Probing Local Asymmetric Site Anchored Anion Based on Multifunctional Polymer Electrolyte for Sustainable Solid-State Sodium-Metal Battery.

Abstract

Solid-state sodium metal batteries (SSMBs) are promising candidates for next-generation energy storage due to their inherent safety and high energy density. Among these various SSMBs, however, conventional polyvinylidene fluoride (PVDF)-based solid polymer electrolytes (SPEs) suffer from low room-temperature ionic conductivity, poor mechanical stability, and unstable electrode-electrolyte interfaces. To alleviate the detrimental effects, the study has designed a multifunctional polymer electrolyte based on localized asymmetric anion anchoring sites. After introducing nanocellulose (NC) fillers to form asymmetric PVDF-NC (PDNC) surface sites locally, the PDNC matrix can effectively coordinate TFSI^- and Na⁺. This coordination facilitates the rapid transport of Na⁺, enabling effective regulation of sodium ion migration pathways and anion behavior. Specifically, -CF₂-, F^-, and N^3- species stemming from the decomposition of CF₃SO₂NSO₂ ^2- and CF₃- groups through cleavage and reduction processes combine with Na to form NaF and Na₃N, thereby enhancing interfacial stability. Theoretical calculations reveal that the asymmetric sites facilitate charge exchange and enhance interactions between the electrolyte and different molecules. The system demonstrates excellent electrochemical performance and universality when paired with diverse cathodes (layered oxides and polyanion compounds). This work provides a sustainable strategy for designing high-performance SPEs, thus paving the way for safe and scalable SSMBs.