Anion‐Cation Co‐Tailored High‐Flash‐Point Phosphate‐based Electrolyte Enables High‐Voltage, Wide‐Temperature, Non‐Flammable Sodium Metal Batteries via an Inorganic‐Rich Solid Electrolyte Interphase

ABSTRACT Sodium‐metal batteries (SMBs) are promising for large‐scale energy storage due to their abundant resources and low cost. However, their practical application is hindered by interrelated challenges, including interface instability, volume expansion, and dendrite growth. In this work, we propose a general design strategy for SMBs and develop a low‐cost, highly synergistic, and non‐flammable ion‐anchored electrolyte. The functionalization of Sn 2+ with PO 2 F 2 − anchors the sodium anode, forming an alloy‐inorganic composite interface layer. Meanwhile, the strong coordination between DFOB − and Na + , along with F δ− ‐H δ+ interactions between the additives and TMP, promotes the formation of an aggregate‐rich solvation structure. Furthermore, the decomposition characteristics of DFOB − and PF 2 O 2 − optimize the cathode interface, broadening the battery's applicability. The designed electrolyte exhibits excellent ionic transport properties and enables the in situ formation of a robust interface. As a result, the Na‐Na 3 V 2 (PO 4 ) 3 battery using the optimized electrolyte achieved a capacity retention of about 80% after 3000 cycles at 3C. Additionally, it demonstrates excellent cycling performance under severe conditions such as working temperatures of −10°C and 60°C, a high potential window of 4.3 V, and limited sodium availability. This work proposes a new approach to address the compatibility issues of metal anodes such as Li/Na/K/Zn/Ca/Mg etc.