Dual-Phase Surface-Modified NaNbO3@Carbon@Na3V2(PO4)3 Enables Stable All-Solid-State Sodium Batteries

Abstract Na3V2(PO4)3 is a promising cathode for all-solid-state sodium batteries (ASSBs) owing to its robust structural stability. However, the direct integration of low electronic conductivity Na3V2(PO4)3 cathode with a solid electrolyte leads to severe interfacial resistance and sluggish reaction kinetics, which limit the electrochemical performance of ASSBs. Herein, a dual-phase interfacial engineering strategy is proposed to simultaneously enhance electronic/ionic transport kinetics and stabilize the cathode/electrolyte interface. A conductive carbon layer is first constructed on the Na3V2(PO4)3 surface to establish an efficient electronic transport network, followed by introducing a NaNbO3 coating layer to facilitate Na+ migration across the cathode/electrolyte interface. Benefiting from this bifunctional NaNbO3/carbon layer, the electronic conductivity of Na3V2(PO4)3 is dramatically increased by seven orders of magnitude from 3.56 × 10–8 to 0.36 S cm–1, and the cathode/electrolyte interfacial impedance is significantly reduced from 248.6 to 12.1 Ω. The assembled 5%NaNbO3@Carbon@Na3V2(PO4)3|Na3.4Zr1.9Zn0.1Si2.2P0.8O12|Na ASSB delivers an initial discharge specific capacity of 115.6 mAh g–1 at 0.1 C and maintains 96.4% of its capacity after 1000 cycles under a high rate of 2 C. This work demonstrates a robust strategy to overcome the interfacial limitations of Na3V2(PO4)3-based ASSBs, paving the way for the development of long cycle life all-solid-state batteries.