In Situ Integration of Rapid Ion-Diffusion Interlayers on Cu Current Collectors toward Ultrafast Anode-Free Sodium Metal Batteries

Anode-free sodium metal batteries (AFSMBs) are acclaimed for their high energy density and low production cost, but they face challenges related to an unstable cycling life due to irreversible Coulombic efficiency and dendrite growth. Although this issue is addressed to some extent by modulating the current collector interface, the effectiveness of these modifications in improving the performance of AFSMBs under extremely high-rate conditions is still insufficient. Here, the Prussian blue analogues (PBAs) as a rapid sodium-ion diffusion interlayer that is integrated in situ on copper current collectors (PBA@Cu) are used to realize high-performance AFSMBs. PBA exhibits a low diffusion energy barrier for sodium ions, boosting sodium ion migration and regulating the Na+ flux to realize uniform sodium plating/stripping. Meanwhile, the strong interaction between PBA@Cu and anions in electrolytes is conducive to the formation of a more inorganic-rich solid-state electrolyte interlayer (SEI), which further accelerates the transport kinetics of sodium ions. Particularly, the anode-free cell PBA@Cu||Na3V2(PO4)3 exhibited stable cycling at a high rate of 5 C for 300 cycles. This work presents a viable approach to the practical implementation of high-energy-density alkaline metal batteries.