Hybrid electrolyte enables solid-state sodium batteries sustaining 50,000 cycles

Solid-state sodium (Na) batteries open the opportunity for more sustainable energy storage due to their safety, low cost and high energy density. Inorganic solid electrolytes show notable advantages for such technologies but suffer from poor interfacial compatibility, rendering hybrid solid–liquid electrolytes an alternative. Here we show that the interfacial failure in the hybrid electrolyte system (Na3Zr2Si2PO12 (NZSP) and 1 M NaClO4 in propylene carbonate/ethylene carbonate/fluoroethylene carbonate) is closely associated with Na vacancies on the surface of NZSP. Asymmetric kinetics of solid and liquid electrolytes lead to the formation of Na vacancies and an unstable environment in the Helmholtz layer, while the organic molecules (propylene carbonate) are energetically favourable towards undesirable dehydrogenation. To eliminate the Na vacancies layer, we designed an ion-anchoring interlayer that serves to minimize the interfacial polarization. The unique O–Na coordination between the interfacial layer and NSZP confers stability to the solid–liquid interface. As demonstrated, the sodium battery with the modified hybrid electrolyte sustains 50,000 cycles with capacity retention of 86.3%. Our work provides a new path for the design of solid-state Na batteries, highlighting their potential for widespread practical applications.