Fast Charging and Low Temperature Capabilities of Sodium Solid-State Batteries Enabled by Thin NASICON Bilayer Architecture

Although sodium solid-state batteries have gained tremendous interest in recent years, achieving stable capacities at high current rates has been a major obstacle in realizing them. Here we report the synthesis of flat and thin (37 μm and down to 18 μm) dense Zn,Mg-dual doped NASICON electrolyte separator layers in a 3D porous–dense bilayer architecture. The anode was formed by filling the porous layer with sodium metal, attaining seamless contact. Full cells with sodium vanadium phosphate cathodes (with a high areal capacity of 1.8 mAh/cm2) and sodium-infiltrated NASICON-bilayers were cycled at record-high room temperature (22 °C) current densities of 10.8 mA/cm2 (6 C), and long-term cycling at 1.7 mA/cm2 (1 C) was demonstrated. Moreover, low-temperature (−10 °C) cycling capability was demonstrated at a 0.1 C rate. This electrolyte architecture promises high energy density (up to 286 Wh/kg), room-temperature sodium solid-state batteries without the need for stack pressure further improving commercial viability at the pack level.