Electrode–Electrolyte Interfacial Chemistry Modulation for Ultra‐High Rate Sodium‐Ion Batteries

Abstract Sodium‐ion batteries capable of operating at rate and temperature extremes are highly desirable, but elusive due to the dynamics and thermodynamics limitations. Herein, a strategy of electrode–electrolyte interfacial chemistry modulation is proposed. The commercial hard carbon demonstrates superior rate performance with 212 mAh g −1 at an ultra‐high current density of 5 A g −1 in the electrolyte with weak ion solvation/desolvation, which is much higher than those in common electrolytes (nearly no capacity in carbonate‐based electrolytes). Even at −20 °C, a high capacity of 175 mAh g −1 (74 % of its room‐temperature capacity) can be maintained at 2 A g −1 . Such an electrode retains 90 % of its initial capacity after 1000 cycles. As proven, weak ion solvation/desolvation of tetrahydrofuran greatly facilitates fast‐ion diffusion at the SEI/electrolyte interface and homogeneous SEI with well‐distributed NaF and organic components ensures fast Na + diffusion through the SEI layer and a stable interface.