Fabricating Wide‐Temperature‐Range Quasi‐Solid Sodium Batteries with Fast Ion Transport via Tin Additives

Abstract Quasi‐solid sodium batteries, employing quasi‐solid polymer electrolytes (QSPEs) renowned for their high energy density and cost‐effective fabrication, are promising candidates for next‐generation energy storage systems. However, their practical application has encountered impediments such as insufficient ion transport and uneven sodium plating/stripping attributed to suboptimal interfacial compatibility. In this work, an innovative QSPE is developed by incorporating functional additives, specifically fluoroethylene carbonate (FEC) and tin trifluoromethanesulfonate (Sn(OTf) 2 ), into the poly(vinylidenefluoride‐co‐hexafluoropropylene) (PVDF‐HFP)/propylene carbonate (PC) polymer electrolyte. Sn(OTf) 2 catalyzes a ring‐opening reaction in PC, thereby reducing transmission barriers and augmenting the transport of sodium ions. Consequently, the resulting HFP‐PC‐FEC‐Sn QSPE demonstrates remarkable ionic conductivity (0.42 mS cm ─1 ) and ion transference number (0.58). Furthermore, it forms a dense and smooth interphase enriched with NaF and metallic Sn, significantly enhancing the long‐term cycling stability of Na symmetric cells, which endure over 3000 h at 0.2 mA cm ─2 , and effectively suppressing the formation of sodium dendrites. This outstanding electrochemical performance extends to Na 3 V 2 (PO 4 ) 3 /Na full coin and pouch cells across a wide temperature range. This work introduces an innovative approach for designing high‐performance QSPEs suitable for wide‐temperature quasi‐solid sodium batteries.