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

Abstract

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_0.75Ni_0.34Mn_0.66O₂ (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.