under high NVP loading of 10.7 mg cm−2. Most importantly, the SMB pouch cell can also deliver a long‐life cycles as well as high‐temperature battery performance, which guarantees the safety of SMBs in practical application. Multifunctionalized safe separator by coating PP separator with a solid‐state NASICON‐type fast ionic conductor layer (NZSP@PP) is successfully constructed to replace the widely used thick glass fiber separator in sodium‐metal batteries, which can well regulate Na+ plating/striping, inhibit dendrite Na formation, stabilize solid electrolyte interphase and possesses good thermal tolerance.