Dual-domain solvent-locked electrolyte enabled durable 4.5 V-class sodium batteries

Sodium-ion batteries hold significant promise for sustainable energy storage by addressing resource scarcity and safety concerns. Elevating the upper-cut-off voltage is crucial for sodium-ion batteries to maximize electrode capacity and narrow their energy-density gap with commercial lithium-ion batteries. However, conventional electrolytes exhibit electrochemical instability on the highly desodiated positive electrode surface, undergoing strongly electrophilic attack and continuous decomposition that results in oligomer-rich interphases and rapid capacity fading. Here, we design a solvent-locked carbonate electrolyte creating electrochemically stable solvent-reinforced solvation structure and anion-rich interfacial shield-derived boride-/fluoride-rich interphase on positive electrode, thereby suppressing current leakage and parasitic reactions. The tailored electrolyte exhibits good compatibility with commercialized oxides and polyanionic positive electrodes. As-assembled Na||Na2.26Fe1.87(SO4)3 cells deliver extended lifespans operating to 4.5 V, retaining 88.2% capacity after 16,500 cycles at 1000 mA g–1 (coin cell) and 93.9% after 500 cycles at 100 mA g–1 (pouch cell). This work will inspire durable electrolyte and interphase design for high-energy batteries and beyond. Traditional electrolytes are electrochemically unstable on the positive electrode surface. Here, the author designed a solvent locked electrolyte to form a stable boride/fluoride interface. The assembled Na||Na2.26Fe1.87(SO4)3 battery maintained 88.2% capacity after 16500 cycles at 1 A g-1.