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

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 Na3V2O2(PO4)(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 Na2CO3 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.