Long‐Life High‐Voltage Sodium‐Ion Batteries Enabled by Electrolytes with Cooperative Na+‐Solvation

Abstract Stabilizing the electrode interphases is urgently required to enhance the lifetime of high‐voltage sodium‐ion batteries (SIBs). However, the continuous anode solid–electrolyte interphase (SEI) growth associated with electron leakage and the fragile cathode–electrolyte interphase (CEI) lead to capacity fade at high voltage; and yet the solvation‐interphase‐performance relationship is inadequately addressed. Herein, a cooperative Na + ‐solvation strategy is reported to stabilize the interphases by a holistic design of electrolytes combining soft and moderate co‐solvents. The rationally regulated Na + ‐solvation leads to CEI/SEI with the desired thickness and component stability. As such, remarkable cycling stability is achieved for 4.3‐V Na 3 V 2 O 2 (PO 4 ) 2 F (NVOPF) cathodes with 83.3% capacity retention over 3000 cycles at 1 C, significantly outperforming the carbonate counterpart (41.6% capacity retention). Meanwhile, the restrained SEI growth via reducing the formation of electron‐leaking Na 2 CO 3 stabilizes the long‐term cycling of the hard carbon (HC) anode. The assembled NVOPF||HC full cells achieve superior rate capability (up to 15 C) and stable cycling stability over 500 cycles. The demonstrated engineering of electrolyte chemistry, Na + ‐solvation, and interphase structure/component contributes toward the rational establishment of design rules for high‐voltage SIBs and possibly other similar chemistries.