Design of solid-state sodium-ion batteries with high mass-loading cathode by porous-dense bilayer electrolyte

Solid-state sodium-ion batteries with sodium metal anodes possess high safety and reliability, which are considered as a promising candidate for the next generation of energy storage technology. However, poor electronic and ionic conductivities at the interface between electrodes and solid-state electrolytes restrict its practical application. Herein, we demonstrate a β″-Al2O3 electrolyte with a vertically porous-dense bilayer structure to solve this problem. The carbon-coated vertically porous layer serves as a high mass-loading host for Na3V2(PO4)3 cathode and provides fast electronically and ionically conductive pathways. In addition, the dense layer is produced to prevent sodium dendrite growth and improve mechanical strength of β″-Al2O3 electrolyte. Experimental results show that the cathode loading in vertically porous layer can reach to 8 mg cm−2, and the porous-dense bilayer β″-Al2O3 electrolyte-based battery exhibits a reversible specific capacity of 87 mAh g−1 and a capacity retention of 95.5% over 100 cycles at a current density of 0.1 C, which is superior to that of the traditional dense β″-Al2O3 electrolyte-based battery. This work based on electrolyte structure design represents an efficient strategy for the development of solid-state sodium-ion batteries with high mass-loading cathode.