SnF <sub>2</sub> ‐Modified Thin Composite Electrolyte With Ultra‐Stable Interface for Solid‐State Sodium Batteries
Jinbo Zhang, Yanxia Su, Zeran Ding, Yuqian Qiu, Chong Li, Yue Ma, Ningyu Zhang, Fei Xu, Hongqiang Wang
Abstract
ABSTRACT The unstable Na/electrolyte interface, plagued by Na dendrites and interface degradation, critically hinders solid‐state Na batteries. We propose the design of thin poly(ethylene oxide) (PEO)‐based composite polymer electrolytes with a stabilized solid electrolyte interphase (SEI). Incorporating SnF 2 into PEO and infusing the composite into an ultrathin polyethylene (PE) scaffold (PEO‐xSnF 2 @PE) promotes a stable Na 15 Sn 4 /NaF‐rich SEI that facilitates uniform Na⁺ deposition, while the PE layer ensures a thin yet mechanically robust structure. Consequently, the optimized composite polymer electrolyte, featuring an ultrathin 20 µm thickness, low areal density of 1.9 mg cm −2 , and ultrahigh tensile strength of 35 MPa, demonstrates exceptional dendrite‐suppressing capability. Such synergistic effects enable Na symmetric cells employing PEO‐4SnF 2 @PE to achieve ultralong cycling exceeding 10800 h (>1 year), alongside a critical current density of 1.0 mA cm −2 . Full cells paired with a Na 3 V 2 (PO 4 ) 3 cathode exhibit exceptional cycling stability, achieving 97.6% capacity retention over 500 cycles. This work demonstrates that combining SnF 2 functional additives with a flexible, high‐strength supporting layer effectively mitigates interfacial instability and dendrite propagation in solid polymer electrolytes, offering new design principles for long‐life solid‐state sodium metal batteries.