Multifunctional built-in ion-conductive phase enabling long cycle life, high specific capacity composite sodium anode for solid-state sodium batteries

Solid-state sodium batteries (SSSBs) based on solid-state electrolytes (SSEs) are prominent in future lithium-free energy storage systems owing to their intrinsic safety, high energy density, and cost-effectiveness. However, the commercial implementation of SSSBs is still limited by the large interface impedance and sodium dendrites caused by the insufficient anode-SSE interface contact. Herein, an ultra-stable composite sodium anode (CSA) with built-in well-dispersed ion-conductive NaxTiO2 is specifically constructed to stabilize the anode interface of the Na3Zr2Si2PO12 (NZSP) electrolyte. The uniformly dispersed ion-conductive phase NaxTiO2 in the CSA can not only enhance the chemical and physical contact of the CSA with NZSP but also improve the inherent ion diffusing ability of the bulk sodium to compensate for the sodium depletion during stripping. Benefiting from these advantages, the CSA|NZSP|CSA cell exhibits an ultra-low interfacial impedance of 3.7 omega cm2, a high critical current density (CCD) of 1.3 mA cm-2, and a stable plating/stripping performance of over 8000 h at 0.1 mA cm-2. The constructed full cell with Na3V2(PO4)3 cathode shows excellent cycling performance of 74.5% capacity retention for 800 cycles at 1 C. This work presents a pioneering composite anode design to achieve a compatible anode|SSE interface for facilitating the evolution of SSSBs.