Ferroelectric interface for efficient sodium metal cycling in anode-free solid-state batteries

Anode-free solid-state batteries (AFSSBs) are considered one of the promising solutions for achieving high energy density and safety of electrochemical energy storage systems. However, owing to mechanochemical contact losses and metallic dendrite growth caused by the degradation at the current collector (CC)/electrolyte interface, the feasibility of AFSSBs is critically limited, especially upon the involvement of rigid ceramic electrolytes. Here, a new strategy is reported for NASICON-structure Na₃Zr₂Si₂PO₁₂ (NZSP) electrolyte-based AFSSBs by introducing a resilient ferroelectric composite substrate coated onto Al CC, eventually achieving efficient and stable operation. Compared with the bare Al foil, the ferroelectric composite substrate not only renders an intimate CC/electrolyte interface compatibility, but also dynamically regulates the distribution and migration of Na⁺ flux at the CC/electrolyte interface through the built-in electric field stem from ferroelectric BaTiO₃, guiding homogeneous and dense sodium metal deposition. Stable plating/stripping cycling can be achieved even at a high current density of 1.2mA cm⁻² with the Coulombic efficiency of (99.7 %). Significantly, the NZSP-based AFSSB integrated with the ferroelectric composite substrate and mainstream sodium ion cathodes demonstrates stable cycling and excellent capacity retention.