Monolithic Interphase Enables Fast Kinetics for High‐Performance Sodium‐Ion Batteries at Subzero Temperature

Abstract In spite of the competitive performance at room temperature, the development of sodium‐ion batteries (SIBs) is still hindered by sluggish electrochemical reaction kinetics and unstable electrode/electrolyte interphase under subzero environments. Herein, a low‐concentration electrolyte, consisting of 0.5M NaPF 6 dissolving in diethylene glycol dimethyl ether solvent, is proposed for SIBs working at low temperature. Such an electrolyte generates a thin, amorphous, and homogeneous cathode/electrolyte interphase at low temperature. The interphase is monolithic and rich in organic components, reducing the limitation of Na + migration through inorganic crystals, thereby facilitating the interfacial Na + dynamics at low temperature. Furthermore, it effectively blocks the unfavorable side reactions between active materials and electrolytes, improving the structural stability. Consequently, Na 0.7 Li 0.03 Mg 0.03 Ni 0.27 Mn 0.6 Ti 0.07 O 2 //Na and hard carbon//Na cells deliver a high capacity retention of 90.8 % after 900 cycles at 1C, a capacity over 310 mAh g −1 under −30 °C, respectively, showing long‐term cycling stability and great rate capability at low temperature.