3D Porous Tin Created by Tuning the Redox Potential Acts as an Advanced Electrode for Sodium‐Ion Batteries

: Sodium-ion batteries (SIBs) have attracted significant research interest for large-scale electric energy storage. However, anodes with good rate capability and long cycle life are still lacking. Here, a three-dimensional (3D) porous Sn on Cu foil (Sn/Cu) is prepared by tuning the redox potential of Cu+ /Cu with a ligand of thiourea to trigger the replacement reaction between Cu and Sn2+ . The as-synthesized Sn/Cu is used as an integrated porous electrode and can be directly applied as an advanced freestanding electrode for SIBs. Such a unique structure can efficiently relieve the strain caused by sodiation/desodiation and benefit penetration of the electrolyte and diffusion of Na+ . This is a merit of its large reversible capacity of about 700 mAh g-1 at 2500 mA g-1 for 400 cycles. A full battery of Sn/Cu//Na3 (VO0.5 )2 (PO4 )3 F2 is constructed, which presents a high energy density of 311.7 Wh kg-1 and long lifespan of 200 cycles. This facile synthesis strategy and good electrochemical performance will encourage more investigations into structure design of functional materials.