Weakly anion-driven solvation towards stable operation of carbonate ester-based sodium metal batteries at −40°C

an optimized carbonate-ester electrolyte with week solvation and low concentration is desgineed to endow fast Na + desolvation and rapid interfacial Na + transport, thereby achieving stable operation of high-cathode-loading (> 10 mg cm −2 ) sodium metal batteries at ultra-low temperature (−40°C). • The weakly solvation with low concentration endows high Na + conductivity and forms stable NaF-rich SEI for fast Na + transport at low temperature. • The SMBs matching the P2-type Na 0.75 Ni 0.34 Mn 0.66 O 2 (NNMO) cathode achieve the high-capacity retention of 85.4 % after 160 cycles at −40°C. • The pouch cell with high-loading cathodes (11.76 mg cm −2 ) delivers high energy density (227.4 W h kg −1 ) and stable cycles (100 cycles) at −20°C. Carbonate ester-based electrolyte are crucial to support practical sodium-metal batteries (SMBs) due to their favourable oxidative stability and low cost. However, the stable operation for SMBs at −40 °C with carbonate ester-based electrolyte remains a tremendous challenge owing to sluggish kinetic of Na + desolvation and Na + migration through solid electrolyte interphase (SEI). Hence, we construct stable operation of ultralow-temperature SMBs at −40 °C via a weakly anion-drived solvation of carbonate-ester electrolyte with low concentration, which endows high Na + conductivity and low Na + desolvation barrier. Anion-driven solvation is favor of forming a roust Na + -conductive NaF-rich SEI film, thereby stabilizing SMBs at low temperature. As a result, symmetrical cells achieve long cyclic stability for 1000 h at −20 °C. In addition, the SMBs matching the P2-type Na 0.75 Ni 0.34 Mn 0.66 O 2 (NNMO) cathode with an electrochemical window of 4.15 V achieve the high capacity retention of 91.5 % after 600 cycles at −20 °C and 85.4 % after 160 cycles at −40 °C. Moreover, pouch cell with high energy density (227.4W h kg −1 ) and high-loading cathode (11.76mg cm −2 ) provides a stable 100 cycle at −20 °C. The optimized carbonate ester electrolyte provides vital insights into developing ultra-low-temperature SMBs.