Highly Safe Electrolyte for Fast‐Charging, High‐Temperature, High‐Voltage Sodium Metal Batteries

Abstract The development of high‐energy and safe sodium metal batteries (SMBs) remains largely challenging due to the lack of a viable electrolyte, especially at high rates and high temperatures. Here a highly safe electrolyte is reported via engineering the fluorinated solvents and potassium trifluoro(2‐fluoropyridin‐3‐yl)borate (PTFB) additive for high‐energy SMBs under extreme conditions. The as‐formulated electrolyte not only exhibits excellent Non‐flammability, heat resistance, and anodic stability but also promotes the formation of a NaF‐dominated solid electrolyte interphase (SEI) with uniform distribution and generates a thin and homogeneous cathode‐electrolyte interphase (CEI) with high ionic conductivity. Thus, the assembled Na||Na symmetric and Na||Cu batteries achieve a durable cycle of over 1200 h and a high average Coulombic efficiency (CE) of 99.07%, respectively. Moreover, the 4.5 V Na||Na 3 V 2 (PO 4 ) 2 O 2 F (NVPF) batteries also deliver stable high‐temperature (55 °C) and fast‐charging (6 min charging) performance. Even with limited Na, the Cu@Na||NVPF full battery retains a high‐capacity retention of 95.4% after 200 cycles. The work provides a promising approach for developing fast‐charging, high‐energy, and safe SMBs.