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

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||Na3V2(PO4)2O2F (NVPF) batteries also deliver stable high-temperature (55 degrees 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.